// Copyright (C) 2016 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 <QtOpenGL/QOpenGLFramebufferObject>
#include <QtGui/QOpenGLContext>
#include <QtGui/QWindow>
#include <QtGui/private/qrhi_p.h>
#include <qpa/qplatformbackingstore.h>

#include "qopenglcompositor_p.h"

QT_BEGIN_NAMESPACE

/*!
    \class QOpenGLCompositor
    \brief A generic OpenGL-based compositor
    \since 5.4
    \internal
    \ingroup qpa

    This class provides a lightweight compositor that maintains the
    basic stacking order of windows and composites them by drawing
    textured quads via OpenGL.

    It it meant to be used by platform plugins that run without a
    windowing system.

    It is up to the platform plugin to manage the lifetime of the
    compositor (instance(), destroy()), set the correct destination
    context and window as early as possible (setTarget()),
    register the composited windows as they are shown, activated,
    raised and lowered (addWindow(), moveToTop(), etc.), and to
    schedule repaints (update()).

    \note To get support for QWidget-based windows, just use
    QOpenGLCompositorBackingStore. It will automatically create
    textures from the raster-rendered content and trigger the
    necessary repaints.
 */

static QOpenGLCompositor *compositor = 0;

QOpenGLCompositor::QOpenGLCompositor()
    : m_context(0),
      m_targetWindow(0),
      m_rotation(0)
{
    Q_ASSERT(!compositor);
    m_updateTimer.setSingleShot(true);
    m_updateTimer.setInterval(0);
    connect(&m_updateTimer, SIGNAL(timeout()), SLOT(handleRenderAllRequest()));
}

QOpenGLCompositor::~QOpenGLCompositor()
{
    Q_ASSERT(compositor == this);
    m_blitter.destroy();
    compositor = 0;
}

void QOpenGLCompositor::setTargetWindow(QWindow *targetWindow, const QRect &nativeTargetGeometry)
{
    m_targetWindow = targetWindow;
    m_nativeTargetGeometry = nativeTargetGeometry;
}

void QOpenGLCompositor::setTargetContext(QOpenGLContext *context)
{
    m_context = context;
}

void QOpenGLCompositor::setRotation(int degrees)
{
    m_rotation = degrees;
    m_rotationMatrix.setToIdentity();
    m_rotationMatrix.rotate(degrees, 0, 0, 1);
}

void QOpenGLCompositor::update()
{
    if (!m_updateTimer.isActive())
        m_updateTimer.start();
}

QImage QOpenGLCompositor::grab()
{
    Q_ASSERT(m_context && m_targetWindow);
    m_context->makeCurrent(m_targetWindow);
    QScopedPointer<QOpenGLFramebufferObject> fbo(new QOpenGLFramebufferObject(m_nativeTargetGeometry.size()));
    renderAll(fbo.data());
    return fbo->toImage();
}

void QOpenGLCompositor::handleRenderAllRequest()
{
    Q_ASSERT(m_context && m_targetWindow);
    m_context->makeCurrent(m_targetWindow);
    renderAll(0);
}

void QOpenGLCompositor::renderAll(QOpenGLFramebufferObject *fbo)
{
    if (fbo)
        fbo->bind();

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
    glViewport(0, 0, m_nativeTargetGeometry.width(), m_nativeTargetGeometry.height());

    if (!m_blitter.isCreated())
        m_blitter.create();

    m_blitter.bind();

    for (int i = 0; i < m_windows.size(); ++i)
        m_windows.at(i)->beginCompositing();

    for (int i = 0; i < m_windows.size(); ++i)
        render(m_windows.at(i));

    m_blitter.release();
    if (!fbo)
        m_context->swapBuffers(m_targetWindow);
    else
        fbo->release();

    for (int i = 0; i < m_windows.size(); ++i)
        m_windows.at(i)->endCompositing();
}

struct BlendStateBinder
{
    BlendStateBinder() : m_blend(false) {
        glDisable(GL_BLEND);
    }
    void set(bool blend) {
        if (blend != m_blend) {
            if (blend) {
                glEnable(GL_BLEND);
                glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            } else {
                glDisable(GL_BLEND);
            }
            m_blend = blend;
        }
    }
    ~BlendStateBinder() {
        if (m_blend)
            glDisable(GL_BLEND);
    }
    bool m_blend;
};

static inline QRect toBottomLeftRect(const QRect &topLeftRect, int windowHeight)
{
    return QRect(topLeftRect.x(), windowHeight - topLeftRect.bottomRight().y() - 1,
                 topLeftRect.width(), topLeftRect.height());
}

static void clippedBlit(const QPlatformTextureList *textures, int idx, const QRect &sourceWindowRect,
                        const QRect &targetWindowRect,
                        QOpenGLTextureBlitter *blitter, QMatrix4x4 *rotationMatrix)
{
    const QRect clipRect = textures->clipRect(idx);
    if (clipRect.isEmpty())
        return;

    const QRect rectInWindow = textures->geometry(idx).translated(sourceWindowRect.topLeft());
    const QRect clippedRectInWindow = rectInWindow & clipRect.translated(rectInWindow.topLeft());
    const QRect srcRect = toBottomLeftRect(clipRect, rectInWindow.height());

    QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(clippedRectInWindow, targetWindowRect);
    if (rotationMatrix)
        target = *rotationMatrix * target;

    const QMatrix3x3 source = QOpenGLTextureBlitter::sourceTransform(srcRect, rectInWindow.size(),
                                                                     QOpenGLTextureBlitter::OriginBottomLeft);

    const uint textureId = textures->texture(idx)->nativeTexture().object;
    blitter->blit(textureId, target, source);
}

void QOpenGLCompositor::render(QOpenGLCompositorWindow *window)
{
    const QPlatformTextureList *textures = window->textures();
    if (!textures)
        return;

    const QRect targetWindowRect(QPoint(0, 0), m_targetWindow->geometry().size());
    float currentOpacity = 1.0f;
    BlendStateBinder blend;
    const QRect sourceWindowRect = window->sourceWindow()->geometry();
    for (int i = 0; i < textures->count(); ++i) {
        const uint textureId = textures->texture(i)->nativeTexture().object;
        const float opacity = window->sourceWindow()->opacity();
        if (opacity != currentOpacity) {
            currentOpacity = opacity;
            m_blitter.setOpacity(currentOpacity);
        }

        if (textures->count() > 1 && i == textures->count() - 1) {
            // Backingstore for a widget with QOpenGLWidget subwidgets
            blend.set(true);
            QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(textures->geometry(i), targetWindowRect);
            if (m_rotation)
                target = m_rotationMatrix * target;
            m_blitter.blit(textureId, target, QOpenGLTextureBlitter::OriginTopLeft);
        } else if (textures->count() == 1) {
            // A regular QWidget window
            const bool translucent = window->sourceWindow()->requestedFormat().alphaBufferSize() > 0;
            blend.set(translucent);
            QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(textures->geometry(i), targetWindowRect);
            if (m_rotation)
                target = m_rotationMatrix * target;
            m_blitter.blit(textureId, target, QOpenGLTextureBlitter::OriginTopLeft);
        } else if (!textures->flags(i).testFlag(QPlatformTextureList::StacksOnTop)) {
            // Texture from an FBO belonging to a QOpenGLWidget or QQuickWidget
            blend.set(false);
            clippedBlit(textures, i, sourceWindowRect, targetWindowRect, &m_blitter, m_rotation ? &m_rotationMatrix : nullptr);
        }
    }

    for (int i = 0; i < textures->count(); ++i) {
        if (textures->flags(i).testFlag(QPlatformTextureList::StacksOnTop)) {
            blend.set(true);
            clippedBlit(textures, i, sourceWindowRect, targetWindowRect, &m_blitter, m_rotation ? &m_rotationMatrix : nullptr);
        }
    }

    m_blitter.setOpacity(1.0f);
}

QOpenGLCompositor *QOpenGLCompositor::instance()
{
    if (!compositor)
        compositor = new QOpenGLCompositor;
    return compositor;
}

void QOpenGLCompositor::destroy()
{
    delete compositor;
    compositor = 0;
}

void QOpenGLCompositor::addWindow(QOpenGLCompositorWindow *window)
{
    if (!m_windows.contains(window)) {
        m_windows.append(window);
        emit topWindowChanged(window);
    }
}

void QOpenGLCompositor::removeWindow(QOpenGLCompositorWindow *window)
{
    m_windows.removeOne(window);
    if (!m_windows.isEmpty())
        emit topWindowChanged(m_windows.last());
}

void QOpenGLCompositor::moveToTop(QOpenGLCompositorWindow *window)
{
    m_windows.removeOne(window);
    m_windows.append(window);
    emit topWindowChanged(window);
}

void QOpenGLCompositor::changeWindowIndex(QOpenGLCompositorWindow *window, int newIdx)
{
    int idx = m_windows.indexOf(window);
    if (idx != -1 && idx != newIdx) {
        m_windows.move(idx, newIdx);
        if (newIdx == m_windows.size() - 1)
            emit topWindowChanged(m_windows.last());
    }
}

QT_END_NAMESPACE

#include "moc_qopenglcompositor_p.cpp"