Skip indexed clears on disabled draw buffers

src/libANGLE/Framebuffer.cpp

@@ -300,6 +300,11 @@ bool IsClearBufferMaskedOut(const Context *context, GLenum buffer, GLint drawbuf
     }
 }
 
+bool IsClearBufferDisabled(const FramebufferState &mState, GLenum buffer, GLint drawbuffer)
+{
+    return buffer == GL_COLOR && !mState.getEnabledDrawBuffers()[drawbuffer];
+}
+
 }  // anonymous namespace
 
 // This constructor is only used for default framebuffers.
@@ -1534,7 +1539,8 @@ angle::Result Framebuffer::clearBufferfv(const Context *context,
                                          GLint drawbuffer,
                                          const GLfloat *values)
 {
-    if (context->getState().isRasterizerDiscardEnabled() ||
+    if (IsClearBufferDisabled(mState, buffer, drawbuffer) ||
+        context->getState().isRasterizerDiscardEnabled() ||
         IsClearBufferMaskedOut(context, buffer, drawbuffer))
     {
         return angle::Result::Continue;
@@ -1550,7 +1556,8 @@ angle::Result Framebuffer::clearBufferuiv(const Context *context,
                                           GLint drawbuffer,
                                           const GLuint *values)
 {
-    if (context->getState().isRasterizerDiscardEnabled() ||
+    if (IsClearBufferDisabled(mState, buffer, drawbuffer) ||
+        context->getState().isRasterizerDiscardEnabled() ||
         IsClearBufferMaskedOut(context, buffer, drawbuffer))
     {
         return angle::Result::Continue;
@@ -1566,7 +1573,8 @@ angle::Result Framebuffer::clearBufferiv(const Context *context,
                                          GLint drawbuffer,
                                          const GLint *values)
 {
-    if (context->getState().isRasterizerDiscardEnabled() ||
+    if (IsClearBufferDisabled(mState, buffer, drawbuffer) ||
+        context->getState().isRasterizerDiscardEnabled() ||
         IsClearBufferMaskedOut(context, buffer, drawbuffer))
     {
         return angle::Result::Continue;

src/libANGLE/renderer/RenderTargetCache.h

@@ -133,7 +133,7 @@ angle::Result RenderTargetCache<RenderTargetT>::updateColorRenderTarget(
 {
     // If the color render target we're updating is also the read buffer, make sure we update the
     // read render target also so it's not stale.
-    if (state.getReadIndex() == colorIndex)
+    if (state.getReadBufferState() != GL_NONE && state.getReadIndex() == colorIndex)
     {
         ANGLE_TRY(updateReadColorRenderTarget(context, state));
     }

src/tests/gl_tests/ClearTest.cpp

@@ -1547,6 +1547,38 @@ TEST_P(ClearTest, InceptionScissorClears)
     EXPECT_EQ(expectedColors, actualColors);
 }
 
+// Test that clearBuffer with disabled non-zero drawbuffer or disabled read source doesn't cause an
+// assert.
+TEST_P(ClearTestES3, ClearDisabledNonZeroAttachmentNoAssert)
+{
+    // http://anglebug.com/4612
+    ANGLE_SKIP_TEST_IF(IsOSX() && IsDesktopOpenGL());
+
+    GLFramebuffer fb;
+    glBindFramebuffer(GL_FRAMEBUFFER, fb);
+
+    GLRenderbuffer rb;
+    glBindRenderbuffer(GL_RENDERBUFFER, rb);
+    glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8, 16, 16);
+
+    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_RENDERBUFFER, rb);
+    glDrawBuffers(0, nullptr);
+    glReadBuffer(GL_NONE);
+
+    ASSERT_GL_FRAMEBUFFER_COMPLETE(GL_FRAMEBUFFER);
+
+    float clearColorf[4] = {0.5, 0.5, 0.5, 0.5};
+    glClearBufferfv(GL_COLOR, 1, clearColorf);
+
+    GLuint clearColorui[4] = {255, 255, 255, 255};
+    glClearBufferuiv(GL_COLOR, 1, clearColorui);
+
+    GLint clearColori[4] = {-127, -127, -127, -127};
+    glClearBufferiv(GL_COLOR, 1, clearColori);
+
+    EXPECT_GL_NO_ERROR();
+}
+
 #ifdef Bool
 // X11 craziness.
 #    undef Bool