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Make blending of foreground more efficient

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Avoids an unnecessary reversal of premultiplication when rendering
interleaved.  Also fixes rendering on wayland which for some reason was
using a different blend function than X11. Fixes #4120
This commit is contained in:
Kovid Goyal 2021-10-14 21:29:02 +05:30
parent f28d9bcd8c
commit 3c2e521dd7
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GPG key ID: 06BC317B515ACE7C
2 changed files with 4 additions and 8 deletions
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10
kitty/cell_fragment.glsl
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@ -82,7 +82,7 @@ vec4 blend_onto_opaque_premul(vec3 over, float over_alpha, vec3 under) {
* 3) Draw the background of cells that don't have the default background if any images were drawn in 2 above
* 4) Draw the images that are supposed to be below text but not background, again in graphics shader.
* 5) Draw the special cells (selection/cursor). Output is same as from step 1, with bg_alpha 1 for special cells and 0 otherwise
* 6) Draw the foreground -- expected output is color with alpha which is blended using the opaque blend func
* 6) Draw the foreground -- expected output is color with alpha premultiplied which is blended using the premult blend func
* 7) Draw the images that are supposed to be above text again in the graphics shader
*
* 2b) Transparent bg with images
@ -137,13 +137,7 @@ void main() {
#endif
#ifdef FOREGROUND
vec4 fg = calculate_foreground(); // pre-multiplied foreground
#ifdef TRANSPARENT
final_color = fg;
#else
final_color = vec4(fg.rgb / fg.a, fg.a);
#endif
final_color = calculate_foreground(); // pre-multiplied foreground
#endif
}

2
kitty/shaders.c
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@ -538,7 +538,9 @@ draw_cells_interleaved(ssize_t vao_idx, ssize_t gvao_idx, Screen *screen, OSWind
glDrawArraysInstanced(GL_TRIANGLE_FAN, 0, 4, screen->lines * screen->columns);
bind_program(CELL_FG_PROGRAM);
BLEND_PREMULT;
glDrawArraysInstanced(GL_TRIANGLE_FAN, 0, 4, screen->lines * screen->columns);
BLEND_ONTO_OPAQUE;
if (screen->grman->num_of_positive_refs) draw_graphics(GRAPHICS_PROGRAM, vao_idx, gvao_idx, screen->grman->render_data, screen->grman->num_of_negative_refs + screen->grman->num_of_below_refs, screen->grman->num_of_positive_refs);