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authorVito Caputo <vcaputo@pengaru.com>2022-06-14 00:09:34 -0700
committerVito Caputo <vcaputo@pengaru.com>2022-08-07 06:43:49 -0700
commit4eb5f55bb0087769e47d0dc745a831440c5041fe (patch)
tree41ecd43cf518517936dbc19c5048e0cffcfc0b9c /.gitignore
parentb710439d328f7fab3f75f01733c0a5704995c328 (diff)
til_fb: introduce til_fb_fragment_t.ops
There's a need for the ability to efficiently snapshot fragments via buffer swapping when possible, for modules that want to do overlay effects which sample the input fragment at arbitrary pixels other than the one being written to, while producing output pixels. Without first making a stable snapshot of the input fragment's contents, you can't implement such algorithms because you destroy the input fragment while writing the output pixels. A simple solution would be to just allocate memory and copy the input fragment's contents into the allocation, then sample the copy while writing to the input (now output) fragment's memory. But when the input fragment represents the entire framebuffer page/window, it's technically practical to instead simply swap out the input fragment for a fresh fragment acquired from the framebuffer/window provider. Then just sample from the original fragment while writing to the freshly acquired one now taking the original's place. Simple enough. Except til_fb_fragment_t is also used to describe subfragments within a larger buffer, and these can't be made discontiguous and swapped out. For these fragments there's no escaping the need for a copy to be made of the contents. So there needs to be a way for the fragment itself to furnish an appropriate snapshotting mechanism, and when what the cloning mechanism returns can vary. Depending on the snapshotting mechanism's implementation, there's also a need for the fragment to furnish an appropriate free method. If the snapshot is an entire page from the native video backend, the backend must free it. If it's just libc heap-allocated memory, then a plain old free() suffices. If for some reason the memory can't be freed, then a NULL free() method would be appropriate to simply do nothing. So this commit introduces such free() and snapshot() methods in the form of a til_fb_fragment_ops_t struct. There's no implementations or use of these as of yet, this is purely preparatory. In addition to free() and snapshot(), a submit() method has also been introduced for submitting ready frames to be displayed. Not all fragments may be submitted, only "root" fragments which represent an entire page from the video backend. It's these fragments which will have a non-NULL submit() method, which the video backend will have initialized appropriately in returning the page's root fragment. This is a preparatory change in anticipation of removing the til_fb_page_t type altogether, replacing it with a simple til_fb_fragment_t having the ops.submit() method set.
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