python

Extending SkoolKit

Extension modules

While creating a disassembly of a game, you may find that SkoolKit's suite of skool macros <skoolMacros> is inadequate for certain tasks. For example, the game might have large tile-based sprites that you want to create images of for the HTML disassembly, and composing long udgArray macros for them would be too tedious. Or you might want to insert a timestamp in the header of the ASM disassembly so that you (or others) can keep track of when your ASM files were written.

One way to solve these problems is to add custom methods that could be called by a call macro. But where to add the methods? SkoolKit's core HTML-writing and ASM-writing classes are skoolkit.skoolhtml.HtmlWriter and skoolkit.skoolasm.AsmWriter, so you could add the methods to those classes. But a better way is to subclass HtmlWriter and AsmWriter in a separate extension module, and add the methods there; then that extension module can be easily used with different versions of SkoolKit, and shared with other people.

A minimal extension module would look like this:

# Extension module in the skoolkit package directory
from .skoolhtml import HtmlWriter
from .skoolasm import AsmWriter

class GameHtmlWriter(HtmlWriter):
    pass

class GameAsmWriter(AsmWriter):
    pass

The next step is to get SkoolKit to use the extension module for your game. First, place the extension module (let's call it game.py) in the skoolkit package directory; to locate this directory, run skool2html.py with the -p option:

$ skool2html.py -p
/usr/lib/python2.7/dist-packages/skoolkit

(The package directory may be different on your system.) With game.py in place, add the following line to the ref-Config section of your disassembly's ref file:

HtmlWriterClass=skoolkit.game.GameHtmlWriter

If you don't have a ref file yet, create one (ideally named game.ref, assuming the skool file is game.skool); if the ref file doesn't have a [Config] section yet, add one.

Now whenever skool2html.py is run on your skool file (or ref file), SkoolKit will use the GameHtmlWriter class instead of the core HtmlWriter class.

To get skool2asm.py to use GameAsmWriter instead of the core AsmWriter class when it's run on your skool file, add the following writer ASM directive somewhere after the @start directive, and before the @end directive (if there is one):

; @writer=skoolkit.game.GameAsmWriter

The skoolkit package directory is a reasonable place for an extension module, but it could be placed in another package, or somewhere else as a standalone module. For example, if you wanted to keep a standalone extension module in ~/.skoolkit, it should look like this:

# Standalone extension module
from skoolkit.skoolhtml import HtmlWriter
from skoolkit.skoolasm import AsmWriter

class GameHtmlWriter(HtmlWriter):
    pass

class GameAsmWriter(AsmWriter):
    pass

Then, assuming the extension module is game.py, the HtmlWriterClass parameter should be set thus:

HtmlWriterClass=~/.skoolkit:game.GameHtmlWriter

and the @writer directive should be set thus:

; @writer=~/.skoolkit:game.GameAsmWriter

#CALL methods

Implementing a method that can be called by a call macro is done by adding the method to the HtmlWriter or AsmWriter subclass in the extension module.

One thing to be aware of when adding a #CALL method to a subclass of HtmlWriter is that the method must accept an extra parameter in addition to those passed from the #CALL macro itself: cwd. This parameter is set to the current working directory of the file from which the #CALL macro is executed, which may be useful if the method needs to provide a hyperlink to some other part of the disassembly (as in the case where an image is being created).

Let's say your sprite-image-creating method will accept two parameters (in addition to cwd): sprite_id (the sprite identifier) and fname (the image filename). The method (let's call it sprite) would look something like this:

from .skoolhtml import HtmlWriter

class GameHtmlWriter(HtmlWriter):
    def sprite(self, cwd, sprite_id, fname):
        img_path = self.image_path(fname)
        if self.need_image(img_path):
            udgs = self.build_sprite(sprite_id)
            self.write_image(img_path, udgs)
        return self.img_element(cwd, img_path)

With this method (and an appropriate implementation of the build_sprite method) in place, it's possible to use a #CALL macro like this:

