kwin/platformsupport/scenes/opengl/backend.h

/*
    KWin - the KDE window manager
    This file is part of the KDE project.

    SPDX-FileCopyrightText: 2006 Lubos Lunak <l.lunak@kde.org>
    SPDX-FileCopyrightText: 2009, 2010, 2011 Martin Gräßlin <mgraesslin@kde.org>

    SPDX-License-Identifier: GPL-2.0-or-later
*/
#ifndef KWIN_SCENE_OPENGL_BACKEND_H
#define KWIN_SCENE_OPENGL_BACKEND_H

#include <QElapsedTimer>
#include <QRegion>

#include <kwin_export.h>

namespace KWin
{
class AbstractOutput;
class OpenGLBackend;
class OverlayWindow;
class SceneOpenGL;
class SceneOpenGLTexture;
class SceneOpenGLTexturePrivate;
class WindowPixmap;
class GLTexture;

/**
 * @brief The OpenGLBackend creates and holds the OpenGL context and is responsible for Texture from Pixmap.
 *
 * The OpenGLBackend is an abstract base class used by the SceneOpenGL to abstract away the differences
 * between various OpenGL windowing systems such as GLX and EGL.
 *
 * A concrete implementation has to create and release the OpenGL context in a way so that the
 * SceneOpenGL does not have to care about it.
 *
 * In addition a major task for this class is to generate the SceneOpenGLTexturePrivate which is
 * able to perform the texture from pixmap operation in the given backend.
 *
 * @author Martin Gräßlin <mgraesslin@kde.org>
 */
class KWIN_EXPORT OpenGLBackend
{
public:
    OpenGLBackend();
    virtual ~OpenGLBackend();

    virtual void init() = 0;
    /**
     * @return Time passes since start of rendering current frame.
     * @see startRenderTimer
     */
    qint64 renderTime() {
        return m_renderTimer.nsecsElapsed();
    }
    virtual void screenGeometryChanged(const QSize &size) = 0;
    virtual SceneOpenGLTexturePrivate *createBackendTexture(SceneOpenGLTexture *texture) = 0;

    /**
     * @brief Backend specific code to prepare the rendering of a frame including flushing the
     * previously rendered frame to the screen if the backend works this way.
     *
     * @return A region that if not empty will be repainted in addition to the damaged region
     */
    virtual QRegion prepareRenderingFrame() = 0;

    /**
     * Notifies about starting to paint.
     *
     * @p damage contains the reported damage as suggested by windows and effects on prepaint calls.
     */
    virtual void aboutToStartPainting(const QRegion &damage);

    /**
     * @brief Backend specific code to handle the end of rendering a frame.
     *
     * @param renderedRegion The possibly larger region that has been rendered
     * @param damagedRegion The damaged region that should be posted
     */
    virtual void endRenderingFrame(const QRegion &damage, const QRegion &damagedRegion) = 0;
    virtual void endRenderingFrameForScreen(int screenId, const QRegion &damage, const QRegion &damagedRegion);
    virtual bool makeCurrent() = 0;
    virtual void doneCurrent() = 0;
    virtual bool usesOverlayWindow() const = 0;
    /**
     * Whether the rendering needs to be split per screen.
     * Default implementation returns @c false.
     */
    virtual bool perScreenRendering() const;
    virtual QRegion prepareRenderingForScreen(int screenId);
    /**
     * @brief Compositor is going into idle mode, flushes any pending paints.
     */
    void idle();

    /**
     * @return bool Whether the scene needs to flush a frame.
     */
    bool hasPendingFlush() const {
        return !m_lastDamage.isEmpty();
    }

    /**
     * @brief Returns the OverlayWindow used by the backend.
     *
     * A backend does not have to use an OverlayWindow, this is mostly for the X world.
     * In case the backend does not use an OverlayWindow it is allowed to return @c null.
     * It's the task of the caller to check whether it is @c null.
     *
     * @return :OverlayWindow*
     */
    virtual OverlayWindow *overlayWindow() const;
    /**
     * @brief Whether the creation of the Backend failed.
     *
     * The SceneOpenGL should test whether the Backend got constructed correctly. If this method
     * returns @c true, the SceneOpenGL should not try to start the rendering.
     *
     * @return bool @c true if the creation of the Backend failed, @c false otherwise.
     */
    bool isFailed() const {
        return m_failed;
    }
    /**
     * @brief Whether the Backend provides VSync.
     *
     * Currently only the GLX backend can provide VSync.
     *
     * @return bool @c true if VSync support is available, @c false otherwise
     */
    bool syncsToVBlank() const {
        return m_syncsToVBlank;
    }
    /**
     * @brief Whether VSync blocks execution until the screen is in the retrace
     *
     * Case for waitVideoSync and non triple buffering buffer swaps
     *
     */
    bool blocksForRetrace() const {
        return m_blocksForRetrace;
    }
    /**
     * @brief Whether the backend uses direct rendering.
     *
     * Some OpenGLScene modes require direct rendering. E.g. the OpenGL 2 should not be used
     * if direct rendering is not supported by the Scene.
     *
     * @return bool @c true if the GL context is direct, @c false if indirect
     */
    bool isDirectRendering() const {
        return m_directRendering;
    }

    bool supportsBufferAge() const {
        return m_haveBufferAge;
    }

    bool supportsPartialUpdate() const
    {
        return m_havePartialUpdate;
    }
    bool supportsSwapBuffersWithDamage() const
    {
        return m_haveSwapBuffersWithDamage;
    }

    bool supportsSurfacelessContext() const
    {
        return m_haveSurfacelessContext;
    }

