|
6136cbcb
|
2020-09-23T21:31:05
|
|
Metal: Implement transform feedback
- XFB is currently emulated by writing to storage buffers.
- Metal doesn't allow vertex shader to both write to storage buffers and
to stage output (i.e clip position). So if GL_RASTERIZER_DISCARD is
NOT enabled, the draw with XFB enabled will have 2 passes:
+ First pass: vertex shader writes to XFB buffers + not write to stage
output + disable rasterizer.
+ Second pass: vertex shader writes to stage output (i.e.
[[position]]) + enable rasterizer. If GL_RASTERIZER_DISCARD is
enabled, the second pass is omitted.
+ This effectively executes the same vertex shader twice. TODO:
possible improvement is writing vertex outputs to buffer in first
pass then re-use that buffer as input for second pass which has a
passthrough vertex shader.
- If GL_RASTERIZER_DISCARD is enabled, and XFB is enabled:
+ Only first pass above will be executed, and the render pass will use
an empty 1x1 texture attachment since rasterization is not needed.
- If GL_RASTERIZER_DISCARD is enabled, but XFB is NOT enabled:
+ we still enable Metal rasterizer.
+ but vertex shader must emulate the discard by writing gl_Position =
(-3, -3, -3, 1). This effectively moves the vertex out of clip
space's visible area.
+ This is because GLSL still allows vertex shader to write to stage
output when rasterizer is disabled. However, Metal doesn't allow
that. In Metal, if rasterizer is disabled, then vertex shader must
not write to stage output.
- See src/libANGLE/renderer/metal/doc/TransformFeedback.md for more
details.
Bug: angleproject:2634
Change-Id: I6c700e031052560326b7f660ee7597202d38e6aa
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2408594
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
|
|
|
1677cf14
|
2020-09-13T20:14:59
|
|
Metal: Implement Uniform buffers
Uniform buffer is implemented in two forms:
- If number of ubo used in shader program is low, each buffer will use
one discrete Metal buffer slot.
- If number of ubo used is large, they will be embedded into one Metal
argument buffer. Argument buffer is similar to Vulkan descriptor set.
This is due to limit of number of Metal's discrete buffer slots which
is only 31 and over half of them are already used by vertex
attributes, default uniforms, driver uniforms, etc. The downside is
that whenever a buffer binding is changed, the argument buffer must be
updated also.
Added empty TransformFeedbackMtl implementation to enable ES3 context
creation on Metal.
Bug: angleproject:2634
Change-Id: I69325696fac735cb45ab88ab55468c0991abc317
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2408593
Commit-Queue: Le Hoang Quyen <le.hoang.q@gmail.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
|