qoi/qoi.h

/*

QOI - The "Quite OK Image" format for fast, lossless image compression

Dominic Szablewski - https://phoboslab.org


-- LICENSE: The MIT License(MIT)

Copyright(c) 2021 Dominic Szablewski

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files(the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and / or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions :
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.


-- About

QOI encodes and decodes images in a lossless format. An encoded QOI image is
usually around 10--30% larger than a decently optimized PNG image.

QOI outperforms simpler PNG encoders in compression ratio and performance. QOI
images are typically 20% smaller than PNGs written with stbi_image. Encoding is 
25-50x faster and decoding is 3-4x faster than stbi_image or libpng.


-- Synopsis

// Define `QOI_IMPLEMENTATION` in *one* C/C++ file before including this
// library to create the implementation.

#define QOI_IMPLEMENTATION
#include "qoi.h"

// Encode and store an RGBA buffer to the file system. The qoi_desc describes
// the input pixel data.
qoi_write("image_new.qoi", rgba_pixels, &(qoi_desc){
	.width = 1920,
	.height = 1080, 
	.channels = 4,
	.colorspace = QOI_SRGB
});

// Load and decode a QOI image from the file system into a 32bbp RGBA buffer.
// The qoi_desc struct will be filled with the width, height, number of channels
// and colorspace read from the file header.
qoi_desc desc;
void *rgba_pixels = qoi_read("image.qoi", &desc, 4);



-- Documentation

This library provides the following functions;
- qoi_read    -- read and decode a QOI file
- qoi_decode  -- decode the raw bytes of a QOI image from memory
- qoi_write   -- encode and write a QOI file
- qoi_encode  -- encode an rgba buffer into a QOI image in memory

See the function declaration below for the signature and more information.

If you don't want/need the qoi_read and qoi_write functions, you can define
QOI_NO_STDIO before including this library.

This library uses malloc() and free(). To supply your own malloc implementation
you can define QOI_MALLOC and QOI_FREE before including this library.

This library uses memset() to zero-initialize the index. To supply your own 
implementation you can define QOI_ZEROARR before including this library.


-- Data Format

A QOI file has a 14 byte header, followed by any number of data "chunks" and an
8-byte end marker.

struct qoi_header_t {
	char     magic[4];   // magic bytes "qoif"
	uint32_t width;      // image width in pixels (BE)
	uint32_t height;     // image height in pixels (BE)
	uint8_t  channels;   // 3 = RGB, 4 = RGBA
	uint8_t  colorspace; // 0 = sRGB with linear alpha, 1 = all channels linear
};

The decoder and encoder start with {r: 0, g: 0, b: 0, a: 255} as the previous
pixel value. Pixels are either encoded as
 - a run of the previous pixel
 - an index into an array of previously seen pixels
 - a difference to the previous pixel value in r,g,b
 - full r,g,b or r,g,b,a values

The color channels are assumed to not be premultiplied with the alpha channel 
("un-premultiplied alpha").

Each chunk starts with a 2- or 8-bit tag, followed by a number of data bits. The 
bit length of chunks is divisible by 8 - i.e. all chunks are byte aligned. All 
values encoded in these data bits have the most significant bit on the left.

The 8-bit tags have precedence over the 2-bit tags. A decoder must check for the
presence of an 8-bit tag first.

The byte stream's end is marked with 7 0x00 bytes followed a single 0x01 byte.

A running FIFO array[64] (zero-initialized) of pixel values is maintained by the
encoder and decoder. Every pixel en-/decoded by the QOI_OP_DIFF, QOI_OP_LUMA, 
QOI_OP_RGB and QOI_OP_RGBA chunks is written to this array. The write position
starts at 0 and is incremented with each pixel written. The position wraps back
to 0 when it reaches 64. I.e:
	index[index_pos % 64] = current_pixel;
	index_pos = index_pos + 1;

An encoder can search this array for the current pixel value and, if a match is
found, emit a QOI_OP_INDEX with the position within the array.


The possible chunks are:


.- QOI_OP_INDEX ----------.
|         Byte[0]         |
|  7  6  5  4  3  2  1  0 |
|-------+-----------------|
|  0  0 |     index       |
`-------------------------`
2-bit tag b00
6-bit index into the color index array: 0..63

A valid encoder must not issue 7 or more consecutive QOI_OP_INDEX chunks to the
index 0, to avoid confusion with the 8 byte end marker. 


