JUCE/modules/juce_opengl/opengl/juce_OpenGLContext.cpp

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

   This file is part of the JUCE 6 technical preview.
   Copyright (c) 2020 - Raw Material Software Limited

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

   For this technical preview, this file is not subject to commercial licensing.

   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
{

#if JUCE_IOS
struct AppInactivityCallback // NB: this is a duplicate of an internal declaration in juce_core
{
    virtual ~AppInactivityCallback() {}
    virtual void appBecomingInactive() = 0;
};

extern Array<AppInactivityCallback*> appBecomingInactiveCallbacks;

// On iOS, all GL calls will crash when the app is running in the background, so
// this prevents them from happening (which some messy locking behaviour)
struct iOSBackgroundProcessCheck  : public AppInactivityCallback
{
    iOSBackgroundProcessCheck()              { isBackgroundProcess(); appBecomingInactiveCallbacks.add (this); }
    ~iOSBackgroundProcessCheck() override    { appBecomingInactiveCallbacks.removeAllInstancesOf (this); }

    bool isBackgroundProcess()
    {
        const bool b = Process::isForegroundProcess();
        isForeground.set (b ? 1 : 0);
        return ! b;
    }

    void appBecomingInactive() override
    {
        int counter = 2000;

        while (--counter > 0 && isForeground.get() != 0)
            Thread::sleep (1);
    }

private:
    Atomic<int> isForeground;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (iOSBackgroundProcessCheck)
};

#endif

#if JUCE_WINDOWS && JUCE_WIN_PER_MONITOR_DPI_AWARE
 extern JUCE_API double getScaleFactorForWindow (HWND);
#endif

//==============================================================================
class OpenGLContext::CachedImage  : public CachedComponentImage,
                                    private ThreadPoolJob
{
public:
    CachedImage (OpenGLContext& c, Component& comp,
                 const OpenGLPixelFormat& pixFormat, void* contextToShare)
        : ThreadPoolJob ("OpenGL Rendering"),
          context (c), component (comp)
    {
        nativeContext.reset (new NativeContext (component, pixFormat, contextToShare,
                                                c.useMultisampling, c.versionRequired));

        if (nativeContext->createdOk())
            context.nativeContext = nativeContext.get();
        else
            nativeContext.reset();
    }

    ~CachedImage() override
    {
        stop();
    }

    //==============================================================================
    void start()
    {
        if (nativeContext != nullptr)
        {
            renderThread.reset (new ThreadPool (1));
            resume();
        }
    }

    void stop()
    {
        if (renderThread != nullptr)
        {
            // make sure everything has finished executing
            destroying = true;

            if (workQueue.size() > 0)
            {
                if (! renderThread->contains (this))
                    resume();

                while (workQueue.size() != 0)
                    Thread::sleep (20);
            }

            pause();
            renderThread.reset();
        }

        hasInitialised = false;
    }

    //==============================================================================
    void pause()
    {
        signalJobShouldExit();
        messageManagerLock.abort();

        if (renderThread != nullptr)
        {
            repaintEvent.signal();
            renderThread->removeJob (this, true, -1);
        }
    }

    void resume()
    {
        if (renderThread != nullptr)
            renderThread->addJob (this, false);
    }

    //==============================================================================
    void paint (Graphics&) override
    {
        updateViewportSize (false);
    }

    bool invalidateAll() override
    {
        validArea.clear();
        triggerRepaint();
        return false;
    }

    bool invalidate (const Rectangle<int>& area) override
    {
        validArea.subtract (area.toFloat().transformedBy (transform).getSmallestIntegerContainer());
        triggerRepaint();
        return false;
    }

    void releaseResources() override
    {
        stop();
    }

    void triggerRepaint()
    {
        needsUpdate = 1;
        repaintEvent.signal();
    }

    //==============================================================================
    bool ensureFrameBufferSize()
    {
        auto fbW = cachedImageFrameBuffer.getWidth();
        auto fbH = cachedImageFrameBuffer.getHeight();

        if (fbW != viewportArea.getWidth() || fbH != viewportArea.getHeight() || ! cachedImageFrameBuffer.isValid())
        {
            if (! cachedImageFrameBuffer.initialise (context, viewportArea.getWidth(), viewportArea.getHeight()))
                return false;

            validArea.clear();
            JUCE_CHECK_OPENGL_ERROR
        }

        return true;
    }

    void clearRegionInFrameBuffer (const RectangleList<int>& list)
    {
        glClearColor (0, 0, 0, 0);
        glEnable (GL_SCISSOR_TEST);

