1 files changed, 535 insertions, 0 deletions
diff --git a/src/Ryujinx.Graphics.Gpu/Engine/Threed/ComputeDraw/VtgAsComputeState.cs b/src/Ryujinx.Graphics.Gpu/Engine/Threed/ComputeDraw/VtgAsComputeState.cs
new file mode 100644
index 00000000..59a92508
--- /dev/null
+++ b/src/Ryujinx.Graphics.Gpu/Engine/Threed/ComputeDraw/VtgAsComputeState.cs
@@ -0,0 +1,535 @@
+using Ryujinx.Common;
+using Ryujinx.Common.Logging;
+using Ryujinx.Graphics.GAL;
+using Ryujinx.Graphics.Gpu.Engine.Types;
+using Ryujinx.Graphics.Gpu.Image;
+using Ryujinx.Graphics.Gpu.Shader;
+using Ryujinx.Graphics.Shader;
+using Ryujinx.Graphics.Shader.Translation;
+using System;
+
+namespace Ryujinx.Graphics.Gpu.Engine.Threed.ComputeDraw
+{
+    /// <summary>
+    /// Vertex, tessellation and geometry as compute shader state.
+    /// </summary>
+    struct VtgAsComputeState
+    {
+        private const int ComputeLocalSize = 32;
+
+        private readonly GpuContext _context;
+        private readonly GpuChannel _channel;
+        private readonly DeviceStateWithShadow<ThreedClassState> _state;
+        private readonly VtgAsComputeContext _vacContext;
+        private readonly ThreedClass _engine;
+        private readonly ShaderAsCompute _vertexAsCompute;
+        private readonly ShaderAsCompute _geometryAsCompute;
+        private readonly IProgram _vertexPassthroughProgram;
+        private readonly PrimitiveTopology _topology;
+        private readonly int _count;
+        private readonly int _instanceCount;
+        private readonly int _firstIndex;
+        private readonly int _firstVertex;
+        private readonly int _firstInstance;
+        private readonly bool _indexed;
+
+        private readonly int _vertexDataOffset;
+        private readonly int _vertexDataSize;
+        private readonly int _geometryVertexDataOffset;
+        private readonly int _geometryVertexDataSize;
+        private readonly int _geometryIndexDataOffset;
+        private readonly int _geometryIndexDataSize;
+        private readonly int _geometryIndexDataCount;
+
+        /// <summary>
+        /// Creates a new vertex, tessellation and geometry as compute shader state.
+        /// </summary>
+        /// <param name="context">GPU context</param>
+        /// <param name="channel">GPU channel</param>
+        /// <param name="state">3D engine state</param>
+        /// <param name="vacContext">Vertex as compute context</param>
+        /// <param name="engine">3D engine</param>
+        /// <param name="vertexAsCompute">Vertex shader converted to compute</param>
+        /// <param name="geometryAsCompute">Optional geometry shader converted to compute</param>
+        /// <param name="vertexPassthroughProgram">Fragment shader with a vertex passthrough shader to feed the compute output into the fragment stage</param>
+        /// <param name="topology">Primitive topology of the draw</param>
+        /// <param name="count">Index or vertex count of the draw</param>
+        /// <param name="instanceCount">Instance count</param>
+        /// <param name="firstIndex">First index on the index buffer, for indexed draws</param>
+        /// <param name="firstVertex">First vertex on the vertex buffer</param>
+        /// <param name="firstInstance">First instance</param>
+        /// <param name="indexed">Whether the draw is indexed</param>
+        public VtgAsComputeState(
+            GpuContext context,
+            GpuChannel channel,
+            DeviceStateWithShadow<ThreedClassState> state,
+            VtgAsComputeContext vacContext,
+            ThreedClass engine,
+            ShaderAsCompute vertexAsCompute,
+            ShaderAsCompute geometryAsCompute,
+            IProgram vertexPassthroughProgram,
