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Update qoi.h

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raysan5 2022-01-26 16:33:38 +01:00
parent e5ee69a0f5
commit 524bf57b74
1 changed files with 60 additions and 54 deletions
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26
src/external/qoi.h vendored
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@ -91,9 +91,9 @@ struct qoi_header_t {
uint8_t colorspace; // 0 = sRGB with linear alpha, 1 = all channels linear
};
Images are encoded from top to bottom, left to right. The decoder and encoder
start with {r: 0, g: 0, b: 0, a: 255} as the previous pixel value. An image is
complete when all pixels specified by width * height have been covered.
Images are encoded row by row, left to right, top to bottom. The decoder and
encoder start with {r: 0, g: 0, b: 0, a: 255} as the previous pixel value. An
image is complete when all pixels specified by width * height have been covered.
Pixels are encoded as
- a run of the previous pixel
@ -135,8 +135,8 @@ The possible chunks are:
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.
A valid encoder must not issue 2 or more consecutive QOI_OP_INDEX chunks to the
same index. QOI_OP_RUN should be used instead.
.- QOI_OP_DIFF -----------.
@ -156,6 +156,8 @@ 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).
The alpha value remains unchanged from the previous pixel.
.- QOI_OP_LUMA -------------------------------------.
| Byte[0] | Byte[1] |
@ -171,8 +173,8 @@ Values are stored as unsigned integers with a bias of 2. E.g. -2 is stored as
The green channel is used to indicate the general direction of change and is
encoded in 6 bits. The red and blue 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)
dr_dg = (cur_px.r - prev_px.r) - (cur_px.g - prev_px.g)
db_dg = (cur_px.b - prev_px.b) - (cur_px.g - prev_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.
@ -180,6 +182,8 @@ 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.
The alpha value remains unchanged from the previous pixel.
.- QOI_OP_RUN ------------.
| Byte[0] |
@ -206,6 +210,8 @@ QOI_OP_RGBA tags.
8-bit green channel value
8-bit blue channel value
The alpha value remains unchanged from the previous pixel.
.- QOI_OP_RGBA ---------------------------------------------------.
| Byte[0] | Byte[1] | Byte[2] | Byte[3] | Byte[4] |
@ -242,7 +248,7 @@ The colorspace in this qoi_desc is an enum where
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. */
how chunks are en-/decoded. */
#define QOI_SRGB 0
#define QOI_LINEAR 1
@ -352,14 +358,14 @@ typedef union {
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) {
static 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) {
static 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)++];