.- QOI_OP_DIFF -----------. 
|         Byte[0]         |
|  7  6  5  4  3  2  1  0 |
|-------+-----+-----+-----|
|  0  1 |  dr |  dg |  db |
`-------------------------`
2-bit tag b01
2-bit   red channel difference from the previous pixel between -2..1
2-bit green channel difference from the previous pixel between -2..1
2-bit  blue channel difference from the previous pixel between -2..1

The difference to the current channel values are using a wraparound operation, 
so "1 - 2" will result in 255, while "255 + 1" will result in 0.

Values are stored as unsigned integers with a bias of 2. E.g. -2 is stored as 
0 (b00). 1 is stored as 3 (b11).


.- QOI_OP_LUMA -------------------------------------. 
|         Byte[0]         |         Byte[1]         |
|  7  6  5  4  3  2  1  0 |  7  6  5  4  3  2  1  0 |
|-------+-----------------+-------------+-----------|
|  1  0 |  green diff     |   dr - dg   |  db - dg  |
`---------------------------------------------------`
2-bit tag b10
6-bit green channel difference from the previous pixel -32..31
4-bit   red channel difference minus green channel difference -8..7
4-bit  blue channel difference minus green channel difference -8..7

The green channel is used to indicate the general direction of change and is 
encoded in 6 bits. The red and green channels (dr and db) base their diffs off
of the green channel difference and are encoded in 4 bits. I.e.:
	dr_dg = (last_px.r - cur_px.r) - (last_px.g - cur_px.g)
	db_dg = (last_px.b - cur_px.b) - (last_px.g - cur_px.g)

The difference to the current channel values are using a wraparound operation, 
so "10 - 13" will result in 253, while "250 + 7" will result in 1.

Values are stored as unsigned integers with a bias of 32 for the green channel 
and a bias of 8 for the red and blue channel.


.- QOI_OP_RUN ------------.
|         Byte[0]         |
|  7  6  5  4  3  2  1  0 |
|-------+-----------------|
|  1  1 |       run       |
`-------------------------`
2-bit tag b11
6-bit run-length repeating the previous pixel: 1..62

The run-length is stored with a bias of 1. Note that the run-lengths 63 and 64 
(b111110 and b111111) are illegal as they are occupied by the QOI_OP_RGB and 
QOI_OP_RGBA tags.


.- QOI_OP_RGB ------------------------------------------.
|         Byte[0]         | Byte[1] | Byte[2] | Byte[3] |
|  7  6  5  4  3  2  1  0 | 7 .. 0  | 7 .. 0  | 7 .. 0  |
|-------------------------+---------+---------+---------|
|  1  1  1  1  1  1  1  0 |   red   |  green  |  blue   |
`-------------------------------------------------------`
8-bit tag b11111110
8-bit   red channel value
8-bit green channel value
8-bit  blue channel value


.- QOI_OP_RGBA ---------------------------------------------------.
|         Byte[0]         | Byte[1] | Byte[2] | Byte[3] | Byte[4] |
|  7  6  5  4  3  2  1  0 | 7 .. 0  | 7 .. 0  | 7 .. 0  | 7 .. 0  |
|-------------------------+---------+---------+---------+---------|
|  1  1  1  1  1  1  1  1 |   red   |  green  |  blue   |  alpha  |
`-----------------------------------------------------------------`
8-bit tag b11111111
8-bit   red channel value
8-bit green channel value
8-bit  blue channel value
8-bit alpha channel value


The byte stream is padded at the end with 8 zero bytes. Since the longest legal 
chunk is 5 bytes (QOI_OP_RGBA), with this padding it is possible to check for an
overrun only once per decode loop iteration. These 0x00 bytes also mark the end
of the data stream, as an encoder should never produce 8 consecutive zero bytes
within the stream.

*/


/* -----------------------------------------------------------------------------
Header - Public functions */

#ifndef QOI_H
#define QOI_H

#ifdef __cplusplus
extern "C" {
#endif

/* A pointer to a qoi_desc struct has to be supplied to all of qoi's functions. 
It describes either the input format (for qoi_write and qoi_encode), or is 
filled with the description read from the file header (for qoi_read and
qoi_decode).

The colorspace in this qoi_desc is an enum where 
	0 = sRGB, i.e. gamma scaled RGB channels and a linear alpha channel
	1 = all channels are linear
You may use the constants QOI_SRGB or QOI_LINEAR. The colorspace is purely 
informative. It will be saved to the file header, but does not affect
en-/decoding in any way. */

#define QOI_SRGB   0
#define QOI_LINEAR 1

typedef struct {
	unsigned int width;
	unsigned int height;
	unsigned char channels;
	unsigned char colorspace;
} qoi_desc;

#ifndef QOI_NO_STDIO

/* Encode raw RGB or RGBA pixels into a QOI image and write it to the file 
system. The qoi_desc struct must be filled with the image width, height, 
number of channels (3 = RGB, 4 = RGBA) and the colorspace. 