+            PrimitiveTopology topology,
+            int count,
+            int instanceCount,
+            int firstIndex,
+            int firstVertex,
+            int firstInstance,
+            bool indexed)
+        {
+            _context = context;
+            _channel = channel;
+            _state = state;
+            _vacContext = vacContext;
+            _engine = engine;
+            _vertexAsCompute = vertexAsCompute;
+            _geometryAsCompute = geometryAsCompute;
+            _vertexPassthroughProgram = vertexPassthroughProgram;
+            _topology = topology;
+            _count = count;
+            _instanceCount = instanceCount;
+            _firstIndex = firstIndex;
+            _firstVertex = firstVertex;
+            _firstInstance = firstInstance;
+            _indexed = indexed;
+
+            int vertexDataSize = vertexAsCompute.Reservations.OutputSizeInBytesPerInvocation * count * instanceCount;
+
+            (_vertexDataOffset, _vertexDataSize) = _vacContext.GetVertexDataBuffer(vertexDataSize);
+
+            if (geometryAsCompute != null)
+            {
+                int totalPrimitivesCount = VtgAsComputeContext.GetPrimitivesCount(topology, count * instanceCount);
+                int maxCompleteStrips = GetMaxCompleteStrips(geometryAsCompute.Info.GeometryVerticesPerPrimitive, geometryAsCompute.Info.GeometryMaxOutputVertices);
+                int totalVerticesCount = totalPrimitivesCount * geometryAsCompute.Info.GeometryMaxOutputVertices * geometryAsCompute.Info.ThreadsPerInputPrimitive;
+                int geometryVbDataSize = totalVerticesCount * geometryAsCompute.Reservations.OutputSizeInBytesPerInvocation;
+                int geometryIbDataCount = totalVerticesCount + totalPrimitivesCount * maxCompleteStrips;
+                int geometryIbDataSize = geometryIbDataCount * sizeof(uint);
+
+                (_geometryVertexDataOffset, _geometryVertexDataSize) = vacContext.GetGeometryVertexDataBuffer(geometryVbDataSize);
+                (_geometryIndexDataOffset, _geometryIndexDataSize) = vacContext.GetGeometryIndexDataBuffer(geometryIbDataSize);
+
+                _geometryIndexDataCount = geometryIbDataCount;
+            }
+        }
+
+        /// <summary>
+        /// Emulates the vertex stage using compute.
+        /// </summary>
+        public readonly void RunVertex()
+        {
+            _context.Renderer.Pipeline.SetProgram(_vertexAsCompute.HostProgram);
+
+            int primitivesCount = VtgAsComputeContext.GetPrimitivesCount(_topology, _count);
+
+            _vacContext.VertexInfoBufferUpdater.SetVertexCounts(_count, _instanceCount, _firstVertex, _firstInstance);
+            _vacContext.VertexInfoBufferUpdater.SetGeometryCounts(primitivesCount);
+
+            for (int index = 0; index < Constants.TotalVertexAttribs; index++)
+            {
+                var vertexAttrib = _state.State.VertexAttribState[index];
+
+                if (!FormatTable.TryGetSingleComponentAttribFormat(vertexAttrib.UnpackFormat(), out Format format, out int componentsCount))
+                {
+                    Logger.Debug?.Print(LogClass.Gpu, $"Invalid attribute format 0x{vertexAttrib.UnpackFormat():X}.");
+
+                    format = vertexAttrib.UnpackType() switch
+                    {
+                        VertexAttribType.Sint => Format.R32Sint,
+                        VertexAttribType.Uint => Format.R32Uint,
+                        _ => Format.R32Float
+                    };
+
+                    componentsCount = 4;
+                }
+
+                if (vertexAttrib.UnpackIsConstant())
+                {
+                    _vacContext.VertexInfoBufferUpdater.SetVertexStride(index, 0, componentsCount);
