VideoCommon: move ViewportCorrection into VideoCommon

D3D doesn't allow bigger viewports than rendertargets. But flipper does, so the viewport will be clipped and the transformation matrix will be changed.
This was done in the D3D backend itself. This is now moved into VideoCommon. This don't reduce code, but in this way, VideoCommon doesn't depend on the backends.

Source/Core/VideoCommon/Src/RenderBase.cpp

@@ -520,8 +520,8 @@ void Renderer::RecordVideoMemory()
 	FifoRecorder::GetInstance().SetVideoMemory(bpMem, cpMem, xfMem, xfRegs, sizeof(XFRegisters) / 4);
 }
 
-void UpdateViewport(Matrix44& vpCorrection)
+void UpdateViewport()
 {
 	if (xfregs.viewport.wd != 0 && xfregs.viewport.ht != 0)
-		g_renderer->UpdateViewport(vpCorrection);
+		g_renderer->UpdateViewport();
 }

Source/Core/VideoCommon/Src/RenderBase.h

@@ -108,7 +108,7 @@ public:
 	// Finish up the current frame, print some stats
 	virtual void Swap(u32 xfbAddr, u32 fbWidth, u32 fbHeight, const EFBRectangle& rc,float Gamma = 1.0f) = 0;
 
-	virtual void UpdateViewport(Matrix44& vpCorrection) = 0;
+	virtual void UpdateViewport() = 0;
 
 	virtual bool SaveScreenshot(const std::string &filename, const TargetRectangle &rc) = 0;
 
@@ -163,6 +163,6 @@ private:
 
 extern Renderer *g_renderer;
 
-void UpdateViewport(Matrix44& vpCorrection);
+void UpdateViewport();
 
 #endif // _COMMON_RENDERBASE_H_

Source/Core/VideoCommon/Src/VertexShaderManager.cpp

@@ -39,13 +39,6 @@ static float s_fViewRotation[2];
 VertexShaderConstants VertexShaderManager::constants;
 bool VertexShaderManager::dirty;
 
-void UpdateViewport(Matrix44& vpCorrection);
-
-void UpdateViewportWithCorrection()
-{
-	UpdateViewport(s_viewportCorrection);
-}
-
 struct ProjectionHack
 {
 	float sign;
@@ -130,6 +123,65 @@ void UpdateProjectionHack(int iPhackvalue[], std::string sPhackvalue[])
 	g_ProjHack3 = bProjHack3;
 }
 
+
+// Viewport correction:
+// In D3D, the viewport rectangle must fit within the render target.
+// Say you want a viewport at (ix, iy) with size (iw, ih),
+// but your viewport must be clamped at (ax, ay) with size (aw, ah).
+// Just multiply the projection matrix with the following to get the same
+// effect:
+// [   (iw/aw)         0     0    ((iw - 2*(ax-ix)) / aw - 1)   ]
+// [         0   (ih/ah)     0   ((-ih + 2*(ay-iy)) / ah + 1)   ]
+// [         0         0     1                              0   ]
+// [         0         0     0                              1   ]
+static void ViewportCorrectionMatrix(Matrix44& result)
+{
+	int scissorXOff = bpmem.scissorOffset.x * 2;
+	int scissorYOff = bpmem.scissorOffset.y * 2;
+
+	// TODO: ceil, floor or just cast to int?
+	// TODO: Directly use the floats instead of rounding them?
+	float intendedX = xfregs.viewport.xOrig - xfregs.viewport.wd - scissorXOff;
+	float intendedY = xfregs.viewport.yOrig + xfregs.viewport.ht - scissorYOff;
+	float intendedWd = 2.0f * xfregs.viewport.wd;
+	float intendedHt = -2.0f * xfregs.viewport.ht;
+	
+        if (intendedWd < 0.f)
+        {
+                intendedX += intendedWd;
+                intendedWd = -intendedWd;
+        }
+        if (intendedHt < 0.f)
+        {
+                intendedY += intendedHt;
+                intendedHt = -intendedHt;
+        }
+
+	// fit to EFB size
+        float X = (intendedX >= 0.f) ? intendedX : 0.f;
+        float Y = (intendedY >= 0.f) ? intendedY : 0.f;
+        float Wd = (X + intendedWd <= EFB_WIDTH) ? intendedWd : (EFB_WIDTH - X);
+        float Ht = (Y + intendedHt <= EFB_HEIGHT) ? intendedHt : (EFB_HEIGHT - Y);
+	
+	Matrix44::LoadIdentity(result);
+	if (Wd == 0 || Ht == 0)
+		return;
+	
+	result.data[4*0+0] = intendedWd / Wd;
+	result.data[4*0+3] = (intendedWd - 2.f * (X - intendedX)) / Wd - 1.f;
+	result.data[4*1+1] = intendedHt / Ht;
+	result.data[4*1+3] = (-intendedHt + 2.f * (Y - intendedY)) / Ht + 1.f;
+}
+
+void UpdateViewport();
+
+void UpdateViewportWithCorrection()
+{
+	// TODO: get rid of this function
+	ViewportCorrectionMatrix(s_viewportCorrection);
+	UpdateViewport();
+}
+
 void VertexShaderManager::Init()
 {
 	Dirty();
@@ -330,8 +382,14 @@ void VertexShaderManager::SetConstants()
 		constants.depthparams[3] = 1.f / g_renderer->EFBToScaledY(ceilf(-2.0f * xfregs.viewport.ht));
 		dirty = true;
 		// This is so implementation-dependent that we can't have it here.
-		UpdateViewport(s_viewportCorrection);
-		bProjectionChanged = true;
+		UpdateViewport();
+		
+		// Update projection if the viewport isn't 1:1 useable
+		if(!g_ActiveConfig.backend_info.bSupportsOversizedViewports)
+		{
+			ViewportCorrectionMatrix(s_viewportCorrection);
+			bProjectionChanged = true;			
+		}
 	}
 
 	if (bProjectionChanged)

Source/Core/VideoCommon/Src/VideoConfig.h

@@ -153,6 +153,7 @@ struct VideoConfig
 		bool bSupportsPixelLighting;
 		bool bSupportsPrimitiveRestart;
 		bool bSupportsSeparateAlphaFunction;
+		bool bSupportsOversizedViewports;
 		bool bSupportsGLSLUBO; // needed by PixelShaderGen, so must stay in VideoCommon
 		bool bSupportsEarlyZ; // needed by PixelShaderGen, so must stay in VideoCommon
 	} backend_info;