axmol/core/renderer/backend/CommandBuffer.h

/****************************************************************************
 Copyright (c) 2018-2019 Xiamen Yaji Software Co., Ltd.

 https://axys1.github.io/

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#pragma once

#include <cstdint>

#include "base/CCRef.h"
#include "base/CCData.h"

#include "Macros.h"
#include "Types.h"
#include "RenderPassDescriptor.h"
#include "PixelBufferDescriptor.h"
#include "CCStdC.h"
#include "ProgramState.h"
#include "VertexLayout.h"

#include <memory>
#include <vector>

NS_AX_BEGIN
struct PipelineDescriptor;

namespace backend
{

class RenderPass;
class RenderPipeline;
class Buffer;
class DepthStencilState;
class TextureBackend;
class RenderTarget;
struct DepthStencilDescriptor;

/**
 * @addtogroup _backend
 * @{
 */

/**
 * @brief Store encoded commands for the GPU to execute.
 * A command buffer stores encoded commands until the buffer is committed for execution by the GPU
 */
class CommandBuffer : public ax::Ref
{
public:
    /**
     * Set depthStencil status once
     * @param depthStencilState Specifies the depth and stencil status
     */
    virtual void setDepthStencilState(DepthStencilState* depthStencilState) = 0;

    /**
     * Sets the current render pipeline state object once
     * @param renderPipeline An object that contains the graphics functions and configuration state used in a render
     * pass.
     */
    virtual void setRenderPipeline(RenderPipeline* renderPipeline) = 0;

    /// @name Setters & Getters
    /**
     * @brief Indicate the begining of a frame
     */
    virtual bool beginFrame() = 0;

    /**
     * Begin a render pass, initial color, depth and stencil attachment.
     * @param descriptor Specifies a group of render targets that hold the results of a render pass.
     */
    virtual void beginRenderPass(const RenderTarget* renderTarget, const RenderPassDescriptor& descriptor) = 0;

    /**
     * Update depthStencil status, improvment: for metal backend cache it
     * @param depthStencilState Specifies the depth and stencil status
     */
    virtual void updateDepthStencilState(const DepthStencilDescriptor& descriptor) = 0;

    /**
     * Update render pipeline status
     * Building a programmable pipeline involves an expensive evaluation of GPU state.
     * So a new render pipeline object will be created only if it hasn't been created before.
     * @param rt Specifies the render target.
     * @param pipelineDescriptor Specifies the pipeline descriptor.
     */
    virtual void updatePipelineState(const RenderTarget* rt, const PipelineDescriptor& descriptor) = 0;

    /**
     * Fixed-function state
     * @param x The x coordinate of the upper-left corner of the viewport.
     * @param y The y coordinate of the upper-left corner of the viewport.
     * @param w The width of the viewport, in pixels.
     * @param h The height of the viewport, in pixels.
     */
    virtual void setViewport(int x, int y, unsigned int w, unsigned int h) = 0;

    /**
     * Fixed-function state
     * @param mode Controls if primitives are culled when front facing, back facing, or not culled at all.
     */
    virtual void setCullMode(CullMode mode) = 0;

    /**
     * Fixed-function state
     * @param winding The winding order of front-facing primitives.
     */
    virtual void setWinding(Winding winding) = 0;

    /**
     * Set a global buffer for all vertex shaders at the given bind point index 0.
     * @param buffer The vertex buffer to be setted in the buffer argument table.
     */
    virtual void setVertexBuffer(Buffer* buffer) = 0;

    /**
     * Set unifroms and textures
     * @param programState A programState object that hold the uniform and texture data.
     */
    virtual void setProgramState(ProgramState* programState) = 0;

    /**
     * Set indexes when drawing primitives with index list
     * @ buffer A buffer object that the device will read indexes from.
     * @ see `drawElements(PrimitiveType primitiveType, IndexFormat indexType, unsigned int count, unsigned int offset)`
     */
    virtual void setIndexBuffer(Buffer* buffer) = 0;

    /**
     * Draw primitives without an index list.
     * @param primitiveType The type of primitives that elements are assembled into.
     * @param start For each instance, the first index to draw
     * @param count For each instance, the number of indexes to draw
     * @see `drawElements(PrimitiveType primitiveType, IndexFormat indexType, unsigned int count, unsigned int offset)`
     */
    virtual void drawArrays(PrimitiveType primitiveType,
                            std::size_t start,
                            std::size_t count,
                            bool wireframe = false) = 0;

    /**
     * Draw primitives with an index list.
     * @param primitiveType The type of primitives that elements are assembled into.
     * @param indexType The type if indexes, either 16 bit integer or 32 bit integer.
     * @param count The number of indexes to read from the index buffer for each instance.
     * @param offset Byte offset within indexBuffer to start reading indexes from.
     * @see `setIndexBuffer(Buffer* buffer)`
     * @see `drawArrays(PrimitiveType primitiveType, unsigned int start,  unsigned int count)`
     */
    virtual void drawElements(PrimitiveType primitiveType,
                              IndexFormat indexType,
                              std::size_t count,
                              std::size_t offset,
                              bool wireframe = false) = 0;

    /**
     * Do some resources release.
     */
    virtual void endRenderPass() = 0;

    /**
     * Present a drawable and commit a command buffer so it can be executed as soon as possible.
     */
    virtual void endFrame() = 0;

    /**
     * Fixed-function state
     * @param lineWidth Specifies the width of rasterized lines.
     */
    virtual void setLineWidth(float lineWidth) = 0;

    /**
     * Fixed-function state
     * @param x, y Specifies the lower left corner of the scissor box
     * @param wdith Specifies the width of the scissor box
     * @param height Specifies the height of the scissor box
     */
    virtual void setScissorRect(bool isEnabled, float x, float y, float width, float height) = 0;

    /**
     * Get a screen snapshot
     * @param callback A callback to deal with screen snapshot image.
     */
    virtual void readPixels(RenderTarget* rt, std::function<void(const PixelBufferDescriptor&)> callback) = 0;

    /**
     * Update both front and back stencil reference value.
     * @param value Specifies stencil reference value.
     */
    void setStencilReferenceValue(unsigned int value);

    /**
     * Update stencil reference value.
     * @param frontRef Specifies front stencil reference value.
     * @param backRef Specifies back stencil reference value.
     */
    void setStencilReferenceValue(unsigned int frontRef, unsigned int backRef);

protected:
    virtual ~CommandBuffer() = default;

    unsigned int _stencilReferenceValueFront = 0;  ///< front stencil reference value.
    unsigned int _stencilReferenceValueBack  = 0;  ///< back stencil reference value.
};

// end of _backend group
/// @}
NS_AX_BACKEND_END