qopenglfunctions.cpp

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// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qopenglfunctions.h"
#include "qopenglextrafunctions.h"
#include "qopenglextensions_p.h"
#include "qdebug.h"
#include <QtGui/private/qopenglcontext_p.h>
#include <QtGui/private/qopengl_p.h>
#include <QtGui/private/qguiapplication_p.h>
#include <qpa/qplatformintegration.h>
#include <qpa/qplatformnativeinterface.h>
 
#ifdef Q_OS_INTEGRITY
#include <EGL/egl.h>
#endif
 
#ifndef GL_FRAMEBUFFER_SRGB_CAPABLE_EXT
#define GL_FRAMEBUFFER_SRGB_CAPABLE_EXT   0x8DBA
#endif
 
QT_BEGIN_NAMESPACE
 
using namespace Qt::StringLiterals;
 
#define QT_OPENGL_COUNT_FUNCTIONS(ret, name, args) +1
#define QT_OPENGL_FUNCTION_NAMES(ret, name, args) \
    "gl"#name"\0"
#define QT_OPENGL_FLAGS(ret, name, args) \
    0,
#define QT_OPENGL_IMPLEMENT(CLASS, FUNCTIONS) \
void CLASS::init(QOpenGLContext *context) \
{ \
    const char *names = FUNCTIONS(QT_OPENGL_FUNCTION_NAMES); \
    const char *name = names; \
    for (int i = 0; i < FUNCTIONS(QT_OPENGL_COUNT_FUNCTIONS); ++i) { \
        functions[i] = QT_PREPEND_NAMESPACE(getProcAddress(context, name)); \
        name += strlen(name) + 1; \
    } \
}
 
// Hidden private fields for additional extension data.
struct QOpenGLFunctionsPrivateEx : public QOpenGLExtensionsPrivate, public QOpenGLSharedResource
{
    QOpenGLFunctionsPrivateEx(QOpenGLContext *context)
        : QOpenGLExtensionsPrivate(context)
        , QOpenGLSharedResource(context->shareGroup())
        , m_features(-1)
        , m_extensions(-1)
    {}
 
    void invalidateResource() override
    {
        m_features = -1;
        m_extensions = -1;
    }
 
    void freeResource(QOpenGLContext *) override
    {
        // no gl resources to free
    }
 
    int m_features;
    int m_extensions;
};
 
Q_GLOBAL_STATIC(QOpenGLMultiGroupSharedResource, qt_gl_functions_resource)
 
static QOpenGLFunctionsPrivateEx *qt_gl_functions(QOpenGLContext *context = nullptr)
{
    if (!context)
        context = QOpenGLContext::currentContext();
    Q_ASSERT(context);
    QOpenGLFunctionsPrivateEx *funcs =
        qt_gl_functions_resource()->value<QOpenGLFunctionsPrivateEx>(context);
    return funcs;
}
 
QOpenGLFunctions::QOpenGLFunctions()
    : d_ptr(nullptr)
{
}
 
QOpenGLFunctions::QOpenGLFunctions(QOpenGLContext *context)
    : d_ptr(nullptr)
{
    if (context && QOpenGLContextGroup::currentContextGroup() == context->shareGroup())
        d_ptr = qt_gl_functions(context);
    else
        qWarning("QOpenGLFunctions created with non-current context");
}
 
QOpenGLExtensions::QOpenGLExtensions()
{
}
 
QOpenGLExtensions::QOpenGLExtensions(QOpenGLContext *context)
    : QOpenGLExtraFunctions(context)
{
}
 
