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A touch GUI for the official MicroPython display

v0.21 29th Oct 2020 Add Scale and Pad widgets.
V0.20 21st Oct 2020 Refactor as a Python package. The refactor is a breaking change: applications must adapt import statements. There is now no need to cross compile on a Pyboard 1.1. Unused widgets no longer consume RAM. The structure also facilitates adding new widgets. Supports Jim Mussared's fast text rendering.
V0.12 21st Sep 2020 Updated for (and requires) uasyncio V3.

Provides a simple touch driven event based GUI interface for the the official LCD160CR colour display. It is based on the official driver and uses uasyncio for scheduling. It has been tested on:

  • Pyboard 1.0 and 1.1
  • Pyboard D
  • ESP32 It should be easy to port to platforms having both I2C and SPI interfaces, given sufficient RAM. The V1.1 display enables a Pyboard D to be plugged in to the rear. The GUI has been tested in this configuration.

It is targeted at hardware control and display applications. GUI objects are drawn using graphics primitives rather than by rendering bitmap images. This ensures that they are scalable. The API is via event driven callbacks.

The library can use the fonts internal to the device and also arbitrary fonts converted from ttf or otf formats.

An extension for plotting simple graphs is described here.

Images from the supplied test programs:

Image Image
Screen selection buttons. Two styles of checkboxes.

Image Image
Assorted pushbutton styles. Radio buttons (1 of N selection).

Image
Highlight buttons change color for a period after touching.

Image Image
Slider controls allow control and display of float values. Also Meter, LED and Dial displays.

Image
The Scale control can accurately display variables having a wide range of values. The scale moves within a window so that the current value aligns with the fixed pointer. The scale color can change dynamically (in the lower instance).

Image
Rotary controls and displays - lkt.py demonstrates the two styles of "greying out" disabled controls.

Image Image
Vector displays. These can display an arbitrary number of vectors in "clock" or "compass" formats. Angle, length and color can change dynamically.

Image Image
Listbox and dropdown list objects (image on right shows dropdown opened).

Image Image
The Textbox control displays scrolling text in a window. Supports tabs with variable pitch fonts. Text can be scrolled by touch or programmatically. Text may be clipped or word-wrapped.

Image
A modal dialog box.

Image Image
The Plot module: Cartesian and polar graphs.

Contents

  1. Pre requisites
    1.1 Pre installation
    1.2 Library Documentation
    1.3 Installation
    1.4 Dependencies and Python files
    1.5 A performance boost
  2. Concepts
    2.1 Terminology
    2.2 Coordinates
    2.3 Colors
    2.4 Callbacks
    2.5 Screens
  3. Program Structure
    3.1 Initialisation
  4. Class Screen
    4.1 Class methods
    4.2 Constructor
    4.3 Callback methods
    4.4 Method
  5. Display Classes
    5.1 Class Label Display static or dynamic text.
    5.2 Class Dial Rotary display of variables.
    5.3 Class LED On/off display.
    5.4 Class Meter Linear "panel meter" device.
    5.5 Vector display Compass and clock style display of multiple vectors.
    5.6 Scale class Linear display with wide dynamic range.
  6. Control Classes
    6.1 Class Button
    6.2 Class ButtonList: emulate a button with multiple states
    6.3 Class RadioButtons
    6.4 Class Slider
    6.5 Class Knob
    6.6 Class Checkbox
    6.7 Class Listbox
    6.8 Class Dropdown
    6.9 Class Pad Invisible touch sensitive region.
    6.10 Class Textbox Scrolling text display with tab support.
         6.10.1 Note on tabs
  7. Dialog Boxes
    7.1 Class Aperture
    7.2 Class DialogBox
  8. Fonts
    8.1 External fonts
    8.2 Internal fonts: Class IFont
  9. Issues A problem encountered with old LCD160CR firmware
  10. Application design note Touch application design
  11. ESP32 Use with non-Pyboard targets

1. Pre requisites

Firmware should be V1.13 or later.

1.1 Pre installation

Before running the GUI the hardware should be tested by working through the tutorial.

Familiarity with callbacks and event driven programming will assist in developing applications. No knowledge of uasyncio is required for application development as the API is callback-based, but the GUI is compatible with uasyncio applications.

1.2 Library Documentation

Documentation for the underlying libraries may be found at these sites.

lcd160cr driver

Other references:
Font format
uasyncio tutorial

1.3 Installation

The file lcd_local.py defines the hardware connection and should be edited to match your hardware. On Pyboard D plugged into the back of a display select the "X" connection. Edit if you plan to use fonts bigger than 23*23 pixels. See External fonts.

Copy the following files to the root directory on the target (on Pyboard /flash or /sd):

  1. lcd_local.py
  2. font6.py (Font files not required if frozen as bytecode).
  3. font10.py

Copy the gui directory and contents to the root directory on the target. If using rshell this may be done from the directory containing gui with:

> rsync gui /sd/gui

For use with non-Pyboard targets, including ESP32, see ESP32.

1.4 Dependencies and Python files

Version 3 of uasyncio is included in firmware V1.13 and later. This is a requirement.

Files in top level directory:

  1. lcd_local.py
  2. font6.py Font file used in demos.
  3. font10.py Ditto.
  4. font14.py Unused example of max font size using unmodified lcd_local.

Fonts are generated from the free font FreeSans.ttf. You can generate your own, see External fonts.

Core files in core subdirectory:

  1. lcd160cr.py Official driver. Check for a newer version in the source tree (drivers/display).
  2. lcd160_gui.py The micro GUI library.
  3. constants.py Constants such as colors and shapes (import using from gui.core.constants import *).
  4. lplot.py Optional graph plotting extension.

