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Guile-PNG Architecture

Copyright (C) Artyom V. Poptsov <[email protected]>

Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.

Architecture

The main goal of the project is to provide pure Scheme implementation of the PNG (RFC 2083) format for GNU Guile.

For the sake of the correctness the library should provide basic graphic primitives to draw and some basic image operations.

Code Map

Overview

All the GNU Guile modules are in modules directory. The library provides the basic png module that contains the procedures for reading/writing PNG images.

Guile-PNG uses OOP style in the form of GOOPS so most of the procedures operate on objects and/or return objects as the result.

Finite-State Machines (FSMs)

Guile-PNG compiles its Finite-State Machines (FSMs) for the PNG reader using Guile-SMC. The source files for FSMs are stored in (png fsm ...) modules.

*.puml files contain PlantUML description of the parser FSMs.

*.-context.scm files are providing the FSMs with the needed callbacks.

context.scm contains the callbacks and types provided by Guile-SMC.

Core Procedures

The core procedures for Guile-PNG are declared in (png core ...) modules.

Those modules contain:

  • PNG chunk types and procedures.
  • Error handling procedures.
  • CRC procedures.
  • PNG filtering procedures. Note that a “filter” in this context means an algorithm that is applied to an image to improve the lossless compression ratio.

Graphics

(png graphics ...) modules contain graphic types and primitives that allow to draw simple forms over PNG images.

All those modules are re-exported in (png graphics) module.

Image Processing

(png image-processing ...) modules contain some image processing procedures.

All those modules are re-exported in (png image-processing) module.

Examples

Examples are important as they provide a hint how the library can be used for real tasks.

Guile-PNG examples are stored in ./examples directory in the root of the repository.

Tests

Tests are in tests directory. They are written using SRFI-61.

When a new functionality is being added a new test case (or several test cases) should be written for it.