+                    _vacContext.VertexInfoBufferUpdater.SetVertexOffset(index, 0, 0);
+                    SetDummyBufferTexture(_vertexAsCompute.Reservations, index, format);
+                    continue;
+                }
+
+                int bufferIndex = vertexAttrib.UnpackBufferIndex();
+
+                GpuVa endAddress = _state.State.VertexBufferEndAddress[bufferIndex];
+                var vertexBuffer = _state.State.VertexBufferState[bufferIndex];
+                bool instanced = _state.State.VertexBufferInstanced[bufferIndex];
+
+                ulong address = vertexBuffer.Address.Pack();
+
+                if (!vertexBuffer.UnpackEnable() || !_channel.MemoryManager.IsMapped(address))
+                {
+                    _vacContext.VertexInfoBufferUpdater.SetVertexStride(index, 0, componentsCount);
+                    _vacContext.VertexInfoBufferUpdater.SetVertexOffset(index, 0, 0);
+                    SetDummyBufferTexture(_vertexAsCompute.Reservations, index, format);
+                    continue;
+                }
+
+                int vbStride = vertexBuffer.UnpackStride();
+                ulong vbSize = GetVertexBufferSize(address, endAddress.Pack(), vbStride, _indexed, instanced, _firstVertex, _count);
+
+                ulong oldVbSize = vbSize;
+
+                ulong attributeOffset = (ulong)vertexAttrib.UnpackOffset();
+                int componentSize = format.GetScalarSize();
+
+                address += attributeOffset;
+
+                ulong misalign = address & ((ulong)_context.Capabilities.TextureBufferOffsetAlignment - 1);
+
+                vbSize = Align(vbSize - attributeOffset + misalign, componentSize);
+
+                SetBufferTexture(_vertexAsCompute.Reservations, index, format, address - misalign, vbSize);
+
+                _vacContext.VertexInfoBufferUpdater.SetVertexStride(index, vbStride / componentSize, componentsCount);
+                _vacContext.VertexInfoBufferUpdater.SetVertexOffset(index, (int)misalign / componentSize, instanced ? vertexBuffer.Divisor : 0);
+            }
+
+            if (_indexed)
+            {
+                SetIndexBufferTexture(_vertexAsCompute.Reservations, _firstIndex, _count, out int ibOffset);
+                _vacContext.VertexInfoBufferUpdater.SetIndexBufferOffset(ibOffset);
+            }
+            else
+            {
+                SetSequentialIndexBufferTexture(_vertexAsCompute.Reservations, _count);
+                _vacContext.VertexInfoBufferUpdater.SetIndexBufferOffset(0);
+            }
+
+            int vertexInfoBinding = _vertexAsCompute.Reservations.VertexInfoConstantBufferBinding;
+            BufferRange vertexInfoRange = new(_vacContext.VertexInfoBufferUpdater.Handle, 0, VertexInfoBuffer.RequiredSize);
+            _context.Renderer.Pipeline.SetUniformBuffers(stackalloc[] { new BufferAssignment(vertexInfoBinding, vertexInfoRange) });
+
+            int vertexDataBinding = _vertexAsCompute.Reservations.VertexOutputStorageBufferBinding;
+            BufferRange vertexDataRange = _vacContext.GetVertexDataBufferRange(_vertexDataOffset, _vertexDataSize);
+            _context.Renderer.Pipeline.SetStorageBuffers(stackalloc[] { new BufferAssignment(vertexDataBinding, vertexDataRange) });
+
+            _vacContext.VertexInfoBufferUpdater.Commit();
+
+            _context.Renderer.Pipeline.DispatchCompute(
+                BitUtils.DivRoundUp(_count, ComputeLocalSize),
+                BitUtils.DivRoundUp(_instanceCount, ComputeLocalSize),
+                1);
+        }
+
+        /// <summary>
+        /// Emulates the geometry stage using compute, if it exists, otherwise does nothing.
