JUCE/modules/juce_opengl/opengl/juce_OpenGLGraphicsContext.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2020 - Raw Material Software Limited

   JUCE is an open source library subject to commercial or open-source
   licensing.

   By using JUCE, you agree to the terms of both the JUCE 5 End-User License
   Agreement and JUCE 5 Privacy Policy (both updated and effective as of the
   22nd April 2020).

   End User License Agreement: www.juce.com/juce-5-licence
   Privacy Policy: www.juce.com/juce-5-privacy-policy

   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

/** Creates a graphics context object that will render into the given OpenGL target.
    The caller is responsible for deleting this object when no longer needed.
*/
std::unique_ptr<LowLevelGraphicsContext> createOpenGLGraphicsContext (OpenGLContext&, int width, int height);

/** Creates a graphics context object that will render into the given OpenGL framebuffer.
    The caller is responsible for deleting this object when no longer needed.
*/
std::unique_ptr<LowLevelGraphicsContext> createOpenGLGraphicsContext (OpenGLContext&, OpenGLFrameBuffer&);

/** Creates a graphics context object that will render into the given OpenGL framebuffer,
    with the given size.
    The caller is responsible for deleting this object when no longer needed.
*/
std::unique_ptr<LowLevelGraphicsContext> createOpenGLGraphicsContext (OpenGLContext&,
                                                                      unsigned int frameBufferID,
                                                                      int width, int height);


//==============================================================================
/**
    Used to create custom shaders for use with an openGL 2D rendering context.

    Given a GL-based rendering context, you can write a fragment shader that applies some
    kind of per-pixel effect.

    @tags{OpenGL}
*/
struct JUCE_API  OpenGLGraphicsContextCustomShader
{
    /** Creates a custom shader.

        The shader code will not be compiled until actually needed, so it's OK to call this
        constructor when no GL context is active.

        The code should be a normal fragment shader. As well as the usual GLSL variables, there is
        also an automatically declared varying vec2 called "pixelPos", which indicates the pixel
        position within the graphics context of the pixel being drawn. There is also a varying value
        "pixelAlpha", which indicates the alpha by which the pixel should be multiplied, so that the
        edges of any clip-region masks are anti-aliased correctly.
    */
    OpenGLGraphicsContextCustomShader (const String& fragmentShaderCode);

    /** Destructor. */
    ~OpenGLGraphicsContextCustomShader();

    /** Returns the program, if it has been linked and is active.
        This can be called when you're about to use fillRect, to set up any uniforms/textures that
        the program may require.
    */
    OpenGLShaderProgram* getProgram (LowLevelGraphicsContext&) const;

    /** Applies the shader to a rectangle within the graphics context. */
    void fillRect (LowLevelGraphicsContext&, Rectangle<int> area) const;

    /** Attempts to compile the program if necessary, and returns an error message if it fails. */
    Result checkCompilation (LowLevelGraphicsContext&);

    /** Returns the code that was used to create this object. */
    const String& getFragmentShaderCode() const noexcept           { return code; }

    /** Optional lambda that will be called when the shader is activated, to allow
        user code to do setup tasks.
    */
    std::function<void(OpenGLShaderProgram&)> onShaderActivated;

private:
    String code, hashName;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (OpenGLGraphicsContextCustomShader)
};

} // namespace juce