message: debug: clear discarded buffers in debug builds
  We now always clear in red/green discarded start/end attachments.
  This is to make sure to expose discard bugs.
diff: @@ -2194,6 +2194,14 @@ void OpenGLDriver::beginRenderPass(Handle<HwRenderTarget> rth,
  clearDepth, params.clearDepth,
  clearStencil, params.clearStencil);
  }
  +
  +#ifndef NDEBUG
  + // clear the discarded (but not the cleared ones) buffers in debug builds
  + setClearColor(1, 0, 0, 1);
  + bindFramebuffer(GL_FRAMEBUFFER, rt->gl.fbo);
  + disable(GL_SCISSOR_TEST);
  + glClear(getDiscardBits(TargetBufferFlags(discardFlags & ~clearFlags)));
  +#endif
  }
  void OpenGLDriver::endRenderPass(int) {
  @@ -2220,6 +2228,14 @@ void OpenGLDriver::endRenderPass(int) {
  }
  }
  +#ifndef NDEBUG
  + // clear the discarded buffers in debug builds
  + setClearColor(0, 1, 0, 1);
  + bindFramebuffer(GL_FRAMEBUFFER, rt->gl.fbo);
  + disable(GL_SCISSOR_TEST);
  + glClear(getDiscardBits(discardFlags));
  +#endif
  +
  mRenderPassTarget.clear();
  }
  