<rdar://problem/70946707>

Thanks for reporting Kimmo. Do you have a test case for this? (Which clip do you mean? Scissor rectangle set?)

Yeah, scissor enable.

void WebGL2RenderingContext::clearBufferiv(GCGLenum buffer, GCGLint drawbuffer, Int32List&& values, GCGLuint srcOffset)
{
    if (isContextLostOrPending() || !validateClearBuffer("clearBufferiv", buffer, values.length(), srcOffset))
        return;

    m_context->clearBufferiv(buffer, drawbuffer, values.data(), srcOffset);
    updateBuffersToAutoClear(ClearBufferCaller::ClearBufferiv, buffer, drawbuffer);
}



void WebGL2RenderingContext::updateBuffersToAutoClear(ClearBufferCaller caller, GCGLenum buffer, GCGLint drawbuffer)
{
    // This method makes sure that we don't auto-clear any buffers which the
    // user has manually cleared using the new ES 3.0 clearBuffer* APIs.

    // If the user has a framebuffer bound, don't update the auto-clear
    // state of the built-in back buffer.
    if (m_framebufferBinding)
        return;

    // If the scissor test is on, assume that we can't short-circuit
    // these clears.
    if (m_scissorEnabled)
        return;

Thanks. Yes, it looks like there's a problem as you describe.

Would you be willing to try writing a test case for this? It could be modeled after https://github.com/KhronosGroup/WebGL/blob/master/sdk/tests/conformance2/rendering/rasterizer-discard-and-implicit-clear.html . Suggestion:

- Use setupQuad to set up a small quad (maybe scale 0.1)

In requestAnimationFrame:
- Enable scissor test (but have the scissor rect cover the entire canvas)
- Use clearBufferiv to clear the color buffer to green
- Draw the scaled quad in green
- Assert the canvas is fully green (with the bug, the surrounding region of the quad will be black)