Simple VP8L bit stream decoder written in both C (or C++, both valid) and Zig. VP8L is a image format used by the WebP format in lossless mode. WebP decoders usually support both lossless and lossy mode, which makes them significantly bigger than necessary if you only want lossless. So Whale does only the absolute minimum to parse VP8L bit stream and output RGBA pixel array.
Use the function
void *whale_decode(
void *user_data,
// interface
unsigned long (*stream) (unsigned char n, void *user_data),
void* (*alloc) (unsigned long n, void *user_data),
void (*free) (void *block, void *user_data),
// output
unsigned *width,
unsigned *height
);to decode VP8L bit stream.
Stream function takes argument n and returns an integer with n least-significant bits set to n bits from bit stream. For example, if n is 5 and next bits in the stream are -> 1 1 1 0 1 ... the function will return 0b00...0010111
Function will return an array of pixels in scan-line order, each pixel represented by 4 bytes first being red, second green, third blue and forth alpha component. So the result is RGBARGBARGBA... No padding or alignment is added between pixels or lines. This array is allocated using interface alloc function and the caller is responsible for freeing it.
There is no need for build system and so no build system or script is provided. Just add whale.c in your sources and whale.h in your include directories.
example.c uses Whale as header-only library (see below). To compile the example, run
gcc example.c -o webp2tga
or whatever equivalent command your favorite c/c++ compiler use.
To compile in visual studio, just add the example.c file to a project and compile.
whale.c can be used as a header-only library.
#include "whale.c"Whale is written to be valid c and c++ code so it can be included into both.
However whale.c can only be included in single source file as no guards or IMPLEMENTATION macros are present and this would result in multiple definitions of whale_decode symbol.
All symbols in whale.c are prefixed using vp8l_ prefix and are static (except whale_decode).
If you know for sure that you are only decoding specific set of images which doesn't use one or more of four transforms used by VP8L, you can disable the transform by defining one of 4 macros:
WHALE_DISABLE_PREDICTOR_TRANSFORM
WHALE_DISABLE_COLOR_TRANSFORM
WHALE_DISABLE_SUBTRACT_GREEN_TRANSFORM
WHALE_DISABLE_INDEX_TRANSFORM
Repository contains whale.zig file which contains whale decoder rewritten in Zig. This version works more-less the same as the C version, just more Zig-ified. See comments in the source code.
The code is currently compatible with 0.13-dev version of the Zig compiler. Let's see how long it is going to take before some breaking change comes.
This library has no error codes, asserts or any runtime checks whatsoever. The input stream has to be correct otherwise your program will output garbage or more likely crash.
Copyright (c) 2023 Matej Fencl
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