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Fix incorrect blending of foreground and background colors when negative z-index images are present

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Also optimize the blending calculation a bit by using the mix() function
and just adding the text and strike alphas.
This commit is contained in:
Kovid Goyal 2017-11-21 14:19:49 +05:30
parent 3b4a242e26
commit 1fb81d2265
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GPG Key ID: 06BC317B515ACE7C
2 changed files with 20 additions and 12 deletions
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30
kitty/cell_fragment.glsl
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@ -15,8 +15,13 @@ in vec4 special_bg;
out vec4 final_color;
vec3 blend(float alpha, vec3 over, vec3 under) {
return over + (1 - alpha) * under;
vec4 alpha_blend(vec3 over, float over_alpha, vec3 under, float under_alpha) {
// Alpha blend two colors returning the resulting color pre-multiplied by its alpha
// and its alpha.
// See https://en.wikipedia.org/wiki/Alpha_compositing
float alpha = mix(under_alpha, 1.0f, over_alpha);
vec3 combined_color = mix(under * under_alpha, over, over_alpha);
return vec4(combined_color, alpha);
}
void main() {
@ -24,17 +29,19 @@ void main() {
float text_alpha = texture(sprites, sprite_pos).r;
float underline_alpha = texture(sprites, underline_pos).r;
float strike_alpha = texture(sprites, strike_pos).r;
vec3 underline = underline_alpha * decoration_fg;
vec3 strike = strike_alpha * foreground;
vec3 fg = text_alpha * foreground;
vec3 decoration = blend(underline_alpha, underline, strike);
vec3 combined_fg = blend(text_alpha, fg, decoration);
float combined_alpha = max(max(underline_alpha, strike_alpha), text_alpha);
// Since strike and text are the same color, we simply add the alpha values
float combined_alpha = min(text_alpha + strike_alpha, 1.0f);
// Underline color might be different, so alpha blend
vec4 fg = alpha_blend(decoration_fg, underline_alpha, foreground, combined_alpha);
#ifdef ALL
final_color = vec4(blend(combined_alpha, combined_fg, background), 1);
// since background alpha is 1.0 and fg color is pre-multiplied by its alpha,
// we can simplify the alpha blend equation
final_color = vec4(fg.rgb + (1.0f - fg.a) * background, 1.0f);
#else
final_color = vec4(combined_fg, combined_alpha);
// FOREGROUND
// fg is pre-multipled so divide it by alpha
final_color = vec4(fg.rgb / fg.a, fg.a);
#endif
#else
@ -42,7 +49,8 @@ void main() {
#ifdef SPECIAL
final_color = special_bg;
#else
final_color = vec4(background, 1);
// BACKGROUND
final_color = vec4(background, 1.0f);
#endif
#endif

2
kitty/shaders.c
View File

@ -317,7 +317,7 @@ draw_cells_interleaved(ssize_t vao_idx, ssize_t gvao_idx, Screen *screen) {
glDrawArraysInstanced(GL_TRIANGLE_FAN, 0, 4, screen->lines * screen->columns);
bind_program(CELL_FOREGROUND_PROGRAM);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glDrawArraysInstanced(GL_TRIANGLE_FAN, 0, 4, screen->lines * screen->columns);
if (screen->grman->num_of_positive_refs) draw_graphics(vao_idx, gvao_idx, screen->grman->render_data, screen->grman->num_of_negative_refs, screen->grman->num_of_positive_refs);