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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
This commit is contained in:
Daniel Eklöf 2022-10-30 19:39:09 +01:00
parent 49fa751953
commit 2c2a39317b
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2 changed files with 12 additions and 1 deletions
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4
CHANGELOG.md
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@ -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

9
render.c
View file

@ -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;
}
}