+        /// </summary>
+        public readonly void RunGeometry()
+        {
+            if (_geometryAsCompute == null)
+            {
+                return;
+            }
+
+            int primitivesCount = VtgAsComputeContext.GetPrimitivesCount(_topology, _count);
+
+            _vacContext.VertexInfoBufferUpdater.SetVertexCounts(_count, _instanceCount, _firstVertex, _firstInstance);
+            _vacContext.VertexInfoBufferUpdater.SetGeometryCounts(primitivesCount);
+            _vacContext.VertexInfoBufferUpdater.Commit();
+
+            int vertexInfoBinding = _vertexAsCompute.Reservations.VertexInfoConstantBufferBinding;
+            BufferRange vertexInfoRange = new(_vacContext.VertexInfoBufferUpdater.Handle, 0, VertexInfoBuffer.RequiredSize);
+            _context.Renderer.Pipeline.SetUniformBuffers(stackalloc[] { new BufferAssignment(vertexInfoBinding, vertexInfoRange) });
+
+            int vertexDataBinding = _vertexAsCompute.Reservations.VertexOutputStorageBufferBinding;
+
+            // Wait until compute is done.
+            // TODO: Batch compute and draw operations to avoid pipeline stalls.
+            _context.Renderer.Pipeline.Barrier();
+            _context.Renderer.Pipeline.SetProgram(_geometryAsCompute.HostProgram);
+
+            SetTopologyRemapBufferTexture(_geometryAsCompute.Reservations, _topology, _count);
+
+            int geometryVbBinding = _geometryAsCompute.Reservations.GeometryVertexOutputStorageBufferBinding;
+            int geometryIbBinding = _geometryAsCompute.Reservations.GeometryIndexOutputStorageBufferBinding;
+
+            BufferRange vertexDataRange = _vacContext.GetVertexDataBufferRange(_vertexDataOffset, _vertexDataSize);
+            BufferRange vertexBuffer = _vacContext.GetGeometryVertexDataBufferRange(_geometryVertexDataOffset, _geometryVertexDataSize);
+            BufferRange indexBuffer = _vacContext.GetGeometryIndexDataBufferRange(_geometryIndexDataOffset, _geometryIndexDataSize);
+
+            _context.Renderer.Pipeline.SetStorageBuffers(stackalloc[]
+            {
+                new BufferAssignment(vertexDataBinding, vertexDataRange),
+                new BufferAssignment(geometryVbBinding, vertexBuffer),
+                new BufferAssignment(geometryIbBinding, indexBuffer),
+            });
+
+            _context.Renderer.Pipeline.DispatchCompute(
+                BitUtils.DivRoundUp(primitivesCount, ComputeLocalSize),
+                BitUtils.DivRoundUp(_instanceCount, ComputeLocalSize),
+                _geometryAsCompute.Info.ThreadsPerInputPrimitive);
+        }
+
+        /// <summary>
+        /// Performs a draw using the data produced on the vertex, tessellation and geometry stages,
+        /// if rasterizer discard is disabled.
+        /// </summary>
+        public readonly void RunFragment()
+        {
+            bool tfEnabled = _state.State.TfEnable;
+
+            if (!_state.State.RasterizeEnable && (!tfEnabled || !_context.Capabilities.SupportsTransformFeedback))
+            {
+                // No need to run fragment if rasterizer discard is enabled,
+                // and we are emulating transform feedback or transform feedback is disabled.
+
+                // Note: We might skip geometry shader here, but right now, this is fine,
+                // because the only cases that triggers VTG to compute are geometry shader
+                // being not supported, or the vertex pipeline doing store operations.
+                // If the geometry shader does not do any store and rasterizer discard is enabled, the geometry shader can be skipped.
+                // If the geometry shader does have stores, it would have been converted to compute too if stores are not supported.
