From 56d2c3e990509d18de31e6009e0d0c6254f99b67 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Thu, 2 Jan 2025 09:08:24 +0100
Subject: [PATCH] config: don't allow colors.flash-alpha to be 1.0

A compositor will not send a frame callback for our main window if it
is fully occluded (for example, by a fully opaque overlay...). This
causes the overlay to stuck.

For regular buffers, it _should_ be enough to *not* hint the
compositor it's opaque. But at least some compositor special cases
single-pixel buffers, and actually look at their pixel value.

Thus, we have two options: implement frame callback handling for the
overlay sub-surface, or ensure we don't use a fully opaque
surface. Since no overlays are fully opaque by default, and the flash
surface is the only one that can be configured to be
opaque (colors.flash-alpha), and since adding frame callback handling
adds a lot of boilerplate code... let's go with the simpler solution
of
---
 CHANGELOG.md |  3 +++
 config.c     |  4 ++--
 render.c     | 21 +++++++++++++++++++++
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index bdc1828b..994805dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -62,6 +62,9 @@
 
 * Runtime changes to the app-id (OSC-176) now limits the app-id string
   to 2048 characters ([#1897][1897]).
+* `colors.flash-alpha` can no longer be set to 1.0 (i.e. fully
+  opaque). This fixes an issue where the window would be stuck in the
+  flash state.
 
 [1897]: https://codeberg.org/dnkl/foot/issues/1897
 
diff --git a/config.c b/config.c
index 7f1ce055..3b8ce7e8 100644
--- a/config.c
+++ b/config.c
@@ -1445,8 +1445,8 @@ parse_section_colors(struct context *ctx)
         if (!value_to_float(ctx, &alpha))
             return false;
 
-        if (alpha < 0. || alpha > 1.) {
-            LOG_CONTEXTUAL_ERR("not in range 0.0-1.0");
+        if (alpha < 0. || alpha >= 1.) {
+            LOG_CONTEXTUAL_ERR("not in range 0.0-0.999");
             return false;
         }
 
diff --git a/render.c b/render.c
index ed6b802e..8fc741b5 100644
--- a/render.c
+++ b/render.c
@@ -1898,6 +1898,27 @@ render_overlay(struct terminal *term)
         break;
 
     case OVERLAY_FLASH:
+        /*
+         * A compositor will not send a frame callback for our main
+         * window if it is fully occluded (for example, by a fully
+         * opaque overlay...). This causes the overlay to stuck.
+         *
+         * For regular buffers, it _should_ be enough to *not* hint
+         * the compositor it's opaque. But at least some compositor
+         * special cases single-pixel buffers, and actually look at
+         * their pixel value.
+         *
+         * Thus, we have two options: implement frame callback
+         * handling for the overlay sub-surface, or ensure we don't
+         * use a fully opaque surface. Since no overlays are fully
+         * opaque by default, and the flash surface is the only one
+         * that can be configured to be opaque (colors.flash-alpha),
+         * and since adding frame callback handling adds a lot of
+         * boilerplate code... let's go with the simpler solution of
+         * not allowing colors.flash-alpha to be 1.0.
+         */
+        xassert(term->conf->colors.flash_alpha != 0xffff);
+
         color = color_hex_to_pixman_with_alpha(
                 term->conf->colors.flash,
                 term->conf->colors.flash_alpha);