        auto previousFrameBufferTarget = OpenGLFrameBuffer::getCurrentFrameBufferTarget();
        cachedImageFrameBuffer.makeCurrentRenderingTarget();
        auto imageH = cachedImageFrameBuffer.getHeight();

        for (auto& r : list)
        {
            glScissor (r.getX(), imageH - r.getBottom(), r.getWidth(), r.getHeight());
            glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
        }

        glDisable (GL_SCISSOR_TEST);
        context.extensions.glBindFramebuffer (GL_FRAMEBUFFER, previousFrameBufferTarget);
        JUCE_CHECK_OPENGL_ERROR
    }

    bool renderFrame()
    {
        MessageManager::Lock::ScopedTryLockType mmLock (messageManagerLock, false);

        auto isUpdatingTestValue = true;
        auto isUpdating = needsUpdate.compare_exchange_strong (isUpdatingTestValue, false);

        if (context.renderComponents && isUpdating)
        {
            // This avoids hogging the message thread when doing intensive rendering.
            if (lastMMLockReleaseTime + 1 >= Time::getMillisecondCounter())
                Thread::sleep (2);

            while (! shouldExit())
            {
                doWorkWhileWaitingForLock (false);

                if (mmLock.retryLock())
                    break;
            }

            if (shouldExit())
                return false;
        }

        if (! context.makeActive())
            return false;

        NativeContext::Locker locker (*nativeContext);

        JUCE_CHECK_OPENGL_ERROR

        doWorkWhileWaitingForLock (true);

        if (context.renderer != nullptr)
        {
            glViewport (0, 0, viewportArea.getWidth(), viewportArea.getHeight());
            context.currentRenderScale = scale;
            context.renderer->renderOpenGL();
            clearGLError();

            bindVertexArray();
        }

        if (context.renderComponents)
        {
            if (isUpdating)
            {
                paintComponent();

                if (! hasInitialised)
                    return false;

                messageManagerLock.exit();
                lastMMLockReleaseTime = Time::getMillisecondCounter();
            }

            glViewport (0, 0, viewportArea.getWidth(), viewportArea.getHeight());
            drawComponentBuffer();
        }

        context.swapBuffers();

        OpenGLContext::deactivateCurrentContext();
        return true;
    }

    void updateViewportSize (bool canTriggerUpdate)
    {
        if (auto* peer = component.getPeer())
        {
            auto localBounds = component.getLocalBounds();
            auto displayScale = Desktop::getInstance().getDisplays().findDisplayForRect (component.getTopLevelComponent()->getScreenBounds()).scale;

            auto newArea = peer->getComponent().getLocalArea (&component, localBounds).withZeroOrigin() * displayScale;

           #if JUCE_WINDOWS && JUCE_WIN_PER_MONITOR_DPI_AWARE
            auto newScale = getScaleFactorForWindow (nativeContext->getNativeHandle());
           #else
            auto newScale = displayScale;
           #endif

            if (scale != newScale || viewportArea != newArea)
            {
                scale = newScale;
                viewportArea = newArea;
                transform = AffineTransform::scale ((float) newArea.getWidth()  / (float) localBounds.getWidth(),
                                                    (float) newArea.getHeight() / (float) localBounds.getHeight());

                nativeContext->updateWindowPosition (peer->getAreaCoveredBy (component));

                if (canTriggerUpdate)
                    invalidateAll();
            }
        }
    }

    void bindVertexArray() noexcept
    {
       #if JUCE_OPENGL3
        if (vertexArrayObject != 0)
            context.extensions.glBindVertexArray (vertexArrayObject);
       #endif
    }

    void checkViewportBounds()
    {
        auto screenBounds = component.getTopLevelComponent()->getScreenBounds();

        if (lastScreenBounds != screenBounds)
            updateViewportSize (true);
    }

    void paintComponent()
    {
        // you mustn't set your own cached image object when attaching a GL context!
        jassert (get (component) == this);

        if (! ensureFrameBufferSize())
            return;

        RectangleList<int> invalid (viewportArea);
        invalid.subtract (validArea);
        validArea = viewportArea;

        if (! invalid.isEmpty())
        {
            clearRegionInFrameBuffer (invalid);

            {
                std::unique_ptr<LowLevelGraphicsContext> g (createOpenGLGraphicsContext (context, cachedImageFrameBuffer));
                g->clipToRectangleList (invalid);
                g->addTransform (transform);

                paintOwner (*g);
                JUCE_CHECK_OPENGL_ERROR
            }

            if (! context.isActive())
                context.makeActive();
        }

        JUCE_CHECK_OPENGL_ERROR
    }

    void drawComponentBuffer()
    {
       #if ! JUCE_ANDROID
        glEnable (GL_TEXTURE_2D);
        clearGLError();
       #endif

