From f8f3b3105db1d7688dcc6eee71456b960bdf83e6 Mon Sep 17 00:00:00 2001
From: Salman Alshamrani <frenzibyte@gmail.com>
Date: Fri, 13 Dec 2024 07:38:36 -0500
Subject: [PATCH] Update all shaders to interpret colours as premultiplied

---
 osu.Framework/Resources/Shaders/sh_CircularBlob.fs     |  2 +-
 osu.Framework/Resources/Shaders/sh_CircularProgress.fs |  2 +-
 osu.Framework/Resources/Shaders/sh_FastCircle.fs       |  2 +-
 osu.Framework/Resources/Shaders/sh_Masking.h           |  8 ++++----
 osu.Framework/Resources/Shaders/sh_Particle.vs         |  2 +-
 osu.Framework/Resources/Shaders/sh_Utils.h             | 10 +---------
 6 files changed, 9 insertions(+), 17 deletions(-)

diff --git a/osu.Framework/Resources/Shaders/sh_CircularBlob.fs b/osu.Framework/Resources/Shaders/sh_CircularBlob.fs
index fa5f027085..a4899f4c96 100644
--- a/osu.Framework/Resources/Shaders/sh_CircularBlob.fs
+++ b/osu.Framework/Resources/Shaders/sh_CircularBlob.fs
@@ -33,7 +33,7 @@ void main(void)
     highp vec2 wrappedCoord = wrap(v_TexCoord, v_TexRect);
     lowp vec4 textureColour = getRoundedColor(wrappedSampler(wrappedCoord, v_TexRect, m_Texture, m_Sampler, -0.9), wrappedCoord);
 
-    o_Colour = vec4(textureColour.rgb, textureColour.a * blobAlphaAt(pixelPos, innerRadius, texelSize, frequency, amplitude, noisePosition));
+    o_Colour = textureColour.rgba * blobAlphaAt(pixelPos, innerRadius, texelSize, frequency, amplitude, noisePosition);
 }
 
 #endif
\ No newline at end of file
diff --git a/osu.Framework/Resources/Shaders/sh_CircularProgress.fs b/osu.Framework/Resources/Shaders/sh_CircularProgress.fs
index 559a064831..bf5f4b8a10 100644
--- a/osu.Framework/Resources/Shaders/sh_CircularProgress.fs
+++ b/osu.Framework/Resources/Shaders/sh_CircularProgress.fs
@@ -32,7 +32,7 @@ void main(void)
     highp vec2 wrappedCoord = wrap(v_TexCoord, v_TexRect);
     lowp vec4 textureColour = getRoundedColor(wrappedSampler(wrappedCoord, v_TexRect, m_Texture, m_Sampler, -0.9), wrappedCoord);
 
-    o_Colour = vec4(textureColour.rgb, textureColour.a * progressAlphaAt(pixelPos, progress, innerRadius, roundedCaps, texelSize));
+    o_Colour = textureColour.rgba * progressAlphaAt(pixelPos, progress, innerRadius, roundedCaps, texelSize);
 }
 
 #endif
\ No newline at end of file
diff --git a/osu.Framework/Resources/Shaders/sh_FastCircle.fs b/osu.Framework/Resources/Shaders/sh_FastCircle.fs
index 307f00a74c..be60600f41 100644
--- a/osu.Framework/Resources/Shaders/sh_FastCircle.fs
+++ b/osu.Framework/Resources/Shaders/sh_FastCircle.fs
@@ -20,7 +20,7 @@ void main(void)
 
     highp float alpha = v_BlendRange.x == 0.0 ? float(dst < radius) : (clamp(radius - dst, 0.0, v_BlendRange.x) / v_BlendRange.x);
 
-    o_Colour = getRoundedColor(vec4(vec3(1.0), alpha), vec2(0.0));
+    o_Colour = getRoundedColor(vec4(alpha), vec2(0.0));
 }
 
 #endif
diff --git a/osu.Framework/Resources/Shaders/sh_Masking.h b/osu.Framework/Resources/Shaders/sh_Masking.h
index 3fdc6c8846..e9e0223052 100644
--- a/osu.Framework/Resources/Shaders/sh_Masking.h
+++ b/osu.Framework/Resources/Shaders/sh_Masking.h
@@ -116,15 +116,15 @@ lowp vec4 getRoundedColor(lowp vec4 texel, mediump vec2 texCoord)
 	lowp vec4 contentColour = v_Colour * texel;
 
 	if (colourWeight == 1.0)
-		return vec4(contentColour.rgb, contentColour.a * alphaFactor);
+		return contentColour.rgba * alphaFactor;
 
 	lowp vec4 borderColour = getBorderColour();
 
 	if (colourWeight <= 0.0)
-		return vec4(borderColour.rgb, borderColour.a * alphaFactor);
+		return borderColour.rgba * alphaFactor;
 
-	contentColour.a *= alphaFactor;
-	borderColour.a *= 1.0 - colourWeight;
+	contentColour.rgba *= alphaFactor;
+	borderColour.rgba *= 1.0 - colourWeight;
 	return blend(borderColour, contentColour);
 }
 
diff --git a/osu.Framework/Resources/Shaders/sh_Particle.vs b/osu.Framework/Resources/Shaders/sh_Particle.vs
index 8da3d9ed64..9a8781f19e 100644
--- a/osu.Framework/Resources/Shaders/sh_Particle.vs
+++ b/osu.Framework/Resources/Shaders/sh_Particle.vs
@@ -23,7 +23,7 @@ void main(void)
 		vec2(0.0, g_Gravity * g_FadeClock * g_FadeClock / 1000000.0);
 
 	gl_Position = g_ProjMatrix * vec4(targetPosition, 1.0, 1.0);
-	v_Colour = vec4(1.0, 1.0, 1.0, 1.0 - clamp(g_FadeClock / m_Time, 0.0, 1.0));
+	v_Colour = vec4(1.0 - clamp(g_FadeClock / m_Time, 0.0, 1.0));
 	v_TexCoord = m_TexCoord;
 }
 
diff --git a/osu.Framework/Resources/Shaders/sh_Utils.h b/osu.Framework/Resources/Shaders/sh_Utils.h
index 6e2e010c25..ffeb972298 100644
--- a/osu.Framework/Resources/Shaders/sh_Utils.h
+++ b/osu.Framework/Resources/Shaders/sh_Utils.h
@@ -8,15 +8,7 @@
 // see http://apoorvaj.io/alpha-compositing-opengl-blending-and-premultiplied-alpha.html
 lowp vec4 blend(lowp vec4 src, lowp vec4 dst)
 {
-    lowp float finalAlpha = src.a + dst.a * (1.0 - src.a);
-
-    if (finalAlpha == 0.0)
-        return vec4(0);
-
-    return vec4(
-        (src.rgb * src.a + dst.rgb * dst.a * (1.0 - src.a)) / finalAlpha,
-        finalAlpha
-    );
+    return src.rgba + dst.rgba * (1.0 - src.a);
 }
 
 // http://lolengine.net/blog/2013/07/27/rgb-to-hsv-in-glsl