Legacy GLSL targets do not support uniform buffers, and as such require
some sort of emulation. There are two alternatives - one is to represent
a uniform buffer as a uniform struct, and another one is to flatten it
into an array of primitive vector types (vec4).
Uniform struct have two disadvantages that make using them prohibitive
in some applications:
- The location assignment for struct members is arbitrary which means
the application has to set each struct member one by one
- Some Android drivers fail to link shader programs if both vertex and
fragment shader use the same uniform struct
Because of this, we need to support flattening uniform buffers into an
array. This is not just important for legacy GLSL but also is sometimes
useful for ESSL 3.0 where some Android drivers do not have stable UBO
support.
The way flattening works is the entire buffer is represented as a vec4
array; each access chain is rewritten into a combination of array
accesses, swizzles and data type constructors. Specifically:
- Extracting a vector or a scalar requires indexing into the array with
an optional swizzle, for example CB0[13].yz for reading vec2
- Extracting a matrix or a struct requires extracting each individual
vector or struct member and then combining them into the resulting
object
- Extracting arrays is not supported, mostly because the resulting
construct is very inefficient and ESSL 1.0 does not support array
constructors.
Additionally, while we try to constant-fold each individual indexing
operation, there are cases where we have to use dynamic index
computation (specifically for indexing arrays with non-constants); so
the general form of the primitive array extraction expression is:
buffer[stride0*index0+...+strideN*indexN+offset]
Where stride/offset are integer literals and index represents variables.
- By default, emit uniform structs for UBOs, like push constant.
- Forward transpose information,
and optimize transpose(matrix) * vector to vector * matrix.
CompilerGLSL add to_function_name() and to_function_args() functions to organize
structure of emit_texture_op() function.
CompilerMSL add support for MSL gather(), gather_compare() and sample_compare() functions.
CompilerGLSL builtin_to_glsl() function outputs gl_ClipDistance for BuiltInClipDistance
builtin, and includes builtin code in output when handling unknown builtin code.
CompilerMSL uses type ID instead of type object where appropriate to support array types,
where type.self is not consistent with actual type ID, plus support array stride calc
even when not explicitly set by SPIR-V code.
For output consistency, CompilerMSL prefers use of standard builtin names over specified
names, and output builtins qualified with output struct while in entry function.
Previously, we would generate parentheses proactively when generating
binary ops, however, this leads to uglier code and hits warnings in
compilers when used as a conditional.
The size of an array can be a specialization constant or a spec constant
op. This complicates things quite a lot.
Reflection becomes very painful in the presence of expressions instead
of literals so add a new array which expresses this.
It is unlikely that we will need to do accurate reflection of interface
types which have specialization constant size.
SSBOs and UBOs will for now throw exception if a dynamic size is used since it
is very difficult to know the real size.
Fix some minor missing pieces from C++.
Type remapping like this doesn't seem to fit MSL backend so well, as it
does a lot of remapping internally on its own.
Type name remapping, really is for fringe extension cases in GLSL which
aren't yet supported in SPIR-V.
- Only consider I/O variables if part of OpEntryPoint.
- Keep a safe fallback if #entry-points is 1 to avoid potentially
breaking previously working shaders.
There was a potential problem if variables were invalidated and SPIR-V
read expressions which depended on other expression which in turn depended on the
invalidated variable.
Also fixes issue where variables were considered immutable if they were
forwardable. This allowed some incorrect optimizations to slip through.