       #if JUCE_WINDOWS
        // some stupidly old drivers are missing this function, so try to at least avoid a crash here,
        // but if you hit this assertion you may want to have your own version check before using the
        // component rendering stuff on such old drivers.
        jassert (context.extensions.glActiveTexture != nullptr);
        if (context.extensions.glActiveTexture != nullptr)
       #endif
            context.extensions.glActiveTexture (GL_TEXTURE0);

        glBindTexture (GL_TEXTURE_2D, cachedImageFrameBuffer.getTextureID());
        bindVertexArray();

        const Rectangle<int> cacheBounds (cachedImageFrameBuffer.getWidth(), cachedImageFrameBuffer.getHeight());
        context.copyTexture (cacheBounds, cacheBounds, cacheBounds.getWidth(), cacheBounds.getHeight(), false);
        glBindTexture (GL_TEXTURE_2D, 0);
        JUCE_CHECK_OPENGL_ERROR
    }

    void paintOwner (LowLevelGraphicsContext& llgc)
    {
        Graphics g (llgc);

      #if JUCE_ENABLE_REPAINT_DEBUGGING
       #ifdef JUCE_IS_REPAINT_DEBUGGING_ACTIVE
        if (JUCE_IS_REPAINT_DEBUGGING_ACTIVE)
       #endif
        {
            g.saveState();
        }
       #endif

        JUCE_TRY
        {
            component.paintEntireComponent (g, false);
        }
        JUCE_CATCH_EXCEPTION

      #if JUCE_ENABLE_REPAINT_DEBUGGING
       #ifdef JUCE_IS_REPAINT_DEBUGGING_ACTIVE
        if (JUCE_IS_REPAINT_DEBUGGING_ACTIVE)
       #endif
        {
            // enabling this code will fill all areas that get repainted with a colour overlay, to show
            // clearly when things are being repainted.
            g.restoreState();

            static Random rng;
            g.fillAll (Colour ((uint8) rng.nextInt (255),
                               (uint8) rng.nextInt (255),
                               (uint8) rng.nextInt (255),
                               (uint8) 0x50));
        }
       #endif
    }

    void handleResize()
    {
        updateViewportSize (true);

       #if JUCE_MAC
        if (hasInitialised)
        {
            [nativeContext->view update];
            renderFrame();
        }
       #endif
    }

    //==============================================================================
    JobStatus runJob() override
    {
        {
            // Allow the message thread to finish setting-up the context before using it..
            MessageManager::Lock::ScopedTryLockType mmLock (messageManagerLock, false);

            do
            {
                if (shouldExit())
                    return ThreadPoolJob::jobHasFinished;

            } while (! mmLock.retryLock());
        }

        if (! initialiseOnThread())
        {
            hasInitialised = false;

            return ThreadPoolJob::jobHasFinished;
        }

        hasInitialised = true;

        while (! shouldExit())
        {
           #if JUCE_IOS
            if (backgroundProcessCheck.isBackgroundProcess())
            {
                repaintEvent.wait (300);
                continue;
            }
           #endif

            if (shouldExit())
                break;

           #if JUCE_MAC
            if (cvDisplayLinkWrapper != nullptr)
            {
                repaintEvent.wait (-1);
                renderFrame();
            }
            else
           #endif
            if (! renderFrame())
                repaintEvent.wait (5); // failed to render, so avoid a tight fail-loop.
            else if (! context.continuousRepaint && ! shouldExit())
                repaintEvent.wait (-1);
        }

        hasInitialised = false;
        context.makeActive();
        shutdownOnThread();
        OpenGLContext::deactivateCurrentContext();

        return ThreadPoolJob::jobHasFinished;
    }

    bool initialiseOnThread()
    {
        // On android, this can get called twice, so drop any previous state..
        associatedObjectNames.clear();
        associatedObjects.clear();
        cachedImageFrameBuffer.release();

        context.makeActive();

        if (! nativeContext->initialiseOnRenderThread (context))
            return false;

       #if JUCE_ANDROID
        // On android the context may be created in initialiseOnRenderThread
        // and we therefore need to call makeActive again
        context.makeActive();
       #endif

        context.extensions.initialise();

       #if JUCE_OPENGL3
        if (OpenGLShaderProgram::getLanguageVersion() > 1.2)
        {
            context.extensions.glGenVertexArrays (1, &vertexArrayObject);
            bindVertexArray();
        }
       #endif

        glViewport (0, 0, component.getWidth(), component.getHeight());

        nativeContext->setSwapInterval (1);

