From 3ae489b1516ba7e90994e074d6b37f022673ed4b Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Wed, 7 Jun 2023 16:23:30 +0530
Subject: [PATCH] Fix #6345

@m4rw3r this is fixing a bug in #6218. Seems fairly straightforward but
since it's your code, please review.
---
 kitty/blit_fragment.glsl | 10 ++++++++++
 kitty/cell_fragment.glsl |  6 +++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/kitty/blit_fragment.glsl b/kitty/blit_fragment.glsl
index e0a47ce60..74e243336 100644
--- a/kitty/blit_fragment.glsl
+++ b/kitty/blit_fragment.glsl
@@ -5,6 +5,16 @@ uniform sampler2D image;
 in vec2 texcoord;
 out vec4 color;
 
+float linear2srgb(float x) {
+    // Linear to sRGB conversion.
+    float lower = 12.92 * x;
+    float upper = 1.055 * pow(x, 1.0f / 2.4f) - 0.055f;
+
+    return mix(lower, upper, step(0.0031308f, x));
+}
+
+
 void main() {
     color = texture(image, texcoord);
+    color.a = linear2srgb(color.a);
 }
diff --git a/kitty/cell_fragment.glsl b/kitty/cell_fragment.glsl
index 8cdc388cf..2d2bec92c 100644
--- a/kitty/cell_fragment.glsl
+++ b/kitty/cell_fragment.glsl
@@ -240,9 +240,9 @@ void main() {
 #ifdef FOREGROUND
     final_color = calculate_foreground();  // pre-multiplied foreground
 
-    // This is the last pass, adjust alpha to compensate for gamma-incorrect
-    // blending in compositor:
-    final_color.a = linear2srgb(final_color.a);
+    // This is the last pass, called both with transparency and without but not in draw_cells_simple().
+    // When transparent it is drawn into a framebuffer and linear2srgb() will be done
+    // when blitting that framebuffer. When not transparent there is not need to do linear2srgb() anyway.
 #endif
 
 }