Test/demo programs in demos subdirectory:

  1. lvst.py A test program for vertical linear sliders. Also demos an asynchronous coroutine and linked sliders.
  2. lhst.py Tests horizontal slider controls, meter and LED. Demos asynchronous coroutine, linked sliders and dynamically changing object colors.
  3. lbt.py Pushbuttons, radio buttons, highlighting buttons and checkboxes. "Reset" buttons respond to short and long presses.
  4. lkt.py Rotary controls. Shows the two styles of "greying out" of disabled controls.
  5. ldd.py Dropdown list and Listbox controls.
  6. ldb.py Modal dialog boxes.
  7. ldb_if.py As above but using an internal font.
  8. lpt.py Demo of plot module.
  9. lptg.py Plot with TSequence simulated real time data acquisition.
  10. vtest.py Test of vector display.
  11. lscale.py Demo of Scale object. This is capable of displaying floats to a high degree of accuracy.
  12. tbox.py Demo of Textbox class for scrolling text.

Synchronisation primitives in primitives subdirectory.
Widgets in widgets subdirectory.

Demos are run with the following syntax:

>>> import gui.demos.lbt

The organisation as a Python package means that cross compilation of lcd160_gui.py is no longer required on a Pyboard 1.1. To conserve RAM it is recommended that font files are implemented as frozen bytecode. To further reduce RAM this may be applied to other Python files, but the directory structure must be maintained.

1.5 A performance boost

This will only make a visible difference to applications rendering substantial amounts of text using Python fonts.

Rendering Python fonts is slow as it is performed pixel by pixel. A potential speedup is to use the framebuf.blit method but as standard it cannot render monochrome objects to color displays. A fix for this was developed by Jim Mussared (@jimmo) and consists of a native C module.

On import, lcd160_gui.py attempts to import a module framebuf_utils. If this succeeds (i.e. a file framebuf_utils.mpy is found), rendering will be substantially faster.

The directory framebuf_utils contains the source file, the makefile and a version of framebuf_utils.mpy for armv7m architecture (e.g. Pyboards). To install copy the directory and its contents to your device. On initialisation the message "Using fast mode" will be printed at the REPL.

On other architectures framebuf_utils.mpy should be recompiled or deleted to disable fast mode.

Jump to Contents

2. Concepts

2.1 Terminology

GUI objects are created on a Screen instance which normally fills the entire physical screen. Displayable GUI objects comprise control and display instances. The former can respond to touch (e.g. Pushbutton instances) while the latter cannot (LED or Dial instances).

2.2 Coordinates

In common with most displays, the top left hand corner of the display is (0, 0) with increasing values of x to the right, and increasing values of y downward. Display objects exist within a rectangular bounding box; in the case of touch sensitive controls this corresponds to the sensitive region. Locations are defined as a 2-tuple (x, y). The location of an object is defined as the location of the top left hand corner of the bounding box.

2.3 Colors

These are defined as a 3-tuple (r, g, b) with values of red, green and blue in range 0 to 255. The interface and this document uses the American spelling (color) throughout. This is for historical reasons.

2.4 Callbacks

The interface is event driven. Controls may have optional callbacks which will be executed when a given event occurs. A callback function receives positional arguments. The first is a reference to the object raising the callback. Subsequent arguments are user defined, and are specified as a tuple or list of items. Callbacks are optional, as are the argument lists - a default null function and empty list are provided. Callbacks are usually bound methods - see the Screens section for a reason why this is useful.

All controls and displays have a tft property which is the LCD160CR_G instance. This enables callbacks to access drawing primitives.

2.5 Screens

GUI controls and displays are rendered on a Screen instance. A user program may instantiate multiple screens, each with its own set of GUI objects. The Screen class has class methods enabling runtime changes of the screen to be rendered to the physical display. This enables nested screens. The feature is demonstrated in lbt.py.

Applications should be designed with a Screen subclass for each of the application's screens (even if the app uses only a single screen). This faciitates sharing data between GUI objects on a screen, and simplifies the handling of control callbacks. These will be methods bound to the user screen. They can access the screen's bound variables via self and the control's bound methods via the callback's first argument (which is a reference to the control). Again lbt.py provides examples.

The Screen class has 3 null methods which may be implemented in subclasses: on_open which runs when a screen is opened but prior to its display, after_open which is called after display, and on_hide which runs when a screen change is about to make the screen disappear. These may be used to instantiate or control threads and to retrieve the results from a modal dialog box.

The Screen class is configured in lcd_local.py.

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3. Program Structure

The following illustrates the structure of a minimal program:

from lcd_local import setup
import font10
from gui.core.constants import *
from gui.core.lcd160_gui import Screen
from gui.widgets.buttons import Button
def quitbutton():
    def quit(button):
        Screen.shutdown()
    Button((109, 107), font = font10, callback = quit, fgcolor = RED,
           text = 'Quit', shape = RECTANGLE)

class BaseScreen(Screen):
    def __init__(self):
        super().__init__()
        quitbutton()
setup()
Screen.change(BaseScreen)

The last line causes the Screen class to instantiate your BaseScreen and to start the scheduler using that screen object. Control then passes to the scheduler: the code following this line will not run until the GUI is shut down and the scheduler is stopped (Screen.shutdown()).

3.1 Initialisation

This is performed by lcd_local.py which instantiates an LCD160CR_G display. This class is derived from the official driver's LCD160CR class: the documentation for the latter may be viewed here. An additional optional constructor keyword argument bufsize is available. See External fonts for its use.

