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Improve Metal vertex buffer bindings (#7293)
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@bejado
bejado authored Oct 25, 2023
1 parent 6e249c4 commit d76cf64
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Showing 4 changed files with 83 additions and 41 deletions.
4 changes: 3 additions & 1 deletion filament/backend/include/private/backend/HandleAllocator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@

#define HandleAllocatorGL HandleAllocator<16, 64, 208>
#define HandleAllocatorVK HandleAllocator<16, 64, 880>
#define HandleAllocatorMTL HandleAllocator<16, 64, 576>
#define HandleAllocatorMTL HandleAllocator<16, 64, 584>

namespace filament::backend {

Expand Down Expand Up @@ -256,6 +256,7 @@ class HandleAllocator {
HandleBase::HandleId allocateHandle() noexcept {
if constexpr (SIZE <= P0) { return allocateHandleInPool<P0>(); }
if constexpr (SIZE <= P1) { return allocateHandleInPool<P1>(); }
static_assert(SIZE <= P2);
return allocateHandleInPool<P2>();
}

Expand All @@ -266,6 +267,7 @@ class HandleAllocator {
} else if constexpr (SIZE <= P1) {
deallocateHandleFromPool<P1>(id);
} else {
static_assert(SIZE <= P2);
deallocateHandleFromPool<P2>(id);
}
}
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25 changes: 11 additions & 14 deletions filament/backend/src/metal/MetalDriver.mm
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Expand Up @@ -1686,26 +1686,23 @@

// Bind the user vertex buffers.

MetalBuffer* buffers[MAX_VERTEX_BUFFER_COUNT] = {};
MetalBuffer* vertexBuffers[MAX_VERTEX_BUFFER_COUNT] = {};
size_t vertexBufferOffsets[MAX_VERTEX_BUFFER_COUNT] = {};
size_t bufferIndex = 0;
size_t maxBufferIndex = 0;

auto vb = primitive->vertexBuffer;
for (uint32_t attributeIndex = 0; attributeIndex < vb->attributes.size(); attributeIndex++) {
const auto& attribute = vb->attributes[attributeIndex];
if (attribute.buffer == Attribute::BUFFER_UNUSED) {
continue;
}

assert_invariant(vb->buffers[attribute.buffer]);
buffers[bufferIndex] = vb->buffers[attribute.buffer];
vertexBufferOffsets[bufferIndex] = attribute.offset;
bufferIndex++;
for (auto m : primitive->bufferMapping) {
assert_invariant(
m.bufferArgumentIndex >= USER_VERTEX_BUFFER_BINDING_START &&
m.bufferArgumentIndex < USER_VERTEX_BUFFER_BINDING_START + MAX_VERTEX_BUFFER_COUNT);
size_t vertexBufferIndex = m.bufferArgumentIndex - USER_VERTEX_BUFFER_BINDING_START;
vertexBuffers[vertexBufferIndex] = vb->buffers[m.sourceBufferIndex];
maxBufferIndex = std::max(maxBufferIndex, vertexBufferIndex);
}

const auto bufferCount = bufferIndex;
const auto bufferCount = maxBufferIndex + 1;
MetalBuffer::bindBuffers(getPendingCommandBuffer(mContext), mContext->currentRenderPassEncoder,
USER_VERTEX_BUFFER_BINDING_START, MetalBuffer::Stage::VERTEX, buffers,
USER_VERTEX_BUFFER_BINDING_START, MetalBuffer::Stage::VERTEX, vertexBuffers,
vertexBufferOffsets, bufferCount);

// Bind the zero buffer, used for missing vertex attributes.
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14 changes: 14 additions & 0 deletions filament/backend/src/metal/MetalHandles.h
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Expand Up @@ -160,6 +160,7 @@ struct MetalIndexBuffer : public HwIndexBuffer {
};

struct MetalRenderPrimitive : public HwRenderPrimitive {
MetalRenderPrimitive();
void setBuffers(MetalVertexBuffer* vertexBuffer, MetalIndexBuffer* indexBuffer);
// The pointers to MetalVertexBuffer and MetalIndexBuffer are "weak".
// The MetalVertexBuffer and MetalIndexBuffer must outlive the MetalRenderPrimitive.
Expand All @@ -169,6 +170,19 @@ struct MetalRenderPrimitive : public HwRenderPrimitive {

// This struct is used to create the pipeline description to describe vertex assembly.
VertexDescription vertexDescription = {};

struct Entry {
uint8_t sourceBufferIndex = 0;
uint8_t stride = 0;
// maps to ->
uint8_t bufferArgumentIndex = 0;

Entry(uint8_t sourceBufferIndex, uint8_t stride, uint8_t bufferArgumentIndex)
: sourceBufferIndex(sourceBufferIndex),
stride(stride),
bufferArgumentIndex(bufferArgumentIndex) {}
};
utils::FixedCapacityVector<Entry> bufferMapping;
};

class MetalProgram : public HwProgram {
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81 changes: 55 additions & 26 deletions filament/backend/src/metal/MetalHandles.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -299,51 +299,80 @@ void presentDrawable(bool presentFrame, void* user) {
uint32_t indexCount) : HwIndexBuffer(elementSize, indexCount),
buffer(context, BufferObjectBinding::VERTEX, usage, elementSize * indexCount, true) { }

