//
// Copyright 2020 Pixar
//
// Licensed under the Apache License, Version 2.0 (the "Apache License")
// with the following modification; you may not use this file except in
// compliance with the Apache License and the following modification to it:
// Section 6. Trademarks. is deleted and replaced with:
//
// 6. Trademarks. This License does not grant permission to use the trade
//    names, trademarks, service marks, or product names of the Licensor
//    and its affiliates, except as required to comply with Section 4(c) of
//    the License and to reproduce the content of the NOTICE file.
//
// You may obtain a copy of the Apache License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Apache License with the above modification is
// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the Apache License for the specific
// language governing permissions and limitations under the Apache License.
//
#ifndef PXR_IMAGING_HGI_SHADERFUNCTION_H
#define PXR_IMAGING_HGI_SHADERFUNCTION_H

#include "pxr/pxr.h"
#include "pxr/imaging/hgi/api.h"
#include "pxr/imaging/hgi/enums.h"
#include "pxr/imaging/hgi/handle.h"
#include "pxr/imaging/hgi/types.h"

#include <string>
#include <vector>


PXR_NAMESPACE_OPEN_SCOPE


/// \struct HgiShaderFunctionDesc
///
/// Describes the properties needed to create a GPU shader function.
///
/// <ul>
/// <li>debugName:
///   This label can be applied as debug label for gpu debugging.</li>
/// <li>shaderStage:
///   The shader stage this function represents.</li>
/// <li>shaderCode:
///   The ascii shader code used to compile the shader.</li>
/// </ul>
///
struct HgiShaderFunctionDesc
{
    HGI_API
    HgiShaderFunctionDesc();

    std::string debugName;
    HgiShaderStage shaderStage;
    const char* shaderCode;
};

HGI_API
inline bool operator==(
    const HgiShaderFunctionDesc& lhs,
    const HgiShaderFunctionDesc& rhs);

HGI_API
inline bool operator!=(
    const HgiShaderFunctionDesc& lhs,
    const HgiShaderFunctionDesc& rhs);


///
/// \class HgiShaderFunction
///
/// Represents one shader stage function (code snippet).
///
/// ShaderFunctions are usually passed to a ShaderProgram, however be careful 
/// not to destroy the ShaderFunction after giving it to the program.
/// While this may be safe for OpenGL after the program is created, it does not 
/// apply to other graphics backends, such as Vulkan, where the shader functions
/// are used during rendering.
///
class HgiShaderFunction
{
public:
    HGI_API
    virtual ~HgiShaderFunction();

    /// The descriptor describes the object.
    HGI_API
    HgiShaderFunctionDesc const& GetDescriptor() const;

    /// Returns false if any shader compile errors occured.
    HGI_API
    virtual bool IsValid() const = 0;

    /// Returns shader compile errors.
    HGI_API
    virtual std::string const& GetCompileErrors() = 0;

    /// Returns the byte size of the GPU shader function.
    /// This can be helpful if the application wishes to tally up memory usage.
    HGI_API
    virtual size_t GetByteSizeOfResource() const = 0;

    /// This function returns the handle to the Hgi backend's gpu resource, cast
    /// to a uint64_t. Clients should avoid using this function and instead
    /// use Hgi base classes so that client code works with any Hgi platform.
    /// For transitioning code to Hgi, it can however we useful to directly
    /// access a platform's internal resource handles.
    /// There is no safety provided in using this. If you by accident pass a
    /// HgiMetal resource into an OpenGL call, bad things may happen.
    /// In OpenGL this returns the GLuint resource name.
    /// In Metal this returns the id<MTLFunction> as uint64_t.
    /// In Vulkan this returns the VkShaderModule as uint64_t.
    /// In DX12 this returns the ID3D12Resource pointer as uint64_t.
    HGI_API
    virtual uint64_t GetRawResource() const = 0;

protected:
    HGI_API
    HgiShaderFunction(HgiShaderFunctionDesc const& desc);

    HgiShaderFunctionDesc _descriptor;

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

/// Explicitly instantiate and define ShaderFunction handle
template class HgiHandle<class HgiShaderFunction>;
using HgiShaderFunctionHandle = HgiHandle<class HgiShaderFunction>;
using HgiShaderFunctionHandleVector = std::vector<HgiShaderFunctionHandle>;


PXR_NAMESPACE_CLOSE_SCOPE

#endif