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4. Class Screen

The Screen class presents a full-screen canvas onto which displayable objects are rendered. Before instantiating GUI objects a Screen instance must be created. This will be current until another is instantiated. When a GUI object is instantiated it is associated with the current screen.

The best way to use the GUI, even in single screen programs, is to create a user screen by subclassing the Screen class. GUI objects are instantiated in the constructor. This arrangement facilitates communication between objects on the screen. The following presents an outline of this approach:

from lcd_local import setup
import font10
from gui.core.constants import *
from gui.core.lcd160_gui import Screen
from gui.widgets.buttons import Button
from gui.widgets.label import Label
def backbutton(x, y):
    def back(button):
        Screen.back()
    Button((x, y), font = font10, fontcolor = BLACK, callback = back,
           fgcolor = CYAN,  text = 'Back')

def fwdbutton(x, y, cls_screen, text='Next'):
    def fwd(button):
        Screen.change(cls_screen)
    Button((x, y), font = font10, callback = fwd, fgcolor = RED, text = text)

def quitbutton():
    def quit(button):
        Screen.shutdown()
    Button((109, 107), font = font10, callback = quit, fgcolor = RED, text = 'Quit')

class Screen_1(Screen):
    def __init__(self):
        super().__init__()
        Label((0, 0), font = font10, value = 'Test screen 1')
        backbutton(0, 100)

class Screen_0(Screen):
    def __init__(self):
        super().__init__()
        Label((0, 0), font = font10, value = 'Test screen 0')
        fwdbutton(0, 107, Screen_1)
        quitbutton()
setup()
Screen.change(Screen_0)

Note that the GUI is started by issuing Screen.change with the class as its argument rather than an instance. This aims to minimise RAM usage.

4.1 Class methods

In normal use the following methods only are required:

  • change Change screen, refreshing the display. Mandatory positional argument: the new screen class name. This must be a class subclassed from Screen. The class will be instantiated and displayed. Optional keyword arguments: args, kwargs. These enable passing positional and keyword arguments to the constructor of the new screen.
  • back Restore previous screen.
  • shutdown Clear the screen and shut down the GUI.
  • set_grey_style Sets the way in which disabled ('greyed-out') objects are displayed. The colors of disabled objects are dimmed by a factor and optionally desaturated (turned to shades of grey). Optional keyword arguments: desaturate default True and factor default 2. A ValueError will result if factor is <= 1. The default style is to desaturate and dim by a factor of 2.

Other method:

  • get_tft Return the LCD160CR instance. This allows direct drawing to the physical screen. Anything so drawn will be lost when the screen is changed. In normal use the TFT instance is acquired via a GUI object's tft property.

See lbt.py and ldb.py for examples of multi-screen design.

4.2 Constructor

This takes no arguments.

4.3 Callback Methods

These do nothing, and may be defined in subclasses if required.

  • on_open Called when a screen is instantiated but prior to display.
  • after_open Called after a screen has been displayed.
  • on_hide Called when a screen ceases to be current.

4.4 Method

  • reg_task args task, on_change=False. This is a convenience method for applications which use uasyncio and provides for the automatic cancellation of tasks. The first arg may be a Task instance or a coroutine. If a Screen runs associated coros it can opt to register these. On shudown, any registered tasks of the base screen are cancelled. On screen change, registered tasks with on_change True are cancelled. For finer control applications can ignore this method and handle cancellation explicitly in code.
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5. Display Classes

These classes provide ways to display data and are not touch sensitive.

5.1 Class Label

Displays text in a fixed length field. The height of a label is determined by the metrics of the specified font.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Keyword only arguments:

  • font Mandatory. Font object to use.
  • width The width of the object in pixels. Default: None - width is determined from the dimensions of the initial text.
  • border Border width in pixels - typically 2. If omitted, no border will be drawn.
  • fgcolor Color of border. Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • fontcolor Text color. Defaults to system text color.
  • value Initial text. Default: None.

Method:

  • value Argument val string, default None. If provided, refreshes the label with the passed text otherwise clears the text in the label.
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5.2 Class Dial

Displays angles in a circular dial. Angles are in radians with zero represented by a vertical pointer. Positive angles appear as clockwise rotation of the pointer. The object can display multiple angles using pointers of differing lengths (like a clock face).

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Keyword only arguments (all optional):

  • height Dimension of the square bounding box. Default 50 pixels.
  • fgcolor Color of border. Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • border Border width in pixels - typically 2. If omitted, no border will be drawn.
  • pointers Tuple of floats in range 0 to 0.9. Defines the length of each pointer as a proportion of the dial diameter. Default (0.9,) i.e. one pointer of length 0.9.
  • ticks Defines the number of graduations around the dial. Default 4.

Method:

  • value Arguments: angle (mandatory), pointer (optional) the pointer index. Displays an angle. A ValueError will be raised if the pointer index exceeds the number of pointers defined by the constructor pointers argument.
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5.3 Class LED

Displays a boolean state. Can display other information by varying the color.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Keyword only arguments (all optional):

  • height Dimension of the square bounding box. Default 20 pixels.
  • fgcolor Color of border. Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • border Border width in pixels - default 2. If None, no border will be drawn.
  • color The color of the LED. Default RED.

