magnum/src/Magnum/Platform/WindowlessGlxApplication.cpp

/*
    This file is part of Magnum.

    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019,
                2020, 2021, 2022, 2023 Vladimír Vondruš <mosra@centrum.cz>
    Copyright © 2021 Konstantinos Chatzilygeroudis <costashatz@gmail.com>

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.
*/

#include "WindowlessGlxApplication.h"

#include <Corrade/Containers/StringView.h>
#include <Corrade/Utility/Assert.h>
#include <Corrade/Utility/Debug.h>

#include "Magnum/GL/Version.h"

#ifndef GLX_ARB_create_context_no_error
#define GLX_CONTEXT_OPENGL_NO_ERROR_ARB 0x31B3
#endif

/* Saner way to define the insane Xlib macros (anyway, FUCK YOU XLIB) */
namespace { enum { None = 0, Success = 0 }; }

namespace Magnum { namespace Platform {

using namespace Containers::Literals;

namespace {

/*
    Mandatory reading -- I hate Xlib and so should you,
        https://www.remlab.net/op/xlib.shtml

    By default, Xlib just hard exits on an error, which is not what we want
    when we need fallback context creation when core context creation fails. To
    override that, we need to set up an error handler, but of course the
    callback doesn't give us any user pointer, so we need to use a global to
    save the state passed to it. Essential code to handle this taken from GLFW:
    https://github.com/glfw/glfw/blob/e65de2941c056ee5833b4dab3db36b297b53aa14/src/x11_init.c#L889-L920
*/
Int xlibErrorCode;
Display* xlibDisplay;
struct XlibErrorHandler {
    explicit XlibErrorHandler(Display* const display) {
        xlibErrorCode = Success;
        xlibDisplay = display;
        XSetErrorHandler([](Display* const display, XErrorEvent* const event) {
            if(xlibDisplay != display) /* Why this? */
                return 0;

            xlibErrorCode = event->error_code;
            return 0;
        });
    }

    ~XlibErrorHandler() {
        /* Synchronize to make sure all commands are processed */
        XSync(xlibDisplay, False);
        XSetErrorHandler(nullptr);
    }
};

}

WindowlessGlxContext::WindowlessGlxContext(const WindowlessGlxContext::Configuration& configuration, GLContext* const magnumContext) {
    _display = XOpenDisplay(nullptr);

    /* Check version */
    int major, minor;
    glXQueryVersion(_display, &major, &minor);
    if(major == 1 && minor < 4) {
        Error() << "Platform::WindowlessGlxContext: GLX version 1.4 or greater is required";
        return;
    }

    /* Choose config */
    int configCount = 0;
    constexpr static const int fbAttributes[] = { None };
    GLXFBConfig* configs = glXChooseFBConfig(_display, DefaultScreen(_display), fbAttributes, &configCount);
    if(!configCount) {
        Error() << "Platform::WindowlessGlxContext: no supported framebuffer configuration found";
        return;
    }

    /* Create pbuffer */
    constexpr static const int pbufferAttributes[] = {
        GLX_PBUFFER_WIDTH,  32,
        GLX_PBUFFER_HEIGHT, 32,
        None
    };
    _pbuffer = glXCreatePbuffer(_display, configs[0], pbufferAttributes);

    /* Get pointer to proper context creation function */
    const PFNGLXCREATECONTEXTATTRIBSARBPROC glXCreateContextAttribsARB = reinterpret_cast<PFNGLXCREATECONTEXTATTRIBSARBPROC>(glXGetProcAddress(reinterpret_cast<const GLubyte*>("glXCreateContextAttribsARB")));

    /* Request debug context if GpuValidation is enabled either via the
       configuration or via command-line */
    Configuration::Flags flags = configuration.flags();
    if((flags & Configuration::Flag::GpuValidation) || (magnumContext && magnumContext->configurationFlags() & GL::Context::Configuration::Flag::GpuValidation))
        flags |= Configuration::Flag::Debug;
    else if((flags & Configuration::Flag::GpuValidationNoError) || (magnumContext && magnumContext->configurationFlags() & GL::Context::Configuration::Flag::GpuValidationNoError))
        flags |= Configuration::Flag::NoError;

