Add test for deferred clear + attachment gaps

This test makes sure the list of clear values given to the render pass
(for deferred clears) are correctly passed.

Bug: angleproject:4862
Change-Id: I4830a72a6f2b01570f6d4427ffb025429b5aa03c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2309109
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>

src/tests/gl_tests/DrawBuffersTest.cpp

@@ -280,6 +280,47 @@ TEST_P(DrawBuffersTest, Gaps)
     glDeleteProgram(program);
 }
 
+// Test that clear works with gaps
+TEST_P(DrawBuffersTest, ClearWithGaps)
+{
+    // TODO(syoussefi): Qualcomm driver crashes in the presence of VK_ATTACHMENT_UNUSED.
+    // http://anglebug.com/3423
+    ANGLE_SKIP_TEST_IF(IsVulkan() && IsAndroid());
+
+    ANGLE_SKIP_TEST_IF(!setupTest());
+
+    glGetIntegerv(GL_MAX_DRAW_BUFFERS, &mMaxDrawBuffers);
+    ASSERT_GE(mMaxDrawBuffers, 4);
+
+    glBindTexture(GL_TEXTURE_2D, mTextures[0]);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, mTextures[0], 0);
+
+    glBindTexture(GL_TEXTURE_2D, mTextures[1]);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT3, GL_TEXTURE_2D, mTextures[1], 0);
+
+    const GLenum bufs[] = {GL_COLOR_ATTACHMENT0, GL_NONE, GL_NONE, GL_COLOR_ATTACHMENT3};
+
+    bool flags[8] = {true, false, false, true};
+    GLuint program;
+    setupMRTProgram(flags, &program);
+
+    setDrawBuffers(4, bufs);
+
+    glClearColor(1.0f, 1.0f, 0.0f, 1.0f);
+    glClear(GL_COLOR_BUFFER_BIT);
+
+    // A bogus draw to make sure clears are done with a render pass in the Vulkan backend.
+    glEnable(GL_BLEND);
+    glBlendFunc(GL_ZERO, GL_ONE);
+    drawQuad(program, positionAttrib(), 0.5);
+    EXPECT_GL_NO_ERROR();
+
+    verifyAttachment2DColor(0, mTextures[0], GL_TEXTURE_2D, 0, GLColor::yellow);
+    verifyAttachment2DColor(3, mTextures[1], GL_TEXTURE_2D, 0, GLColor::yellow);
+
+    EXPECT_GL_NO_ERROR();
+}
+
 TEST_P(DrawBuffersTest, FirstAndLast)
 {
     ANGLE_SKIP_TEST_IF(!setupTest());