From cf390655114d4e70f8bd90f5789fb5150bfe3435 Mon Sep 17 00:00:00 2001
From: sfan5 <sfan5@live.de>
Date: Sat, 10 Jan 2026 10:52:48 +0100
Subject: [PATCH] OpenGL: don't use alpha test for GLSL materials (#16832)

This fixes crack for transparent textures on legacy GL (overlay was visible even if base was transparent),
because our shader code assumed that transparent pixels would be discarded early.
---
 irr/src/COpenGLSLMaterialRenderer.cpp | 20 ++++----------------
 irr/src/COpenGLSLMaterialRenderer.h   |  1 -
 src/client/shader.cpp                 |  9 +--------
 3 files changed, 5 insertions(+), 25 deletions(-)

diff --git a/irr/src/COpenGLSLMaterialRenderer.cpp b/irr/src/COpenGLSLMaterialRenderer.cpp
index 373f79b54f..4471b95466 100644
--- a/irr/src/COpenGLSLMaterialRenderer.cpp
+++ b/irr/src/COpenGLSLMaterialRenderer.cpp
@@ -40,7 +40,7 @@ COpenGLSLMaterialRenderer::COpenGLSLMaterialRenderer(video::COpenGLDriver *drive
 		E_MATERIAL_TYPE baseMaterial,
 		s32 userData) :
 		Driver(driver),
-		CallBack(callback), Alpha(false), Blending(false), AlphaTest(false), Program(0), Program2(0), UserData(userData)
+		CallBack(callback), Alpha(false), Blending(false), Program(0), Program2(0), UserData(userData)
 {
 	switch (baseMaterial) {
 	case EMT_TRANSPARENT_VERTEX_ALPHA:
@@ -50,9 +50,6 @@ COpenGLSLMaterialRenderer::COpenGLSLMaterialRenderer(video::COpenGLDriver *drive
 	case EMT_ONETEXTURE_BLEND:
 		Blending = true;
 		break;
-	case EMT_TRANSPARENT_ALPHA_CHANNEL_REF:
-		AlphaTest = true;
-		break;
 	default:
 		break;
 	}
@@ -72,7 +69,7 @@ COpenGLSLMaterialRenderer::COpenGLSLMaterialRenderer(COpenGLDriver *driver,
 		IShaderConstantSetCallBack *callback,
 		E_MATERIAL_TYPE baseMaterial, s32 userData) :
 		Driver(driver),
-		CallBack(callback), Alpha(false), Blending(false), AlphaTest(false), Program(0), Program2(0), UserData(userData)
+		CallBack(callback), Alpha(false), Blending(false), Program(0), Program2(0), UserData(userData)
 {
 	switch (baseMaterial) {
 	case EMT_TRANSPARENT_VERTEX_ALPHA:
@@ -82,9 +79,6 @@ COpenGLSLMaterialRenderer::COpenGLSLMaterialRenderer(COpenGLDriver *driver,
 	case EMT_ONETEXTURE_BLEND:
 		Blending = true;
 		break;
-	case EMT_TRANSPARENT_ALPHA_CHANNEL_REF:
-		AlphaTest = true;
-		break;
 	default:
 		break;
 	}
@@ -210,11 +204,11 @@ void COpenGLSLMaterialRenderer::OnSetMaterial(const video::SMaterial &material,
 
 	Driver->setBasicRenderStates(material, lastMaterial, resetAllRenderstates);
 
+	cacheHandler->setAlphaTest(false);
+
 	if (Alpha) {
 		cacheHandler->setBlend(true);
 		cacheHandler->setBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
-		cacheHandler->setAlphaTest(true);
-		cacheHandler->setAlphaFunc(GL_GREATER, 0.f);
 	} else if (Blending) {
 		E_BLEND_FACTOR srcRGBFact, dstRGBFact, srcAlphaFact, dstAlphaFact;
 		E_MODULATE_FUNC modulate;
@@ -229,9 +223,6 @@ void COpenGLSLMaterialRenderer::OnSetMaterial(const video::SMaterial &material,
 		}
 
 		cacheHandler->setBlend(true);
-	} else if (AlphaTest) {
-		cacheHandler->setAlphaTest(true);
-		cacheHandler->setAlphaFunc(GL_GREATER, 0.5f);
 	}
 
 	if (CallBack)
@@ -249,9 +240,6 @@ void COpenGLSLMaterialRenderer::OnUnsetMaterial()
 	if (Alpha || Blending) {
 		cacheHandler->setBlend(false);
 	}
-	if (Alpha || AlphaTest) {
-		cacheHandler->setAlphaTest(false);
-	}
 }
 
 //! Returns if the material is transparent.
diff --git a/irr/src/COpenGLSLMaterialRenderer.h b/irr/src/COpenGLSLMaterialRenderer.h
index 3b8e83674b..de15f9fbbe 100644
--- a/irr/src/COpenGLSLMaterialRenderer.h
+++ b/irr/src/COpenGLSLMaterialRenderer.h
@@ -96,7 +96,6 @@ protected:
 
 	bool Alpha;
 	bool Blending;
-	bool AlphaTest;
 
 	struct SUniformInfo
 	{
diff --git a/src/client/shader.cpp b/src/client/shader.cpp
index 9a1cdc409b..034a8ffb12 100644
--- a/src/client/shader.cpp
+++ b/src/client/shader.cpp
@@ -790,14 +790,7 @@ void ShaderSource::generateShader(ShaderInfo &shaderinfo)
 
 	ShaderConstants constants = input_const;
 
-	bool use_discard = m_fully_programmable;
-	if (!use_discard) {
-		// workaround for a certain OpenGL implementation lacking GL_ALPHA_TEST
-		const char *renderer = reinterpret_cast<const char*>(GL.GetString(GL.RENDERER));
-		if (strstr(renderer, "GC7000"))
-			use_discard = true;
-	}
-	if (use_discard) {
+	{
 		if (shaderinfo.base_material == video::EMT_TRANSPARENT_ALPHA_CHANNEL)
 			constants["USE_DISCARD"] = 1;
 		else if (shaderinfo.base_material == video::EMT_TRANSPARENT_ALPHA_CHANNEL_REF)