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[vulkan] Switch to pre-multiplied alpha for 2d

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I have recently learned that pre-multiplied alpha is the correct way to
do compositing, which is pretty much what the 2d pass does (actually,
all passes, but...). This required ensuring the color factor passed to
the fragment shader is pre-multiplied (a little silly for cshifts as
they used to be pre-multiplied but were un-pre-multiplied early in QF's
history and I don't feel like fixing that right now as it affects all
renderers), and also pre-multiplying alpha when converting from 8-bit
palette to rgba as the palette entry for transparent has that funky pink
(which is used in full-brights).
This commit is contained in:
Bill Currie 2022-08-30 14:29:22 +09:00
parent 4d5b38f0c9
commit 8c270a0a9e
2 changed files with 19 additions and 8 deletions
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4
libs/video/renderer/vulkan/qfpipeline.plist
View file

@ -624,10 +624,10 @@
};
alpha_blend = {
blendEnable = true;
srcColorBlendFactor = src_alpha;
srcColorBlendFactor = one;
dstColorBlendFactor = one_minus_src_alpha;
colorBlendOp = add;
srcAlphaBlendFactor = src_alpha;
srcAlphaBlendFactor = one;
dstAlphaBlendFactor = one_minus_src_alpha;
alphaBlendOp = add;
colorWriteMask = r|g|b|a;

23
libs/video/renderer/vulkan/vulkan_draw.c
View file

@ -284,10 +284,12 @@ pic_data (const char *name, int w, int h, const byte *data, drawctx_t *dctx)
for (size_t i = 0; i < size; i++) {
byte pix = *data++;
byte *col = vid.palette + pix * 3;
*picdata++ = *col++;
*picdata++ = *col++;
*picdata++ = *col++;
*picdata++ = (pix == 255) - 1;
byte alpha = (pix == 255) - 1;
// pre-multiply alpha.
*picdata++ = *col++ & alpha;
*picdata++ = *col++ & alpha;
*picdata++ = *col++ & alpha;
*picdata++ = alpha;
}
//FIXME live updates of the scrap aren't
//syncronized properly for some reason and result in stale texels being
@ -755,7 +757,9 @@ Vulkan_Draw_ConsoleBackground (int lines, byte alpha, vulkan_ctx_t *ctx)
drawctx_t *dctx = ctx->draw_context;
drawframe_t *frame = &dctx->frames.a[ctx->curFrame];
quat_t color = { 1, 1, 1, bound (0, alpha, 255) / 255.0};
float a = bound (0, alpha, 255) / 255.0;
// use pre-multiplied alpha
quat_t color = { a, a, a, a};
qpic_t *cpic;
cpic = Vulkan_Draw_CachePic ("gfx/conback.lmp", false, ctx);
int ofs = max (0, cpic->height - lines);
@ -929,6 +933,13 @@ void
Vulkan_Draw_BlendScreen (quat_t color, vulkan_ctx_t *ctx)
{
if (color[3]) {
draw_blendscreen (color, ctx);
quat_t c;
// pre-multiply alpha.
// FIXME this is kind of silly because q1source pre-multiplies alpha
// for blends, but this was un-done early in QF's history in order
// to avoid a pair of state changes
VectorScale (color, color[3], c);
c[3] = color[3];
draw_blendscreen (c, ctx);
}
}