From e0fef60241397ce12be4ce311382060fe6db707d Mon Sep 17 00:00:00 2001
From: Stephan Unverwerth <s.unverwerth@serenityos.org>
Date: Wed, 11 Aug 2021 22:06:07 +0200
Subject: [PATCH] LibGL: Implement "mirrored repeat" wrap mode

---
 Userland/Libraries/LibGL/GL/gl.h           |  1 +
 Userland/Libraries/LibGL/Tex/Sampler2D.cpp | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/Userland/Libraries/LibGL/GL/gl.h b/Userland/Libraries/LibGL/GL/gl.h
index 93609a8b27..84f60d96c3 100644
--- a/Userland/Libraries/LibGL/GL/gl.h
+++ b/Userland/Libraries/LibGL/GL/gl.h
@@ -201,6 +201,7 @@ extern "C" {
 #define GL_NEAREST_MIPMAP_LINEAR 0x2602
 #define GL_CLAMP 0x2900
 #define GL_REPEAT 0x2901
+#define GL_MIRRORED_REPEAT 0x8370
 #define GL_CLAMP_TO_BORDER 0x812D
 #define GL_CLAMP_TO_EDGE 0x812F
 
diff --git a/Userland/Libraries/LibGL/Tex/Sampler2D.cpp b/Userland/Libraries/LibGL/Tex/Sampler2D.cpp
index f2d1aeeb1f..45cd98405e 100644
--- a/Userland/Libraries/LibGL/Tex/Sampler2D.cpp
+++ b/Userland/Libraries/LibGL/Tex/Sampler2D.cpp
@@ -16,6 +16,14 @@ static constexpr float wrap_repeat(float value)
     return value - floorf(value);
 }
 
+static constexpr float wrap_mirrored_repeat(float value)
+{
+    float integer = floorf(value);
+    float frac = value - integer;
+    bool iseven = fmodf(integer, 2.0f) == 0.0f;
+    return iseven ? frac : 1 - frac;
+}
+
 static constexpr float wrap_clamp(float value)
 {
     return clamp(value, 0.0f, 1.0f);
@@ -43,6 +51,10 @@ FloatVector4 Sampler2D::sample(FloatVector2 const& uv) const
         x = wrap_clamp(x);
         break;
 
+    case GL_MIRRORED_REPEAT:
+        x = wrap_mirrored_repeat(x);
+        break;
+
     default:
         VERIFY_NOT_REACHED();
     }
@@ -59,6 +71,10 @@ FloatVector4 Sampler2D::sample(FloatVector2 const& uv) const
         y = wrap_clamp(y);
         break;
 
+    case GL_MIRRORED_REPEAT:
+        y = wrap_mirrored_repeat(y);
+        break;
+
     default:
         VERIFY_NOT_REACHED();
     }