       #if ! JUCE_OPENGL_ES
        JUCE_CHECK_OPENGL_ERROR
        shadersAvailable = OpenGLShaderProgram::getLanguageVersion() > 0;
        clearGLError();
       #endif

        if (context.renderer != nullptr)
            context.renderer->newOpenGLContextCreated();

       #if JUCE_MAC
        if (context.continuousRepaint)
            cvDisplayLinkWrapper = std::make_unique<CVDisplayLinkWrapper> (this);
       #endif

        return true;
    }

    void shutdownOnThread()
    {
       #if JUCE_MAC
        cvDisplayLinkWrapper = nullptr;
       #endif

        if (context.renderer != nullptr)
            context.renderer->openGLContextClosing();

       #if JUCE_OPENGL3
        if (vertexArrayObject != 0)
            context.extensions.glDeleteVertexArrays (1, &vertexArrayObject);
       #endif

        associatedObjectNames.clear();
        associatedObjects.clear();
        cachedImageFrameBuffer.release();
        nativeContext->shutdownOnRenderThread();
    }

    //==============================================================================
    struct BlockingWorker  : public OpenGLContext::AsyncWorker
    {
        BlockingWorker (OpenGLContext::AsyncWorker::Ptr && workerToUse)
            : originalWorker (std::move (workerToUse))
        {}

        void operator() (OpenGLContext& calleeContext)
        {
            if (originalWorker != nullptr)
                (*originalWorker) (calleeContext);

            finishedSignal.signal();
        }

        void block() noexcept  { finishedSignal.wait(); }

        OpenGLContext::AsyncWorker::Ptr originalWorker;
        WaitableEvent finishedSignal;
    };

    bool doWorkWhileWaitingForLock (bool contextIsAlreadyActive)
    {
        bool contextActivated = false;

        for (OpenGLContext::AsyncWorker::Ptr work = workQueue.removeAndReturn (0);
             work != nullptr && (! shouldExit()); work = workQueue.removeAndReturn (0))
        {
            if ((! contextActivated) && (! contextIsAlreadyActive))
            {
                if (! context.makeActive())
                    break;

                contextActivated = true;
            }

            NativeContext::Locker locker (*nativeContext);

            (*work) (context);
            clearGLError();
        }

        if (contextActivated)
            OpenGLContext::deactivateCurrentContext();

        return shouldExit();
    }

    void execute (OpenGLContext::AsyncWorker::Ptr workerToUse, bool shouldBlock, bool calledFromDestructor = false)
    {
        if (calledFromDestructor || ! destroying)
        {
            if (shouldBlock)
            {
                auto blocker = new BlockingWorker (std::move (workerToUse));
                OpenGLContext::AsyncWorker::Ptr worker (*blocker);
                workQueue.add (worker);

                messageManagerLock.abort();
                context.triggerRepaint();

                blocker->block();
            }
            else
            {
                workQueue.add (std::move (workerToUse));

                messageManagerLock.abort();
                context.triggerRepaint();
            }
        }
        else
        {
            jassertfalse; // you called execute AFTER you detached your openglcontext
        }
    }

    //==============================================================================
    static CachedImage* get (Component& c) noexcept
    {
        return dynamic_cast<CachedImage*> (c.getCachedComponentImage());
    }

    //==============================================================================
    friend class NativeContext;
    std::unique_ptr<NativeContext> nativeContext;

    OpenGLContext& context;
    Component& component;

    OpenGLFrameBuffer cachedImageFrameBuffer;
    RectangleList<int> validArea;
    Rectangle<int> viewportArea, lastScreenBounds;
    double scale = 1.0;
    AffineTransform transform;
   #if JUCE_OPENGL3
    GLuint vertexArrayObject = 0;
   #endif

    StringArray associatedObjectNames;
    ReferenceCountedArray<ReferenceCountedObject> associatedObjects;

    WaitableEvent canPaintNowFlag, finishedPaintingFlag, repaintEvent;
   #if JUCE_OPENGL_ES
    bool shadersAvailable = true;
   #else
    bool shadersAvailable = false;
   #endif
    std::atomic<bool> hasInitialised { false }, needsUpdate { true }, destroying { false };
    uint32 lastMMLockReleaseTime = 0;

   #if JUCE_MAC
    struct CVDisplayLinkWrapper
    {
        CVDisplayLinkWrapper (CachedImage* im)
        {
            CVDisplayLinkCreateWithActiveCGDisplays (&displayLink);
            CVDisplayLinkSetOutputCallback (displayLink, &displayLinkCallback, im);
            CVDisplayLinkStart (displayLink);
        }

