diff --git a/kitty/cell_vertex.glsl b/kitty/cell_vertex.glsl
index b7c9ecc423..a8ca9c7e7f 100644
--- a/kitty/cell_vertex.glsl
+++ b/kitty/cell_vertex.glsl
@@ -194,14 +194,14 @@ void main() {
     // }}}
 
     // Background {{{
-    float cell_has_non_default_bg = step(1, float(abs(
+    float bg_is_not_transparent = step(1, float(abs(
         (bg_as_uint - default_colors[1]) * (bg_as_uint - second_transparent_bg)
-    )));
+    )));  // bg_is_not_transparent = 0 if bg_as_uint in (default_colors[1], second_transparent_bg) else 1
     draw_bg = 1;
 
 #if (PHASE == PHASE_BACKGROUND)
     // draw_bg_bitfield has bit 0 set to draw default bg cells and bit 1 set to draw non-default bg cells
-    uint draw_bg_mask = uint(2 * cell_has_non_default_bg + (1 - cell_has_non_default_bg));
+    uint draw_bg_mask = uint(2 * bg_is_not_transparent + (1 - bg_is_not_transparent));
     draw_bg = step(1, float(draw_bg_bitfield & draw_bg_mask));
 #endif
 
@@ -213,12 +213,12 @@ void main() {
     // selections/block cursor and 0 everywhere else.
     float is_special_cell = cell_data.has_block_cursor + float(is_selected & ONE);
 #if (PHASE != PHASE_SPECIAL)
-    is_special_cell += cell_has_non_default_bg + float(is_reversed);
+    is_special_cell += bg_is_not_transparent + float(is_reversed);
 #endif
-    bg_alpha = step(0.5, is_special_cell);
+    bg_alpha = step(0.5, is_special_cell); // bg_alpha = 1 if is_special_cell else 0
 #if (PHASE != PHASE_SPECIAL)
-    bg_alpha = bg_alpha + (1.0f - bg_alpha) * background_opacity;
-    bg_alpha *= draw_bg;
+    bg_alpha = bg_alpha + (1.0f - bg_alpha) * background_opacity;  // bg_alpha = 1 if bg_alpha else background_opacity
+    bg_alpha *= draw_bg;  // if not draw_bg: bg_alpha = 0
 #endif
 #endif