Major overhaul of Renderer abstraction, to support a new example (#624)

The original goal here was to bring up a second example program: `model-viewer`.
While the existing `hello-world` example is enough to get somebody up to speed with the basics of the Slang API (as a drop-in replacement for `D3DCompile` or similar), it doesn't really show any of the big-picture stuff that Slang is meant to enable.
There wasn't any use of D3D12/Vulkan descriptor tables/sets, and there wasn't any use of interfaces, generics, or `ParameterBlock`s in the shader code.

The `model-viewer` example addresses these issues. Its shader code involves generics, interfaces, and multiple `ParameterBlock`s, and the host-side code demonstrates a few key things for working with Slang:

* There is an application-level abstraction for parameter blocks, that combines the graphics-API descriptor set object with Slang type information

* There is a shader cache layer used to look up an appropriate variant of a rendering effect by using parameter block types to "plug in" global type variables

* There is a clear separation between the phases of compilation: a first phase that does semantic checking and enables reflection-based allocation of graphics API objects, followed by one or more code generation passes for specialized kernels.

This example is certainly not perfect, and it will need to be revamped more going forward. In particular:

* The output picture is ugly as sin. We need a plan for how to get this to load better content, perhaps even popping up an error message to note that the required input data isn't present in the basic repository.

* The shader code is too simplistic. There isn't any real material variety, and the `IMaterial` abstraction is completely wrong.

* The use of parameter blocks is facile because there are no resource parameters right now. Fixing that will likely expose issues around interfacing with Slang's reflection API.

* The whole example exposes the issue that Slang's current APIs aren't really designed for the benefit of two-phase compilation (since our many client application has been stuck on one-phase compilation).

* Global type parameters are actually a Bad Idea that we only did for compatibility with existing codebases. We should not be showing them off in an example of the Right Way to use Slang, but the language support for type parameters on entry points is still not complete.

Of course, the majority of the changes here are *not* inside the example applications, and instead involve a major overhaul of the `Renderer` abstraction that is used for both tests and examples. The main thrust of the change is to make the abstraction layer be closer to the D3D12/Vulkan model than to a D3D11-style model. This is important for the `model-viewer` example, since it aspires to show how Slang can be incorporated into a renderer that targets a modern API. The most important bit is actually the use of descriptor sets and "pipeline layouts" a la Vulkan, since without these Slang's `ParameterBlock` abstraction won't make a lot of sense.

Implementation of the abstraction for the various APIs has very much been on an as-needed basis. The current implementation is just enough for the two examples to work, plus enough to get all the tests to pass in both debug and release builds on Windows.

A big missing feature in the API abstraction right now is memory lifetime management. The code had been trending toward something D3D11-like where a constant buffer could be mapped per-frame with the implementation doing behind-the-scenes allocation for targets like D3D12/Vulkan. I'd like to shift more toward a model of just exposing "transient" allocations that are only valid for one frame, because these are more representation of how an efficient renderer for next-generation APIs will work. That transition isn't actually complete, though, so there are problems with the existing examples where `hello-world` is actually scribbling into memory that the GPU might still be using, while `model-viewer` is doing full-on heavy-weight allocations on a per-frame basis with no real concern for the performance implications.

All together, there are a lot of things here that need more work, but this branch has been way too long-lived already, and so I'd like to get this checked in as long as all the tests pass.

