JUCE/modules/juce_opengl/opengl/juce_OpenGLHelpers.cpp

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

   This file is part of the JUCE library.
   Copyright (c) 2022 - 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 7 End-User License
   Agreement and JUCE Privacy Policy.

   End User License Agreement: www.juce.com/juce-7-licence
   Privacy Policy: www.juce.com/juce-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
{

class Version
{
public:
    constexpr Version() = default;

    constexpr explicit Version (int majorIn)
        : Version (majorIn, 0) {}

    constexpr Version (int majorIn, int minorIn)
        : major (majorIn), minor (minorIn) {}

    int major = 0, minor = 0;

    constexpr bool operator== (const Version& other) const noexcept
    {
        return toTuple() == other.toTuple();
    }

    constexpr bool operator!= (const Version& other) const noexcept
    {
        return toTuple() != other.toTuple();
    }

    constexpr bool operator< (const Version& other) const noexcept
    {
        return toTuple() < other.toTuple();
    }

    constexpr bool operator<= (const Version& other) const noexcept
    {
        return toTuple() <= other.toTuple();
    }

    constexpr bool operator> (const Version& other) const noexcept
    {
        return toTuple() > other.toTuple();
    }

    constexpr bool operator>= (const Version& other) const noexcept
    {
        return toTuple() >= other.toTuple();
    }

private:
    constexpr std::tuple<int, int> toTuple() const noexcept
    {
        return std::make_tuple (major, minor);
    }
};


template <typename Char>
static auto* findNullTerminator (const Char* ptr)
{
    while (*ptr != 0)
        ++ptr;

    return ptr;
}

static Version getOpenGLVersion()
{
    const auto* versionBegin = glGetString (GL_VERSION);

    if (versionBegin == nullptr)
        return {};

    const auto* versionEnd = findNullTerminator (versionBegin);
    const std::string versionString (versionBegin, versionEnd);
    const auto spaceSeparated = StringArray::fromTokens (versionString.c_str(), false);

    for (const auto& token : spaceSeparated)
    {
        const auto pointSeparated = StringArray::fromTokens (token, ".", "");

        const auto major = pointSeparated[0].getIntValue();
        const auto minor = pointSeparated[1].getIntValue();

        if (major != 0)
            return { major, minor };
    }

    return {};
}

void OpenGLHelpers::resetErrorState()
{
    while (glGetError() != GL_NO_ERROR) {}
}

void* OpenGLHelpers::getExtensionFunction (const char* functionName)
{
   #if JUCE_WINDOWS
    return (void*) wglGetProcAddress (functionName);
   #elif JUCE_LINUX || JUCE_BSD
    return (void*) glXGetProcAddress ((const GLubyte*) functionName);
   #else
    static void* handle = dlopen (nullptr, RTLD_LAZY);
    return dlsym (handle, functionName);
   #endif
}

bool OpenGLHelpers::isExtensionSupported (const char* const extensionName)
{
    jassert (extensionName != nullptr); // you must supply a genuine string for this.
    jassert (isContextActive()); // An OpenGL context will need to be active before calling this.

    if (getOpenGLVersion().major >= 3)
    {
        using GetStringi = const GLubyte* (*) (GLenum, GLuint);

        if (auto* thisGlGetStringi = reinterpret_cast<GetStringi> (getExtensionFunction ("glGetStringi")))
        {
            GLint n = 0;
            glGetIntegerv (GL_NUM_EXTENSIONS, &n);

            for (auto i = (decltype (n)) 0; i < n; ++i)
                if (StringRef (extensionName) == StringRef ((const char*) thisGlGetStringi (GL_EXTENSIONS, (GLuint) i)))
                    return true;

            return false;
        }
    }

    const char* extensions = (const char*) glGetString (GL_EXTENSIONS);
    jassert (extensions != nullptr); // Perhaps you didn't activate an OpenGL context before calling this?

    for (;;)
    {
        const char* found = strstr (extensions, extensionName);

        if (found == nullptr)
            break;

        extensions = found + strlen (extensionName);

        if (extensions[0] == ' ' || extensions[0] == 0)
            return true;
    }

    return false;
}

void OpenGLHelpers::clear (Colour colour)
{
    glClearColor (colour.getFloatRed(), colour.getFloatGreen(),
                  colour.getFloatBlue(), colour.getFloatAlpha());

    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
}

void OpenGLHelpers::enableScissorTest (Rectangle<int> clip)
{
    glEnable (GL_SCISSOR_TEST);
    glScissor (clip.getX(), clip.getY(), clip.getWidth(), clip.getHeight());
}

String OpenGLHelpers::getGLSLVersionString()
{
    if (getOpenGLVersion() >= Version (3, 2))
    {
       #if JUCE_OPENGL_ES
        return "#version 300 es";
       #else
        return "#version 150";
       #endif
    }

    return "#version 110";
}

String OpenGLHelpers::translateVertexShaderToV3 (const String& code)
{
    if (getOpenGLVersion() >= Version (3, 2))
    {
        String output;

       #if JUCE_ANDROID
        {
            int numAttributes = 0;

            for (int p = code.indexOf (0, "attribute "); p >= 0; p = code.indexOf (p + 1, "attribute "))
                numAttributes++;

            int last = 0;

            for (int p = code.indexOf (0, "attribute "); p >= 0; p = code.indexOf (p + 1, "attribute "))
            {
                output += code.substring (last, p) + "layout(location=" + String (--numAttributes) + ") in ";

                last = p + 10;
            }

            output += code.substring (last);
        }
       #else
        output = code.replace ("attribute", "in");
       #endif

        return getGLSLVersionString() + "\n" + output.replace ("varying", "out");
    }

    return code;
}

String OpenGLHelpers::translateFragmentShaderToV3 (const String& code)
{
    if (getOpenGLVersion() >= Version (3, 2))
        return getGLSLVersionString() + "\n"
               "out " JUCE_MEDIUMP " vec4 fragColor;\n"
                + code.replace ("varying", "in")
                      .replace ("texture2D", "texture")
                      .replace ("gl_FragColor", "fragColor");

    return code;
}

} // namespace juce