- fixed: The depth clamp setting needs to be tracked per portal so that it can be properly restored afterward.

Regular skies need it off but SkyViewpoints need it on - and all others need to use the parent's setting.
So without engine side tracking we can end up rendering the sky with this setting off, resulting in omission of the fog layer.

src/gl/renderer/gl_renderstate.cpp

@@ -90,6 +90,7 @@ void FRenderState::Reset()
 	stSrcBlend = stDstBlend = -1;
 	stBlendEquation = -1;
 	stAlphaThreshold = -1.f;
+	mLastDepthClamp = true;
 }
 
 //==========================================================================

src/gl/renderer/gl_renderstate.h

@@ -63,6 +63,7 @@ class FRenderState
 	float mInterpolationFactor;
 	float mClipHeightTop, mClipHeightBottom;
 	float mShaderTimer;
+	bool mLastDepthClamp;
 
 	FVertexBuffer *mVertexBuffer, *mCurrentVertexBuffer;
 	FStateVec4 mColor;
@@ -309,6 +310,16 @@ public:
 		}
 	}
 
+	// This wraps the depth clamp setting because we frequently need to read it which OpenGL is not particularly performant at...
+	bool SetDepthClamp(bool on)
+	{
+		bool res = mLastDepthClamp;
+		if (!on) glDisable(GL_DEPTH_CLAMP);
+		else glEnable(GL_DEPTH_CLAMP);
+		mLastDepthClamp = on;
+		return res;
+	}
+
 	void Set2DMode(bool on)
 	{
 		m2D = on;

src/gl/scene/gl_portal.cpp

@@ -633,8 +633,7 @@ void GLSkyboxPortal::DrawContents()
 
 	PlaneMirrorMode=0;
 
-	glDisable(GL_DEPTH_CLAMP);
-
+	bool oldclamp = gl_RenderState.SetDepthClamp(false);
 	viewx = origin->PrevX + FixedMul(r_TicFrac, origin->x - origin->PrevX);
 	viewy = origin->PrevY + FixedMul(r_TicFrac, origin->y - origin->PrevY);
 	viewz = origin->PrevZ + FixedMul(r_TicFrac, origin->z - origin->PrevZ);
@@ -663,7 +662,7 @@ void GLSkyboxPortal::DrawContents()
 	GLRenderer->DrawScene();
 	origin->flags&=~MF_JUSTHIT;
 	inskybox=false;
-	glEnable(GL_DEPTH_CLAMP);
+	gl_RenderState.SetDepthClamp(oldclamp);
 	skyboxrecursion--;
 
 	PlaneMirrorMode=old_pm;

src/gl/scene/gl_skydome.cpp

@@ -475,6 +475,7 @@ void GLSkyPortal::DrawContents()
 	gl_RenderState.EnableFog(false);
 	gl_RenderState.AlphaFunc(GL_GEQUAL, 0.f);
 	gl_RenderState.BlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+	bool oldClamp = gl_RenderState.SetDepthClamp(true);
 
 	gl_MatrixStack.Push(gl_RenderState.mViewMatrix);
 	GLRenderer->SetupView(0, 0, 0, viewangle, !!(MirrorFlag&1), !!(PlaneMirrorFlag&1));
@@ -519,5 +520,6 @@ void GLSkyPortal::DrawContents()
 	gl_MatrixStack.Pop(gl_RenderState.mViewMatrix);
 	gl_RenderState.ApplyMatrices();
 	glset.lightmode = oldlightmode;
+	gl_RenderState.SetDepthClamp(oldClamp);
 }