Fragment shaders that require explicit early fragment tests are incompatible
with specifying depth and stencil values within the shader. If explicit early
fragment tests is specified, remove the depth and stencil outputs from the
output structure, and replace them with dummy local variables.
Add CompilerMSL:uses_explicit_early_fragment_test() function to consolidate
testing for whether early fragment tests are required.
Add two unit tests for depth-out with, and without, early fragment tests.
SPIR-V allows an image to be marked as a depth image, but with a non-depth
format. Such images should be read or sampled as vectors instead of scalars,
except when they are subject to compare operations.
Don't mark an OpSampledImage as using a compare operation just because the
image contains a depth marker. Instead, require that a compare operation
is actually used on that image.
Compiler::image_is_comparison() was really testing whether an image is a
depth image, since it incorporates the depth marker. Rename that function
to is_depth_image(), to clarify what it is really testing.
In Compiler::is_depth_image(), do not treat an image as a depth image
if it has been explicitly marked with a color format, unless the image
is subject to compare operations.
In CompilerMSL::to_function_name(), test for compare operations
specifically, rather than assuming them from the depth-image marker.
CompilerGLSL and CompilerMSL still contain a number of internal tests that
use is_depth_image() both for testing for a depth image, and for testing
whether compare operations are being used. I've left these as they are
for now, but these should be cleaned up at some point.
Add unit tests for fetch/sample depth images with color formats and no compare ops.
Previous test for SPIRVCrossDecorationPhysicalTypePacked on parent struct
when unpacking member struct was too restrictive, and not needed as long
as padding compensates.
Populate member_type_index_redirection as reverse lookup, not forward lookup.
Move use of member_type_index_redirection from CompilerMSL::to_member_reference()
to CompilerGLSL::access_chain_internal() to access all redirected type info,
not just name.
Promote to short instead and do simple casts on load/store instead.
Not 100% complete fix since structs can contain booleans, but this is
getting into pretty ridiculously complicated territory.
Add test shader for new functionality.
Add legacy test reference shader for unrelated buffer-bitcast
test, that doesn't seem to have been added previously.
When gl_Position is defined by SPIR-V, but neither used nor initialized,
it appeared twice in the MSL output, as gl_Position and glPosition_1.
The existing tests for whether an output is active check only that it is
used by an op, or initialized. Adding the implicit gl_Position also marked
the existing gl_Position as active, duplicating the output variable.
Fix is that when checking for the need to add an implicit gl_Position
output, also check if the var is already defined in the shader,
and just needs to be marked as active.
Add test shader.
Vulkan specifies that the Sample Mask Test occurs before fragment shading.
This means gl_SampleMaskIn should be influenced by both sample-shading and
VkPipelineMultisampleStateCreateInfo::pSampleMask.
CTS tests dEQP-VK.pipeline.multisample_shader_builtin.* bear this out.
For sample-shading, gl_SampleMaskIn should only have a single bit set,
Since Metal does not filter for this, apply a bitmask based on gl_SampleID.
For a fixed sample mask, since Metal is unaware of
VkPipelineMultisampleStateCreateInfo::pSampleMask, we need to ensure that
we apply it to both gl_SampleMaskIn and gl_SampleMask. This has the side
effect of a redundant application of pSampleMask if the shader already
includes gl_SampleMaskIn when setting gl_SampleMask, but I don't see an
easy way around this.
Also, simplify the logic for including the fixed sample mask in gl_ShaderMask,
and print the fixed sample mask as a hex value for readability of bits.
We'll need to force a temporary and mark it as precise.
MSL is a little weird here, but we can piggyback on top of the invariant
float math option here to force fma() operations everywhere.
Firstly, never flatten inputs or outputs in multi-patch mode.
The main scenario where we do need to care is Block IO.
In this case, we should only flatten the top-level member, and after
that we use access chains as normal.
Using structs in Input storage class is now possible as well. We don't
need to consider per-location fixups at all here. In Vulkan, IO structs
must match exactly. Only plain vectors can have smaller vector sizes as
a special case.
In Metal, the `[[position]]` input to a fragment shader remains at
fragment center, even at sample rate, like OpenGL and Direct3D. In
Vulkan, however, when the fragment shader runs at sample rate, the
`FragCoord` builtin moves to the sample position in the framebuffer,
instead of the fragment center. To account for this difference, adjust
the `FragCoord`, if present, by the sample position. The -0.5 offset is
because the fragment center is at (0.5, 0.5).
