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BLF: Gamma Correction

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Gamma correction for glyph coverage values.

See D13376 for details and examples.

Differential Revision: https://developer.blender.org/D13376

Reviewed by Julian Eisel
This commit is contained in:
Harley Acheson
2022-08-18 12:34:23 -07:00
parent 9707080a9d
commit d772e11b5a
1 changed files with 49 additions and 0 deletions
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49
source/blender/blenfont/intern/blf_glyph.c
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@@ -42,6 +42,11 @@
#include "BLI_strict_flags.h"
#include "BLI_string_utf8.h"
/* Convert glyph converage amounts to lightness values. Uses a LUT that perceptually improves
* anti-aliasing and results in text that looks a bit fuller and slightly brighter. This should
* be reconsidered in some - or all - cases when we transform the entire UI. */
#define BLF_GAMMA_CORRECT_GLYPHS
/* -------------------------------------------------------------------- */
/** \name Internal Utilities
* \{ */
@@ -183,6 +188,42 @@ static GlyphBLF *blf_glyph_cache_find_glyph(GlyphCacheBLF *gc, uint charcode)
return NULL;
}
#ifdef BLF_GAMMA_CORRECT_GLYPHS
/* Gamma correction of glyph converage values with widely-recommended gamma of 1.43.
* "The reasons are historical. Because so many programmers have neglected gamma blending for so
* long, people who have created fonts have tried to work around the problem of fonts looking too
* thin by just making the fonts thicker! Obviously it doesn’t help the jaggedness, but it does
* make them look the proper weight, as originally intended. The obvious problem with this is
* that if we want to gamma blend correctly many older fonts will look wrong. So we compromise,
* and use a lower gamma value, so we get a bit better antialiasing, but the fonts don’t look too
* heavy."
* https://www.puredevsoftware.com/blog/2019/01/22/sub-pixel-gamma-correct-font-rendering/
*/
static char blf_glyph_gamma(char c)
{
/* The following is (char)(powf(c / 256.0f, 1.0f / 1.43f) * 256.0f). */
static const char gamma[256] = {
0, 5, 9, 11, 14, 16, 19, 21, 23, 25, 26, 28, 30, 32, 34, 35, 37, 38,
40, 41, 43, 44, 46, 47, 49, 50, 52, 53, 54, 56, 57, 58, 60, 61, 62, 64,
65, 66, 67, 69, 70, 71, 72, 73, 75, 76, 77, 78, 79, 80, 82, 83, 84, 85,
86, 87, 88, 89, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104,
105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122,
123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 133, 134, 135, 136, 137, 138, 139,
140, 141, 142, 143, 143, 144, 145, 146, 147, 148, 149, 150, 151, 151, 152, 153, 154, 155,
156, 157, 157, 158, 159, 160, 161, 162, 163, 163, 164, 165, 166, 167, 168, 168, 169, 170,
171, 172, 173, 173, 174, 175, 176, 177, 178, 178, 179, 180, 181, 182, 182, 183, 184, 185,
186, 186, 187, 188, 189, 190, 190, 191, 192, 193, 194, 194, 195, 196, 197, 198, 198, 199,
200, 201, 201, 202, 203, 204, 205, 205, 206, 207, 208, 208, 209, 210, 211, 211, 212, 213,
214, 214, 215, 216, 217, 217, 218, 219, 220, 220, 221, 222, 223, 223, 224, 225, 226, 226,
227, 228, 229, 229, 230, 231, 231, 232, 233, 234, 234, 235, 236, 237, 237, 238, 239, 239,
240, 241, 242, 242, 243, 244, 244, 245, 246, 247, 247, 248, 249, 249, 250, 251, 251, 252,
253, 254, 254, 255};
return gamma[c];
}
#endif /* BLF_GAMMA_CORRECT_GLYPHS */
/**
* Add a rendered glyph to a cache.
*/
@@ -218,6 +259,14 @@ static GlyphBLF *blf_glyph_cache_add_glyph(
glyph->bitmap.buffer[i] = glyph->bitmap.buffer[i] ? 255 : 0;
}
}
else {
#ifdef BLF_GAMMA_CORRECT_GLYPHS
/* Convert coverage amounts to perceptually-improved lightness values. */
for (int i = 0; i < buffer_size; i++) {
glyph->bitmap.buffer[i] = blf_glyph_gamma(glyph->bitmap.buffer[i]);
}
#endif /* BLF_GAMMA_CORRECT_GLYPHS */
}
g->bitmap = MEM_mallocN((size_t)buffer_size, "glyph bitmap");
memcpy(g->bitmap, glyph->bitmap.buffer, (size_t)buffer_size);
}