WebGL validation of constant color & alpha blend.

src/libANGLE/validationES2.cpp

@@ -3848,7 +3848,8 @@ bool ValidateBlendFuncSeparate(ValidationContext *context,
         return false;
     }
 
-    if (context->getLimitations().noSimultaneousConstantColorAndAlphaBlendFunc)
+    if (context->getLimitations().noSimultaneousConstantColorAndAlphaBlendFunc ||
+        context->getExtensions().webglCompatibility)
     {
         bool constantColorUsed =
             (srcRGB == GL_CONSTANT_COLOR || srcRGB == GL_ONE_MINUS_CONSTANT_COLOR ||
@@ -3860,14 +3861,22 @@ bool ValidateBlendFuncSeparate(ValidationContext *context,
 
         if (constantColorUsed && constantAlphaUsed)
         {
-            ERR() << "Simultaneous use of GL_CONSTANT_ALPHA/GL_ONE_MINUS_CONSTANT_ALPHA and "
-                     "GL_CONSTANT_COLOR/GL_ONE_MINUS_CONSTANT_COLOR not supported by this "
-                     "implementation.";
-            context->handleError(Error(GL_INVALID_OPERATION,
-                                       "Simultaneous use of "
-                                       "GL_CONSTANT_ALPHA/GL_ONE_MINUS_CONSTANT_ALPHA and "
-                                       "GL_CONSTANT_COLOR/GL_ONE_MINUS_CONSTANT_COLOR not "
-                                       "supported by this implementation."));
+            const char *msg;
+            if (context->getExtensions().webglCompatibility)
+            {
+                msg =
+                    "Invalid simultaneous use of GL_CONSTANT_ALPHA/GL_ONE_MINUS_CONSTANT_ALPHA and "
+                    "GL_CONSTANT_COLOR/GL_ONE_MINUS_CONSTANT_COLOR.";
+            }
+            else
+            {
+                msg =
+                    "Simultaneous use of GL_CONSTANT_ALPHA/GL_ONE_MINUS_CONSTANT_ALPHA and "
+                    "GL_CONSTANT_COLOR/GL_ONE_MINUS_CONSTANT_COLOR not supported by this "
+                    "implementation.";
+                ERR() << msg;
+            }
+            context->handleError(Error(GL_INVALID_OPERATION, msg));
             return false;
         }
     }

src/tests/gl_tests/WebGLCompatibilityTest.cpp

@@ -10,6 +10,30 @@
 
 #include "test_utils/gl_raii.h"
 
+namespace
+{
+
+bool ConstantColorAndAlphaBlendFunctions(GLenum first, GLenum second)
+{
+    return (first == GL_CONSTANT_COLOR || first == GL_ONE_MINUS_CONSTANT_COLOR) &&
+           (second == GL_CONSTANT_ALPHA || second == GL_ONE_MINUS_CONSTANT_ALPHA);
+}
+
+void CheckBlendFunctions(GLenum src, GLenum dst)
+{
+    if (ConstantColorAndAlphaBlendFunctions(src, dst) ||
+        ConstantColorAndAlphaBlendFunctions(dst, src))
+    {
+        EXPECT_GL_ERROR(GL_INVALID_OPERATION);
+    }
+    else
+    {
+        ASSERT_GL_NO_ERROR();
+    }
+}
+
+}  // namespace
+
 namespace angle
 {
 
@@ -436,6 +460,50 @@ TEST_P(WebGLCompatibilityTest, DepthRange)
     EXPECT_GL_ERROR(GL_INVALID_OPERATION);
 }
 
+// Test all blend function combinations.
+// In WebGL it is invalid to combine constant color with constant alpha.
+TEST_P(WebGLCompatibilityTest, BlendWithConstantColor)
+{
+    constexpr GLenum srcFunc[] = {
+        GL_ZERO,
+        GL_ONE,
+        GL_SRC_COLOR,
+        GL_ONE_MINUS_SRC_COLOR,
+        GL_DST_COLOR,
+        GL_ONE_MINUS_DST_COLOR,
+        GL_SRC_ALPHA,
+        GL_ONE_MINUS_SRC_ALPHA,
+        GL_DST_ALPHA,
+        GL_ONE_MINUS_DST_ALPHA,
+        GL_CONSTANT_COLOR,
+        GL_ONE_MINUS_CONSTANT_COLOR,
+        GL_CONSTANT_ALPHA,
+        GL_ONE_MINUS_CONSTANT_ALPHA,
+        GL_SRC_ALPHA_SATURATE,
+    };
+
+    constexpr GLenum dstFunc[] = {
+        GL_ZERO,           GL_ONE,
+        GL_SRC_COLOR,      GL_ONE_MINUS_SRC_COLOR,
+        GL_DST_COLOR,      GL_ONE_MINUS_DST_COLOR,
+        GL_SRC_ALPHA,      GL_ONE_MINUS_SRC_ALPHA,
+        GL_DST_ALPHA,      GL_ONE_MINUS_DST_ALPHA,
+        GL_CONSTANT_COLOR, GL_ONE_MINUS_CONSTANT_COLOR,
+        GL_CONSTANT_ALPHA, GL_ONE_MINUS_CONSTANT_ALPHA,
+    };
+
+    for (GLenum src : srcFunc)
+    {
+        for (GLenum dst : dstFunc)
+        {
+            glBlendFunc(src, dst);
+            CheckBlendFunctions(src, dst);
+            glBlendFuncSeparate(src, dst, GL_ONE, GL_ONE);
+            CheckBlendFunctions(src, dst);
+        }
+    }
+}
+
 // Test the checks for OOB reads in the vertex buffers, instanced version
 TEST_P(WebGL2CompatibilityTest, DrawArraysBufferOutOfBoundsInstanced)
 {