Methods:

  • value Argument val boolean, default None. If provided, lights or extinguishes the LED. Always returns its current state.
  • color Argument color. Change the LED color without altering its state.
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5.4 Class Meter

This displays a single value in range 0.0 to 1.0 on a vertical linear meter.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Keyword only arguments:

  • height Dimension of the bounding box. Default 100 pixels.
  • width Dimension of the bounding box. Default 26 pixels.
  • font Font to use in any legends. Default: None No legends will be displayed.
  • legends A tuple of strings to display on the centreline of the meter. These should be short to physically fit. They will appear equidistant along the vertical scale, with string 0 at the bottom. Default None: no legends will be shown.
  • divisions Count of graduations on the meter scale. Default 10.
  • fgcolor Color of border. Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • fontcolor Text color. Defaults to system text color.
  • pointercolor Color of meter pointer. Defaults to fgcolor.
  • value Initial value to display. Default 0.

Methods:

  • value Optional argument val. If provided, refreshes the meter display with a new value. Range 0.0 to 1.0: out of range values will be constrained to full scale or 0. Always returns its current value.
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5.5 Vector display

Provides a means of displaying one or more vectors. A vector is a complex with magnitude in the range of 0 to 1.0. In use a VectorDial is instantiated, followed by a Pointer instance for each vector to be displayed on it. The VectorDial can display its vectors as lines (as on a clock face) or as arrows (as on a compass).

By contrast with the Dial class the pointers have lengths and colors which can vary dynamically.

from gui.widgets.vectors import Pointer, VectorDial

Class VectorDial

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Keyword only arguments (all optional):

  • height=100 Dimension of the square bounding box.
  • fgcolor=None Foreground color. Defaults to system color.
  • bgcolor=None Background color of object. Defaults to system background.
  • border=None Border width in pixels - typically 2. Default: no border.
  • ticks=4 Defines the number of graduations around the dial.
  • arrow=False If True vectors will appear as arrows.
  • pip=None By default a small circular "pip" is drawn at the centre of the dial. If False is passed this is omitted. If a color is passed, it will be drawn using that color. If the shortest pointer has a length below a threshold the "pip" is omitted to ensure visibility.

Class Pointer

Constructor mandatory positional arg:

  • dial The dial on which it is to be displayed.

Method:

  • value Args v=None, col=None. Returns the current value. If a complex is passed as the value v it is scaled to ensure its magnitude is <= 1 and the pointer is redrawn. If a color is passed as col the pointer's color is updated.
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5.6 Scale class

This displays floating point data having a wide dynamic range. It is modelled on old radios where a large scale scrolls past a small window having a fixed pointer. This enables a scale with (say) 200 graduations (ticks) to readily be visible on a small display, with sufficient resolution to enable the user to interpolate between ticks. Default settings enable estimation of a value to within +-0.1%.

Legends for the scale are created dynamically as it scrolls past the window. The user may control this by means of a callback. The example lscale.py illustrates a variable with range 88.0 to 108.0, the callback ensuring that the display legends match the user variable. A further callback enables the scale's color to change over its length or in response to other circumstances.

The scale displays floats in range -1.0 <= V <= 1.0.

Constructor mandatory positional arguments:

  1. location 2-tuple defining position.
  2. font Font for labels.

Keyword only arguments (all optional):

  • ticks=200 Number of "tick" divisions on scale. Must be divisible by 2.
  • legendcb=None Callback for populating scale legends (see below).
  • tickcb=None Callback for setting tick colors (see below).
  • height=0 Default is a minimum height based on the font height.
  • width=100
  • border=2 Border width in pixels.
  • fgcolor=None Foreground color. Defaults to system color.
  • bgcolor=None Background color of object. Defaults to system background.
  • pointercolor=None Color of pointer. Defaults to .fgcolor.
  • fontcolor=None Color of legends. Default WHITE.
  • value=0.0 Initial value.

Method:

  • value=None Set or get the current value. Always returns the current value. A passed float is constrained to the range -1.0 <= V <= 1.0 and becomes the Scale's current value. The Scale is updated. Passing None enables reading the current value.

Callback legendcb

The display window contains 20 ticks comprising two divisions; by default a division covers a range of 0.1. A division has a legend at the start and end whose text is defined by the legendcb callback. If no user callback is supplied, legends will be of the form 0.3, 0.4 etc. User code may override these to cope with cases where a user variable is mapped onto the control's range. The callback takes a single float arg which is the value of the tick (in range -1.0 <= v <= 1.0). It must return a text string. An example from the lscale.py demo shows FM radio frequencies:

def legendcb(f):
    return '{:2.0f}'.format(88 + ((f + 1) / 2) * (108 - 88))

The above arithmetic aims to show the logic. It can be simplified.

Callback tickcb

This callback enables the tick color to be changed dynamically. For example a scale might change from green to orange, then to red as it nears the extremes. The callback takes two args, being the value of the tick (in range -1.0 <= v <= 1.0) and the default color. It must return a color. This example is taken from the lscale.py demo:

def tickcb(f, c):
    if f > 0.8:
        return RED
    if f < -0.8:
        return BLUE
    return c

increasing the ticks value

This increases the precision of the display.

It does this by lengthening the scale while keeping the window the same size, with 20 ticks displayed. If the scale becomes 10x longer, the value diference between consecutive large ticks and legends is divided by 10. This means that the tickcb callback must return a string having an additional significant digit. If this is not done, consecutive legends will have the same value.

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6. Control Classes

These classes provide touch-sensitive objects capable of both the display and entry of data. If the user moves the control, its value will change and an optional callback will be executed. If another control's callback or a coroutine alters a control's value, its appearance will change accordingly.

