• Chris Wilson's avatar
    app: Use SHM transport for data transfer for display · 4a81849e
    Chris Wilson authored
    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 share the
    transport surface between all canvases by attaching it to the common
    screen.
    
    v3: Fix a couple of typos in insert_node() introduced when switching
    variables names.
    
    v4: Encapsulating within an image surface rather than a subsurface was
    hiding the backing SHM segment from cairo, causing it to allocate
    further SHM resources to stream the upload. We should be able to use a
    sub-surface here, but it is more convenient to wrap the pixels in an
    image surface for rendering the filters (and conveniently masking the
    callee flushes from invalidating our parent transport surface).
    
    Cc: Michael Natterer <mitch@gimp.org>
    4a81849e
configure.ac 65.1 KB