1. override
void renderTextureQuad(RenderState renderState, RenderTextureQuad renderTextureQuad)

Source 

@override
void renderTextureQuad(
    RenderState renderState,
    RenderTextureQuad renderTextureQuad) {

  activateRenderProgram(renderProgramSimple);
  activateBlendMode(renderState.globalBlendMode);
  activateRenderTexture(renderTextureQuad.renderTexture);
  renderProgramSimple.renderTextureQuad(renderState, renderTextureQuad);
}