Fix text_fg_override_threshold not working with multi-pass rendering

This has the side-effect of also applying the same luminance based gamma
adjustment for multipass rendering as we do for single pass rendering.
This *may* make things look worse with very low background_opacity
values, since in such cases the actual background color can be quite
different from the background color we are adjusting against.

Author: kovidgoyal

kitty/cell_fragment.glsl

@@ -2,13 +2,11 @@
 #pragma kitty_include_shader <linear2srgb.glsl>
 #pragma kitty_include_shader <cell_defines.glsl>
 
-#ifdef NEEDS_BACKROUND
 in vec3 background;
 in float draw_bg;
 #ifdef NEEDS_BG_ALPHA
 in float bg_alpha;
 #endif
-#endif
 
 #ifdef NEEDS_FOREGROUND
 uniform sampler2DArray sprites;
@@ -199,6 +197,7 @@ void main() {
 
 #if (PHASE == PHASE_FOREGROUND)
     vec4 text_fg = load_text_foreground_color();
+    text_fg = adjust_foreground_contrast_with_background(text_fg, background);
     vec4 text_fg_premul = calculate_premul_foreground_from_sprites(text_fg);
     final_color = text_fg_premul;
 #ifdef TRANSPARENT

kitty/cell_vertex.glsl

@@ -34,13 +34,11 @@ const uvec2 cell_pos_map[] = uvec2[4](
 // }}}
 
 
-#ifdef NEEDS_BACKROUND
 out vec3 background;
 out float draw_bg;
 #ifdef NEEDS_BG_ALPHA
 out float bg_alpha;
 #endif
-#endif
 
 #ifdef NEEDS_FOREGROUND
 uniform float inactive_text_alpha;
@@ -198,7 +196,6 @@ void main() {
     // }}}
 
     // Background {{{
-#ifdef NEEDS_BACKROUND
     float cell_has_non_default_bg = step(1, float(abs(bg_as_uint - default_colors[1])));
     draw_bg = 1;
 
@@ -235,7 +232,6 @@ void main() {
 #endif
 #endif
 
-#endif
     // }}}
 
 }

kitty/options/definition.py

@@ -276,9 +276,7 @@
 foreground and background is below this threshold, the foreground color will be set
 to white if the background is dark or black if the background is light. The default
 value is :code:`0`, which means no overriding is performed. Useful when working with applications
-that use colors that do not contrast well with your preferred color scheme. Note that this
-will not work in situations where kitty has to render in multiple passes, for example,
-when rendering with images under text or with non-opaque background and images.
+that use colors that do not contrast well with your preferred color scheme.
 ''')
 
 egr()  # }}}
@@ -1352,21 +1350,24 @@
     option_type='unit_float', ctype='float',
     long_text='''
 The opacity of the background. A number between zero and one, where one is
-opaque and zero is fully transparent. This will only work if supported by the OS
-(for instance, when using a compositor under X11). Note that it only sets the
-background color's opacity in cells that have the same background color as the
-default terminal background, so that things like the status bar in vim,
+opaque and zero is fully transparent. This will only work if supported by the
+OS (for instance, when using a compositor under X11). Note that it only sets
+the background color's opacity in cells that have the same background color as
+the default terminal background, so that things like the status bar in vim,
 powerline prompts, etc. still look good. But it means that if you use a color
 theme with a background color in your editor, it will not be rendered as
 transparent. Instead you should change the default background color in your
 kitty config and not use a background color in the editor color scheme. Or use
-the escape codes to set the terminals default colors in a shell script to launch
-your editor. Be aware that using a value less than 1.0 is a (possibly
-significant) performance hit. If you want to dynamically change transparency of
-windows, set :opt:`dynamic_background_opacity` to :code:`yes` (this is off by
-default as it has a performance cost). Changing this option when reloading the
-config will only work if :opt:`dynamic_background_opacity` was enabled in the
-original config.
+the escape codes to set the terminals default colors in a shell script to
+launch your editor. Be aware that using a value less than 1.0 is a (possibly
+significant) performance hit. When using a low value for this setting, it is
+desirable that you set the :opt:`background` color to a color the matches the
+general color of the desktop background, for best text rendering.  If you want
+to dynamically change transparency of windows, set
+:opt:`dynamic_background_opacity` to :code:`yes` (this is off by default as it
+has a performance cost). Changing this option when reloading the config will
+only work if :opt:`dynamic_background_opacity` was enabled in the original
+config.
 '''
     )