indirectCommandEncoder.h

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//
// Copyright 2022 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_IMAGING_HGI_INDIRECT_COMMAND_ENCODER_H
#define PXR_IMAGING_HGI_INDIRECT_COMMAND_ENCODER_H

#include "pxr/pxr.h"
#include "pxr/imaging/hgi/api.h"
#include "pxr/imaging/hgi/cmds.h"
#include "pxr/imaging/hgi/resourceBindings.h"
#include "pxr/imaging/hgi/graphicsPipeline.h"

#include <memory>
#include <stdint.h>

PXR_NAMESPACE_OPEN_SCOPE

class Hgi;
class HgiComputeCmds;
class HgiGraphicsCmds;

struct HgiIndirectCommands
{
    HgiIndirectCommands(uint32_t drawCount,
                        HgiGraphicsPipelineHandle const &graphicsPipeline,
                        HgiResourceBindingsHandle const &resourceBindings)
        : drawCount(drawCount)
        , graphicsPipeline(graphicsPipeline)
        , resourceBindings(resourceBindings)
    {
    }

    virtual ~HgiIndirectCommands() = default;

    uint32_t drawCount;
    HgiGraphicsPipelineHandle graphicsPipeline;
    HgiResourceBindingsHandle resourceBindings;
};

using HgiIndirectCommandsUniquePtr = std::unique_ptr<HgiIndirectCommands>;

/// \class HgiIndirectCommandEncoder
///
/// The indirect command encoder is used to record the drawing primitives for a
/// batch and capture the resource bindings so that it can be executed
/// efficently in a later stage of rendering.
/// The EncodeDraw and EncodeDrawIndexed functions store all the necessary state
/// in the HgiIndirectCommands structure.  This is sub-classed based on the
/// platform implementation to maintain all the custom state.
/// Execute draw takes the HgiIndirectCommands structure and replays it on the
/// device.  Currently this is only implemented on the Metal HGI device.
///
class HgiIndirectCommandEncoder : public HgiCmds
{
public:
    HGI_API
    ~HgiIndirectCommandEncoder() override;
    
    /// Encodes a batch of draw commands from the drawParameterBuffer.
    /// Returns a HgiIndirectCommands which holds the necessary buffers and
    /// state for replaying the batch.
    HGI_API
    virtual HgiIndirectCommandsUniquePtr EncodeDraw(
        HgiComputeCmds * computeCmds,
        HgiGraphicsPipelineHandle const& pipeline,
        HgiResourceBindingsHandle const& resourceBindings,
        HgiVertexBufferBindingVector const& vertexBindings,
        HgiBufferHandle const& drawParameterBuffer,
        uint32_t drawBufferByteOffset,
        uint32_t drawCount,
        uint32_t stride) = 0;
    
    /// Encodes a batch of indexed draw commands from the drawParameterBuffer.
    /// Returns a HgiIndirectCommands which holds the necessary buffers and
    /// state for replaying the batch.
    HGI_API
    virtual HgiIndirectCommandsUniquePtr EncodeDrawIndexed(
        HgiComputeCmds * computeCmds,
        HgiGraphicsPipelineHandle const& pipeline,
        HgiResourceBindingsHandle const& resourceBindings,
        HgiVertexBufferBindingVector const& vertexBindings,
        HgiBufferHandle const& indexBuffer,
        HgiBufferHandle const& drawParameterBuffer,
        uint32_t drawBufferByteOffset,
        uint32_t drawCount,
        uint32_t stride,
        uint32_t patchBaseVertexByteOffset) = 0;
    
    /// Excutes an indirect command batch from the HgiIndirectCommands
    /// structure.
    HGI_API
    virtual void ExecuteDraw(
        HgiGraphicsCmds * gfxCmds,
        HgiIndirectCommands const* commands) = 0;

protected:
    HGI_API
    HgiIndirectCommandEncoder();

private:
    HgiIndirectCommandEncoder & operator=(const HgiIndirectCommandEncoder&) = delete;
    HgiIndirectCommandEncoder(const HgiIndirectCommandEncoder&) = delete;
};

PXR_NAMESPACE_CLOSE_SCOPE

#endif