Do not write depth value if we need to skip a fragment

Rendering/Volume/Testing/Cxx/TestGPURayCastRenderDepthToImage2.cxx

@@ -46,7 +46,6 @@ int TestGPURayCastRenderDepthToImage2(int argc, char *argv[])
   volumeMapper->RenderToImageOn();
 
   vtkNew<vtkColorTransferFunction> colorFunction;
-  colorFunction->AddRGBPoint(900.0, 198/255.0, 134/255.0, 66/255.0);
   colorFunction->AddRGBPoint(37.35310363769531, 0.231373, 0.298039, 0.752941);
   colorFunction->AddRGBPoint(157.0909652709961, 0.865003, 0.865003, 0.865003);
   colorFunction->AddRGBPoint(276.8288269042969, 0.705882, 0.0156863, 0.14902);
@@ -59,7 +58,7 @@ int TestGPURayCastRenderDepthToImage2(int argc, char *argv[])
 
   vtkNew<vtkPiecewiseFunction> scalarOpacity;
   scalarOpacity->RemoveAllPoints();
-  scalarOpacity->AddPoint(center, 0.01);
+  scalarOpacity->AddPoint(center, 0.0);
   scalarOpacity->AddPoint(dataRange[1], 0.4);
 
   vtkNew<vtkVolumeProperty> volumeProperty;

Rendering/Volume/Testing/Data/Baseline/TestGPURayCastRenderDepthToImage.png.md5

+56f8c9f08e341337b2a8b4c22ded5817

Rendering/Volume/Testing/Data/Baseline/TestGPURayCastRenderDepthToImage2.png.md5

+6bc09829bf703f9687728384102e108a

Rendering/Volume/Testing/Data/Baseline/TestGPURayCastRenderDepthToTexture.png.md5

-06cca1b201823f9aebfa104cfff16abe

Rendering/VolumeOpenGL2/vtkVolumeShaderComposer.h

@@ -1080,7 +1080,7 @@ namespace vtkvolume
           \n        {\
           \n        for (int i = 0; i < in_noOfComponents; ++i)\
           \n          {\
-          \n          tmp.x += color[i].x * color[i].w * in_componentWeight[i] ;\
+          \n          tmp.x += color[i].x * color[i].w * in_componentWeight[i];\
           \n          tmp.y += color[i].y * color[i].w * in_componentWeight[i];\
           \n          tmp.z += color[i].z * color[i].w * in_componentWeight[i];\
           \n          tmp.w += ((color[i].w * color[i].w)/totalAlpha);\
@@ -1113,7 +1113,7 @@ namespace vtkvolume
            \n        // alpha from the previous steps. Next, this alpha is\
            \n        // multiplied with the current sample colour\
            \n        // and accumulated to the composited colour. The alpha\
-           \n        // value from\ the previous steps is then accumulated\
+           \n        // value from the previous steps is then accumulated\
            \n        // to the composited colour alpha.\
            \n        g_srcColor.rgb *= g_srcColor.a;\
            \n        g_fragColor = (1.0f - g_fragColor.a) * g_srcColor + g_fragColor;"