static int qt_gl_resolve_features()
{
    QOpenGLContext *ctx = QOpenGLContext::currentContext();
    QOpenGLExtensionMatcher extensions;
    int features = 0;
    if ((extensions.match("GL_KHR_blend_equation_advanced")
        || extensions.match("GL_NV_blend_equation_advanced")) &&
        (extensions.match("GL_KHR_blend_equation_advanced_coherent")
        || extensions.match("GL_NV_blend_equation_advanced_coherent"))) {
        // We need both the advanced equations and the coherency for us
        // to be able to easily use the new blend equations
        features |= QOpenGLFunctions::BlendEquationAdvanced;
    }
    if (ctx->isOpenGLES()) {
        // OpenGL ES
        features |= QOpenGLFunctions::Multitexture |
            QOpenGLFunctions::Shaders |
            QOpenGLFunctions::Buffers |
            QOpenGLFunctions::Framebuffers |
            QOpenGLFunctions::BlendColor |
            QOpenGLFunctions::BlendEquation |
            QOpenGLFunctions::BlendEquationSeparate |
            QOpenGLFunctions::BlendFuncSeparate |
            QOpenGLFunctions::BlendSubtract |
            QOpenGLFunctions::CompressedTextures |
            QOpenGLFunctions::Multisample |
            QOpenGLFunctions::StencilSeparate;
        if (extensions.match("GL_IMG_texture_npot"))
            features |= QOpenGLFunctions::NPOTTextures;
        if (extensions.match("GL_OES_texture_npot"))
            features |= QOpenGLFunctions::NPOTTextures |
                QOpenGLFunctions::NPOTTextureRepeat;
        if (ctx->format().majorVersion() >= 3 || extensions.match("GL_EXT_texture_rg")) {
            // Mesa's GLES implementation (as of 10.6.0) is unable to handle this, even though it provides 3.0.
            const char *renderer = reinterpret_cast<const char *>(ctx->functions()->glGetString(GL_RENDERER));
            if (!(renderer && strstr(renderer, "Mesa")))
                features |= QOpenGLFunctions::TextureRGFormats;
        }
        if (ctx->format().majorVersion() >= 3) {
            features |= QOpenGLFunctions::MultipleRenderTargets;
            if (ctx->format().minorVersion() >= 2 && extensions.match("GL_KHR_blend_equation_advanced_coherent")) {
                // GL_KHR_blend_equation_advanced is included in OpenGL ES/3.2
                features |= QOpenGLFunctions::BlendEquationAdvanced;
            }
        }
        return features;
    } else {
        // OpenGL
        features |= QOpenGLFunctions::TextureRGFormats;
        QSurfaceFormat format = QOpenGLContext::currentContext()->format();
 
        if (format.majorVersion() >= 3)
            features |= QOpenGLFunctions::Framebuffers | QOpenGLFunctions::MultipleRenderTargets;
        else if (extensions.match("GL_EXT_framebuffer_object") || extensions.match("GL_ARB_framebuffer_object"))
            features |= QOpenGLFunctions::Framebuffers | QOpenGLFunctions::MultipleRenderTargets;
 
        if (format.majorVersion() >= 2) {
            features |= QOpenGLFunctions::BlendColor |
                QOpenGLFunctions::BlendEquation |
                QOpenGLFunctions::BlendSubtract |
                QOpenGLFunctions::Multitexture |
                QOpenGLFunctions::CompressedTextures |
                QOpenGLFunctions::Multisample |
                QOpenGLFunctions::BlendFuncSeparate |
                QOpenGLFunctions::Buffers |
                QOpenGLFunctions::Shaders |
                QOpenGLFunctions::StencilSeparate |
                QOpenGLFunctions::BlendEquationSeparate |
                QOpenGLFunctions::NPOTTextures |
                QOpenGLFunctions::NPOTTextureRepeat;
        } else {
            // Recognize features by extension name.
            if (extensions.match("GL_ARB_multitexture"))
                features |= QOpenGLFunctions::Multitexture;
            if (extensions.match("GL_ARB_shader_objects"))
                features |= QOpenGLFunctions::Shaders;
            if (extensions.match("GL_EXT_blend_color"))
                features |= QOpenGLFunctions::BlendColor;
            if (extensions.match("GL_EXT_blend_equation_separate"))
                features |= QOpenGLFunctions::BlendEquationSeparate;
            if (extensions.match("GL_EXT_blend_subtract"))
                features |= QOpenGLFunctions::BlendSubtract;
            if (extensions.match("GL_EXT_blend_func_separate"))
                features |= QOpenGLFunctions::BlendFuncSeparate;
            if (extensions.match("GL_ARB_texture_compression"))
                features |= QOpenGLFunctions::CompressedTextures;
            if (extensions.match("GL_ARB_multisample"))
                features |= QOpenGLFunctions::Multisample;
            if (extensions.match("GL_ARB_texture_non_power_of_two"))
                features |= QOpenGLFunctions::NPOTTextures |
                    QOpenGLFunctions::NPOTTextureRepeat;
        }
 
