tiny_webp.h
Reasonably tiny, single-header WebP library in C99.
Examples
The API is explained in more detail below, but here are some quick examples:
Load RGB/RGBA:
// If you already have the file in memory, use twp_read_from_memory() instead.intwidth, height; unsigned char*data=twp_read("path/to/file.webp", &width, &height, twp_FORMAT_RGBA, // or twp_FORMAT_RGB0); // no flagsif (data) { } // Do something with the datafree(data);Get information about a .webp file:
// If you already have the file in memory, use twp_get_info_from_memory() instead.intwidth, height, lossless, alpha; intok=twp_get_info("path/to/file.webp", &width, &height, &lossless, &alpha); if (ok) { } // Do something with the infoLoad YUV/YUVA:
// This will return NULL if the image is lossless, use twp_get_info() to check first.// Note that WebP is 4:2:0, so width and height will be half for chroma.intwidth, height; unsigned char*data=twp_read("path/to/file.webp", &width, &height, twp_FORMAT_YUV, // or twp_FORMAT_YUVA0); // no flagsif (data) { unsigned char*y, *u, *v; intluma_stride, chroma_stride; twp_unpack_yuv(data, width, height, &y, &u, &v, NULL, // alpha plane is NULL since we want YUV&luma_stride, &chroma_stride, NULL); // alpha stride is NULL// Do something with the YUV datafree(data); // y, u and v are now invalid. Do not free() them! }Compilation
Copy tiny_webp.h into your project, then #define twp_IMPLEMENTATION in exactly one C/C++ file that #includes tiny_webp.h. For example:
#include<stdio.h>#include<stdlib.h>#definetwp_IMPLEMENTATION#include"tiny_webp.h"You can also do the #define twp_IMPLEMENTATION part at the end of a file. That way you don't see all the private symbols in your autocomplete:
#include"tiny_webp.h"intmain() { ... } #definetwp_IMPLEMENTATION#include"tiny_webp.h"Alternatively, you could also just create a .c file that is empty except for the #define and the #include.
API
unsigned char*twp_read(constchar*file_path, int*width, int*height, twp_formatformat, twp_flagsflags)Loads a .webp image from a file. You must free the result.
Returns NULL on error.
Formats:
twp_FORMAT_RGBA
twp_FORMAT_RGB
twp_FORMAT_YUV
twp_FORMAT_YUVA
YUV and YUVA will return NULL for lossless images. Use twp_get_info() to first check if you have a lossless or a lossy image.
For YUV and YUVA, you must call twp_unpack_yuv() on the result.
Flags:
twp_FLAG_SKIP_LOOP_FILTER: Skips loop filtering, which saves some decoding time, but slightly lowers quality.
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unsigned char*twp_read_from_memory(void*data, intdata_len, int*width, int*height, twp_formatformat, twp_flagsflags)The same as twp_read(), except it reads from memory instead.
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voidtwp_unpack_yuv(unsigned char*ptr, intwidth, intheight, unsigned char**y, unsigned char**u, unsigned char**v, unsigned char**a, int*luma_stride, int*chroma_stride, int*alpha_stride)If you loaded an image and requested either YUV or YUVA as the format, you must call this function to unpack the returned pointer into the individual planes and get the strides.
Do not free the returned Y, U, V, A pointers. Just free the original pointer returned from twp_read(). Y, U, V and A will be valid for as long as the original pointer is valid.
You can pass NULL if you don't care about a certain plane. For example, if you requested format YUV, there is no alpha, so pass NULL for the a and alpha_stride parameters.
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inttwp_get_info(constchar*file_path, int*width, int*height, int*lossless, int*alpha)Get information about a .webp file.
You can pass NULL if you don't care about something.
Returns 0 on error and 1 on success.
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inttwp_get_info_from_memory(void*data, intdata_len, int*width, int*height, int*lossless, int*alpha)The same as twp_get_info(), except it reads from memory instead.
Compile Time Options
Simply #define any of these. twp_STATIC needs to be seen by the header and the implementation. For all the others, only the implementation needs to see the #define. I recommend just putting them at the top of tiny_webp.h.
twp_STATIC: Define extern function to be static instead.
twp_NO_SIMD: Disable all SIMD optimizations.
twp_FORCE_SSE2: If for some reason SSE2 support wasn't correctly detected, you can force-enable it.
twp_SIGNED_RIGHT_SHIFT_FIX: This library heavily relies on right-shifting negative integers to compile to arithmetic shifts. Enable this option if your compiler does not guarantee this (which is unlikely, all major compilers do).
Current Limitations
Probably not as fast as libwebp
No encoding
No animations
SIMD optimizations are SSE2 only
License is not 0BSD, which would be my preference (but that's not my fault, see the next section)
License
As far as I understand, it's actually impossible to release an implementation of the WebP spec under anything more permissive than BSD3. The reason for this is that the spec uses C code everywhere, meaning if you read the code and then write an implementation, you have created a derivative work. If the spec was written purely in English, this would not be a problem, because implementing something described in English does not count as a derivative work of that description. The spec further says that "the bitstream is defined by the reference source code and not this narrative." So, really, the source code is the spec, and therefore any implementation of the spec is a derivative work.
It seems to me, then, that a bunch of WebP/WebM/VP8 implementations floating around the web are quite openly violating the license.
If Google could re-license the spec to 0BSD or something, that would be great.