From 8da082f805d4ed19be9764f5cafe957ccec8fd28 Mon Sep 17 00:00:00 2001
From: Swung0x48 <swung0x48@outlook.com>
Date: Fri, 2 Oct 2026 12:50:36 -0400
Subject: [PATCH] [Fix] (State): start the clear colour at GL's (0, 0, 0, 0),
 not opaque black

---
 MobileGL/MG_Pipe/MGPipeValueTypes.h        |  6 ++++--
 MobileGL/MG_Test/State/RenderStateTest.cpp | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/MobileGL/MG_Pipe/MGPipeValueTypes.h b/MobileGL/MG_Pipe/MGPipeValueTypes.h
index 5749fb4d..3b04eb83 100644
--- a/MobileGL/MG_Pipe/MGPipeValueTypes.h
+++ b/MobileGL/MG_Pipe/MGPipeValueTypes.h
@@ -304,8 +304,10 @@ namespace MobileGL {
         Bool DepthClampEnabled = false;
         Bool TextureCubeMapSeamlessEnabled = false;
 
-        // Clear State
-        FloatVec4 ClearColor = FloatVec4(0.0f, 0.0f, 0.0f, 1.0f);
+        // Clear State. GL's initial clear colour is (0, 0, 0, 0) (GL 4.6 core table 23.24): an
+        // application that never calls glClearColor - or caches it and skips the redundant call -
+        // clears to transparent, and offscreen layers depend on it.
+        FloatVec4 ClearColor = FloatVec4(0.0f, 0.0f, 0.0f, 0.0f);
         Float ClearDepth = 1.0f;
         Uint32 ClearStencil = 0;
         FloatVec4 BlendColor = FloatVec4(0.0f, 0.0f, 0.0f, 0.0f);
diff --git a/MobileGL/MG_Test/State/RenderStateTest.cpp b/MobileGL/MG_Test/State/RenderStateTest.cpp
index 986f056b..0f883a34 100644
--- a/MobileGL/MG_Test/State/RenderStateTest.cpp
+++ b/MobileGL/MG_Test/State/RenderStateTest.cpp
@@ -645,6 +645,21 @@ TEST_F(RenderStateTest, TheFirstScissorWriteBumpsTheVersionEvenWhenTheValueDoesN
 // were absent too, which is what KHR-GL4x.tessellation_shader.single.
 // default_values_of_context_wide_properties dies on.
 
+// GL 4.6 core table 23.24 / ES 3.2 table 21.13: GL_COLOR_CLEAR_VALUE starts at (0, 0, 0, 0). An
+// opaque-black default made every glClear of an application that relies on the initial value -
+// a layer that caches GL state and skips the redundant glClearColor(0, 0, 0, 0) - write alpha 1,
+// so offscreen layers meant to be transparent composited as solid black squares.
+TEST_F(RenderStateTest, ClearColorStartsAtTransparentBlack) {
+    const SharedPtr<MG_State::GLState::GLContext> previous = MG_State::pGLContext;
+    MG_State::pGLContext = MakeShared<MG_State::GLState::GLContext>();
+    GLfloat clear[4] = {-1.0f, -1.0f, -1.0f, -1.0f};
+    MG_Impl::GLImpl::GetFloatv(GL_COLOR_CLEAR_VALUE, clear);
+    const GLenum error = MG_Impl::GLImpl::GetError();
+    MG_State::pGLContext = previous;
+    EXPECT_EQ(error, GL_NO_ERROR);
+    for (const GLfloat channel : clear) EXPECT_FLOAT_EQ(channel, 0.0f);
+}
+
 TEST_F(RenderStateTest, PatchDefaultLevelsStartAtTheGLDefault) {
     GLfloat outer[4] = {-1.0f, -1.0f, -1.0f, -1.0f};
     MG_Impl::GLImpl::GetFloatv(GL_PATCH_DEFAULT_OUTER_LEVEL, outer);