        const QPair<int, int> version = format.version();
        if (version < qMakePair(3, 0)
            || (version == qMakePair(3, 0) && format.testOption(QSurfaceFormat::DeprecatedFunctions))
            || (version == qMakePair(3, 1) && extensions.match("GL_ARB_compatibility"))
            || (version >= qMakePair(3, 2) && format.profile() == QSurfaceFormat::CompatibilityProfile)) {
            features |= QOpenGLFunctions::FixedFunctionPipeline;
        }
        return features;
    }
}
 
static int qt_gl_resolve_extensions()
{
    int extensions = 0;
    QOpenGLExtensionMatcher extensionMatcher;
    QOpenGLContext *ctx = QOpenGLContext::currentContext();
    QSurfaceFormat format = ctx->format();
 
    if (extensionMatcher.match("GL_EXT_bgra"))
        extensions |= QOpenGLExtensions::BGRATextureFormat;
    if (extensionMatcher.match("GL_ARB_texture_rectangle"))
        extensions |= QOpenGLExtensions::TextureRectangle;
    if (extensionMatcher.match("GL_ARB_texture_compression"))
        extensions |= QOpenGLExtensions::TextureCompression;
    if (extensionMatcher.match("GL_EXT_texture_compression_s3tc"))
        extensions |= QOpenGLExtensions::DDSTextureCompression;
    if (extensionMatcher.match("GL_OES_compressed_ETC1_RGB8_texture"))
        extensions |= QOpenGLExtensions::ETC1TextureCompression;
    if (extensionMatcher.match("GL_IMG_texture_compression_pvrtc"))
        extensions |= QOpenGLExtensions::PVRTCTextureCompression;
    if (extensionMatcher.match("GL_KHR_texture_compression_astc_ldr"))
        extensions |= QOpenGLExtensions::ASTCTextureCompression;
    if (extensionMatcher.match("GL_ARB_texture_mirrored_repeat"))
        extensions |= QOpenGLExtensions::MirroredRepeat;
    if (extensionMatcher.match("GL_EXT_stencil_two_side"))
        extensions |= QOpenGLExtensions::StencilTwoSide;
    if (extensionMatcher.match("GL_EXT_stencil_wrap"))
        extensions |= QOpenGLExtensions::StencilWrap;
    if (extensionMatcher.match("GL_NV_float_buffer"))
        extensions |= QOpenGLExtensions::NVFloatBuffer;
    if (extensionMatcher.match("GL_ARB_pixel_buffer_object"))
        extensions |= QOpenGLExtensions::PixelBufferObject;
    if (extensionMatcher.match("GL_ARB_texture_swizzle") || extensionMatcher.match("GL_EXT_texture_swizzle"))
        extensions |= QOpenGLExtensions::TextureSwizzle;
    if (extensionMatcher.match("GL_OES_standard_derivatives"))
        extensions |= QOpenGLExtensions::StandardDerivatives;
    if (extensionMatcher.match("GL_ARB_half_float_vertex"))
        extensions |= QOpenGLExtensions::HalfFloatVertex;
    if (extensionMatcher.match("GL_OVR_multiview"))
        extensions |= QOpenGLExtensions::MultiView;
    if (extensionMatcher.match("GL_OVR_multiview2"))
        extensions |= QOpenGLExtensions::MultiViewExtended;
 
    if (ctx->isOpenGLES()) {
        if (format.majorVersion() >= 2)
            extensions |= QOpenGLExtensions::GenerateMipmap;
 
        if (format.majorVersion() >= 3) {
            extensions |= QOpenGLExtensions::PackedDepthStencil
                | QOpenGLExtensions::Depth24
                | QOpenGLExtensions::ElementIndexUint
                | QOpenGLExtensions::MapBufferRange
                | QOpenGLExtensions::FramebufferBlit
                | QOpenGLExtensions::FramebufferMultisample
                | QOpenGLExtensions::Sized8Formats
                | QOpenGLExtensions::StandardDerivatives
                | QOpenGLExtensions::ETC2TextureCompression
                | QOpenGLExtensions::HalfFloatVertex;
#ifndef Q_OS_WASM
            // WebGL 2.0 specification explicitly does not support texture swizzles
            // https://www.khronos.org/registry/webgl/specs/latest/2.0/#5.19
            extensions |= QOpenGLExtensions::TextureSwizzle;
#endif
        } else {
            // Recognize features by extension name.
            if (extensionMatcher.match("GL_OES_packed_depth_stencil"))
                extensions |= QOpenGLExtensions::PackedDepthStencil;
            if (extensionMatcher.match("GL_OES_depth24"))
                extensions |= QOpenGLExtensions::Depth24;
            if (extensionMatcher.match("GL_ANGLE_framebuffer_blit"))
                extensions |= QOpenGLExtensions::FramebufferBlit;
            if (extensionMatcher.match("GL_ANGLE_framebuffer_multisample"))
                extensions |= QOpenGLExtensions::FramebufferMultisample;
            if (extensionMatcher.match("GL_NV_framebuffer_blit"))
                extensions |= QOpenGLExtensions::FramebufferBlit;
            if (extensionMatcher.match("GL_NV_framebuffer_multisample"))
                extensions |= QOpenGLExtensions::FramebufferMultisample;
            if (extensionMatcher.match("GL_OES_rgb8_rgba8"))
                extensions |= QOpenGLExtensions::Sized8Formats;
            if (extensionMatcher.match("GL_OES_compressed_ETC2_RGB8_texture"))
                extensions |= QOpenGLExtensions::ETC2TextureCompression;
        }
 
