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Recent Cairo uses SHM transports when available, and exposes the ability for its users to manage images shared between it and the display. This allows us to eliminate copies, and if the architecture supports it even to upload directly into GPU addressable memory without any copies (all in normal system memory so we suffer no performance penalty when applying the filters). The caveat is that we need to be aware of the synchronize requirements, the cairo_surface_flush and cairo_surface_mark_dirty, around access to the transport image. To reduce the frequency of these barriers, we can subdivide the transport image into small chunks as to satisfy individual updates and delay the synchronisation barrier until we are forced to reuse earlier pixels. Note this bumps the required Cairo version to 1.12, and please be aware that the XSHM transport requires bug fixes from cairo.git (will be 1.12.12) v2: After further reflections with Mitch, we realized we can sha...
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