Add missing buffer validation to BeginTransformFeedback.

src/libANGLE/ErrorStrings.h

@@ -527,6 +527,7 @@ MSG kTransfomFeedbackAlreadyActive = "Transform feedback is already active.";
 MSG kTransformFeedbackActiveDelete = "Attempt to delete an active transform feedback.";
 MSG kTransformFeedbackActiveDuringLink = "Cannot link program while program is associated with an active transform feedback object.";
 MSG kTransformFeedbackBufferDoubleBound = "A transform feedback buffer that would be written to is also bound to a non-transform-feedback target, which would cause undefined behavior.";
+MSG kTransformFeedbackBufferMissing = "Every binding point used in transform feedback mode must have a buffer object bound.";
 MSG kTransformFeedbackBufferMultipleOutputs = "Transform feedback has a buffer bound to multiple outputs.";
 MSG kTransformFeedbackBufferTooSmall = "Not enough space in bound transform feedback buffers.";
 MSG kTransformFeedbackDoesNotExist = "Transform feedback object that does not exist.";

src/libANGLE/validationES3.cpp

@@ -2684,7 +2684,7 @@ bool ValidateBeginTransformFeedback(const Context *context, PrimitiveMode primit
 
     for (size_t i = 0; i < transformFeedback->getIndexedBufferCount(); i++)
     {
-        const auto &buffer = transformFeedback->getIndexedBuffer(i);
+        const OffsetBindingPointer<Buffer> &buffer = transformFeedback->getIndexedBuffer(i);
         if (buffer.get())
         {
             if (buffer->isMapped())
@@ -2704,20 +2704,30 @@ bool ValidateBeginTransformFeedback(const Context *context, PrimitiveMode primit
     }
 
     const ProgramExecutable *programExecutable = context->getState().getProgramExecutable();
-    if (programExecutable)
+    if (!programExecutable)
     {
-        if (programExecutable->getLinkedTransformFeedbackVaryings().size() == 0)
-        {
-            context->validationError(GL_INVALID_OPERATION, kNoTransformFeedbackOutputVariables);
-            return false;
-        }
+        context->validationError(GL_INVALID_OPERATION, kProgramNotBound);
+        return false;
     }
-    else
+
+    if (programExecutable->getLinkedTransformFeedbackVaryings().empty())
     {
-        context->validationError(GL_INVALID_OPERATION, kProgramNotBound);
+        context->validationError(GL_INVALID_OPERATION, kNoTransformFeedbackOutputVariables);
         return false;
     }
 
+    size_t programXfbCount = programExecutable->getTransformFeedbackBufferCount();
+    for (size_t programXfbIndex = 0; programXfbIndex < programXfbCount; ++programXfbIndex)
+    {
+        const OffsetBindingPointer<Buffer> &buffer =
+            transformFeedback->getIndexedBuffer(programXfbIndex);
+        if (!buffer.get())
+        {
+            context->validationError(GL_INVALID_OPERATION, kTransformFeedbackBufferMissing);
+            return false;
+        }
+    }
+
     return true;
 }
 

src/tests/gl_tests/TransformFeedbackTest.cpp

@@ -3258,6 +3258,46 @@ void main()
     }
 }
 
+// Tests transform feedback with no buffer bound.
+TEST_P(TransformFeedbackTest, MissingBuffer)
+{
+    constexpr char kVS[] = R"(#version 300 es
+in vec2 position;
+in float attrib;
+out float varyingAttrib;
+void main() {
+  gl_Position = vec4(position, 0, 1);
+  varyingAttrib = attrib;
+})";
+
+    const std::vector<std::string> tfVaryings = {"varyingAttrib"};
+    ANGLE_GL_PROGRAM_TRANSFORM_FEEDBACK(prog, kVS, essl3_shaders::fs::Green(), tfVaryings,
+                                        GL_INTERLEAVED_ATTRIBS);
+    glUseProgram(prog);
+
+    GLTransformFeedback xfb;
+    glBindTransformFeedback(GL_TRANSFORM_FEEDBACK, xfb);
+    glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, 0);
+
+    std::vector<float> attribData;
+    for (unsigned int cnt = 0; cnt < 100; ++cnt)
+    {
+        attribData.push_back(static_cast<float>(cnt));
+    }
+
+    GLint attribLocation = glGetAttribLocation(prog, "attrib");
+    ASSERT_NE(-1, attribLocation);
+
+    glVertexAttribPointer(attribLocation, 1, GL_FLOAT, GL_FALSE, 4, &attribData[0]);
+    glEnableVertexAttribArray(attribLocation);
+
+    // GLES 3.1 spec: 12.1. TRANSFORM FEEDBACK
+    // The error INVALID_OPERATION is generated by BeginTransformFeedback if any binding point used
+    // in transform feedback mode does not have a buffer object bound.
+    glBeginTransformFeedback(GL_TRIANGLES);
+    EXPECT_GL_ERROR(GL_INVALID_OPERATION);
+}
+
 GTEST_ALLOW_UNINSTANTIATED_PARAMETERIZED_TEST(TransformFeedbackTest);
 ANGLE_INSTANTIATE_TEST_ES3(TransformFeedbackTest);