int error = ChangeBufferSize(APTR handle, int width, int height, ULONG flags, struct hwTagList *tags);
Please note that the back buffer size is not necessarily the same as the window's physical dimensions. If autoscaling is active, back buffer size and the window's physical dimensions can be different.
If you don't use a back buffer you won't have to do anything here. This is often the case for plugins which are designed to draw in hardware double buffer mode. In that case, an additional back buffer is not necessary and would only slow things down.
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