6.1 Class Button

This emulates a pushbutton, with a callback being executed each time the button is pressed. Buttons may be any one of three shapes: CIRCLE, RECTANGLE or CLIPPED_RECT.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Mandatory keyword only argument:

  • font Font for button text

Optional keyword only arguments:

  • shape CIRCLE, RECTANGLE or CLIPPED_RECT. Default RECTANGLE.
  • height Height of the bounding box. Default 20 pixels.
  • width Width of the bounding box. Default 50 pixels.
  • fill Boolean. If True the button will be filled with the current fgcolor.
  • fgcolor Color of foreground (the control itself). Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • fontcolor Text color. Defaults to system text color.
  • litcolor If provided the button will display this color for one second after being pressed.
  • text Shown in centre of button. Default: an empty string.
  • callback Callback function which runs when button is pressed.
  • args A list/tuple of arguments for the above callback. Default [].
  • onrelease Default True. If True the callback will occur when the button is released otherwise it will occur when pressed. See Application design note for the reason for this default.
  • lp_callback Callback to be used if button is to respond to a long press. Default None.
  • lp_args A list/tuple of arguments for above callback. Default [].

Method:

  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.

Class variables:

  • lit_time Period in seconds the litcolor is displayed. Default 1.
  • long_press_time Press duration for a long press. Default 1 second.
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6.2 Class ButtonList emulate a button with multiple states

A ButtonList groups a number of buttons together to implement a button which changes state each time it is pressed. For example it might toggle between a green Start button and a red Stop button. The buttons are defined and added in turn to the ButtonList object. Typically they will be the same size, shape and location but will differ in color and/or text. At any time just one of the buttons will be visible, initially the first to be added to the object.

Buttons in a ButtonList should not have callbacks. The ButtonList has its own user supplied callback which will run each time the object is pressed. However each button can have its own list of args. Callback arguments comprise the currently visible button followed by its arguments.

Constructor argument:

  • callback The callback function. Default does nothing.

Methods:

  • add_button Adds a button to the ButtonList. Arguments: as per the Button constructor. Returns the button object.
  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
  • value Optional argument: a button in the set. If supplied and the button is not active the currency changes to the supplied button and its callback is run. Always returns the active button.

Typical usage is as follows: ``python def callback(button, arg): print(arg)

table = [ {'fgcolor' : GREEN, 'shape' : CLIPPED_RECT, 'text' : 'Start', 'args' : ['Live']}, {'fgcolor' : RED, 'shape' : CLIPPED_RECT, 'text' : 'Stop', 'args' : ['Die']}, ] bl = ButtonList(callback) for t in table: # Buttons overlay each other at same location bl.add_button((10, 10), font = font14, fontcolor = BLACK, **t) ``

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6.3 Class RadioButtons

These comprise a set of buttons at different locations. When a button is pressed, it becomes highlighted and remains so until another button is pressed. A callback runs each time the current button is changed.

Constructor positional arguments:

  • highlight Color to use for the highlighted button. Mandatory.
  • callback Callback when a new button is pressed. Default does nothing.
  • selected Index of initial button to be highlighted. Default 0.

Methods:

  • add_button Adds a button. Arguments: as per the Button constructor. Returns the Button instance.
  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
  • value Optional argument: a button in the set. If supplied, and the button is not currently active, the currency changes to the supplied button and its callback is run. Always returns the currently active button.

Typical usage:

def callback(button, arg):
    print(arg)

table = [
    {'text' : '1', 'args' : ['1']},
    {'text' : '2', 'args' : ['2']},
    {'text' : '3', 'args' : ['3']},
    {'text' : '4', 'args' : ['4']},
]
x = 0
rb = RadioButtons(callback, BLUE) # color of selected button
for t in table:
    rb.add_button((x, 180), font = font14, fontcolor = WHITE,
                    fgcolor = LIGHTBLUE, height = 40, **t)
    x += 60 # Horizontal row of buttons
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6.4 Class Slider

These emulate linear potentiometers. Vertical Slider and horizontal HorizSlider variants are available. These are constructed and used similarly. The short forms (v) or (h) are used below to identify these variants. See the note above on callbacks.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Optional keyword only arguments:

  • font Font to use for any legends. Default None: no legends will be drawn.
  • height Dimension of the bounding box. Default 120 pixels (v), 20 (h).
  • width Dimension of the bounding box. Default 20 pixels (v), 120 (h).
  • divisions Number of graduations on the scale. Default 10.
  • legends A tuple of strings to display near the slider. These Label instances will be distributed evenly along its length, starting at the bottom (v) or left (h).
  • fgcolor Color of foreground (the control itself). Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • fontcolor Text color. Defaults to system text color.
  • slidecolor Color for the slider. Defaults to the foreground color.
  • border Width of border. Default None: no border will be drawn. If a value (typically 2) is provided, a border line will be drawn around the control.
  • cb_end Callback function which will run when the user stops touching the control.
  • cbe_args A list/tuple of arguments for above callback. Default [].
  • cb_move Callback function which will run when the user moves the slider or the value is changed programmatically.
  • cbm_args A list/tuple of arguments for above callback. Default [].
  • value The initial value. Default 0.0: slider will be at the bottom (v), left (h).

Methods:

  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
  • value Optional arguments val (default None). If supplied the slider moves to reflect the new value and the cb_move callback is triggered. The method constrains the range to 0.0 to 1.0. Always returns the control's value.
  • color Mandatory arg color The control is rendered in the selected color. This supports dynamic color changes
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6.5 Class Knob

This emulates a rotary control capable of being rotated through a predefined arc.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Optional keyword only arguments:

  • height Dimension of the square bounding box. Default 50 pixels.
  • arc Amount of movement available. Default 2*PI radians (360 degrees).
  • ticks Number of graduations around the dial. Default 9.
  • fgcolor Color of foreground (the control itself). Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • color Fill color for the control knob. Default: no fill.
  • border Width of border. Default None: no border will be drawn. If a value (typically 2) is provided, a border line will be drawn around the control.
  • cb_end Callback function which will run when the user stops touching the control.
  • cbe_args A list/tuple of arguments for above callback. Default [].
  • cb_move Callback function which will run when the user moves the knob or the value is changed.
  • cbm_args A list/tuple of arguments for above callback. Default [].
  • value Initial value. Default 0.0: knob will be at its most counter-clockwise position.