+
+                return;
+            }
+
+            int vertexDataBinding = _vertexAsCompute.Reservations.VertexOutputStorageBufferBinding;
+
+            _context.Renderer.Pipeline.Barrier();
+
+            _vacContext.VertexInfoBufferUpdater.SetVertexCounts(_count, _instanceCount, _firstVertex, _firstInstance);
+            _vacContext.VertexInfoBufferUpdater.Commit();
+
+            if (_geometryAsCompute != null)
+            {
+                BufferRange vertexBuffer = _vacContext.GetGeometryVertexDataBufferRange(_geometryVertexDataOffset, _geometryVertexDataSize);
+                BufferRange indexBuffer = _vacContext.GetGeometryIndexDataBufferRange(_geometryIndexDataOffset, _geometryIndexDataSize);
+
+                _context.Renderer.Pipeline.SetProgram(_vertexPassthroughProgram);
+                _context.Renderer.Pipeline.SetIndexBuffer(indexBuffer, IndexType.UInt);
+                _context.Renderer.Pipeline.SetStorageBuffers(stackalloc[] { new BufferAssignment(vertexDataBinding, vertexBuffer) });
+
+                _context.Renderer.Pipeline.SetPrimitiveRestart(true, -1);
+                _context.Renderer.Pipeline.SetPrimitiveTopology(GetGeometryOutputTopology(_geometryAsCompute.Info.GeometryVerticesPerPrimitive));
+
+                _context.Renderer.Pipeline.DrawIndexed(_geometryIndexDataCount, 1, 0, 0, 0);
+
+                _engine.ForceStateDirtyByIndex(StateUpdater.IndexBufferStateIndex);
+                _engine.ForceStateDirtyByIndex(StateUpdater.PrimitiveRestartStateIndex);
+            }
+            else
+            {
+                BufferRange vertexDataRange = _vacContext.GetVertexDataBufferRange(_vertexDataOffset, _vertexDataSize);
+
+                _context.Renderer.Pipeline.SetProgram(_vertexPassthroughProgram);
+                _context.Renderer.Pipeline.SetStorageBuffers(stackalloc[] { new BufferAssignment(vertexDataBinding, vertexDataRange) });
+                _context.Renderer.Pipeline.Draw(_count, _instanceCount, 0, 0);
+            }
+        }
+
+        /// <summary>
+        /// Gets a strip primitive topology from the vertices per primitive count.
+        /// </summary>
+        /// <param name="verticesPerPrimitive">Vertices per primitive count</param>
+        /// <returns>Primitive topology</returns>
+        private static PrimitiveTopology GetGeometryOutputTopology(int verticesPerPrimitive)
+        {
+            return verticesPerPrimitive switch
+            {
+                3 => PrimitiveTopology.TriangleStrip,
+                2 => PrimitiveTopology.LineStrip,
+                _ => PrimitiveTopology.Points,
+            };
+        }
+
+        /// <summary>
+        /// Gets the maximum number of complete primitive strips for a vertex count.
+        /// </summary>
+        /// <param name="verticesPerPrimitive">Vertices per primitive count</param>
+        /// <param name="maxOutputVertices">Maximum geometry shader output vertices count</param>
+        /// <returns>Maximum number of complete primitive strips</returns>
+        private static int GetMaxCompleteStrips(int verticesPerPrimitive, int maxOutputVertices)
+        {
+            return maxOutputVertices / verticesPerPrimitive;
+        }
+
+        /// <summary>
+        /// Binds a dummy buffer as vertex buffer into a buffer texture.
+        /// </summary>
+        /// <param name="reservations">Shader resource binding reservations</param>
+        /// <param name="index">Buffer texture index</param>
+        /// <param name="format">Buffer texture format</param>
+        private readonly void SetDummyBufferTexture(ResourceReservations reservations, int index, Format format)
+        {
+            ITexture bufferTexture = _vacContext.EnsureBufferTexture(index + 2, format);
+            bufferTexture.SetStorage(_vacContext.GetDummyBufferRange());
+
+            _context.Renderer.Pipeline.SetTextureAndSampler(ShaderStage.Compute, reservations.GetVertexBufferTextureBinding(index), bufferTexture, null);
+        }
+
+        /// <summary>
+        /// Binds a vertex buffer into a buffer texture.
