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This is README for QLogo.


QLogo is in a state of transition. This version barely works!

If you want a fully working version of QLogo source you need to checkout Version 0.92! You can get this either by issuing the following command in your local QLogo repository:

$ git checkout v0.92

OR, you can download QLogo Version 0.92 source on QLogo's download page:

QLogo is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

QLogo is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with QLogo. If not, see

QLogo Icon

QLogo is an interpreter for the Logo language written in C++ using Qt and OpenGL. It mimics (as much as I find reasonable) the UCBLogo interpreter developed by Brian Harvey at U.C. Berkeley.

You can find the UCBLogo Manual here:

The differences between QLogo and UCBLogo are described in the nuances section below.


QLogo requires Qt6 and is currently being developed and tested on the following platforms:

  • Windows 10 using MinGW 8.1.0
  • OpenSUSE LEAP 15.2 using gcc 7.5.0
  • Mac OS X 11.3 using Clang 12.0.5

To build:

$ cmake CMakeLists.txt

$ make

This will give you two executables:

  1. "logo": this is the Logo interpreter that can be run from the command line.

  2. "QLogo": this is the graphical user interface that runs logo and gives you the turtle. (The turtle is one of the many things that's broken right now, but when it works again this is where you'll find it.)

There is no "make install" step yet.

There are a few nuances:

  • Colors can be specified in one of three ways:

    • as a palette index (0 to 100)

    • as a list of 3 percentages, one for each of red, green, blue [0 0 0] is black, [100 100 100] is white

    • as a named color from the X Color Database, e.g. white or lemonchiffon. The X Color database can be found here:

  • Changes in font properties (size, color, family) do not affect characters already printed. This enables multiple colors and fonts on the same console, but it disables any flash or strobe effect.

  • The entire Logo standard library is loaded internally and buried. There is no library directory at this time.

  • QLogo does not look for nor automatically load STARTUP.LG.

  • If ERRACT is set and its size is greater than zero, then any errors execute PAUSE. This was necessary because I couldn't find a reliable way to prevent infinite loops during error handling.

  • Garbage collection is on-the-fly, meaning that memory is freed the moment a word/list/array is no longer needed. GC and .SETSEGMENTSIZE are no-ops.

  • SAVEPICT saves a copy of the canvas in the format given by the filename's extension. For example: SAVEPICT "MY_PICTURE.PNG will save in PNG format. QLogo can save an image in the following formats: BMP, JPG/JPEG, PNG, PPM, XBM, and XPM

  • HELP is functional, but the text is a copy of the UCBLogo help text. As such, it should be 99.9% correct. This will be fixed.

  • There is no facility yet for translation/internationalization. Yet.

The following commands are not implemented:


The original purpose of the command was to enable text to be visible on projectors which cut off outer boundaries of a computer screen. Projectors and monitors produced in the last few years show all of the computer screen. On top of that QLogo is a windowed application so an instructor or presentor can move the window to a different position.


Two reasons: One of the user interface principles was that the canvas should be device resolution-independent. That means when the QLogo window is resized or the separator between the text and the graphics is moved the graphics will remain consistent. The Flood Fill algorithm depends on specific pixels which means that the display can change dramatically depending on the size of the canvas. The other reason is that the Flood Fill algorithm can slow down window resizing. Use FILLED instead.


This will be implemented soon.


This will be replaced by SVGPICT.


Not implemented yet.


Not implemented yet.


QLogo uses a built-in editor.


The QLogo library is stored internally.


The help text is stored internally by the application. There is no external file.


QLogo doesn't create temporary files at this time.

The following variables have no special meaning:


QLogo is a GUI application at the moment, although a significant amount of thought is being given to make this also a command-line program.


Qt has strong support for internationalization, but QLogo is not designed at this time to take advantage of that. Internationalization will be supported soon.



The following commands are NEW:


Returns a list of all the fonts available on your system.


Sets cursor to insert mode, this is the default.


Sets cursor to overwrite mode.


Outputs either INSERT or OVERWRITE.


Outputs a list of two numbers giving the maximum bounds (x,y) of the canvas. e.g. bounds of [350 150] means that the turtle is visible if its X-coordinate is between -350 and 350 and its Y-coordinate is between -150 and 150. The coordinate [0, 0] is always in the center. See SETBOUNDS


Takes two integers and sets outer bounds of the canvas. See BOUNDS.


This exists for debugging and may be removed. Outputs a list of four lists, each sublist contains four numbers. This is the matrix that represents the current turtle state. In row-major order.


QLogo is a rewrite of the UCBLogo language and user interface with UCB compatibility. It is cross-platform and uses hardware-accelerated graphics.








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