    /** @todo needs a growable DynamicArray with disabled alloc or somesuch */
    /* Optimistically choose core context first */
    GLint contextAttributes[11] = {
        #ifdef MAGNUM_TARGET_GLES
        #ifdef MAGNUM_TARGET_GLES2
        GLX_CONTEXT_MAJOR_VERSION_ARB, 2,
        #else
        GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
        #endif
        GLX_CONTEXT_MINOR_VERSION_ARB, 0,
        GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_ES2_PROFILE_BIT_EXT,
        /* Mask out the upper 32bits used for other flags */
        GLX_CONTEXT_FLAGS_ARB, GLint(UnsignedLong(flags) & 0xffffffffu),
        #else
        GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
        GLX_CONTEXT_MINOR_VERSION_ARB, 1,
        GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
        /* Mask out the upper 32bits used for other flags */
        GLX_CONTEXT_FLAGS_ARB, GLint(UnsignedLong(flags) & 0xffffffffu),
        #endif

        /* The rest is added optionally */
        0, 0, /* GLX_CONTEXT_OPENGL_NO_ERROR_ARB */
        0
    };

    std::size_t nextAttribute = 8;
    CORRADE_INTERNAL_ASSERT(!contextAttributes[nextAttribute]);

    if(flags & Configuration::Flag::NoError) {
        contextAttributes[nextAttribute++] = GLX_CONTEXT_OPENGL_NO_ERROR_ARB;
        contextAttributes[nextAttribute++] = true;
    }

    CORRADE_INTERNAL_ASSERT(nextAttribute < Containers::arraySize(contextAttributes));

    {
        XlibErrorHandler eh{_display};
        _context = glXCreateContextAttribsARB(_display, configs[0], configuration.sharedContext(), True, contextAttributes);
    }

    #ifndef MAGNUM_TARGET_GLES
    /* Fall back to (forward compatible) GL 2.1 if core context creation fails */
    if(!_context) {
        Warning w;
        w << "Platform::WindowlessGlxContext: cannot create core context, falling back to compatibility context";
        if(xlibErrorCode != Success) {
            char buffer[256];
            XGetErrorText(_display, xlibErrorCode, buffer, sizeof(buffer));
            w << Debug::nospace << ":" << buffer;
        }

        /** @todo duplicated three times, do better */
        GLint fallbackContextAttributes[5] = {
            /* Discard the ForwardCompatible flag for the fallback. Having it
               set makes the fallback context creation fail on Mesa's Zink
               (which is just 2.1) and I assume on others as well.

               Also mask out the upper 32bits used for other flags. */
            GLX_CONTEXT_FLAGS_ARB, GLint(UnsignedLong(flags & ~Configuration::Flag::ForwardCompatible) & 0xffffffffu),

            /* The rest is added dynamically */
            0, 0, /* GLX_CONTEXT_OPENGL_NO_ERROR_ARB */
            0
        };
        std::size_t nextFallbackAttribute = 2;
        CORRADE_INTERNAL_ASSERT(!fallbackContextAttributes[nextFallbackAttribute]);

        if(flags & Configuration::Flag::NoError) {
            fallbackContextAttributes[nextFallbackAttribute++] = GLX_CONTEXT_OPENGL_NO_ERROR_ARB;
            fallbackContextAttributes[nextFallbackAttribute++] = true;
        }

        CORRADE_INTERNAL_ASSERT(nextFallbackAttribute < Containers::arraySize(fallbackContextAttributes));

        {
            XlibErrorHandler eh{_display};
            _context = glXCreateContextAttribsARB(_display, configs[0], configuration.sharedContext(), True, fallbackContextAttributes);
        }

    /* Fall back to (forward compatible) GL 2.1 if we are on binary NVidia/AMD
       drivers on Linux. Instead of creating forward-compatible context with
       highest available version, they force the version to the one specified,
       which is completely useless behavior. */
    } else {
        /* We need to make the context current to read out vendor string, so
           save the previous values so we can safely revert back without
           messing up the state */
        GLXDrawable currentDrawable = glXGetCurrentDrawable();
        GLXDrawable currentReadDrawable = glXGetCurrentReadDrawable();
        GLXContext currentContext = glXGetCurrentContext();
        if(!glXMakeContextCurrent(_display, _pbuffer, _pbuffer, _context)) {
            Error() << "Platform::WindowlessGlxContext: cannot make context current";
            return;
        }

        /* The workaround check is the last so it doesn't appear in workaround
           list on unrelated drivers */
        const Containers::StringView vendorString = reinterpret_cast<const char*>(glGetString(GL_VENDOR));
        if((vendorString == "NVIDIA Corporation"_s ||
            vendorString == "ATI Technologies Inc."_s)
           && (!magnumContext || !magnumContext->isDriverWorkaroundDisabled("no-forward-compatible-core-context"_s)))
        {
            /* Destroy the core context and create a compatibility one */
            glXDestroyContext(_display, _context);

            /** @todo duplicated three times, do better */
            GLint fallbackContextAttributes[5] = {
                /* Discard the ForwardCompatible flag for the fallback.
                   Compared to the above case of a 2.1 fallback it's not really
                   needed here (AFAIK it works in both cases), but let's be
                   consistent.

