SDL: Update testgpurender_effects_grayscale.frag.hlsl

SDL Commits
1 
From 902484f65c4b4d25e321f5a0e9a96880412031b9 Mon Sep 17 00:00:00 2001
From: momoko-h <[EMAIL REDACTED]>
Date: Sun, 23 Aug 2026 17:49:03 +0200
Subject: [PATCH] Update testgpurender_effects_grayscale.frag.hlsl

The formular did not use blue at all but red twice and the factor intended for blue was off.
---
 test/testgpurender_effects_grayscale.frag.hlsl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/testgpurender_effects_grayscale.frag.hlsl b/test/testgpurender_effects_grayscale.frag.hlsl
index 439196ca241cd..ff7731179f198 100644
--- a/test/testgpurender_effects_grayscale.frag.hlsl
+++ b/test/testgpurender_effects_grayscale.frag.hlsl
@@ -13,7 +13,7 @@ struct PSOutput {
 PSOutput main(PSInput input) {
     PSOutput output;
     float4 color = u_texture.Sample(u_sampler, input.v_uv) * input.v_color;
-    float gray = color.r * 0.2126 + color.g * 0.7152 + color.r * 0.722;
+    float gray = color.r * 0.2126 + color.g * 0.7152 + color.b * 0.0722;
     output.o_color = float4(gray, gray, gray, color.a);
     return output;
 }