Replace the second_transparent_bg option

This is backwards incompatible, but only for a feature released 3 weeks
ago.

docs/changelog.rst

@@ -136,7 +136,7 @@ Detailed list of changes
 
 - launch command: A new :option:`launch --bias` option to adjust the size of newly created windows declaratively (:iss:`7634`)
 
-- A new option :opt:`second_transparent_bg` to make a second background color semi-transparent via :opt:`background_opacity`. Useful for things like cursor line highlight in editors (:iss:`7646`)
+- A new option :opt:`transparent_background_colors` to make a second background color semi-transparent via :opt:`background_opacity`. Useful for things like cursor line highlight in editors (:iss:`7646`)
 
 - A new :doc:`notify </kittens/notify>` kitten to show desktop notifications
   from the command line with support for icons, buttons and more.

kitty/cell_vertex.glsl

@@ -6,7 +6,7 @@
 layout(std140) uniform CellRenderData {
     float xstart, ystart, dx, dy, sprite_dx, sprite_dy, use_cell_bg_for_selection_fg, use_cell_fg_for_selection_fg, use_cell_for_selection_bg;
 
-    uint default_fg, highlight_fg, highlight_bg, cursor_fg, cursor_bg, url_color, url_style, inverted, second_transparent_bg;
+    uint default_fg, highlight_fg, highlight_bg, cursor_fg, cursor_bg, url_color, url_style, inverted;
 
     uint xnum, ynum, cursor_fg_sprite_idx;
     float cursor_x, cursor_y, cursor_w, cursor_opacity;

kitty/options/definition.py

@@ -1527,16 +1527,22 @@ opt('background_image_linear', 'no',
     long_text='When background image is scaled, whether linear interpolation should be used.'
     )
 
-opt('transparent_background_colors', '', option_type='transparent_background_colors', ctype='!transparent_background_colors')
+opt('transparent_background_colors', '', option_type='transparent_background_colors', ctype='!transparent_background_colors', long_text='''
+A space separated list of upto 7 colors, with opacity. When the background color of a cell matches one of these colors,
+it is rendered semi-transparent using the specified opacity.
 
-opt('second_transparent_bg', 'none', option_type='to_color_or_none', long_text='''
-When the background color matches this color, :opt:`background_opacity` is applied to it
-to render it as semi-transparent, just as for colors matching the main :opt:`background` color.
 Useful in more complex UIs like editors where you could want more than a single background color
-to be rendered as transparent, for instance, for a cursor highlight line background.
+to be rendered as transparent, for instance, for a cursor highlight line background or a highlighted block.
 Terminal applications can set this color using :ref:`The kitty color control <color_control>`
 escape code.
-''')
+
+The syntax for specifiying colors is: :code:`color@opacity`, where the :code:`@opacity`
+part is optional. When unspecified, the value of :opt:`background_opacity` is used. For example::
+
+    transparent_background_colors red@0.5 #00ff00@0.3
+
+'''
+)
 
 opt('dynamic_background_opacity', 'no',
     option_type='to_bool', ctype='bool',

kitty/shaders.c

@@ -295,7 +295,7 @@ cell_update_uniform_block(ssize_t vao_idx, Screen *screen, int uniform_buffer, c
     struct GPUCellRenderData {
         GLfloat xstart, ystart, dx, dy, sprite_dx, sprite_dy, use_cell_bg_for_selection_fg, use_cell_fg_for_selection_color, use_cell_for_selection_bg;
 
-        GLuint default_fg, highlight_fg, highlight_bg, cursor_fg, cursor_bg, url_color, url_style, inverted, second_transparent_bg;
+        GLuint default_fg, highlight_fg, highlight_bg, cursor_fg, cursor_bg, url_color, url_style, inverted;
 
         GLuint xnum, ynum, cursor_fg_sprite_idx;
         GLfloat cursor_x, cursor_y, cursor_w, cursor_opacity;