- on older ATI drivers where the clip planes are broken, only disable the clip planes themselves, but not OpenGL 3.x so that dynamic lights still work as intended.

- only disable clip planes on Windows, but not on Linux or macOS.
- If a driver reports full OpenGL 4.5 support, assume that all features are working properly.

src/gl/renderer/gl_renderstate.cpp

@@ -344,12 +344,12 @@ void FRenderState::SetClipHeight(float height, float direction)
 	mClipHeightDirection = direction;
 #if 1
 	// This still doesn't work... :(
-	if (gl.glslversion < 1.3f) return;
+	if (gl.flags & RFL_NO_CLIP_PLANES) return;
 #endif
 	if (direction != 0.f)
 	{
 		/*
-		if (gl.glslversion < 1.3f) 
+		if (gl.flags & RFL_NO_CLIP_PLANES)
 		{
 			glMatrixMode(GL_MODELVIEW);
 			glPushMatrix();

src/gl/renderer/gl_renderstate.h

@@ -237,7 +237,7 @@ public:
 
 	void EnableSplit(bool on)
 	{
-		if (gl.glslversion >= 1.3f)
+		if (!(gl.flags & RFL_NO_CLIP_PLANES))
 		{
 			mSplitEnabled = on;
 			if (on)
@@ -260,7 +260,7 @@ public:
 
 	void EnableClipLine(bool on)
 	{
-		if (gl.glslversion >= 1.3f)
+		if (!(gl.flags & RFL_NO_CLIP_PLANES))
 		{
 			mClipLineEnabled = on;
 			if (on)

src/gl/scene/gl_sprite.cpp

@@ -972,7 +972,7 @@ void GLSprite::Process(AActor* thing, sector_t * sector, int thruportal)
 	if (thing->Sector->e->XFloor.lightlist.Size() != 0 && gl_fixedcolormap == CM_DEFAULT && !fullbright &&
 		RenderStyle.BlendOp != STYLEOP_Shadow && RenderStyle.BlendOp != STYLEOP_RevSub)
 	{
-		if (gl.glslversion < 1.3)	// on old hardware we are rather limited...
+		if (gl.flags & RFL_NO_CLIP_PLANES)	// on old hardware we are rather limited...
 		{
 			lightlist = NULL;
 			if (!drawWithXYBillboard && !modelframe)

src/gl/scene/gl_walls.cpp

@@ -403,7 +403,7 @@ void GLWall::SplitWall(sector_t * frontsector, bool translucent)
 				(maplightbottomleft<zbottom[0] && maplightbottomright>zbottom[1]) ||
 				(maplightbottomleft > zbottom[0] && maplightbottomright < zbottom[1]))
 			{
-				if (gl.glslversion >= 1.3f)
+				if (!(gl.flags & RFL_NO_CLIP_PLANES))
 				{
 					// Use hardware clipping if this cannot be done cleanly.
 					this->lightlist = &lightlist;

src/gl/shaders/gl_shader.cpp

@@ -169,6 +169,12 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 		FShaderProgram::PatchVertShader(vp_comb);
 		FShaderProgram::PatchFragShader(fp_comb);
 	}
+	else if (gl.flags & RFL_NO_CLIP_PLANES)
+	{
+		// On ATI's GL3 drivers we have to disable gl_ClipDistance because it's hopelessly broken.
+		// This will cause some glitches and regressions but is the only way to avoid total display garbage.
+		vp_comb.Substitute("gl_ClipDistance", "//");
+	}
 
 	hVertProg = glCreateShader(GL_VERTEX_SHADER);
 	hFragProg = glCreateShader(GL_FRAGMENT_SHADER);	

src/gl/system/gl_interface.cpp

@@ -192,6 +192,7 @@ void gl_LoadExtensions()
 		gl.version = 2.11f;
 		gl.glslversion = 0;
 		gl.lightmethod = LM_SOFTWARE;
+		gl.flags |= RFL_NO_CLIP_PLANES;
 	}
 	else if (gl.version < 3.0f)
 	{
@@ -200,17 +201,18 @@ void gl_LoadExtensions()
 
 		if (!CheckExtension("GL_EXT_packed_float")) gl.flags |= RFL_NO_RGBA16F;
 		if (!CheckExtension("GL_EXT_packed_depth_stencil")) gl.flags |= RFL_NO_DEPTHSTENCIL;
+		gl.flags |= RFL_NO_CLIP_PLANES;
 	}
 	else if (gl.version < 4.f)
 	{
+#ifdef _WIN32
 		if (strstr(gl.vendorstring, "ATI Tech")) 
 		{
-			gl.version = 2.11f;
+			gl.flags |= RFL_NO_CLIP_PLANES;	// gl_ClipDistance is horribly broken on ATI GL3 drivers for Windows.
-			gl.glslversion = 1.21f;
-			gl.lightmethod = LM_SOFTWARE;		// do not use uniform buffers with the fallback shader, it may cause problems.
 		}
+#endif
 	}
-	else
+	else if (gl.version < 4.5f)
 	{
 		// don't use GL 4.x features when running in GL 3 emulation mode.
 		if (CheckExtension("GL_ARB_buffer_storage"))
@@ -234,6 +236,13 @@ void gl_LoadExtensions()
 			gl.version = 3.3f;
 		}
 	}
+	else
+	{
+		// Assume that everything works without problems on GL 4.5 drivers where these things are core features.
+		gl.flags |= RFL_SHADER_STORAGE_BUFFER | RFL_BUFFER_STORAGE;
+		gl.lightmethod = LM_DIRECT;
+		gl.buffermethod = BM_PERSISTENT;
+	}
 
 	const char *lm = Args->CheckValue("-lightmethod");
 	if (lm != NULL)

src/gl/system/gl_interface.h

@@ -22,7 +22,8 @@ enum RenderFlags
 	RFL_SAMPLER_OBJECTS = 16,
 
 	RFL_NO_RGBA16F = 32,
-	RFL_NO_DEPTHSTENCIL = 64
+	RFL_NO_DEPTHSTENCIL = 64,
+	RFL_NO_CLIP_PLANES = 128
 };
 
 enum TexMode