        if (extensionMatcher.match("GL_OES_mapbuffer"))
            extensions |= QOpenGLExtensions::MapBuffer;
        if (extensionMatcher.match("GL_OES_element_index_uint"))
            extensions |= QOpenGLExtensions::ElementIndexUint;
        // We don't match GL_APPLE_texture_format_BGRA8888 here because it has different semantics.
        if (extensionMatcher.match("GL_IMG_texture_format_BGRA8888") || extensionMatcher.match("GL_EXT_texture_format_BGRA8888"))
            extensions |= QOpenGLExtensions::BGRATextureFormat;
#ifdef Q_OS_ANDROID
        QString *deviceName =
                static_cast<QString *>(QGuiApplication::platformNativeInterface()->nativeResourceForIntegration("AndroidDeviceName"));
        static bool wrongfullyReportsBgra8888Support = deviceName != 0
                                                        && (deviceName->compare("samsung SM-T211"_L1, Qt::CaseInsensitive) == 0
                                                            || deviceName->compare("samsung SM-T210"_L1, Qt::CaseInsensitive) == 0
                                                            || deviceName->compare("samsung SM-T215"_L1, Qt::CaseInsensitive) == 0);
        if (wrongfullyReportsBgra8888Support)
            extensions &= ~QOpenGLExtensions::BGRATextureFormat;
#endif
 
        if (extensionMatcher.match("GL_EXT_discard_framebuffer"))
            extensions |= QOpenGLExtensions::DiscardFramebuffer;
        if (extensionMatcher.match("GL_EXT_texture_norm16"))
            extensions |= QOpenGLExtensions::Sized16Formats;
    } else {
        extensions |= QOpenGLExtensions::ElementIndexUint
            | QOpenGLExtensions::MapBuffer
            | QOpenGLExtensions::Sized16Formats;
 
        if (format.version() >= qMakePair(1, 2))
            extensions |= QOpenGLExtensions::BGRATextureFormat;
 
        if (format.version() >= qMakePair(1, 4) || extensionMatcher.match("GL_SGIS_generate_mipmap"))
            extensions |= QOpenGLExtensions::GenerateMipmap;
 
        if (format.majorVersion() >= 2)
            extensions |= QOpenGLExtensions::StandardDerivatives;
 
        if (format.majorVersion() >= 3 || extensionMatcher.match("GL_ARB_framebuffer_object")) {
            extensions |= QOpenGLExtensions::FramebufferMultisample
                | QOpenGLExtensions::FramebufferBlit
                | QOpenGLExtensions::PackedDepthStencil
                | QOpenGLExtensions::Sized8Formats;
        } else {
            // Recognize features by extension name.
            if (extensionMatcher.match("GL_EXT_framebuffer_multisample"))
                extensions |= QOpenGLExtensions::FramebufferMultisample;
            if (extensionMatcher.match("GL_EXT_framebuffer_blit"))
                extensions |= QOpenGLExtensions::FramebufferBlit;
            if (extensionMatcher.match("GL_EXT_packed_depth_stencil"))
                extensions |= QOpenGLExtensions::PackedDepthStencil;
        }
 
        if (format.version() >= qMakePair(3, 2) || extensionMatcher.match("GL_ARB_geometry_shader4"))
            extensions |= QOpenGLExtensions::GeometryShaders;
 
        if (format.version() >= qMakePair(3, 3))
            extensions |= QOpenGLExtensions::TextureSwizzle;
 