1 files changed, 222 insertions, 0 deletions

diff --git a/tools/gfx/circular-resource-heap-d3d12.cpp b/tools/gfx/circular-resource-heap-d3d12.cpp
new file mode 100644
index 000000000..20e47c4dd
--- /dev/null
+++ b/tools/gfx/circular-resource-heap-d3d12.cpp
@@ -0,0 +1,222 @@
+#include "circular-resource-heap-d3d12.h"
+
+namespace gfx {
+using namespace Slang;
+
+D3D12CircularResourceHeap::D3D12CircularResourceHeap():
+	m_fence(nullptr),
+	m_device(nullptr),
+	m_blockFreeList(sizeof(Block), SLANG_ALIGN_OF(Block), 16),
+	m_blocks(nullptr)
+{
+	m_back.m_block = nullptr;
+	m_back.m_position = nullptr;
+	m_front.m_block = nullptr;
+	m_front.m_position = nullptr;
+}
+
+D3D12CircularResourceHeap::~D3D12CircularResourceHeap()
+{
+	_freeBlockListResources(m_blocks);
+}
+
+void D3D12CircularResourceHeap::_freeBlockListResources(const Block* start)
+{
+	if (start)
+	{
+        const Block* block = start;
+        do
+        {
+            ID3D12Resource* resource = block->m_resource;
+
+            resource->Unmap(0, nullptr);
+            resource->Release();
+
+            // Next in list
+            block = block->m_next;
+
+        } while (block != start);
+	}
+}
+
+Result D3D12CircularResourceHeap::init(ID3D12Device* device, const Desc& desc, D3D12CounterFence* fence)
+{
+	assert(m_blocks == nullptr);
+	assert(desc.m_blockSize > 0);
+
+	m_fence = fence;
+	m_desc = desc;
+	m_device = device;
+
+	return SLANG_OK;
+}
+
+void D3D12CircularResourceHeap::addSync(uint64_t signalValue)
+{
+	assert(signalValue == m_fence->getCurrentValue());
+	PendingEntry entry;
+	entry.m_completedValue = signalValue;
+	entry.m_cursor = m_front;
+	m_pendingQueue.Add(entry);
+}
+
+void D3D12CircularResourceHeap::updateCompleted()
+{
+	const uint64_t completedValue = m_fence->getCompletedValue();
+
+#if 0
+	while (m_pendingQueue.Count() != 0)
+	{
+		const PendingEntry& entry = m_pendingQueue[0];
+		if (entry.m_completedValue <= completedValue)
+		{
+			m_back = entry.m_cursor;
+			m_pendingQueue.RemoveAt(0);
+		}
+		else
+		{
+			break;
+		}
+	}
+#else
+	// A more efficient implementation is m_pendingQueue is implemented as a vector like type
+	const int size = int(m_pendingQueue.Count());
+	int end = 0;
+	while (end < size && m_pendingQueue[end].m_completedValue <= completedValue)
+	{
+		end++;
+	}
+
+	if (end > 0)
+	{
+		// Set the back position
+		m_back = m_pendingQueue[end - 1].m_cursor;
+		if (end == size)
+		{
+			m_pendingQueue.Clear();
+		}
+		else
+		{
+			m_pendingQueue.RemoveRange(0, size);
+		}
+	}
+#endif
+}
+
+D3D12CircularResourceHeap::Block* D3D12CircularResourceHeap::_newBlock()
+{
+	D3D12_RESOURCE_DESC desc;
+
+	desc.Dimension = D3D12_RESOURCE_DIMENSION_BUFFER;
+	desc.Alignment = 0;
+	desc.Width = m_desc.m_blockSize;
+	desc.Height = 1;
+	desc.DepthOrArraySize = 1;
+	desc.MipLevels = 1;
+	desc.Format = DXGI_FORMAT_UNKNOWN;
+	desc.SampleDesc.Count = 1;
+	desc.SampleDesc.Quality = 0;
+	desc.Layout = D3D12_TEXTURE_LAYOUT_ROW_MAJOR;
+	desc.Flags = D3D12_RESOURCE_FLAG_NONE;
+
+	ComPtr<ID3D12Resource> resource;
+	Result res = m_device->CreateCommittedResource(&m_desc.m_heapProperties, m_desc.m_heapFlags, &desc, m_desc.m_initialState, nullptr, IID_PPV_ARGS(resource.writeRef()));
+	if (SLANG_FAILED(res))
+	{
+		assert(!"Resource allocation failed");
+		return nullptr;
+	}
+
+	uint8_t* data = nullptr;
+	if (m_desc.m_heapProperties.Type == D3D12_HEAP_TYPE_READBACK)
+	{
+	}
+	else
+	{
+		// Map it, and keep it mapped
+		resource->Map(0, nullptr, (void**)&data);
+	}
+
+	// We have no blocks -> so lets allocate the first
+	Block* block = (Block*)m_blockFreeList.allocate();
+	block->m_next = nullptr;
+
+	block->m_resource = resource.detach();
+	block->m_start = data;
+	return block;
+}
+
+D3D12CircularResourceHeap::Cursor D3D12CircularResourceHeap::allocate(size_t size, size_t alignment)
+{
+	const size_t blockSize = getBlockSize();
+
+	assert(size <= blockSize);
+
+	// If nothing is allocated add the first block
+	if (m_blocks == nullptr)
+	{
+		Block* block = _newBlock();
+		if (!block)
+		{
+			Cursor cursor = {};
+			return cursor;
+		}
+		m_blocks = block;
+		// Make circular
+		block->m_next = block;
+
+		// Point front and back to same position, as currently it is all free
+		m_back = { block, block->m_start };
+		m_front = m_back;
+	}
+
+	// If front and back are in the same block then front MUST be ahead of back (as that defined as
+	// an invariant and is required for block insertion to be possible
+	Block* block = m_front.m_block;
+
+	// Check the invariant
+	assert(block != m_back.m_block || m_front.m_position >= m_back.m_position);
+
+	{
+		uint8_t* cur = (uint8_t*)((size_t(m_front.m_position) + alignment - 1) & ~(alignment - 1));
+		// Does the the allocation fit?
+		if (cur + size <= block->m_start + blockSize)
+		{
+			// It fits
+			// Move the front forward
+			m_front.m_position = cur + size;
+			Cursor cursor = { block, cur };
+			return cursor;
+		}
+	}
+
+	// Okay I can't fit into current block...
+
+	// If the next block contains front, we need to add a block, else we can use that block
+	if (block->m_next == m_back.m_block)
+	{
+		Block* newBlock = _newBlock();
+		// Insert into the list
+		newBlock->m_next = block->m_next;
+		block->m_next = newBlock;
+	}
+
+	// Use the block we are going to add to
+	block = block->m_next;
+	uint8_t* cur = (uint8_t*)((size_t(block->m_start) + alignment - 1) & ~(alignment - 1));
+	// Does the the allocation fit?
+	if (cur + size > block->m_start + blockSize)
+	{
+		assert(!"Couldn't fit into a free block(!) Alignment breaks it?");
+		Cursor cursor = {};
+		return cursor;
+	}
+	// It fits
+	// Move the front forward
+	m_front.m_block = block;
+	m_front.m_position = cur + size;
+	Cursor cursor = { block, cur };
+	return cursor;
+}
+
+} // namespace gfx