Also, add an option to force sample-rate shading in a fragment shader.
Since Metal has no explicit control for this, this is done by adding a
dummy `[[sample_id]]` which is otherwise unused, if none is already
present. This is intended to be used from e.g. MoltenVK when a
pipeline's `minSampleShading` value is nonzero.
Instead of checking if any `Input` variables have `Sample`
interpolation, I've elected to check that the `SampleRateShading`
capability is present. Since `SampleId`, `SamplePosition`, and the
`Sample` interpolation decoration require this cap, this should be
equivalent for any valid SPIR-V module. If this isn't acceptable, let me
know.
New in MSL 2.3 is a template that can be used in the place of a scalar
type in a stage-in struct. This template has methods which interpolate
the varying at the given points. Curiously, you can't set interpolation
attributes on such a varying; perspective-correctness is encoded in the
type, while interpolation must be done using one of the methods. This
makes using this somewhat awkward from SPIRV-Cross, requiring us to jump
through a bunch of hoops to make this all work.
Using varyings from functions in particular is a pain point, requiring
us to pass the stage-in struct itself around. An alternative is to pass
references to the interpolants; except this will fall over badly with
composite types, which naturally must be flattened. As with
tessellation, dynamic indexing isn't supported with pull-model
interpolation. This is because of the need to reference the original
struct member in order to call one of the pull-model interpolation
methods on it. Also, this is done at the variable level; this means that
if one varying in a struct is used with the pull-model functions, then
the entire struct is emitted as pull-model interpolants.
For some reason, this was not documented in the MSL spec, though there
is a property on `MTLDevice`, `supportsPullModelInterpolation`,
indicating support for this, which *is* documented. This does not appear
to be implemented yet for AMD: it returns `NO` from
`supportsPullModelInterpolation`, and pipelines with shaders using the
templates fail to compile. It *is* implemeted for Intel. It's probably
also implemented for Apple GPUs: on Apple Silicon, OpenGL calls down to
Metal, and it wouldn't be possible to use the interpolation functions
without this implemented in Metal.
Based on my testing, where SPIR-V and GLSL have the offset relative to
the pixel center, in Metal it appears to be relative to the pixel's
upper-left corner, as in HLSL. Therefore, I've added an offset 0.4375,
i.e. one half minus one sixteenth, to all arguments to
`interpolate_at_offset()`.
This also fixes a long-standing bug: if a pull-model interpolation
function is used on a varying, make sure that varying is declared. We
were already doing this only for the AMD pull-model function,
`interpolateAtVertexAMD()`; for reasons which are completely beyond me,
we weren't doing this for the base interpolation functions. I also note
that there are no tests for the interpolation functions for GLSL or
HLSL.
I kept the code to replace constant zero arguments, because `Bias` and
`Grad` still have some problems on desktop GPUs.
`Bias` works on AMD GPUs. `Grad` does not. Both work on Intel. Still
needs testing on NV. It will definitely work with Apple GPUs.
`half` cannot be bitcasted to `float`, because the two types are not the
same size. Use an expanding cast instead.
We were already doing this for stores to the tessellation levels; why I
didn't also do this for loads is beyond me.
MSL 2.3 has everything needed to support this extension on all
platforms. The existing `discard_fragment()` function was given demote
semantics, similar to Direct3D, and the `simd_is_helper_thread()`
function was finally added to iOS.
I've left the old test alone. Should I remove it in favor of these?
These need to use arrayed texture types, or Metal will complain when
binding the resource. The target layer is addressed relative to the
Layer output by the vertex pipeline, or to the ViewIndex if in a
multiview pipeline. Unlike with the s/t coordinates, Vulkan does not
forbid non-zero layer coordinates here, though this cannot be expressed
in Vulkan GLSL.
Supporting 3D textures will require additional work. Part of the problem
is that Metal does not allow texture views to subset a 3D texture, so we
need some way to pass the base depth to the shader.
Some older iOS devices don't support layered rendering. In that case,
don't set `[[render_target_array_index]]`, because the compiler will
reject the shader in that case. The client will then have to unroll the
render pass manually.
