This is intended to be used to support `VK_KHR_maintenance2`'s
tessellation domain origin feature. If `tess_domain_origin_lower_left`
is `true`, the `v` coordinate will be inverted with respect to the
domain. Additionally, in `Triangles` mode, the `v` and `w` coordinates
will be swapped. This is because the winding order is interpreted
differently in lower-left mode.
These are mapped to Metal's post-tessellation vertex functions. The
semantic difference is much less here, so this change should be simpler
than the previous one. There are still some hairy parts, though.
In MSL, the array of control point data is represented by a special
type, `patch_control_point<T>`, where `T` is a valid stage-input type.
This object must be embedded inside the patch-level stage input. For
this reason, I've added a new type to the type system to represent this.
On Mac, the number of input control points to the function must be
specified in the `patch()` attribute. This is optional on iOS.
SPIRV-Cross takes this from the `OutputVertices` execution mode; the
intent is that if it's not set in the shader itself, MoltenVK will set
it from the tessellation control shader. If you're translating these
offline, you'll have to update the control point count manually, since
this number must match the number that is passed to the
`drawPatches:...` family of methods.
Fixes#120.
This should fix a whole host of issues related to structs in the `Input`
class in a tessellation control shader.
Also, use pointer arithmetic instead of dereferencing the `ops` array.
This is critical in case we wind up stepping beyond the bounds of the
array.
When we force recompile, the old var.self name we used as a fallback
name might have been disturbed, so we should recover certain names back
to their original form in case we are forced to take a recompile to make
the naming algorithm more deterministic.
There's no need to do so, since these are not stage-out structs being
returned, but regular structures being written to a buffer. This also
neatly avoids issues writing to composite (e.g. arrayed) per-patch
outputs from a tessellation control shader.
These are transpiled to kernel functions that write the output of the
shader to three buffers: one for per-vertex varyings, one for per-patch
varyings, and one for the tessellation levels. This structure is
mandated by the way Metal works, where the tessellation factors are
supplied to the draw method in their own buffer, while the per-patch and
per-vertex varyings are supplied as though they were vertex attributes;
since they have different step rates, they must be in separate buffers.
The kernel is expected to be run in a workgroup whose size is the
greater of the number of input or output control points. It uses Metal's
support for vertex-style stage input to a compute shader to get the
input values; therefore, at least one instance must run per input point.
Meanwhile, Vulkan mandates that it run at least once per output point.
Overrunning the output array is a concern, but any values written should
either be discarded or overwritten by subsequent patches. I'm probably
going to put some slop space in the buffer when I integrate this into
MoltenVK to be on the safe side.
This is necessary to deal with indirect draws, where the draw parameters
are given in a buffer instead of passed by the CPU. For normal draws,
the draw parameters are set with Metal's `setVertexBytes:` method.
This undoes the change to add the vertex count to the aux buffer,
rendering that entire discussion largely moot. Oh well. It was a
discussion that needed to happen anyway.
`bitcast_glsl_op()` is sometimes called for `Boolean` types, e.g. for
specialization constants. We don't want the assert to trip if this is
going to be a no-op anyway.
Storage was in place already, so mostly just dealing with bitcasts and
constants.
Simplies some of the bitcasting logic, and this exposed some bugs in the
implementation. Refactor to use correct width integers with explicit bitcast opcodes.
Structs are aligned as you would expect in MSL (maximum member
alignment), and it is not minimum 16 bytes like in std140.
Also rename the dummy "pad" members to a reserved naming scheme.
