JUCE/modules/juce_opengl/opengl/juce_OpenGLHelpers.cpp

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

   This file is part of the JUCE 7 technical preview.
   Copyright (c) 2022 - Raw Material Software Limited

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

   For the technical preview this file cannot be licensed commercially.

   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