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.
When a member of a struct is a struct, get_declared_struct_member_size
instead returned the size of the entire outer struct because it added
the offset of the last field to the size of the last field.
Restructure the function so that it handles all arrays in the same way
(by using array stride) and for the rest reuses get_declared_struct_size
if possible - this simplifies the function and fixes the issue.
- By default, emit uniform structs for UBOs, like push constant.
- Forward transpose information,
and optimize transpose(matrix) * vector to vector * matrix.
Combine all vertex attributes into a single stage_in structure.
Remove unneeded structure members from MSLConfiguration, MSLVertexAttr and Meta::Decoration.
Remove unneeded CompilerMSL functions that supported struct offsets and padding.
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.
Make Compiler::OpcodeHandler and Compiler::traverse_all_reachable_opcodes protected
instead of private, for use by subclasses.
Add CompilerMSL::CustomFunctionHandler and traverse_all_reachable_opcodes() to detect
active opcodes that require the output of a custom function.
CompilerMSL::custom_function_ops use std::set to retain ordering to improve testability.
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.
Arseny Kapoulkine
Hans-Kristian Arntzen
Endre Oma
Bill Hollings
Graham Wihlidal
Panagiotis Christopoulos Charitos