svgascreen->sws->fence_reference(svgascreen->sws, pfence, fence);
svgascreen->sws->fence_reference(svgascreen->sws, &fence, NULL);
svgascreen->sws->fence_reference(svgascreen->sws, pfence, fence);
svgascreen->sws->fence_reference(svgascreen->sws, &fence, NULL);