+        /// </summary>
+        /// <param name="reservations">Shader resource binding reservations</param>
+        /// <param name="index">Buffer texture index</param>
+        /// <param name="format">Buffer texture format</param>
+        /// <param name="address">Address of the vertex buffer</param>
+        /// <param name="size">Size of the buffer in bytes</param>
+        private readonly void SetBufferTexture(ResourceReservations reservations, int index, Format format, ulong address, ulong size)
+        {
+            var memoryManager = _channel.MemoryManager;
+
+            address = memoryManager.Translate(address);
+            BufferRange range = memoryManager.Physical.BufferCache.GetBufferRange(address, size);
+
+            ITexture bufferTexture = _vacContext.EnsureBufferTexture(index + 2, format);
+            bufferTexture.SetStorage(range);
+
+            _context.Renderer.Pipeline.SetTextureAndSampler(ShaderStage.Compute, reservations.GetVertexBufferTextureBinding(index), bufferTexture, null);
+        }
+
+        /// <summary>
+        /// Binds the index buffer into a buffer texture.
+        /// </summary>
+        /// <param name="reservations">Shader resource binding reservations</param>
+        /// <param name="firstIndex">First index of the index buffer</param>
+        /// <param name="count">Index count</param>
+        /// <param name="misalignedOffset">Offset that should be added when accessing the buffer texture on the shader</param>
+        private readonly void SetIndexBufferTexture(ResourceReservations reservations, int firstIndex, int count, out int misalignedOffset)
+        {
+            ulong address = _state.State.IndexBufferState.Address.Pack();
+            ulong indexOffset = (ulong)firstIndex;
+            ulong size = (ulong)count;
+
+            int shift = 0;
+            Format format = Format.R8Uint;
+
+            switch (_state.State.IndexBufferState.Type)
+            {
+                case IndexType.UShort:
+                    shift = 1;
+                    format = Format.R16Uint;
+                    break;
+                case IndexType.UInt:
+                    shift = 2;
+                    format = Format.R32Uint;
+                    break;
+            }
+
+            indexOffset <<= shift;
+            size <<= shift;
+
+            var memoryManager = _channel.MemoryManager;
+
+            address = memoryManager.Translate(address + indexOffset);
+            ulong misalign = address & ((ulong)_context.Capabilities.TextureBufferOffsetAlignment - 1);
+            BufferRange range = memoryManager.Physical.BufferCache.GetBufferRange(address - misalign, size + misalign);
+            misalignedOffset = (int)misalign >> shift;
+
+            SetIndexBufferTexture(reservations, range, format);
+        }
+
+        /// <summary>
+        /// Sets the host buffer texture for the index buffer.
+        /// </summary>
+        /// <param name="reservations">Shader resource binding reservations</param>
+        /// <param name="range">Index buffer range</param>
+        /// <param name="format">Index buffer format</param>
+        private readonly void SetIndexBufferTexture(ResourceReservations reservations, BufferRange range, Format format)
+        {
+            ITexture bufferTexture = _vacContext.EnsureBufferTexture(0, format);
+            bufferTexture.SetStorage(range);
+
+            _context.Renderer.Pipeline.SetTextureAndSampler(ShaderStage.Compute, reservations.IndexBufferTextureBinding, bufferTexture, null);
+        }
+
+        /// <summary>
+        /// Sets the host buffer texture for the topology remap buffer.