Methods:

  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
  • value Optional argument val. If set, adjusts the pointer to correspond to the new value. The move callback will run. The method constrains the range to 0.0 to 1.0. Always returns the control's value.
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6.6 Class Checkbox

This provides for boolean data entry and display. In the True state the control can show an 'X' or a filled block of any color.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Optional keyword only arguments:

  • height Dimension of the square bounding box. Default 20 pixels.
  • fillcolor Fill color of checkbox when True. Default None: an 'X' will be drawn.
  • fgcolor Color of foreground (the control itself). Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • border Width of border. Default None: no border will be drawn. If a value (typically 2) is provided, a border line will be drawn around the control.
  • callback Callback function which will run when the value changes.
  • args A list/tuple of arguments for above callback. Default [].
  • value Initial value. Default False.

Methods:

  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
  • value Optional boolean argument val. If the provided value does not correspond to the control's current value, updates it; the checkbox is re-drawn and the callback executed. Always returns the control's value.
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6.7 Class Listbox

The height of a listbox is determined by the number of entries in it and the font in use. Scrolling is not supported.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Mandatory keyword only arguments:

  • font
  • elements A list or tuple of strings to display. Must have at least one entry.

Optional keyword only arguments:

  • width Control width in pixels, default 80.
  • value Index of currently selected list item. Default 0.
  • border Space between border and contents. Default 2 pixels. If None no border will be drawn.
  • fgcolor Color of foreground (the control itself). Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • fontcolor Text color. Defaults to system text color.
  • select_color Background color for selected item in list. Default LIGHTBLUE.
  • callback Callback function which runs when a list entry is picked.
  • args A list/tuple of arguments for above callback. Default [].

Methods:

  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
  • value Argument val default None. If the argument is provided which is a valid index into the list that entry becomes current and the callback is executed. Always returns the index of the currently active entry.
  • textvalue Argument text a string default None. If the argument is provided and is in the control's list, that item becomes current. Returns the current string, unless the arg was provided but did not correspond to any list item. In this event the control's state is not changed and None is returned.

The callback is triggered whenever a listbox item is pressed, even if that item is already currently selected.

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6.8 Class Dropdown

A dropdown list. The list, when active, is drawn below the control. The height of the control is determined by the height of the font in use. The height of the list is determined by the number of entries in it and the font in use. Scrolling is not supported.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Mandatory keyword only arguments:

  • font
  • elements A list or tuple of strings to display. Must have at least one entry.

Optional keyword only arguments:

  • width Control width in pixels, default 100.
  • value Index of currently selected list item. Default 0.
  • fgcolor Color of foreground (the control itself). Defaults to system color.
  • bgcolor Background color of object. Defaults to system background.
  • fontcolor Text color. Defaults to system text color.
  • select_color Background color for selected item in list. Default LIGHTBLUE.
  • callback Callback function which runs when a list entry is picked.
  • args A list/tuple of arguments for above callback. Default [].

Methods:

  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
  • value Argument val default None. If the argument is provided which is a valid index into the list that entry becomes current and the callback is executed. Always returns the index of the currently active entry.
  • textvalue Argument text a string default None. If the argument is provided and is in the control's list, that item becomes current. Returns the current string, unless the arg was provided but did not correspond to any list item. In this event the control's state is not changed and None is returned.

The callback is triggered if an item on the dropdown list is touched and that item is not currently selected (i.e. when a change occurs).

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6.9 Class Pad

This rectangular touchable control is invisible. It can be used to enable display class instances to respond to touch, or to create other touch sensitive regions.

Constructor mandatory positional argument:

  1. location 2-tuple defining position.

Optional keyword only arguments:

  • height=20 Dimensions.
  • width=50
  • onrelease=True If True the callback will occur when the pad is released otherwise it will occur when pressed. See Application design note for the reason for this default.
  • callback=None Callback function which runs when button is pressed.
  • args=[] A list/tuple of arguments for the above callback.
  • lp_callback=None Callback to be used if button is to respond to a long press.
  • lp_args=[] A list/tuple of arguments for above callback.

Method:

  • greyed_out Optional boolean argument val default None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it - there is no visible effect.
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6.10 Class Textbox

Displays multiple lines of text in a field of fixed dimensions. Text may be clipped to the width of the control or may be word-wrapped. If the number of lines of text exceeds the height available, scrolling will occur. Access to text that has scrolled out of view may be achieved by touching the control or by calling a method.

Works with fixed and variable pitch fonts. Tab characters are supported for Python fonts (not for internal fonts): see Note on tabs.

from gui.widgets.textbox import Textbox

Constructor mandatory positional arguments:

  1. location 2-tuple defining position.
  2. width Width of the object in pixels.
  3. nlines Number of lines of text to display. The object's height is determined from the height of the font:
    height in pixels = nlines*font_height + 2*border
  4. font Font to use. The internal font IFont(3) renders faster than the Python fonts.

Keyword only arguments:

  • border=2 Border width in pixels - typically 2. If None, no border will be drawn.
  • fgcolor=None Color of border. Defaults to system color.
  • bgcolor=None Background color of object. Defaults to system background.
  • fontcolor=None Text color. Defaults to system text color.
  • clip=True By default lines too long to display are right clipped. If False is passed, word-wrap is attempted. If the line contains no spaces it will be wrapped at the right edge of the window.
  • repeat=True Controls the behaviour of touch-based scrolling. By default a long press causes repeated scrolling. False requires a discrete press for each line movement.
  • tab=32 Tab space in pixels: see Note on tabs.