    /**
     * Returns the damage that has accumulated since a buffer of the given age was presented.
     */
    QRegion accumulatedDamageHistory(int bufferAge) const;

    /**
     * Saves the given region to damage history.
     */
    void addToDamageHistory(const QRegion &region);

    /**
     * The backend specific extensions (e.g. EGL/GLX extensions).
     *
     * Not the OpenGL (ES) extension!
     */
    QList<QByteArray> extensions() const {
        return m_extensions;
    }

    /**
     * @returns whether the backend specific extensions contains @p extension.
     */
    bool hasExtension(const QByteArray &extension) const {
        return m_extensions.contains(extension);
    }

    /**
     * Copy a region of pixels from the current read to the current draw buffer
     */
    void copyPixels(const QRegion &region);

    virtual QSharedPointer<GLTexture> textureForOutput(AbstractOutput *output) const;

protected:
    /**
     * @brief Backend specific flushing of frame to screen.
     */
    virtual void present() = 0;
    /**
     * @brief Sets the backend initialization to failed.
     *
     * This method should be called by the concrete subclass in case the initialization failed.
     * The given @p reason is logged as a warning.
     *
     * @param reason The reason why the initialization failed.
     */
    void setFailed(const QString &reason);
    /**
     * @brief Sets whether the backend provides VSync.
     *
     * Should be called by the concrete subclass once it is determined whether VSync is supported.
     * If the subclass does not call this method, the backend defaults to @c false.
     * @param enabled @c true if VSync support available, @c false otherwise.
     */
    void setSyncsToVBlank(bool enabled) {
        m_syncsToVBlank = enabled;
    }
    /**
     * @brief Sets whether the VSync iplementation blocks
     *
     * Should be called by the concrete subclass once it is determined how VSync works.
     * If the subclass does not call this method, the backend defaults to @c false.
     * @param enabled @c true if VSync blocks, @c false otherwise.
     */
    void setBlocksForRetrace(bool enabled) {
        m_blocksForRetrace = enabled;
    }
    /**
     * @brief Sets whether the OpenGL context is direct.
     *
     * Should be called by the concrete subclass once it is determined whether the OpenGL context is
     * direct or indirect.
     * If the subclass does not call this method, the backend defaults to @c false.
     *
     * @param direct @c true if the OpenGL context is direct, @c false if indirect
     */
    void setIsDirectRendering(bool direct) {
        m_directRendering = direct;
    }

    void setSupportsBufferAge(bool value) {
        m_haveBufferAge = value;
    }

    void setSupportsPartialUpdate(bool value)
    {
        m_havePartialUpdate = value;
    }

    void setSupportsSwapBuffersWithDamage(bool value)
    {
        m_haveSwapBuffersWithDamage = value;
    }

    void setSupportsSurfacelessContext(bool value)
    {
        m_haveSurfacelessContext = value;
    }

    /**
     * @return const QRegion& Damage of previously rendered frame
     */
    const QRegion &lastDamage() const {
        return m_lastDamage;
    }
    void setLastDamage(const QRegion &damage) {
        m_lastDamage = damage;
    }
    /**
     * @brief Starts the timer for how long it takes to render the frame.
     *
     * @see renderTime
     */
    void startRenderTimer() {
        m_renderTimer.start();
    }

    /**
     * Sets the platform-specific @p extensions.
     *
     * These are the EGL/GLX extensions, not the OpenGL extensions
     */
    void setExtensions(const QList<QByteArray> &extensions) {
        m_extensions = extensions;
    }

private:
    /**
     * @brief Whether VSync is available and used, defaults to @c false.
     */
    bool m_syncsToVBlank;
    /**
     * @brief Whether present() will block execution until the next vertical retrace @c false.
     */
    bool m_blocksForRetrace;
    /**
     * @brief Whether direct rendering is used, defaults to @c false.
     */
    bool m_directRendering;
    /**
     * @brief Whether the backend supports GLX_EXT_buffer_age / EGL_EXT_buffer_age.
     */
    bool m_haveBufferAge;
    /**
     * @brief Whether the backend supports EGL_KHR_partial_update
     */
    bool m_havePartialUpdate;
    bool m_haveSwapBuffersWithDamage = false;
    /**
     * @brief Whether the backend supports EGL_KHR_surfaceless_context.
     */
    bool m_haveSurfacelessContext = false;
    /**
     * @brief Whether the initialization failed, of course default to @c false.
     */
    bool m_failed;
    /**
     * @brief Damaged region of previously rendered frame.
     */
    QRegion m_lastDamage;
    /**
     * @brief The damage history for the past 10 frames.
     */
    QList<QRegion> m_damageHistory;
    /**
     * @brief Timer to measure how long a frame renders.
     */
    QElapsedTimer m_renderTimer;

    QList<QByteArray> m_extensions;
};

}

#endif