In a multi GPU scenario, it may be desirable to use different GPUs
for decode and display responsibilities. For example, if a secondary
GPU has better video decoding capabilities.
In such a scenario, we need to initialise a separate context for each
GPU, and use the display context in hwdec_cuda, while passing the
decode context to avcodec.
Once that's done, the actually hand-off between the two GPUs is
transparent to us (It happens during the cuMemcpy2D operation which
copies the decoded frame from a cuda buffer to the OpenGL texture).
In the end, the bulk of the work is around introducing a new
configuration option to specify the decode device.
gl_headers.h is basically header_fixes.h done consequently. It contains
all OpenGL defines (and some typedefs) we need. We don't include GL
headers provided by the system anymore.
Some care has to be taken by certain windowing APIs including all of
gl.h anyway. Then the definitions could clash. Fortunately, redefining
preprocessor symbols to the same content is allowed and ignored. Also,
redefining typedefs to the same thing is allowed in C11. Apparently the
latter is not allowed in C99, so there is an imperfect attempt to avoid
the typedefs if required API symbols are apparently present already.
The nost risky part about this are the standard typedefs and GLAPIENTRY.
The latter is different only on win32 (and at least consistently so).
The typedefs are mostly based on stdint.h typedefs, which khrplatform.h
clumsily emulates on platforms which don't have it. The biggest
difference is that we define GLsizeiptr directly to ptrdiff_t, instead
of checking for the _WIN64 symbol and defining it to long or long long.
This also typedefs GLsync to __GLsync, just like the khronos headers.
Although symbols prefixed with __ are implementation reserved, khronos
also violates this rule, and having the same definition as khronos will
avoid problems on duplicate definitions.
We can simplify the build scripts too. The ios-gl check seems a bit
wrong now (what we really want to test for is EAGLContext), but I can't
test and thus can't improve it.
cuda_dynamic.h redefined two GL symbols; just include the new headers
directly instead.
We want to avoid causing problems if libmpv is used in an application
that links cuda, or if the libav* libraries are linked with cuda,
as might happen if the scale_npp filter is used.
The test ended up failing if cuda.h wasn't present, even if cuda.h
isn't used during the actual build.
This test is attempting to establish if the ffmpeg being built
against has dynlink_cuda support. While it might theoretically be
possible to build against the older normally-linked-cuda version
of ffmpeg, it seems more trouble than it's worth.
Philip Langdale
wm4