Methods:

  • append Args s, ntrim=None, line=None Append the string s to the display and scroll up as required to show it. By default only the number of lines which will fit on screen are retained. If an integer ntrim=N is passed, only the last N lines are retained; ntrim may be greater than can be shown in the control, hidden lines being accessed by scrolling.
    If an integer (typically 0) is passed in line the display will scroll to show that line.
  • scroll Arg n Number of lines to scroll. A negative number scrolls up. If scrolling would achieve nothing because there are no extra lines to display, nothing will happen. Returns True if scrolling occurred, otherwise False.
  • value No args. Returns the number of lines of text stored in the widget.
  • clear No args. Clears all lines from the widget and refreshes the display.
  • goto Arg line=None Fast scroll to a line. By default shows the end of the text. 0 shows the start.

Fast updates:
Rendering text to the screen is relatively slow. To send a large amount of text the fastest way is to perform a single append. Text may contain newline ('\n') characters as required. In that way rendering occurs once only.

ntrim__ If text is regularly appended to a Textbox its buffer grows, using RAM. The value of ntrim sets a limit to the number of lines which are retained, with the oldest (topmost) being discarded as required.

6.10.1 Note on tabs

The purpose of tab characters is to align columns of text when using variable pitch fonts. With fixed pitch fonts (such as internal fonts) they serve no purpose which cannot be achieved by the Python format command. Hence they are unsupported for internal fonts whose rendering prioritises speed.

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7. Dialog Boxes

In general Screen objects occupy the entire physical display. The principal exception to this is modal dialog boxes which are rendered in a window which accepts all touch events until it is closed. Dialog boxes are created by instantiating an Aperture which is a Screen superclass. In effect this is a window, but a 'micro' implementation lacking chrome beyond a simple border and occupying a fixed location on the screen.

In use the user program creates a class subclassed from Aperture. This is populated in the same way as per Screen subclasses. The class name can then be passed to Screen.change to invoke the dialog box. The GUI provides a simple way to build dialog boxes based on a small set of pushbuttons such as 'Yes/No/Cancel' in the form of the DialogBox class.

A convenience method locn is provided to assist in populating dialog boxes. Given coordinates relative to the dialog box, it provides an absolute location 2-tuple suitable as a constructor argument for control or display classes. See ldb.py for example usage.

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7.1 Class Aperture

Provides a window for objects in a modal dialog box.

Constructor mandatory positional args:

  1. location 2-tuple defining the window position.
  2. height Dimensions in pixels.
  3. width

Optional keyword only args:

  • draw_border Boolean, default True. If set a single pixel window border will be drawn.
  • bgcolor Background color of window. Defaults to system background.
  • fgcolor Color of border. Defaults to system foreground.

Instance variables:

  • location 2-tuple defining the window position.
  • height Dimensions in pixels.
  • width

Method:

  • locn Args: x, y. Returns an absolute location 2-tuple given a pair of coordinates relative to the dialog box.

Class method:

  • value Optional arg val default None. Provides a mechanism for returning the outcome of a dialog box which can be queried by the calling object. If the arg is provided, the value is set. The arg may be any Python object. Returns the value of the Aperture class. The calling Screen can query this by implementing an on_open method which calls Aperture.value() (see ldb.py).
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7.2 Class DialogBox

Eases building a dialog box subset based on a row of pushbuttons. Any button press will close the dialog. The caller can determine which button was pressed. The size of the buttons and the width of the dialog box are calculated from the strings assigned to the buttons. This ensures that buttons are evenly spaced and identically sized.

Constructor mandatory positional args:

  1. font The font for buttons and label.

Optional keyword only args:

  • elements A list or tuple of 2-tuples. Each defines the text and color of a pushbutton, e.g. (('Yes', RED), ('No', GREEN)).
  • location 2-tuple defining the dialog box location. Default (20, 20).
  • label Text for an optional label displayed in the centre of the dialog box. Default None.
  • bgcolor Background color of window. Default DARKGREEN.
  • buttonwidth Minimum width of buttons. Default 25. In general button dimensions are calculated from the size of the strings in elements.
  • closebutton Boolean. If set, a close button will be displayed at the top RH corner of the dialog box.

Pressing any button closes the dialog and sets the Aperture value to the text of the button pressed or 'Close' in the case of the close button.

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8. Fonts

The LCD160CR contains internal fixed pitch fonts. These may be used as an alternative to external fonts converted from ttf or otf files and are likely to result in better text rendering at small sizes. External fonts enable arbitrary fonts to be used including ones with variable pitch.

8.1 External fonts

Fonts may be created using the font_to_py.py utility documented here. The -x argument should be employed. The resultant Python file may be imported and the module passed to the constructor of GUI objects. These files may be frozen as bytecode to radically reduce RAM usage.

The LCD160CR_G constructor has an optional constructor keyword argument bufsize. This defines the size of an internal character buffer, required if using external fonts. If an application's largest external font has dimensions h*w pixels, the buffer must be at least h*w*2 bytes in size. The default of 1058 bytes provides for external fonts up to 23 by 23 pixels.

A UguiException will be raised if an application attempts to use a font too large for the buffer.

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8.2 Internal fonts Class IFont

To use internal fonts an IFont is instantiated. The instance is then passed to GUI constructors in the same way as for external fonts. See test program ldb_if.py for an example.

