/*
* Copyright 2016 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SKIASL_MEMORYLAYOUT
#define SKIASL_MEMORYLAYOUT
#include <algorithm>
#include "src/sksl/ir/SkSLType.h"
namespace SkSL {
class MemoryLayout {
public:
enum class Standard {
// GLSL std140 layout as described in OpenGL Spec v4.5, 7.6.2.2.
k140,
// GLSL std430 layout. This layout is like std140 but with optimizations. This layout can
// ONLY be used with shader storage blocks.
k430,
// MSL memory layout.
kMetal,
// WebGPU Shading Language buffer layout constraints for the uniform address space.
kWGSLUniform_Base,
// treats f16 as a full 32-bit float
kWGSLUniform_EnableF16,
// treats f16 as a 16-bit half float
// WebGPU Shading Language buffer layout constraints for the storage address space.
kWGSLStorage_Base,
kWGSLStorage_EnableF16,
};
MemoryLayout(Standard std) : fStd(std) {}
bool isWGSL_Base()
const {
return fStd == Standard::kWGSLUniform_Base ||
fStd == Standard::kWGSLStorage_Base;
}
bool isWGSL_F16()
const {
return fStd == Standard::kWGSLUniform_EnableF16 ||
fStd == Standard::kWGSLStorage_EnableF16;
}
bool isWGSL_Uniform()
const {
return fStd == Standard::kWGSLUniform_Base ||
fStd == Standard::kWGSLUniform_EnableF16;
}
bool isWGSL()
const {
return fStd == Standard::kWGSLUniform_Base ||
fStd == Standard::kWGSLStorage_Base ||
fStd == Standard::kWGSLUniform_EnableF16 ||
fStd == Standard::kWGSLStorage_EnableF16;
}
bool isMetal()
const {
return fStd == Standard::kMetal;
}
/**
* WGSL and std140 require various types of variables (structs, arrays, and matrices) in the
* uniform address space to be rounded up to the nearest multiple of 16. This function performs
* the rounding depending on the given `type` and the current memory layout standard.
*
* (For WGSL, see https://www.w3.org/TR/WGSL/#address-space-layout-constraints).
*/
size_t roundUpIfNeeded(size_t raw, Type::TypeKind type)
const {
if (fStd == Standard::k140) {
return roundUp16(raw);
}
// WGSL uniform matrix layout is simply the alignment of the matrix columns and
// doesn't have a 16-byte multiple alignment constraint.
if (this->isWGSL_Uniform() && type != Type::TypeKind::kMatrix) {
return roundUp16(raw);
}
return raw;
}
/**
* Rounds up the integer `n` to the smallest multiple of 16 greater than `n`.
*/
size_t roundUp16(size_t n)
const {
return (n + 15) & ~15; }
/**
* Returns a type's required alignment when used as a standalone variable.
*/
size_t alignment(
const Type& type)
const {
// See OpenGL Spec 7.6.2.2 Standard Uniform Block Layout
switch (type.typeKind()) {
case Type::TypeKind::kScalar:
case Type::TypeKind::kAtomic:
return this->size(type);
case Type::TypeKind::kVector:
return GetVectorAlignment(this->size(type.componentType()), type.columns());
case Type::TypeKind::kMatrix:
return this->roundUpIfNeeded(
GetVectorAlignment(this->size(type.componentType()), type.rows()),
type.typeKind());
case Type::TypeKind::kArray:
return this->roundUpIfNeeded(this->alignment(type.componentType()),
type.typeKind());
case Type::TypeKind::kStruct: {
size_t result = 0;
for (
const auto& f : type.fields()) {
size_t alignment = this->alignment(*f.fType);
if (alignment > result) {
result = alignment;
}
}
return this->roundUpIfNeeded(result, type.typeKind());
}
default:
SK_ABORT(
"cannot determine alignment of type '%s'", type.displayName().c_str());
}
}
/**
* For matrices and arrays, returns the number of bytes from the start of one entry (row, in
* the case of matrices) to the start of the next.
*/
size_t stride(
const Type& type)
const {
switch (type.typeKind()) {
case Type::TypeKind::kMatrix:
return this->alignment(type);
case Type::TypeKind::kArray: {
int stride = this->size(type.componentType());
if (stride > 0) {
int align = this->alignment(type.componentType());
stride += align - 1;
stride -= stride % align;
stride = this->roundUpIfNeeded(stride, type.typeKind());
}
return stride;
}
default:
SK_ABORT(
"type '%s' does not have a stride", type.displayName().c_str());
}
}
/**
* Returns the size of a type in bytes. Returns 0 if the given type is not supported.
*/
size_t size(
const Type& type)
const {
switch (type.typeKind()) {
case Type::TypeKind::kScalar:
if (type.isBoolean()) {
return this->isWGSL() ? 0 : 1;
}
if (this->isMetal() && !type.highPrecision() && type.isNumber()) {
return 2;
}
if (this->isWGSL_F16() && !type.highPrecision() && type.isFloat()) {
return 2;
}
return 4;
case Type::TypeKind::kAtomic:
// Our atomic types (currently atomicUint) always occupy 4 bytes.
return 4;
case Type::TypeKind::kVector:
if (this->isMetal() && type.columns() == 3) {
return 4 * this->size(type.componentType());
}
return type.columns() * this->size(type.componentType());
case Type::TypeKind::kMatrix:
// fall through
case Type::TypeKind::kArray:
return type.isUnsizedArray() ? 0 : (type.columns() * this->stride(type));
case Type::TypeKind::kStruct: {
size_t total = 0;
for (
const auto& f : type.fields()) {
size_t alignment = this->alignment(*f.fType);
if (total % alignment != 0) {
total += alignment - total % alignment;
}
SkASSERT(total % alignment == 0);
total += this->size(*f.fType);
}
size_t alignment = this->alignment(type);
SkASSERT(!type.fields().size() ||
(0 == alignment % this->alignment(*type.fields()[0].fType)));
return (total + alignment - 1) & ~(alignment - 1);
}
default:
SK_ABORT(
"cannot determine size of type '%s'", type.displayName().c_str());
}
}
/**
* Not all types are compatible with memory layout.
*/
size_t isSupported(
const Type& type)
const {
switch (type.typeKind()) {
case Type::TypeKind::kAtomic:
return true;
case Type::TypeKind::kScalar:
// bool is not host-shareable in WGSL.
return this->isWGSL() ? !type.isBoolean() :
true;
case Type::TypeKind::kVector:
case Type::TypeKind::kMatrix:
case Type::TypeKind::kArray:
return this->isSupported(type.componentType());
case Type::TypeKind::kStruct:
return std::all_of(
type.fields().begin(), type.fields().end(), [
this](
const Field& f) {
return this->isSupported(*f.fType);
});
default:
return false;
}
}
Standard getStandard()
const {
return fStd; }
private:
static size_t GetVectorAlignment(size_t componentSize,
int columns) {
return componentSize * (columns + columns % 2);
}
const Standard fStd;
};
}
// namespace SkSL
#endif