                   Also mask out the upper 32bits used for other flags. */
                GLX_CONTEXT_FLAGS_ARB, GLint(UnsignedLong(flags & ~Configuration::Flag::ForwardCompatible) & 0xffffffffu),

                /* The rest is added dynamically */
                0, 0, /* GLX_CONTEXT_OPENGL_NO_ERROR_ARB */
                0
            };
            std::size_t nextFallbackAttribute = 2;
            CORRADE_INTERNAL_ASSERT(!fallbackContextAttributes[nextFallbackAttribute]);

            if(flags & Configuration::Flag::NoError) {
                fallbackContextAttributes[nextFallbackAttribute++] = GLX_CONTEXT_OPENGL_NO_ERROR_ARB;
                fallbackContextAttributes[nextFallbackAttribute++] = true;
            }

            CORRADE_INTERNAL_ASSERT(nextFallbackAttribute < Containers::arraySize(fallbackContextAttributes));

            {
                XlibErrorHandler eh{_display};
                _context = glXCreateContextAttribsARB(_display, configs[0], configuration.sharedContext(), True, fallbackContextAttributes);
            }
        }

        /* Revert back the old context */
        if(!glXMakeContextCurrent(_display, currentDrawable, currentReadDrawable, currentContext)) {
            Error() << "Platform::WindowlessGlxContext: cannot make the previous context current";
            return;
        }
    }
    #else
    static_cast<void>(magnumContext);
    #endif

    XFree(configs);

    if(!_context) {
        Error e;
        e << "Platform::WindowlessGlxContext: cannot create context";
        if(xlibErrorCode != Success) {
            char buffer[256];
            XGetErrorText(_display, xlibErrorCode, buffer, sizeof(buffer));
            e << Debug::nospace << ":" << buffer;
        }
    }
}

WindowlessGlxContext::WindowlessGlxContext(WindowlessGlxContext&& other) noexcept: _display{other._display}, _pbuffer{other._pbuffer}, _context{other._context} {
    other._display = {};
    other._context = {};
    other._pbuffer = {};
}

WindowlessGlxContext::~WindowlessGlxContext() {
    if(_context) glXDestroyContext(_display, _context);
    if(_pbuffer) glXDestroyPbuffer(_display, _pbuffer);
    if(_display) XCloseDisplay(_display);
}

WindowlessGlxContext& WindowlessGlxContext::operator=(WindowlessGlxContext&& other) noexcept {
    using Utility::swap;
    swap(other._display, _display);
    swap(other._pbuffer, _pbuffer);
    swap(other._context, _context);
    return *this;
}

bool WindowlessGlxContext::makeCurrent() {
    if(glXMakeContextCurrent(_display, _pbuffer, _pbuffer, _context))
        return true;

    Error() << "Platform::WindowlessGlxContext::makeCurrent(): cannot make context current";
    return false;
}

bool WindowlessGlxContext::release() {
    if(glXMakeContextCurrent(_display, 0, 0, nullptr))
        return true;

    Error() << "Platform::WindowlessGlxContext::release(): cannot release current context";
    return false;
}

WindowlessGlxContext::Configuration::Configuration() {
    GL::Context::Configuration::addFlags(GL::Context::Configuration::Flag::Windowless);
    #ifndef MAGNUM_TARGET_GLES
    addFlags(Flag::ForwardCompatible);
    #endif
}

WindowlessGlxApplication::WindowlessGlxApplication(const Arguments& arguments, const Configuration& configuration): WindowlessGlxApplication{arguments, NoCreate} {
    createContext(configuration);
}

WindowlessGlxApplication::WindowlessGlxApplication(const Arguments& arguments, NoCreateT): _glContext{NoCreate}, _context{NoCreate, arguments.argc, arguments.argv} {}

void WindowlessGlxApplication::createContext() { createContext({}); }

void WindowlessGlxApplication::createContext(const Configuration& configuration) {
    if(!tryCreateContext(configuration)) std::exit(1);
}

bool WindowlessGlxApplication::tryCreateContext(const Configuration& configuration) {
    CORRADE_ASSERT(_context.version() == GL::Version::None, "Platform::WindowlessGlxApplication::tryCreateContext(): context already created", false);

    WindowlessGlxContext glContext{configuration, &_context};
    if(!glContext.isCreated() || !glContext.makeCurrent() || !_context.tryCreate(configuration))
        return false;

    _glContext = Utility::move(glContext);
    return true;
}

WindowlessGlxApplication::~WindowlessGlxApplication() = default;

}}