#UDGTABLE
{ #CALL:sprite(3,jumping) }
{ Sprite 3 (jumping) }
TABLE#

Adding a #CALL method to the AsmWriter subclass is equally simple. The timestamp-creating method (let's call it timestamp) would look something like this:

import time
from .skoolasm import AsmWriter

class GameAsmWriter(AsmWriter):
    def timestamp(self):
        return time.strftime("%a %d %b %Y %H:%M:%S %Z")

With this method in place, it's possible to use a #CALL macro like this:

; This ASM file was generated on #CALL:timestamp()

Skool macros

Another way to add a custom method is to implement it as a skool macro. The main differences between a skool macro and a #CALL method are:

a #CALL macro's parameters are automatically evaluated and passed to the #CALL method; a skool macro's parameters must be parsed and evaluated manually (typically by using one or more of the macro-parsing utility functions <ext-MacroParsing>)
every optional parameter in a skool macro can be assigned a default value if omitted; in a #CALL method, only the optional arguments at the end can be assigned default values if omitted, whereas any others are set to None
numeric parameters in a #CALL macro are automatically converted to numbers before being passed to the #CALL method; no automatic conversion is done on the parameters of a skool macro

In summary: a #CALL method is generally simpler to implement than a skool macro, but skool macros are more flexible.

Implementing a skool macro is done by adding a method named expand_macroname to the HtmlWriter or AsmWriter subclass in the extension module. So, to implement a #SPRITE or #TIMESTAMP macro, we would add a method named expand_sprite or expand_timestamp.

A skool macro method must accept either two or three parameters, depending on whether it is implemented on a subclass of AsmWriter or HtmlWriter:

text - the text that contains the skool macro
index - the index of the character after the last character of the macro name (that is, where to start looking for the macro's parameters)
cwd - the current working directory of the file from which the macro is being executed; this parameter must be supported by skool macro methods on an HtmlWriter subclass

A skool macro method must return a 2-tuple of the form (end, string), where end is the index of the character after the last character of the macro's parameter string, and string is the HTML or text to which the macro should be expanded.

The expand_sprite method on GameHtmlWriter may therefore look something like this:

from .skoolhtml import HtmlWriter

class GameHtmlWriter(HtmlWriter):
    # #SPRITEspriteId[{X,Y,W,H}](fname)
    def expand_sprite(self, text, index, cwd):
        end, img_path, crop_rect, sprite_id = self.parse_image_params(text, index, 1)
        if self.need_image(img_path):
            udgs = self.build_sprite(sprite_id)
            self.write_image(img_path, udgs, crop_rect)
        return end, self.img_element(cwd, img_path)

With this method (and an appropriate implementation of the build_sprite method) in place, the #SPRITE macro might be used like this:

#UDGTABLE
{ #SPRITE3(jumping) }
{ Sprite 3 (jumping) }
TABLE#

The expand_timestamp method on GameAsmWriter would look something like this:

import time
from .skoolasm import AsmWriter

class GameAsmWriter(AsmWriter):
    def expand_timestamp(self, text, index):
        return index, time.strftime("%a %d %b %Y %H:%M:%S %Z")

Parsing skool macros

The skoolkit.skoolmacro module provides some utility functions that may be used to parse the parameters of a skool macro.

skoolkit.skoolmacro.parse_ints

skoolkit.skoolmacro.parse_params

3.6 The except_chars and only_chars parameters.

HtmlWriter also provides a method for parsing the parameters of an image-creating skool macro.

skoolkit.skoolhtml.HtmlWriter.parse_image_params

3.6 If path_id is blank or None, image_path is equal to fname.

3.6 The ints parameter.

Parsing ref files

HtmlWriter provides some convenience methods for extracting text and data from ref files. These methods are described below.

skoolkit.skoolhtml.HtmlWriter.get_section

skoolkit.skoolhtml.HtmlWriter.get_sections

skoolkit.skoolhtml.HtmlWriter.get_dictionary

skoolkit.skoolhtml.HtmlWriter.get_dictionaries

Memory snapshots

The snapshot attribute on HtmlWriter and AsmWriter is a 65536-element list that is populated with the contents of any DEFB, DEFM, DEFS and DEFW statements in the skool file.

