Backing texture does not get updated with the output of a filter call

Created by: codeanticode

After applying a filter() on a P2D/P3D surface, the contents of the backing texture do not reflect the output of the filter operation. This becomes apparent in this issue reported in the Syphon library: https://github.com/Syphon/Processing/issues/32

The backing texture gets updated in the next frame (probably due to front/back texture swapping), but not clear why the backing texture is not ready by the end of the current frame

該 issue 沒有列出原始檔案或測試；首先在 P2D/P3D 表面上重現 filter() 的行為，並追蹤 backing texture 在影格期間如何更新。將其行為與 Syphon issue 進行比較，並考量需要完成的工作，以便 backing texture 在目前影格結束時反映濾鏡輸出。