PipelineState.h

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/* Copyright (C) 2022 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef INCLUDED_RENDERER_BACKEND_PIPELINESTATE
#define INCLUDED_RENDERER_BACKEND_PIPELINESTATE

#include "graphics/Color.h"
#include "renderer/backend/CompareOp.h"
#include "renderer/backend/IDeviceObject.h"
#include "renderer/backend/IShaderProgram.h"

class CStr;

namespace Renderer
{

namespace Backend
{

enum class StencilOp
{
    // Keeps the current value.
    KEEP,
    // Sets the value to zero.
    ZERO,
    // Sets the value to reference.
    REPLACE,
    // Increments the value and clamps to the maximum representable unsigned
    // value.
    INCREMENT_AND_CLAMP,
    // Decrements the value and clamps to zero.
    DECREMENT_AND_CLAMP,
    // Bitwise inverts the value.
    INVERT,
    // Increments the value and wraps it to zero when incrementing the maximum
    // representable unsigned value.
    INCREMENT_AND_WRAP,
    // Decrements the value and wraps it to the maximum representable unsigned
    // value when decrementing zero.
    DECREMENT_AND_WRAP
};

struct SStencilOpState
{
    StencilOp failOp;
    StencilOp passOp;
    StencilOp depthFailOp;
    CompareOp compareOp;
};

struct SDepthStencilStateDesc
{
    bool depthTestEnabled;
    CompareOp depthCompareOp;
    bool depthWriteEnabled;
    bool stencilTestEnabled;
    uint32_t stencilReadMask;
    uint32_t stencilWriteMask;
    uint32_t stencilReference;
    SStencilOpState stencilFrontFace;
    SStencilOpState stencilBackFace;
};

// TODO: add per constant description.

enum class BlendFactor
{
    ZERO,
    ONE,
    SRC_COLOR,
    ONE_MINUS_SRC_COLOR,
    DST_COLOR,
    ONE_MINUS_DST_COLOR,
    SRC_ALPHA,
    ONE_MINUS_SRC_ALPHA,
    DST_ALPHA,
    ONE_MINUS_DST_ALPHA,
    CONSTANT_COLOR,
    ONE_MINUS_CONSTANT_COLOR,
    CONSTANT_ALPHA,
    ONE_MINUS_CONSTANT_ALPHA,
    SRC_ALPHA_SATURATE,
    SRC1_COLOR,
    ONE_MINUS_SRC1_COLOR,
    SRC1_ALPHA,
    ONE_MINUS_SRC1_ALPHA,
};

enum class BlendOp
{
    ADD,
    SUBTRACT,
    REVERSE_SUBTRACT,
    MIN,
    MAX
};

// Using a namespace instead of a enum allows using the same syntax while
// avoiding adding operator overrides and additional checks on casts.
namespace ColorWriteMask
{
constexpr uint8_t RED = 0x01;
constexpr uint8_t GREEN = 0x02;
constexpr uint8_t BLUE = 0x04;
constexpr uint8_t ALPHA = 0x08;
} // namespace ColorWriteMask

struct SBlendStateDesc
{
    bool enabled;
    BlendFactor srcColorBlendFactor;
    BlendFactor dstColorBlendFactor;
    BlendOp colorBlendOp;
    BlendFactor srcAlphaBlendFactor;
    BlendFactor dstAlphaBlendFactor;
    BlendOp alphaBlendOp;
    CColor constant;
    uint8_t colorWriteMask;
};

enum class PolygonMode
{
    FILL,
    LINE
};

enum class CullMode
{
    NONE,
    FRONT,
    BACK
};

enum class FrontFace
{
    COUNTER_CLOCKWISE,
    CLOCKWISE
};

struct SRasterizationStateDesc
{
    PolygonMode polygonMode;
    CullMode cullMode;
    FrontFace frontFace;
    bool depthBiasEnabled;
    float depthBiasConstantFactor;
    float depthBiasSlopeFactor;
};

struct SGraphicsPipelineStateDesc
{
    // It's a backend client reponsibility to keep the shader program alive
    // while it's bound.
    IShaderProgram* shaderProgram;
    SDepthStencilStateDesc depthStencilState;
    SBlendStateDesc blendState;
    SRasterizationStateDesc rasterizationState;
};

// We don't provide additional helpers intentionally because all custom states
// should be described with a related shader and should be switched together.
SGraphicsPipelineStateDesc MakeDefaultGraphicsPipelineStateDesc();

StencilOp ParseStencilOp(const CStr& str);

BlendFactor ParseBlendFactor(const CStr& str);
BlendOp ParseBlendOp(const CStr& str);

PolygonMode ParsePolygonMode(const CStr& str);
CullMode ParseCullMode(const CStr& str);
FrontFace ParseFrontFace(const CStr& str);

/**
 * A holder for precompiled graphics pipeline description.
 */
class IGraphicsPipelineState : public IDeviceObject<IGraphicsPipelineState>
{
public:
    virtual IShaderProgram* GetShaderProgram() const = 0;
};

} // namespace Backend

} // namespace Renderer

#endif // INCLUDED_RENDERER_BACKEND_PIPELINESTATE