Merge pull request #380 from KhronosGroup/fix-368

Add support for gl_ViewportIndex.

reference/opt/shaders/desktop-only/geom/viewport-index.desktop.geom

@@ -0,0 +1,9 @@
+#version 450
+layout(triangles) in;
+layout(max_vertices = 4, triangle_strip) out;
+
+void main()
+{
+    gl_ViewportIndex = 1;
+}
+

reference/shaders/desktop-only/geom/viewport-index.desktop.geom

@@ -0,0 +1,9 @@
+#version 450
+layout(triangles) in;
+layout(max_vertices = 4, triangle_strip) out;
+
+void main()
+{
+    gl_ViewportIndex = 1;
+}
+

shaders/desktop-only/geom/viewport-index.desktop.geom

@@ -0,0 +1,11 @@
+#version 450
+
+layout(triangles) in;
+layout(triangle_strip) out;
+layout(max_vertices = 4) out;
+
+void main()
+{
+	gl_ViewportIndex = 1;
+}
+

spirv_glsl.cpp

@@ -4163,6 +4163,8 @@ string CompilerGLSL::builtin_to_glsl(BuiltIn builtin, StorageClass storage)
 		return "gl_InvocationID";
 	case BuiltInLayer:
 		return "gl_Layer";
+	case BuiltInViewportIndex:
+		return "gl_ViewportIndex";
 	case BuiltInTessLevelOuter:
 		return "gl_TessLevelOuter";
 	case BuiltInTessLevelInner: