Vulkan: Always write to swapchain alpha channel

src/libANGLE/renderer/vulkan/FramebufferVk.cpp

@@ -2382,9 +2382,24 @@ angle::Result FramebufferVk::startNewRenderPass(ContextVk *contextVk,
                                                   ? VK_ATTACHMENT_LOAD_OP_LOAD
                                                   : VK_ATTACHMENT_LOAD_OP_DONT_CARE;
 
-            renderPassAttachmentOps.setOps(colorIndexVk, loadOp, storeOp);
-            packedClearValues.store(colorIndexVk, VK_IMAGE_ASPECT_COLOR_BIT,
-                                    kUninitializedClearValue);
+            if (loadOp == VK_ATTACHMENT_LOAD_OP_DONT_CARE &&
+                mEmulatedAlphaAttachmentMask[colorIndexGL])
+            {
+                // This color attachment has a format with no alpha channel, but is emulated with a
+                // format that does have an alpha channel, which must be cleared to 1.0 in order to
+                // be visible.
+                renderPassAttachmentOps.setOps(colorIndexVk, VK_ATTACHMENT_LOAD_OP_CLEAR, storeOp);
+                VkClearValue emulatedAlphaClearValue =
+                    getCorrectedColorClearValue(colorIndexGL, {});
+                packedClearValues.store(colorIndexVk, VK_IMAGE_ASPECT_COLOR_BIT,
+                                        emulatedAlphaClearValue);
+            }
+            else
+            {
+                renderPassAttachmentOps.setOps(colorIndexVk, loadOp, storeOp);
+                packedClearValues.store(colorIndexVk, VK_IMAGE_ASPECT_COLOR_BIT,
+                                        kUninitializedClearValue);
+            }
         }
         renderPassAttachmentOps.setStencilOps(colorIndexVk, VK_ATTACHMENT_LOAD_OP_DONT_CARE,
                                               vk::RenderPassStoreOp::DontCare);

src/tests/gl_tests/ClearTest.cpp

@@ -344,6 +344,33 @@ TEST_P(ClearTestRGB, DefaultFramebufferRGB)
     EXPECT_PIXEL_NEAR(0, 0, 64, 128, 128, 255, 1.0);
 }
 
+// Invalidate the RGB default framebuffer and verify that the alpha channel is not cleared, and
+// stays set after drawing.
+TEST_P(ClearTestRGB, InvalidateDefaultFramebufferRGB)
+{
+    ANGLE_GL_PROGRAM(blueProgram, essl1_shaders::vs::Simple(), essl1_shaders::fs::Blue());
+
+    // Some GPUs don't support RGB format default framebuffer,
+    // so skip if the back buffer has alpha bits.
+    EGLWindow *window          = getEGLWindow();
+    EGLDisplay display         = window->getDisplay();
+    EGLConfig config           = window->getConfig();
+    EGLint backbufferAlphaBits = 0;
+    eglGetConfigAttrib(display, config, EGL_ALPHA_SIZE, &backbufferAlphaBits);
+    ANGLE_SKIP_TEST_IF(backbufferAlphaBits != 0);
+    // glInvalidateFramebuffer() isn't supported with GLES 2.0
+    ANGLE_SKIP_TEST_IF(getClientMajorVersion() < 3);
+    ANGLE_SKIP_TEST_IF(IsD3D11());
+
+    const GLenum discards[] = {GL_COLOR};
+    glInvalidateFramebuffer(GL_FRAMEBUFFER, 1, discards);
+    EXPECT_PIXEL_NEAR(0, 0, 0, 0, 0, 255, 1.0);
+
+    // Don't explicitly clear, but draw blue (make sure alpha is not cleared)
+    drawQuad(blueProgram, essl1_shaders::PositionAttrib(), 0.5f);
+    EXPECT_PIXEL_NEAR(0, 0, 0, 0, 255, 255, 1.0);
+}
+
 // Test clearing a RGBA8 Framebuffer
 TEST_P(ClearTest, RGBA8Framebuffer)
 {