The function returns 0 on failure (invalid parameters, or fopen or malloc 
failed) or the number of bytes written on success. */

int qoi_write(const char *filename, const void *data, const qoi_desc *desc);


/* Read and decode a QOI image from the file system. If channels is 0, the
number of channels from the file header is used. If channels is 3 or 4 the
output format will be forced into this number of channels.

The function either returns NULL on failure (invalid data, or malloc or fopen
failed) or a pointer to the decoded pixels. On success, the qoi_desc struct 
will be filled with the description from the file header.

The returned pixel data should be free()d after use. */

void *qoi_read(const char *filename, qoi_desc *desc, int channels);

#endif /* QOI_NO_STDIO */


/* Encode raw RGB or RGBA pixels into a QOI image in memory.

The function either returns NULL on failure (invalid parameters or malloc 
failed) or a pointer to the encoded data on success. On success the out_len 
is set to the size in bytes of the encoded data.

The returned qoi data should be free()d after use. */

void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len);


/* Decode a QOI image from memory.

The function either returns NULL on failure (invalid parameters or malloc 
failed) or a pointer to the decoded pixels. On success, the qoi_desc struct 
is filled with the description from the file header.

The returned pixel data should be free()d after use. */

void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels);


#ifdef __cplusplus
}
#endif
#endif /* QOI_H */


/* -----------------------------------------------------------------------------
Implementation */

#ifdef QOI_IMPLEMENTATION
#include <stdlib.h>
#include <string.h>

#ifndef QOI_MALLOC
	#define QOI_MALLOC(sz) malloc(sz)
	#define QOI_FREE(p)    free(p)
#endif
#ifndef QOI_ZEROARR
	#define QOI_ZEROARR(a) memset((a),0,sizeof(a))
#endif

#define QOI_OP_INDEX  0x00 /* 00xxxxxx */
#define QOI_OP_DIFF   0x40 /* 01xxxxxx */
#define QOI_OP_LUMA   0x80 /* 10xxxxxx */
#define QOI_OP_RUN    0xc0 /* 11xxxxxx */
#define QOI_OP_RGB    0xfe /* 11111110 */
#define QOI_OP_RGBA   0xff /* 11111111 */

#define QOI_MASK_2    0xc0 /* 11000000 */

#define QOI_MAGIC \
	(((unsigned int)'q') << 24 | ((unsigned int)'o') << 16 | \
	 ((unsigned int)'i') <<  8 | ((unsigned int)'f'))
#define QOI_HEADER_SIZE 14

/* To not have to linearly search through the color index array, we use a hash 
of the color value to quickly lookup the index position in a hash table. */
#define QOI_COLOR_HASH(C) (C.rgba.r*3 + C.rgba.g*5 + C.rgba.b*7 + C.rgba.a*11)
#define QOI_COLOR_HASH_SIZE 1024

/* 2GB is the max file size that this implementation can safely handle. We guard
against anything larger than that, assuming the worst case with 5 bytes per 
pixel, rounded down to a nice clean value. 400 million pixels ought to be 
enough for anybody. */
#define QOI_PIXELS_MAX ((unsigned int)400000000)

typedef union {
	struct { unsigned char r, g, b, a; } rgba;
	unsigned int v;
} qoi_rgba_t;

static const unsigned char qoi_padding[8] = {0,0,0,0,0,0,0,1};

void qoi_write_32(unsigned char *bytes, int *p, unsigned int v) {
	bytes[(*p)++] = (0xff000000 & v) >> 24;
	bytes[(*p)++] = (0x00ff0000 & v) >> 16;
	bytes[(*p)++] = (0x0000ff00 & v) >> 8;
	bytes[(*p)++] = (0x000000ff & v);
}

unsigned int qoi_read_32(const unsigned char *bytes, int *p) {
	unsigned int a = bytes[(*p)++];
	unsigned int b = bytes[(*p)++];
	unsigned int c = bytes[(*p)++];
	unsigned int d = bytes[(*p)++];
	return a << 24 | b << 16 | c << 8 | d;
}

void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len) {
	int i, max_size, p, run;
	int px_len, px_end, px_pos, channels;
	unsigned char *bytes;
	const unsigned char *pixels;
	unsigned int index_lookup[QOI_COLOR_HASH_SIZE];
	unsigned int index_pos = 0;
	qoi_rgba_t index[64];
	qoi_rgba_t px, px_prev;

