From 7053672d3a2fba68aca2bb0687123a81a6e42e21 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Felix=20=22xq=22=20Quei=C3=9Fner?= Date: Sun, 28 Nov 2021 01:08:52 +0100 Subject: [PATCH] Starts to improve the documentation. --- qoi.h | 108 +++++++++++++++++++++++++++++++++++----------------------- 1 file changed, 66 insertions(+), 42 deletions(-) diff --git a/qoi.h b/qoi.h index 5f43c38..b87c1ca 100644 --- a/qoi.h +++ b/qoi.h @@ -109,54 +109,78 @@ index matches the current pixel, this index position is written to the stream. Each chunk starts with a 2, 3 or 4 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. -QOI_INDEX { - u8 tag : 2; // b00 - u8 idx : 6; // 6-bit index into the color index array: 0..63 -} +The possible chunks are: -QOI_RUN_8 { - u8 tag : 3; // b010 - u8 run : 5; // 5-bit run-length repeating the previous pixel: 1..32 -} + | QOI_INDEX | + | Byte + 0 | + | 7 6 5 4 3 2 1 0 | + |-------------------------| + | 0 0 i5 i4 i3 i2 i1 i0 | -QOI_RUN_16 { - u8 tag : 3; // b011 - u16 run : 13; // 13-bit run-length repeating the previous pixel: 33..8224 -} + i5...i0 forming the 6-bit index into the color index array: 0..63 -QOI_DIFF_8 { - u8 tag : 2; // b10 - u8 dr : 2; // 2-bit red channel difference: -2..1 - u8 dg : 2; // 2-bit green channel difference: -2..1 - u8 db : 2; // 2-bit blue channel difference: -2..1 -} -QOI_DIFF_16 { - u8 tag : 3; // b110 - u8 dr : 5; // 5-bit red channel difference: -16..15 - u8 dg : 4; // 4-bit green channel difference: -8.. 7 - u8 db : 4; // 4-bit blue channel difference: -8.. 7 -} + | QOI_INDEX | + | Byte + 0 | + | 7 6 5 4 3 2 1 0 | + |-------------------------| + | 0 1 0 i4 i3 i2 i1 i0 | -QOI_DIFF_24 { - u8 tag : 4; // b1110 - u8 dr : 5; // 5-bit red channel difference: -16..15 - u8 dg : 5; // 5-bit green channel difference: -16..15 - u8 db : 5; // 5-bit blue channel difference: -16..15 - u8 da : 5; // 5-bit alpha channel difference: -16..15 -} + i4...i0 forming the 5-bit run-length repeating the previous pixel: 1..32 + + + | QOI_RUN_16 | + | Byte + 0 | Byte + 1 | + | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | + |--------------------------------|-------------------------| + | 0 1 1 r12 r11 r10 r9 r8 | r7 r6 r5 r4 r3 r2 r1 r0 | + + r12...r0 forming the 13-bit run-length repeating the previous pixel: 33..8224 + + + | QOI_DIFF_8 | + | Byte + 0 | + | 7 6 5 4 3 2 1 0 | + |-------------------------| + | 1 0 r1 r0 g1 g0 b1 b0 | + + r1...r0 forming the red channel difference between -2..1 + g1...g0 forming the green channel difference between -2..1 + b1...b0 forming the blue channel difference between -2..1 + + + | QOI_DIFF_16 | + | Byte + 0 | Byte + 1 | + | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | + |-------------------------|-------------------------| + | 1 1 0 r4 r3 r2 r1 r0 | g3 g2 g1 g0 b3 b2 b1 b0 | + + r4...r0 forming the red channel difference between -16..15 + g3...g0 forming the green channel difference between -8..7 + b3...b0 forming the blue channel difference between -8..7 + + + | QOI_DIFF_24 | + | Byte + 0 | Byte + 1 | Byte + 1 | + | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | + |-------------------------|-------------------------|-------------------------| + | 1 1 1 0 r4 r3 r2 r1 | r0 g4 g3 g2 g1 g0 b4 b3 | b2 b1 b0 a4 a3 a2 a1 a0 | + + r4...r0 forming the red channel difference between -16..15 + g4...g0 forming the green channel difference between -16..15 + b4...b0 forming the blue channel difference between -16..15 + a4...a0 forming the alpha channel difference between -16..15 + + + | QOI_COLOR | + | Byte + 0 | + | 7 6 5 4 3 2 1 0 | + |-------------------------| + | 1 1 1 1 r g b a | + + for each set bit r, g, b and a another byte follows in the order written here. If such a byte follows, + it will replace the current color channel value with the value of this byte. -QOI_COLOR { - u8 tag : 4; // b1111 - u8 has_r: 1; // red byte follows - u8 has_g: 1; // green byte follows - u8 has_b: 1; // blue byte follows - u8 has_a: 1; // alpha byte follows - u8 r; // red value if has_r == 1: 0..255 - u8 g; // green value if has_g == 1: 0..255 - u8 b; // blue value if has_b == 1: 0..255 - u8 a; // alpha value if has_a == 1: 0..255 -} The byte stream is padded with 4 zero bytes. Size the longest chunk we can encounter is 5 bytes (QOI_COLOR with RGBA set), with this padding we just have