        ~CVDisplayLinkWrapper()
        {
            CVDisplayLinkStop (displayLink);
            CVDisplayLinkRelease (displayLink);
        }

        static CVReturn displayLinkCallback (CVDisplayLinkRef, const CVTimeStamp*, const CVTimeStamp*,
                                             CVOptionFlags, CVOptionFlags*, void* displayLinkContext)
        {
            auto* self = (CachedImage*) displayLinkContext;
            self->repaintEvent.signal();
            return kCVReturnSuccess;
        }

        CVDisplayLinkRef displayLink;
    };

    std::unique_ptr<CVDisplayLinkWrapper> cvDisplayLinkWrapper;
   #endif

    std::unique_ptr<ThreadPool> renderThread;
    ReferenceCountedArray<OpenGLContext::AsyncWorker, CriticalSection> workQueue;
    MessageManager::Lock messageManagerLock;

   #if JUCE_IOS
    iOSBackgroundProcessCheck backgroundProcessCheck;
   #endif

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (CachedImage)
};

//==============================================================================
class OpenGLContext::Attachment  : public ComponentMovementWatcher,
                                   private Timer
{
public:
    Attachment (OpenGLContext& c, Component& comp)
       : ComponentMovementWatcher (&comp), context (c)
    {
        if (canBeAttached (comp))
            attach();
    }

    ~Attachment() override
    {
        detach();
    }

    void detach()
    {
        auto& comp = *getComponent();
        stop();
        comp.setCachedComponentImage (nullptr);
        context.nativeContext = nullptr;
    }

    void componentMovedOrResized (bool /*wasMoved*/, bool /*wasResized*/) override
    {
        auto& comp = *getComponent();

        if (isAttached (comp) != canBeAttached (comp))
            componentVisibilityChanged();

        if (comp.getWidth() > 0 && comp.getHeight() > 0
             && context.nativeContext != nullptr)
        {
            if (auto* c = CachedImage::get (comp))
                c->handleResize();

            if (auto* peer = comp.getTopLevelComponent()->getPeer())
                context.nativeContext->updateWindowPosition (peer->getAreaCoveredBy (comp));
        }
    }

    using ComponentMovementWatcher::componentMovedOrResized;

    void componentPeerChanged() override
    {
        detach();
        componentVisibilityChanged();
    }

    void componentVisibilityChanged() override
    {
        auto& comp = *getComponent();

        if (canBeAttached (comp))
        {
            if (isAttached (comp))
                comp.repaint(); // (needed when windows are un-minimised)
            else
                attach();
        }
        else
        {
            detach();
        }
    }

    using ComponentMovementWatcher::componentVisibilityChanged;

   #if JUCE_DEBUG || JUCE_LOG_ASSERTIONS
    void componentBeingDeleted (Component& c) override
    {
        /* You must call detach() or delete your OpenGLContext to remove it
           from a component BEFORE deleting the component that it is using!
        */
        jassertfalse;

        ComponentMovementWatcher::componentBeingDeleted (c);
    }
   #endif

    void update()
    {
        auto& comp = *getComponent();

        if (canBeAttached (comp))
            start();
        else
            stop();
    }

private:
    OpenGLContext& context;

    bool canBeAttached (const Component& comp) noexcept
    {
        return (! context.overrideCanAttach) && comp.getWidth() > 0 && comp.getHeight() > 0 && isShowingOrMinimised (comp);
    }

    static bool isShowingOrMinimised (const Component& c)
    {
        if (! c.isVisible())
            return false;

        if (auto* p = c.getParentComponent())
            return isShowingOrMinimised (*p);

        return c.getPeer() != nullptr;
    }

    static bool isAttached (const Component& comp) noexcept
    {
        return comp.getCachedComponentImage() != nullptr;
    }

    void attach()
    {
        auto& comp = *getComponent();
        auto* newCachedImage = new CachedImage (context, comp,
                                                context.openGLPixelFormat,
                                                context.contextToShareWith);
        comp.setCachedComponentImage (newCachedImage);

        start();
    }

    void stop()
    {
        stopTimer();

        auto& comp = *getComponent();

       #if JUCE_MAC
        [[(NSView*) comp.getWindowHandle() window] disableScreenUpdatesUntilFlush];
       #endif

        if (auto* oldCachedImage = CachedImage::get (comp))
            oldCachedImage->stop(); // (must stop this before detaching it from the component)
    }

    void start()
    {
        auto& comp = *getComponent();

        if (auto* cachedImage = CachedImage::get (comp))
        {
            cachedImage->start(); // (must wait until this is attached before starting its thread)
            cachedImage->updateViewportSize (true);

            startTimer (400);
        }
    }

    void timerCallback() override
    {
        if (auto* cachedImage = CachedImage::get (*getComponent()))
            cachedImage->checkViewportBounds();
    }
};

//==============================================================================
OpenGLContext::OpenGLContext()
{
}

