vo_gpu: d3d11: initial implementation

This is a new RA/vo_gpu backend that uses Direct3D 11. The GLSL
generated by vo_gpu is cross-compiled to HLSL with SPIRV-Cross.

What works:

- All of mpv's internal shaders should work, including compute shaders.

- Some external shaders have been tested and work, including RAVU and
  adaptive-sharpen.

- Non-dumb mode works, even on very old hardware. Most features work at
  feature level 9_3 and all features work at feature level 10_0. Some
  features also work at feature level 9_1 and 9_2, but without high-bit-
  depth FBOs, it's not very useful. (Hardware this old is probably not
  fast enough for advanced features anyway.)

  Note: This is more compatible than ANGLE, which requires 9_3 to work
  at all (GLES 2.0,) and 10_1 for non-dumb-mode (GLES 3.0.)

- Hardware decoding with D3D11VA, including decoding of 10-bit formats
  without truncation to 8-bit.

What doesn't work / can be improved:

- PBO upload and direct rendering does not work yet. Direct rendering
  requires persistent-mapped PBOs because the decoder needs to be able
  to read data from images that have already been decoded and uploaded.
  Unfortunately, it seems like persistent-mapped PBOs are fundamentally
  incompatible with D3D11, which requires all resources to use driver-
  managed memory and requires memory to be unmapped (and hence pointers
  to be invalidated) when a resource is used in a draw or copy
  operation.

  However it might be possible to use D3D11's limited multithreading
  capabilities to emulate some features of PBOs, like asynchronous
  texture uploading.

- The blit() and clear() operations don't have equivalents in the D3D11
  API that handle all cases, so in most cases, they have to be emulated
  with a shader. This is currently done inside ra_d3d11, but ideally it
  would be done in generic code, so it can take advantage of mpv's
  shader generation utilities.

- SPIRV-Cross is used through a NIH C-compatible wrapper library, since
  it does not expose a C interface itself.

  The library is available here: https://github.com/rossy/crossc

- The D3D11 context could be made to support more modern DXGI features
  in future. For example, it should be possible to add support for
  high-bit-depth and HDR output with DXGI 1.5/1.6.

1 files changed, 13 insertions, 4 deletions

diff --git a/wscript b/wscript
index ad17012bec..50cbccf2ce 100644
--- a/wscript
+++ b/wscript
@@ -754,6 +754,19 @@ video_output_features = [
         'deps': 'win32-desktop && gpl',
         'func': check_cc(header_name='d3d9.h'),
     }, {
+        'name': '--shaderc',
+        'desc': 'libshaderc SPIR-V compiler',
+        'func': check_cc(header_name='shaderc/shaderc.h', lib='shaderc_shared'),
+    }, {
+        'name': '--crossc',
+        'desc': 'libcrossc SPIR-V translator',
+        'func': check_pkg_config('crossc'),
+    }, {
+        'name': '--d3d11',
+        'desc': 'Direct3D 11 video output',
+        'deps': 'win32-desktop && shaderc && crossc',
+        'func': check_cc(header_name=['d3d11_1.h', 'dxgi1_2.h']),
+    }, {
         # We need MMAL/bcm_host/dispmanx APIs. Also, most RPI distros require
         # every project to hardcode the paths to the include directories. Also,
         # these headers are so broken that they spam tons of warnings by merely
@@ -807,10 +820,6 @@ video_output_features = [
         'desc':  'Vulkan context support',
         'func': check_pkg_config('vulkan'),
     }, {
-        'name': '--shaderc',
-        'desc': 'libshaderc SPIR-V compiler',
-        'func': check_cc(header_name='shaderc/shaderc.h', lib='shaderc_shared'),
-    }, {
         'name': 'egl-helpers',
         'desc': 'EGL helper functions',
         'deps': 'egl-x11 || mali-fbdev || rpi || gl-wayland || egl-drm || ' +