From 54889fc4ff117f59efb392955a18b414fee570c7 Mon Sep 17 00:00:00 2001
From: Kirill Chibisov <contact@kchibisov.com>
Date: Fri, 24 Nov 2023 23:57:43 +0400
Subject: [PATCH] Make AA stronger for undercurl

This improves undercurl rendering preserving its original thickness.
This also makes it look not out-of place when places next to other
lines.
---
 alacritty/res/rect.f.glsl | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/alacritty/res/rect.f.glsl b/alacritty/res/rect.f.glsl
index 65701da3..9951861f 100644
--- a/alacritty/res/rect.f.glsl
+++ b/alacritty/res/rect.f.glsl
@@ -45,7 +45,11 @@ color_t draw_undercurl(float_t x, float_t y) {
   // cosine curve.
   float_t alpha = 1.;
   if (y > undercurlTop || y < undercurlBottom) {
-    alpha = 1. - min(abs(undercurlTop - y), abs(undercurlBottom - y));
+    // Doing proper SDF is complicated for this shader, so just make AA
+    // stronger by 1/x^2, which renders preserving underline thickness and
+    // being bold enough.
+    float_t dst = min(abs(undercurlTop - y), abs(undercurlBottom - y));
+    alpha -= dst * dst;
   }
 
   // The result is an alpha mask on a rect, which leaves only curve opaque.