Constructor mandatory positional arg:

  • family 0 to 3. Determines the size of the font.

Optional args:

  • scale Pixels are drawn as a square with side length equal to scale + 1. The value can be between 0 and 63 (default 0).
  • bold_h Controls the number of pixels to overdraw each character pixel in the horizontal direction making a bold effect. Value 0 to 3 (default 0).
  • bold_v Controls the number of pixels to overdraw each character pixel in the vertical direction making a bold effect. Value 0 to 3 (default 0).
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9. Issues

There was a problem with detection of long button presses (MicroPython issue #2879). This was resolved in early 2017 by an upgrade to the LCD160CR firmware. If running an old display device you may need to request an upgrade.

10. Application design note

There is an issue in a touch application where a control causes a new screen to overlay the current screen, or closes a screen to reveal the one below. Consider a X screen close button at the top right hand corner of each screen. If touched, the screen closes revealing the one below with its X button: the touch causes this immediately to be activated closing that screen too.

For this reason the Button class defaults to running the callback on release. While this fixes the problem of close buttons, it can introduce problems where buttons open screens: if multiple buttons are pressed at once, unexpected screen changes can occur. Either set such buttons to run the callback on press or use a control such as a listbox.

The general point, where screens change, is to consider how continuing touch will affect the new screen.

11. ESP32

The official display may be connected to non-Pyboard targets via I2C and SPI interfaces. Both interfaces are required by the GUI. The display has an AP2210 LDO voltage regulator so it may be powered from 5V or 3.3V. Connections may be made via the downward facing pins or the black connector at the end of the PCB. In my testing the SPI connections on that connector do not work, however the power and I2C connections were OK.

The downward facing pins are as follows. The table is arranged such that the black connector is at the top. The view is looking at the display surface.

Pin names are those on a mating Pyboard 1.x. Only signals with an entry in the Link column require connection to the target.

Pin Signal Link Signal Link Pin
Y1 UART Rx Vin 5V Vin
Y2 UART Tx NC 3V3
Y3 LCD CS1 Gnd Gnd Gnd
Y4 PWR PWR Rst Rst
Y5 SS\ LCD BL Y12
Y6 SCK SPI T-IRQ Y11
Y7 MISO SDA I2C Y10
Y8 MOSI SPI SCL I2C Y9

The PWR signal enables power to the display by turning on the internal LDO 3.3V regulator. It should be assigned to an arbitrary I/O pin. In testing I found it necessary to assert PWR and wait before instantiating the display (see code below). The display board has no I2C pullups. If the target lacks them, pullups to 3.3V on SDA and SCL are essential. Values are uncritical: 1.5KΩ to 4.7KΩ are typical.

Note on the SPI interface: the LCD160CR hardware does not implement MISO: SPI is from target to display only. Nor does it implement SS\ (also known as CS\) which means it requires exclusive access to the SPI bus.

The ESP32 allows arbitrary pin assignments, but the docs recommend hardware SPI on default pins for performance and reliability. Owing to the limited performance of I2C I would expect any pin configuration to work with this interface but I haven't tested this.

I tested with this wiring. The ESP column represents ESP32 GPIO numbers, the Pin column represents the name of the downward facing pin on the display. This is the Pyboard pin it would mate with, not the names on the silkscreen which refer to edge connectors. Once again this is the view looking down on the display with the 10-way black edge connector at the top.

Pin Signal ESP Signal ESP Pin
Y1 Vin 5V Vin
Y2
Y3 Gnd Gnd Gnd
Y4 PWR 25 Rst
Y5 Y12
Y6 SCK 14 Y11
Y7 SDA 19 Y10
Y8 MOSI 13 SCL 18 Y9

This code works on the reference board wired as above:

from gui.core import lcd160cr
from gui.core.lcd160_gui import Screen, LCD160CR_G
from gui.widgets.label import Label
import font10

from time import sleep_ms
from machine import Pin, I2C, SPI

class BaseScreen(Screen):
    def __init__(self):
        super().__init__()
        Label((0, 0), font = font10, value = 'Hello world')

def main():
    pwr = Pin(25, Pin.OUT)
    pwr(1)
    sleep_ms(100)  # Ensure device is ready
    # Hardware SPI on native pins for performance
    spi = SPI(1, 10_000_000, sck=Pin(14), mosi=Pin(13), miso=Pin(12))
    i2c = I2C(0, freq=1_000_000)  # scl=Pin(18), sda=Pin(19)
    lcd = LCD160CR_G(pwr=pwr, spi=spi, i2c=i2c)  # Set connection
    lcd.set_orient(lcd160cr.LANDSCAPE)  # and orientation
    Screen.setup(lcd)
    Screen.change(BaseScreen)

main()

To install the library on ESP32 the file lcd_local_esp.py should be copied to /pyboard/lcd_local.py after making any edits to support your physical connection and maximum font size.

The supplied framebuf_utils.mpy will produce a harmless warning message because the supplied example is compiled for STM architecture. To enable fast text rendering on ESP32 it is necessary to recompile framebuf_utils.mpy for xtensawin. This is discussed here.

When instantiating I2C and SPI buses on default pins, the I2C constructor does not require the pins to be explicitly specified. The SPI constructor does. The docs don't explicitly state this, but the provided code examples illustrate it.

Debug notes

If changing the pins or migrating to a different target the following errors can occur.

  • ENOENT or timeout exception: I2C problem. Check wiring, pullups and pwr state.
  • Blank display: check power connections and the pwr pin.
  • The GUI works but lacks text on buttons. Meters and sliders show corruption: this is an SPI problem.

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Touch GUI for the official MicroPython LCD display

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