From 2c2a39317be3df4ff9899896067684408526fb29 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Sun, 30 Oct 2022 19:39:09 +0100
Subject: [PATCH] render: never apply alpha to text color
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When drawing a block cursor using inversed fg/bg colors, we didn’t
strip the alpha from the background color. This meant that the text
"behind" the cursor was rendered with transparency. If alpha was set
to 0, the text was completely invisible.

We should never apply alpha to the text color. So, detect this, and
force alpha to 1.0.

Normally, when selecting the cursor’s color, we don’t really know
_where_ the background color is coming from (or more accurately,
_what_ it is).

However, the *only* background color that can have a non-1.0 alpha is
the *default* background color.

This is why we can ignore the bg parameter, and use term->colors.fg/bg
instead.

Closes #1205
---
 CHANGELOG.md | 4 ++++
 render.c     | 9 ++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3022836d..3546d92e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -91,9 +91,13 @@
 * Crash when a sixel image exceeds the current sixel max height.
 * Crash after reverse-scrolling (`CSI Ps T`) in the ‘normal’
   (non-alternate) screen ([#1190][1190]).
+* Background transparency being applied to the text "behind" the
+  cursor. Only applies to block cursor using inversed fg/bg
+  colors. ([#1205][1205]).
 
 [1173]: https://codeberg.org/dnkl/foot/issues/1173
 [1190]: https://codeberg.org/dnkl/foot/issues/1190
+[1205]: https://codeberg.org/dnkl/foot/issues/1205
 
 
 ### Security
diff --git a/render.c b/render.c
index 76f4b7c6..822667ae 100644
--- a/render.c
+++ b/render.c
@@ -419,7 +419,14 @@ cursor_colors_for_cell(const struct terminal *term, const struct cell *cell,
         }
     } else {
         *cursor_color = *fg;
-        *text_color = *bg;
+
+        if (unlikely(text_color->alpha != 0xffff)) {
+            /* We *know* this only happens when bg is the default bg
+             * color */
+            *text_color = color_hex_to_pixman(
+                term->reverse ? term->colors.fg : term->colors.bg);
+        } else
+            *text_color = *bg;
     }
 }