MetalRenderPrimitive::MetalRenderPrimitive()
: bufferMapping(utils::FixedCapacityVector<Entry>::with_capacity(MAX_VERTEX_BUFFER_COUNT)) {}

void MetalRenderPrimitive::setBuffers(MetalVertexBuffer* vertexBuffer, MetalIndexBuffer*
indexBuffer) {
this->vertexBuffer = vertexBuffer;
this->indexBuffer = indexBuffer;

const size_t attributeCount = vertexBuffer->attributes.size();

auto& mapping = bufferMapping;
mapping.clear();
vertexDescription = {};

// Each attribute gets its own vertex buffer, starting at logical buffer 1.
uint32_t bufferIndex = 1;
// Set the layout for the zero buffer, which unused attributes are mapped to.
vertexDescription.layouts[ZERO_VERTEX_BUFFER_LOGICAL_INDEX] = {
.step = MTLVertexStepFunctionConstant, .stride = 16
};

// Here we map each source buffer to a Metal buffer argument.
// Each attribute has a source buffer, offset, and stride.
// Two source buffers with the same index and stride can share the same Metal buffer argument
// index.
//
// The source buffer is the buffer index that the Filament client sets.
// * source buffer
// .attribute(VertexAttribute::POSITION, 0, VertexBuffer::AttributeType::FLOAT2, 0, 12)
// .attribute(VertexAttribute::UV, 0, VertexBuffer::AttributeType::HALF2, 8, 12)
// .attribute(VertexAttribute::COLOR, 1, VertexBuffer::AttributeType::UBYTE4, 0, 4)

auto allocateOrGetBufferArgumentIndex =
[&mapping, currentBufferArgumentIndex = USER_VERTEX_BUFFER_BINDING_START, this](
auto sourceBuffer, auto sourceBufferStride) mutable -> uint8_t {
auto match = [&](const auto& e) {
return e.sourceBufferIndex == sourceBuffer && e.stride == sourceBufferStride;
};
if (auto it = std::find_if(mapping.begin(), mapping.end(), match); it != mapping.end()) {
return it->bufferArgumentIndex;
} else {
auto bufferArgumentIndex = currentBufferArgumentIndex++;
mapping.emplace_back(sourceBuffer, sourceBufferStride, bufferArgumentIndex);
vertexDescription.layouts[bufferArgumentIndex] = {
.step = MTLVertexStepFunctionPerVertex, .stride = sourceBufferStride
};
return bufferArgumentIndex;
}
};

for (uint32_t attributeIndex = 0; attributeIndex < attributeCount; attributeIndex++) {
const auto& attribute = vertexBuffer->attributes[attributeIndex];
if (attribute.buffer == Attribute::BUFFER_UNUSED) {
const uint8_t flags = attribute.flags;
const MTLVertexFormat format = (flags & Attribute::FLAG_INTEGER_TARGET) ?
MTLVertexFormatUInt4 : MTLVertexFormatFloat4;

// If the attribute is not enabled, bind it to the zero buffer. It's a Metal error for a
// shader to read from missing vertex attributes.
// If the attribute is unused, bind it to the zero buffer. It's a Metal error for a shader
// to read from missing vertex attributes.
if (attribute.buffer == Attribute::BUFFER_UNUSED) {
const MTLVertexFormat format = (attribute.flags & Attribute::FLAG_INTEGER_TARGET)
? MTLVertexFormatUInt4
: MTLVertexFormatFloat4;
vertexDescription.attributes[attributeIndex] = {
.format = format,
.buffer = ZERO_VERTEX_BUFFER_LOGICAL_INDEX,
.offset = 0
};
vertexDescription.layouts[ZERO_VERTEX_BUFFER_LOGICAL_INDEX] = {
.step = MTLVertexStepFunctionConstant,
.stride = 16
.format = format, .buffer = ZERO_VERTEX_BUFFER_LOGICAL_INDEX, .offset = 0
};
continue;
}

// Map the source buffer and stride of this attribute to a Metal buffer argument.
auto bufferArgumentIndex =
allocateOrGetBufferArgumentIndex(attribute.buffer, attribute.stride);

vertexDescription.attributes[attributeIndex] = {
.format = getMetalFormat(attribute.type,
attribute.flags & Attribute::FLAG_NORMALIZED),
.buffer = bufferIndex,
.offset = 0
.format = getMetalFormat(
attribute.type, attribute.flags & Attribute::FLAG_NORMALIZED),
.buffer = uint32_t(bufferArgumentIndex),
.offset = attribute.offset
};
vertexDescription.layouts[bufferIndex] = {
.step = MTLVertexStepFunctionPerVertex,
.stride = attribute.stride
};

bufferIndex++;
};
}
}

MetalProgram::MetalProgram(MetalContext& context, Program&& program) noexcept
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