+        /// </summary>
+        /// <param name="reservations">Shader resource binding reservations</param>
+        /// <param name="topology">Input topology</param>
+        /// <param name="count">Input vertex count</param>
+        private readonly void SetTopologyRemapBufferTexture(ResourceReservations reservations, PrimitiveTopology topology, int count)
+        {
+            ITexture bufferTexture = _vacContext.EnsureBufferTexture(1, Format.R32Uint);
+            bufferTexture.SetStorage(_vacContext.GetOrCreateTopologyRemapBuffer(topology, count));
+
+            _context.Renderer.Pipeline.SetTextureAndSampler(ShaderStage.Compute, reservations.TopologyRemapBufferTextureBinding, bufferTexture, null);
+        }
+
+        /// <summary>
+        /// Sets the host buffer texture to a generated sequential index buffer.
+        /// </summary>
+        /// <param name="reservations">Shader resource binding reservations</param>
+        /// <param name="count">Vertex count</param>
+        private readonly void SetSequentialIndexBufferTexture(ResourceReservations reservations, int count)
+        {
+            BufferHandle sequentialIndexBuffer = _vacContext.GetSequentialIndexBuffer(count);
+
+            ITexture bufferTexture = _vacContext.EnsureBufferTexture(0, Format.R32Uint);
+            bufferTexture.SetStorage(new BufferRange(sequentialIndexBuffer, 0, count * sizeof(uint)));
+
+            _context.Renderer.Pipeline.SetTextureAndSampler(ShaderStage.Compute, reservations.IndexBufferTextureBinding, bufferTexture, null);
+        }
+
+        /// <summary>
+        /// Gets the size of a vertex buffer based on the current 3D engine state.
+        /// </summary>
+        /// <param name="vbAddress">Vertex buffer address</param>
+        /// <param name="vbEndAddress">Vertex buffer end address (exclusive)</param>
+        /// <param name="vbStride">Vertex buffer stride</param>
+        /// <param name="indexed">Whether the draw is indexed</param>
+        /// <param name="instanced">Whether the draw is instanced</param>
+        /// <param name="firstVertex">First vertex index</param>
+        /// <param name="vertexCount">Vertex count</param>
+        /// <returns>Size of the vertex buffer, in bytes</returns>
+        private readonly ulong GetVertexBufferSize(ulong vbAddress, ulong vbEndAddress, int vbStride, bool indexed, bool instanced, int firstVertex, int vertexCount)
+        {
+            IndexType indexType = _state.State.IndexBufferState.Type;
+            bool indexTypeSmall = indexType == IndexType.UByte || indexType == IndexType.UShort;
+            ulong vbSize = vbEndAddress - vbAddress + 1;
+            ulong size;
+
+            if (indexed || vbStride == 0 || instanced)
+            {
+                // This size may be (much) larger than the real vertex buffer size.
+                // Avoid calculating it this way, unless we don't have any other option.
+
+                size = vbSize;
+
+                if (vbStride > 0 && indexTypeSmall && indexed && !instanced)
+                {
+                    // If the index type is a small integer type, then we might be still able
+                    // to reduce the vertex buffer size based on the maximum possible index value.
+
+                    ulong maxVertexBufferSize = indexType == IndexType.UByte ? 0x100UL : 0x10000UL;
+
+                    maxVertexBufferSize += _state.State.FirstVertex;
+                    maxVertexBufferSize *= (uint)vbStride;
+
+                    size = Math.Min(size, maxVertexBufferSize);
+                }
+            }
+            else
+            {
+                // For non-indexed draws, we can guess the size from the vertex count
+                // and stride.
+
+                int firstInstance = (int)_state.State.FirstInstance;
+
+                size = Math.Min(vbSize, (ulong)((firstInstance + firstVertex + vertexCount) * vbStride));
+            }
+
+            return size;
+        }
+
+        /// <summary>
+        /// Aligns a size to a given alignment value.
+        /// </summary>
+        /// <param name="size">Size</param>
+        /// <param name="alignment">Alignment</param>
+        /// <returns>Aligned size</returns>
+        private static ulong Align(ulong size, int alignment)
+        {
+            ulong align = (ulong)alignment;
+
+            size += align - 1;
+
+            size /= align;
+            size *= align;
+
+            return size;
+        }
+    }
+}