	if (
		data == NULL || out_len == NULL || desc == NULL ||
		desc->width == 0 || desc->height == 0 ||
		desc->channels < 3 || desc->channels > 4 ||
		desc->colorspace > 1 ||
		desc->height >= QOI_PIXELS_MAX / desc->width
	) {
		return NULL;
	}

	max_size = 
		desc->width * desc->height * (desc->channels + 1) + 
		QOI_HEADER_SIZE + (int)sizeof(qoi_padding);

	p = 0;
	bytes = (unsigned char *) QOI_MALLOC(max_size);
	if (!bytes) {
		return NULL;
	}

	qoi_write_32(bytes, &p, QOI_MAGIC);
	qoi_write_32(bytes, &p, desc->width);
	qoi_write_32(bytes, &p, desc->height);
	bytes[p++] = desc->channels;
	bytes[p++] = desc->colorspace;


	pixels = (const unsigned char *)data;

	QOI_ZEROARR(index);
	QOI_ZEROARR(index_lookup);

	run = 0;
	px_prev.rgba.r = 0;
	px_prev.rgba.g = 0;
	px_prev.rgba.b = 0;
	px_prev.rgba.a = 255;
	px = px_prev;
	
	px_len = desc->width * desc->height * desc->channels;
	px_end = px_len - desc->channels;
	channels = desc->channels;

	for (px_pos = 0; px_pos < px_len; px_pos += channels) {
		if (channels == 4) {
			px = *(qoi_rgba_t *)(pixels + px_pos);
		}
		else {
			px.rgba.r = pixels[px_pos + 0];
			px.rgba.g = pixels[px_pos + 1];
			px.rgba.b = pixels[px_pos + 2];
		}

		if (px.v == px_prev.v) {
			run++;
			if (run == 62 || px_pos == px_end) {
				bytes[p++] = QOI_OP_RUN | (run - 1);
				run = 0;
			}
		}
		else {
			int hash = QOI_COLOR_HASH(px) % QOI_COLOR_HASH_SIZE;

			if (run > 0) {
				bytes[p++] = QOI_OP_RUN | (run - 1);
				run = 0;
			}

			if (index[index_lookup[hash]].v == px.v) {
				bytes[p++] = QOI_OP_INDEX | index_lookup[hash];
			}
			else {
				index_lookup[hash] = index_pos;
				index[index_pos] = px;
				index_pos = (index_pos + 1) % 64;

				if (px.rgba.a == px_prev.rgba.a) {
					signed char vr = px.rgba.r - px_prev.rgba.r;
					signed char vg = px.rgba.g - px_prev.rgba.g;
					signed char vb = px.rgba.b - px_prev.rgba.b;

					signed char vg_r = vr - vg;
					signed char vg_b = vb - vg;

					if (
						vr > -3 && vr < 2 &&
						vg > -3 && vg < 2 && 
						vb > -3 && vb < 2
					) {
						bytes[p++] = QOI_OP_DIFF | (vr + 2) << 4 | (vg + 2) << 2 | (vb + 2);
					}
					else if (
						vg_r >  -9 && vg_r <  8 && 
						vg   > -33 && vg   < 32 && 
						vg_b >  -9 && vg_b <  8
					) {
						bytes[p++] = QOI_OP_LUMA     | (vg   + 32);
						bytes[p++] = (vg_r + 8) << 4 | (vg_b +  8);
					}
					else {
						bytes[p++] = QOI_OP_RGB;
						bytes[p++] = px.rgba.r;
						bytes[p++] = px.rgba.g;
						bytes[p++] = px.rgba.b;
					}
				}
				else {
					bytes[p++] = QOI_OP_RGBA;
					bytes[p++] = px.rgba.r;
					bytes[p++] = px.rgba.g;
					bytes[p++] = px.rgba.b;
					bytes[p++] = px.rgba.a;
				}
			}
		}
		px_prev = px;
	}

	for (i = 0; i < (int)sizeof(qoi_padding); i++) {
		bytes[p++] = qoi_padding[i];
	}