A simple #PEEK macro that expands to the value of the byte at a given address might be implemented by using snapshot like this:

from .skoolhtml import HtmlWriter
from .skoolasm import AsmWriter
from .skoolmacro import parse_ints

class GameHtmlWriter(HtmlWriter):
    # #PEEKaddress
    def expand_peek(self, text, index, cwd):
        end, address = parse_ints(text, index, 1)
        return end, str(self.snapshot[address])

class GameAsmWriter(AsmWriter):
    # #PEEKaddress
    def expand_peek(self, text, index):
        end, address = parse_ints(text, index, 1)
        return end, str(self.snapshot[address])

HtmlWriter also provides some methods for saving and restoring memory snapshots, which can be useful for temporarily changing graphic data or the contents of data tables. These methods are described below.

skoolkit.skoolhtml.HtmlWriter.push_snapshot

skoolkit.skoolhtml.HtmlWriter.pop_snapshot

skoolkit.skoolhtml.HtmlWriter.get_snapshot_name

Graphics

If you are going to implement custom image-creating #CALL methods or skool macros, you will need to make use of the skoolkit.skoolhtml.Udg class.

The Udg class represents an 8x8 graphic (8 bytes) with a single attribute byte, and an optional mask.

skoolkit.skoolhtml.Udg

A simple #INVERSE macro that creates an inverse image of a UDG might be implemented like this:

from .skoolhtml import HtmlWriter, Udg
from .skoolmacro import parse_ints

class GameHtmlWriter(HtmlWriter):
    # #INVERSEaddress,attr
    def expand_inverse(self, text, index, cwd):
        end, address, attr = parse_ints(text, index, 2)
        img_path = self.image_path('inverse{0}_{1}'.format(address, attr))
        if self.need_image(img_path):
            udg_data = [b ^ 255 for b in self.snapshot[address:address + 8]]
            udg = Udg(attr, udg_data)
            self.write_image(img_path, [[udg]])
        return end, self.img_element(cwd, img_path)

The Udg class provides two methods for manipulating an 8x8 graphic: flip and rotate.

skoolkit.skoolhtml.Udg.flip

skoolkit.skoolhtml.Udg.rotate

If you are going to implement #CALL methods or skool macros that create animated images, you will need to make use of the skoolkit.skoolhtml.Frame class.

The Frame class represents a single frame of an animated image.

skoolkit.skoolhtml.Frame

3.6

HtmlWriter provides the following image-related convenience methods.

skoolkit.skoolhtml.HtmlWriter.image_path

skoolkit.skoolhtml.HtmlWriter.need_image

skoolkit.skoolhtml.HtmlWriter.write_image

skoolkit.skoolhtml.HtmlWriter.write_animated_image

3.6

skoolkit.skoolhtml.HtmlWriter.img_element

skoolkit.skoolhtml.HtmlWriter.screenshot

skoolkit.skoolhtml.HtmlWriter.flip_udgs

skoolkit.skoolhtml.HtmlWriter.rotate_udgs

HtmlWriter initialisation

If your HtmlWriter subclass needs to perform some initialisation tasks, such as creating instance variables, or parsing ref file sections, the place to do that is the init() method.

skoolkit.skoolhtml.HtmlWriter.init

For example:

from .skoolhtml import HtmlWriter

class GameHtmlWriter(HtmlWriter):
    def init(self):
        # Get character names from the ref file
        self.characters = self.get_dictionary('Characters')

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extending.rst

extending.rst

Extending SkoolKit

Extension modules

#CALL methods

Skool macros

Parsing skool macros

Parsing ref files

Memory snapshots

Graphics

HtmlWriter initialisation

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Extending SkoolKit

Extension modules

#CALL methods

Skool macros

Parsing skool macros

Parsing ref files

Memory snapshots

Graphics

HtmlWriter initialisation