        if (extensionMatcher.match("GL_ARB_map_buffer_range"))
            extensions |= QOpenGLExtensions::MapBufferRange;
 
        if (extensionMatcher.match("GL_EXT_framebuffer_sRGB")) {
            GLboolean srgbCapableFramebuffers = false;
            ctx->functions()->glGetBooleanv(GL_FRAMEBUFFER_SRGB_CAPABLE_EXT, &srgbCapableFramebuffers);
            if (srgbCapableFramebuffers)
                extensions |= QOpenGLExtensions::SRGBFrameBuffer;
        }
 
        if (extensionMatcher.match("GL_ARB_ES3_compatibility"))
            extensions |= QOpenGLExtensions::ETC2TextureCompression;
    }
 
    return extensions;
}
 
QOpenGLFunctions::OpenGLFeatures QOpenGLFunctions::openGLFeatures() const
{
    QOpenGLFunctionsPrivateEx *d = static_cast<QOpenGLFunctionsPrivateEx *>(d_ptr);
    if (!d)
        return { };
    if (d->m_features == -1)
        d->m_features = qt_gl_resolve_features();
    return QOpenGLFunctions::OpenGLFeatures(d->m_features);
}
 
bool QOpenGLFunctions::hasOpenGLFeature(QOpenGLFunctions::OpenGLFeature feature) const
{
    QOpenGLFunctionsPrivateEx *d = static_cast<QOpenGLFunctionsPrivateEx *>(d_ptr);
    if (!d)
        return false;
    if (d->m_features == -1)
        d->m_features = qt_gl_resolve_features();
    return (d->m_features & int(feature)) != 0;
}
 
QOpenGLExtensions::OpenGLExtensions QOpenGLExtensions::openGLExtensions()
{
    QOpenGLFunctionsPrivateEx *d = static_cast<QOpenGLFunctionsPrivateEx *>(d_ptr);
    if (!d)
        return { };
    if (d->m_extensions == -1)
        d->m_extensions = qt_gl_resolve_extensions();
    return QOpenGLExtensions::OpenGLExtensions(d->m_extensions);
}
 
bool QOpenGLExtensions::hasOpenGLExtension(QOpenGLExtensions::OpenGLExtension extension) const
{
    QOpenGLFunctionsPrivateEx *d = static_cast<QOpenGLFunctionsPrivateEx *>(d_ptr);
    if (!d)
        return false;
    if (d->m_extensions == -1)
        d->m_extensions = qt_gl_resolve_extensions();
    return (d->m_extensions & int(extension)) != 0;
}
 
void QOpenGLFunctions::initializeOpenGLFunctions()
{
    d_ptr = qt_gl_functions();
}
 
namespace {
 
// this function tries hard to get the opengl function we're looking for by also
// trying to resolve it with some of the common extensions if the generic name
// can't be found.
static QFunctionPointer getProcAddress(QOpenGLContext *context, const char *funcName)
{
    QFunctionPointer function = context->getProcAddress(funcName);
 
    static const struct {
        const char *name;
        int len; // includes trailing \0
    } extensions[] = {
        { "ARB", 4 },
        { "OES", 4 },
        { "EXT", 4 },
        { "ANGLE", 6 },
        { "NV", 3 },
    };
 
    if (!function) {
        char fn[512];
        size_t size = strlen(funcName);
        Q_ASSERT(size < 500);
        memcpy(fn, funcName, size);
        char *ext = fn + size;
 
        for (const auto &e : extensions) {
            memcpy(ext, e.name, e.len);
            function = context->getProcAddress(fn);
            if (function)
                break;
        }
    }
 
    return function;
}
 
template <typename Func>
Func resolve(QOpenGLContext *context, const char *name, Func)
{
    return reinterpret_cast<Func>(getProcAddress(context, name));
}
 
}
 
#define RESOLVE(name) \
    resolve(context, "gl"#name, name)
 
#if !QT_CONFIG(opengles2)
 