	*out_len = p;
	return bytes;
}

void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels) {
	const unsigned char *bytes;
	unsigned int header_magic;
	unsigned char *pixels;
	qoi_rgba_t index[64];
	qoi_rgba_t px;
	int px_len, chunks_len, px_pos;
	int p = 0, run = 0;
	int index_pos = 0;

	if (
		data == NULL || desc == NULL ||
		(channels != 0 && channels != 3 && channels != 4) ||
		size < QOI_HEADER_SIZE + (int)sizeof(qoi_padding)
	) {
		return NULL;
	}

	bytes = (const unsigned char *)data;

	header_magic = qoi_read_32(bytes, &p);
	desc->width = qoi_read_32(bytes, &p);
	desc->height = qoi_read_32(bytes, &p);
	desc->channels = bytes[p++];
	desc->colorspace = bytes[p++];

	if (
		desc->width == 0 || desc->height == 0 || 
		desc->channels < 3 || desc->channels > 4 ||
		desc->colorspace > 1 ||
		header_magic != QOI_MAGIC ||
		desc->height >= QOI_PIXELS_MAX / desc->width
	) {
		return NULL;
	}

	if (channels == 0) {
		channels = desc->channels;
	}

	px_len = desc->width * desc->height * channels;
	pixels = (unsigned char *) QOI_MALLOC(px_len);
	if (!pixels) {
		return NULL;
	}

	QOI_ZEROARR(index);
	px.rgba.r = 0;
	px.rgba.g = 0;
	px.rgba.b = 0;
	px.rgba.a = 255;

	chunks_len = size - (int)sizeof(qoi_padding);
	for (px_pos = 0; px_pos < px_len; px_pos += channels) {
		if (run > 0) {
			run--;
		}
		else if (p < chunks_len) {
			int b1 = bytes[p++];

			if (b1 == QOI_OP_RGB) {
				px.rgba.r = bytes[p++];
				px.rgba.g = bytes[p++];
				px.rgba.b = bytes[p++];
				index[index_pos++ % 64] = px;
			}
			else if (b1 == QOI_OP_RGBA) {
				px.rgba.r = bytes[p++];
				px.rgba.g = bytes[p++];
				px.rgba.b = bytes[p++];
				px.rgba.a = bytes[p++];
				index[index_pos++ % 64] = px;
			}
			else if ((b1 & QOI_MASK_2) == QOI_OP_INDEX) {
				px = index[b1];
			}
			else if ((b1 & QOI_MASK_2) == QOI_OP_DIFF) {
				px.rgba.r += ((b1 >> 4) & 0x03) - 2;
				px.rgba.g += ((b1 >> 2) & 0x03) - 2;
				px.rgba.b += ( b1       & 0x03) - 2;
				index[index_pos++ % 64] = px;
			}
			else if ((b1 & QOI_MASK_2) == QOI_OP_LUMA) {
				int b2 = bytes[p++];
				int vg = (b1 & 0x3f) - 32;
				px.rgba.r += vg - 8 + ((b2 >> 4) & 0x0f);
				px.rgba.g += vg;
				px.rgba.b += vg - 8 +  (b2       & 0x0f);
				index[index_pos++ % 64] = px;
			}
			else if ((b1 & QOI_MASK_2) == QOI_OP_RUN) {
				run = (b1 & 0x3f);
			}
		}

		if (channels == 4) { 
			*(qoi_rgba_t*)(pixels + px_pos) = px;
		}
		else {
			pixels[px_pos + 0] = px.rgba.r;
			pixels[px_pos + 1] = px.rgba.g;
			pixels[px_pos + 2] = px.rgba.b;
		}
	}

	return pixels;
}

#ifndef QOI_NO_STDIO
#include <stdio.h>

int qoi_write(const char *filename, const void *data, const qoi_desc *desc) {
	FILE *f = fopen(filename, "wb");
	int size;
	void *encoded;

	if (!f) {
		return 0;
	}

	encoded = qoi_encode(data, desc, &size);
	if (!encoded) {
		fclose(f);
		return 0;
	}	
	
	fwrite(encoded, 1, size, f);
	fclose(f);
	
	QOI_FREE(encoded);
	return size;
}

void *qoi_read(const char *filename, qoi_desc *desc, int channels) {
	FILE *f = fopen(filename, "rb");
	int size, bytes_read;
	void *pixels, *data;

	if (!f) {
		return NULL;
	}

	fseek(f, 0, SEEK_END);
	size = ftell(f);
	if (size <= 0) {
		fclose(f);
		return NULL;
	}
	fseek(f, 0, SEEK_SET);

	data = QOI_MALLOC(size);
	if (!data) {
		fclose(f);
		return NULL;
	}

	bytes_read = fread(data, 1, size, f);
	fclose(f);

	pixels = qoi_decode(data, bytes_read, desc, channels);
	QOI_FREE(data);
	return pixels;
}

#endif /* QOI_NO_STDIO */
#endif /* QOI_IMPLEMENTATION */