OpenGLContext::~OpenGLContext()
{
    detach();
}

void OpenGLContext::setRenderer (OpenGLRenderer* rendererToUse) noexcept
{
    // This method must not be called when the context has already been attached!
    // Call it before attaching your context, or use detach() first, before calling this!
    jassert (nativeContext == nullptr);

    renderer = rendererToUse;
}

void OpenGLContext::setComponentPaintingEnabled (bool shouldPaintComponent) noexcept
{
    // This method must not be called when the context has already been attached!
    // Call it before attaching your context, or use detach() first, before calling this!
    jassert (nativeContext == nullptr);

    renderComponents = shouldPaintComponent;
}

void OpenGLContext::setContinuousRepainting (bool shouldContinuouslyRepaint) noexcept
{
    continuousRepaint = shouldContinuouslyRepaint;

    #if JUCE_MAC
     if (auto* component = getTargetComponent())
     {
         detach();
         attachment.reset (new Attachment (*this, *component));
     }
    #endif

    triggerRepaint();
}

void OpenGLContext::setPixelFormat (const OpenGLPixelFormat& preferredPixelFormat) noexcept
{
    // This method must not be called when the context has already been attached!
    // Call it before attaching your context, or use detach() first, before calling this!
    jassert (nativeContext == nullptr);

    openGLPixelFormat = preferredPixelFormat;
}

void OpenGLContext::setTextureMagnificationFilter (OpenGLContext::TextureMagnificationFilter magFilterMode) noexcept
{
    texMagFilter = magFilterMode;
}

void OpenGLContext::setNativeSharedContext (void* nativeContextToShareWith) noexcept
{
    // This method must not be called when the context has already been attached!
    // Call it before attaching your context, or use detach() first, before calling this!
    jassert (nativeContext == nullptr);

    contextToShareWith = nativeContextToShareWith;
}

void OpenGLContext::setMultisamplingEnabled (bool b) noexcept
{
    // This method must not be called when the context has already been attached!
    // Call it before attaching your context, or use detach() first, before calling this!
    jassert (nativeContext == nullptr);

    useMultisampling = b;
}

void OpenGLContext::setOpenGLVersionRequired (OpenGLVersion v) noexcept
{
    versionRequired = v;
}

void OpenGLContext::attachTo (Component& component)
{
    component.repaint();

    if (getTargetComponent() != &component)
    {
        detach();
        attachment.reset (new Attachment (*this, component));
    }
}

void OpenGLContext::detach()
{
    if (auto* a = attachment.get())
    {
        a->detach(); // must detach before nulling our pointer
        attachment.reset();
    }

    nativeContext = nullptr;
}

bool OpenGLContext::isAttached() const noexcept
{
    return nativeContext != nullptr;
}

Component* OpenGLContext::getTargetComponent() const noexcept
{
    return attachment != nullptr ? attachment->getComponent() : nullptr;
}

OpenGLContext* OpenGLContext::getContextAttachedTo (Component& c) noexcept
{
    if (auto* ci = CachedImage::get (c))
        return &(ci->context);

    return nullptr;
}

static ThreadLocalValue<OpenGLContext*> currentThreadActiveContext;

OpenGLContext* OpenGLContext::getCurrentContext()
{
    return currentThreadActiveContext.get();
}

bool OpenGLContext::makeActive() const noexcept
{
    auto& current = currentThreadActiveContext.get();

    if (nativeContext != nullptr && nativeContext->makeActive())
    {
        current = const_cast<OpenGLContext*> (this);
        return true;
    }

    current = nullptr;
    return false;
}

bool OpenGLContext::isActive() const noexcept
{
    return nativeContext != nullptr && nativeContext->isActive();
}

void OpenGLContext::deactivateCurrentContext()
{
    NativeContext::deactivateCurrentContext();
    currentThreadActiveContext.get() = nullptr;
}

void OpenGLContext::triggerRepaint()
{
    if (auto* cachedImage = getCachedImage())
        cachedImage->triggerRepaint();
}

void OpenGLContext::swapBuffers()
{
    if (nativeContext != nullptr)
        nativeContext->swapBuffers();
}

unsigned int OpenGLContext::getFrameBufferID() const noexcept
{
    return nativeContext != nullptr ? nativeContext->getFrameBufferID() : 0;
}

bool OpenGLContext::setSwapInterval (int numFramesPerSwap)
{
    return nativeContext != nullptr && nativeContext->setSwapInterval (numFramesPerSwap);
}

int OpenGLContext::getSwapInterval() const
{
    return nativeContext != nullptr ? nativeContext->getSwapInterval() : 0;
}

void* OpenGLContext::getRawContext() const noexcept
{
    return nativeContext != nullptr ? nativeContext->getRawContext() : nullptr;
}