// some fallback functions
static void QOPENGLF_APIENTRY qopenglfSpecialClearDepthf(GLclampf depth)
{
    QOpenGLContext *context = QOpenGLContext::currentContext();
    QOpenGLFunctionsPrivate *funcs = qt_gl_functions(context);
    funcs->f.ClearDepth((GLdouble) depth);
}
 
static void QOPENGLF_APIENTRY qopenglfSpecialDepthRangef(GLclampf zNear, GLclampf zFar)
{
    QOpenGLContext *context = QOpenGLContext::currentContext();
    QOpenGLFunctionsPrivate *funcs = qt_gl_functions(context);
    funcs->f.DepthRange((GLdouble) zNear, (GLdouble) zFar);
}
 
static void QOPENGLF_APIENTRY qopenglfSpecialGetShaderPrecisionFormat(GLenum shadertype, GLenum precisiontype, GLint* range, GLint* precision)
{
    Q_UNUSED(shadertype);
    Q_UNUSED(precisiontype);
    range[0] = range[1] = precision[0] = 0;
}
 
static GLboolean QOPENGLF_APIENTRY qopenglfSpecialIsProgram(GLuint program)
{
    return program != 0;
}
 
static GLboolean QOPENGLF_APIENTRY qopenglfSpecialIsShader(GLuint shader)
{
    return shader != 0;
}
 
static void QOPENGLF_APIENTRY qopenglfSpecialReleaseShaderCompiler()
{
}
 
#endif // !QT_CONFIG(opengles2)
 
 
QOpenGLFunctionsPrivate::QOpenGLFunctionsPrivate(QOpenGLContext *c)
{
    init(c);
 
#if !QT_CONFIG(opengles2)
    // setup fallbacks in case some methods couldn't get resolved
    bool es = QOpenGLContext::currentContext()->isOpenGLES();
    if (!f.ClearDepthf || !es)
        f.ClearDepthf = qopenglfSpecialClearDepthf;
    if (!f.DepthRangef || !es)
        f.DepthRangef = qopenglfSpecialDepthRangef;
    if (!f.GetShaderPrecisionFormat)
        f.GetShaderPrecisionFormat = qopenglfSpecialGetShaderPrecisionFormat;
    if (!f.IsProgram)
        f.IsProgram = qopenglfSpecialIsProgram;
    if (!f.IsShader)
        f.IsShader = qopenglfSpecialIsShader;
    if (!f.ReleaseShaderCompiler)
        f.ReleaseShaderCompiler = qopenglfSpecialReleaseShaderCompiler;
#endif
}
 
 
QT_OPENGL_IMPLEMENT(QOpenGLFunctionsPrivate, QT_OPENGL_FUNCTIONS)
 
 
QOpenGLExtraFunctions::QOpenGLExtraFunctions()
{
}
 
QOpenGLExtraFunctions::QOpenGLExtraFunctions(QOpenGLContext *context)
    : QOpenGLFunctions(context)
{
}
 
QOpenGLExtraFunctionsPrivate::QOpenGLExtraFunctionsPrivate(QOpenGLContext *ctx)
    : QOpenGLFunctionsPrivate(ctx)
{
    init(ctx);
}
 
QT_OPENGL_IMPLEMENT(QOpenGLExtraFunctionsPrivate, QT_OPENGL_EXTRA_FUNCTIONS)
 
QOpenGLExtensionsPrivate::QOpenGLExtensionsPrivate(QOpenGLContext *ctx)
    : QOpenGLExtraFunctionsPrivate(ctx),
      flushVendorChecked(false)
{
    QOpenGLContext *context = QOpenGLContext::currentContext();
 
    MapBuffer = RESOLVE(MapBuffer);
    GetBufferSubData = RESOLVE(GetBufferSubData);
    DiscardFramebuffer = RESOLVE(DiscardFramebuffer);
 }
 
void QOpenGLExtensions::flushShared()
{
    Q_D(QOpenGLExtensions);
 
    if (!d->flushVendorChecked) {
        d->flushVendorChecked = true;
        // It is not quite clear if glFlush() is sufficient to synchronize access to
        // resources between sharing contexts in the same thread. On most platforms this
        // is enough (e.g. iOS explicitly documents it), while certain drivers only work
        // properly when doing glFinish().
        d->flushIsSufficientToSyncContexts = false; // default to false, not guaranteed by the spec
        const char *vendor = (const char *) glGetString(GL_VENDOR);
        if (vendor) {
            static const char *const flushEnough[] = { "Apple", "ATI", "Intel", "NVIDIA" };
            for (size_t i = 0; i < sizeof(flushEnough) / sizeof(const char *); ++i) {
                if (strstr(vendor, flushEnough[i])) {
                    d->flushIsSufficientToSyncContexts = true;
                    break;
                }
            }
        }
    }
 
    if (d->flushIsSufficientToSyncContexts)
        glFlush();
    else
        glFinish();
}
 
QT_END_NAMESPACE