OpenGLContext::CachedImage* OpenGLContext::getCachedImage() const noexcept
{
    if (auto* comp = getTargetComponent())
        return CachedImage::get (*comp);

    return nullptr;
}

bool OpenGLContext::areShadersAvailable() const
{
    auto* c = getCachedImage();
    return c != nullptr && c->shadersAvailable;
}

ReferenceCountedObject* OpenGLContext::getAssociatedObject (const char* name) const
{
    jassert (name != nullptr);

    auto* c = getCachedImage();

    // This method must only be called from an openGL rendering callback.
    jassert (c != nullptr && nativeContext != nullptr);
    jassert (getCurrentContext() != nullptr);

    auto index = c->associatedObjectNames.indexOf (name);
    return index >= 0 ? c->associatedObjects.getUnchecked (index).get() : nullptr;
}

void OpenGLContext::setAssociatedObject (const char* name, ReferenceCountedObject* newObject)
{
    jassert (name != nullptr);

    if (auto* c = getCachedImage())
    {
        // This method must only be called from an openGL rendering callback.
        jassert (nativeContext != nullptr);
        jassert (getCurrentContext() != nullptr);

        const int index = c->associatedObjectNames.indexOf (name);

        if (index >= 0)
        {
            if (newObject != nullptr)
            {
                c->associatedObjects.set (index, newObject);
            }
            else
            {
                c->associatedObjectNames.remove (index);
                c->associatedObjects.remove (index);
            }
        }
        else if (newObject != nullptr)
        {
            c->associatedObjectNames.add (name);
            c->associatedObjects.add (newObject);
        }
    }
}

void OpenGLContext::setImageCacheSize (size_t newSize) noexcept     { imageCacheMaxSize = newSize; }
size_t OpenGLContext::getImageCacheSize() const noexcept            { return imageCacheMaxSize; }

void OpenGLContext::execute (OpenGLContext::AsyncWorker::Ptr workerToUse, bool shouldBlock)
{
    if (auto* c = getCachedImage())
        c->execute (std::move (workerToUse), shouldBlock);
    else
        jassertfalse; // You must have attached the context to a component
}

//==============================================================================
struct DepthTestDisabler
{
    DepthTestDisabler() noexcept
    {
        glGetBooleanv (GL_DEPTH_TEST, &wasEnabled);

        if (wasEnabled)
            glDisable (GL_DEPTH_TEST);
    }

    ~DepthTestDisabler() noexcept
    {
        if (wasEnabled)
            glEnable (GL_DEPTH_TEST);
    }

    GLboolean wasEnabled;
};

//==============================================================================
void OpenGLContext::copyTexture (const Rectangle<int>& targetClipArea,
                                 const Rectangle<int>& anchorPosAndTextureSize,
                                 const int contextWidth, const int contextHeight,
                                 bool flippedVertically)
{
    if (contextWidth <= 0 || contextHeight <= 0)
        return;

    JUCE_CHECK_OPENGL_ERROR
    glBlendFunc (GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glEnable (GL_BLEND);

    DepthTestDisabler depthDisabler;

    if (areShadersAvailable())
    {
        struct OverlayShaderProgram  : public ReferenceCountedObject
        {
            OverlayShaderProgram (OpenGLContext& context)
                : program (context), builder (program), params (program)
            {}

            static const OverlayShaderProgram& select (OpenGLContext& context)
            {
                static const char programValueID[] = "juceGLComponentOverlayShader";
                OverlayShaderProgram* program = static_cast<OverlayShaderProgram*> (context.getAssociatedObject (programValueID));

                if (program == nullptr)
                {
                    program = new OverlayShaderProgram (context);
                    context.setAssociatedObject (programValueID, program);
                }

                program->program.use();
                return *program;
            }

            struct ProgramBuilder
            {
                ProgramBuilder (OpenGLShaderProgram& prog)
                {
                    prog.addVertexShader (OpenGLHelpers::translateVertexShaderToV3 (
                        "attribute " JUCE_HIGHP " vec2 position;"
                        "uniform " JUCE_HIGHP " vec2 screenSize;"
                        "uniform " JUCE_HIGHP " float textureBounds[4];"
                        "uniform " JUCE_HIGHP " vec2 vOffsetAndScale;"
                        "varying " JUCE_HIGHP " vec2 texturePos;"
                        "void main()"
                        "{"
                          JUCE_HIGHP " vec2 scaled = position / (0.5 * screenSize.xy);"
                          "gl_Position = vec4 (scaled.x - 1.0, 1.0 - scaled.y, 0, 1.0);"
                          "texturePos = (position - vec2 (textureBounds[0], textureBounds[1])) / vec2 (textureBounds[2], textureBounds[3]);"
                          "texturePos = vec2 (texturePos.x, vOffsetAndScale.x + vOffsetAndScale.y * texturePos.y);"
                        "}"));

                    prog.addFragmentShader (OpenGLHelpers::translateFragmentShaderToV3 (
                        "uniform sampler2D imageTexture;"
                        "varying " JUCE_HIGHP " vec2 texturePos;"
                        "void main()"
                        "{"
                          "gl_FragColor = texture2D (imageTexture, texturePos);"
                        "}"));

                    prog.link();
                }
            };

            struct Params
            {
                Params (OpenGLShaderProgram& prog)
                    : positionAttribute (prog, "position"),
                      screenSize (prog, "screenSize"),
                      imageTexture (prog, "imageTexture"),
                      textureBounds (prog, "textureBounds"),
                      vOffsetAndScale (prog, "vOffsetAndScale")
                {}

                void set (const float targetWidth, const float targetHeight, const Rectangle<float>& bounds, bool flipVertically) const
                {
                    const GLfloat m[] = { bounds.getX(), bounds.getY(), bounds.getWidth(), bounds.getHeight() };
                    textureBounds.set (m, 4);
                    imageTexture.set (0);
                    screenSize.set (targetWidth, targetHeight);

                    vOffsetAndScale.set (flipVertically ? 0.0f : 1.0f,
                                         flipVertically ? 1.0f : -1.0f);
                }

                OpenGLShaderProgram::Attribute positionAttribute;
                OpenGLShaderProgram::Uniform screenSize, imageTexture, textureBounds, vOffsetAndScale;
            };

            OpenGLShaderProgram program;
            ProgramBuilder builder;
            Params params;
        };

        auto left   = (GLshort) targetClipArea.getX();
        auto top    = (GLshort) targetClipArea.getY();
        auto right  = (GLshort) targetClipArea.getRight();
        auto bottom = (GLshort) targetClipArea.getBottom();
        const GLshort vertices[] = { left, bottom, right, bottom, left, top, right, top };

        auto& program = OverlayShaderProgram::select (*this);
        program.params.set ((float) contextWidth, (float) contextHeight, anchorPosAndTextureSize.toFloat(), flippedVertically);

        GLuint vertexBuffer = 0;
        extensions.glGenBuffers (1, &vertexBuffer);
        extensions.glBindBuffer (GL_ARRAY_BUFFER, vertexBuffer);
        extensions.glBufferData (GL_ARRAY_BUFFER, sizeof (vertices), vertices, GL_STATIC_DRAW);

        auto index = (GLuint) program.params.positionAttribute.attributeID;
        extensions.glVertexAttribPointer (index, 2, GL_SHORT, GL_FALSE, 4, nullptr);
        extensions.glEnableVertexAttribArray (index);
        JUCE_CHECK_OPENGL_ERROR

        if (extensions.glCheckFramebufferStatus (GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE)
        {
            glDrawArrays (GL_TRIANGLE_STRIP, 0, 4);

            extensions.glBindBuffer (GL_ARRAY_BUFFER, 0);
            extensions.glUseProgram (0);
            extensions.glDisableVertexAttribArray (index);
            extensions.glDeleteBuffers (1, &vertexBuffer);
        }
        else
        {
            clearGLError();
        }
    }
    else
    {
        jassert (attachment == nullptr); // Running on an old graphics card!
    }

    JUCE_CHECK_OPENGL_ERROR
}

#if JUCE_ANDROID
EGLDisplay OpenGLContext::NativeContext::display = EGL_NO_DISPLAY;
EGLDisplay OpenGLContext::NativeContext::config;

void OpenGLContext::NativeContext::surfaceCreated (LocalRef<jobject> holder)
{
    ignoreUnused (holder);

    if (auto* cachedImage = CachedImage::get (component))
    {
        if (auto* pool = cachedImage->renderThread.get())
        {
            if (! pool->contains (cachedImage))
            {
                cachedImage->resume();
                cachedImage->context.triggerRepaint();
            }
        }
    }
}

void OpenGLContext::NativeContext::surfaceDestroyed (LocalRef<jobject> holder)
{
    ignoreUnused (holder);

    // unlike the name suggests this will be called just before the
    // surface is destroyed. We need to pause the render thread.
    if (auto* cachedImage = CachedImage::get (component))
    {
        cachedImage->pause();

        if (auto* threadPool = cachedImage->renderThread.get())
            threadPool->waitForJobToFinish (cachedImage, -1);
    }
}
#endif

} // namespace juce