Implement high-dpi support

Wayland 1.2 added support for display scaling, where wl_output
has a "scale" event informing the the client that the compositor
will scale the output surfaces by the given factor. The client
then has the option of providing large surfaces to match the
target pixel densety and bypass the compositor's scaling. This
is done by calling wl_surface::set_buffer_scale.

Re-use the current high-dpi support in Qt by implementing
devicePixelRatio() for QWaylandScreen and QWaylandWindow.
Provide high resolution buffers both for raster and OpenGL
graphics.

Introduce a new coordinate system: buffer coordinates, which
is related to the window coordinate system via an "int scale"
scale factor. This scale factor corresponds to Qts qreal
devicePixelRatio, but we keep the name and the type in the
QtWayland implementation.

Change-Id: Ie10d7e5b4833480a9a25d96a26ad02150eb6e83f
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>

src/plugins/platforms/wayland/qwaylandbuffer_p.h

@@ -58,6 +58,7 @@ public:
     virtual ~QWaylandBuffer() { }
     wl_buffer *buffer() {return mBuffer;}
     virtual QSize size() const = 0;
+    virtual int scale() const { return 1; }
 
 protected:
     struct wl_buffer *mBuffer;

src/plugins/platforms/wayland/qwaylandscreen.cpp

@@ -59,6 +59,7 @@ QWaylandScreen::QWaylandScreen(QWaylandDisplay *waylandDisplay, int version, uin
     , m_outputId(id)
     , mWaylandDisplay(waylandDisplay)
     , mExtendedOutput(0)
+    , mScale(1)
     , mDepth(32)
     , mRefreshRate(60000)
     , mTransform(-1)
@@ -83,7 +84,9 @@ QWaylandDisplay * QWaylandScreen::display() const
 
 QRect QWaylandScreen::geometry() const
 {
-    return mGeometry;
+    // Scale geometry for QScreen. This makes window and screen
+    // geometry be in the same coordinate system.
+    return QRect(mGeometry.topLeft(), mGeometry.size() / mScale);
 }
 
 int QWaylandScreen::depth() const
@@ -127,6 +130,16 @@ Qt::ScreenOrientation QWaylandScreen::orientation() const
     return m_orientation;
 }
 
+int QWaylandScreen::scale() const
+{
+    return mScale;
+}
+
+qreal QWaylandScreen::devicePixelRatio() const
+{
+    return qreal(mScale);
+}
+
 qreal QWaylandScreen::refreshRate() const
 {
     return mRefreshRate / 1000.f;
@@ -188,6 +201,11 @@ void QWaylandScreen::output_geometry(int32_t x, int32_t y,
     mGeometry.moveTopLeft(QPoint(x, y));
 }
 
+void QWaylandScreen::output_scale(int32_t factor)
+{
+    mScale = factor;
+}
+
 void QWaylandScreen::output_done()
 {
     // the done event is sent after all the geometry and the mode events are sent,

src/plugins/platforms/wayland/qwaylandscreen_p.h

@@ -72,6 +72,8 @@ public:
     void setOrientationUpdateMask(Qt::ScreenOrientations mask);
 
     Qt::ScreenOrientation orientation() const;
+    int scale() const;
+    qreal devicePixelRatio() const Q_DECL_OVERRIDE;
     qreal refreshRate() const;
 
     QString name() const { return mOutputName; }
@@ -95,12 +97,14 @@ private:
                          const QString &make,
                          const QString &model,
                          int32_t transform) Q_DECL_OVERRIDE;
+    void output_scale(int32_t factor) Q_DECL_OVERRIDE;
     void output_done() Q_DECL_OVERRIDE;
 
     int m_outputId;
     QWaylandDisplay *mWaylandDisplay;
     QWaylandExtendedOutput *mExtendedOutput;
     QRect mGeometry;
+    int mScale;
     int mDepth;
     int mRefreshRate;
     int mTransform;

src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp

@@ -56,7 +56,7 @@
 QT_BEGIN_NAMESPACE
 
 QWaylandShmBuffer::QWaylandShmBuffer(QWaylandDisplay *display,
-                     const QSize &size, QImage::Format format)
+                     const QSize &size, QImage::Format format, int scale)
     : mMarginsImage(0)
 {
     int stride = size.width() * 4;
@@ -87,6 +87,8 @@ QWaylandShmBuffer::QWaylandShmBuffer(QWaylandDisplay *display,
     }
 
     mImage = QImage(data, size.width(), size.height(), stride, format);
+    mImage.setDevicePixelRatio(qreal(scale));
+
     mShmPool = wl_shm_create_pool(display->shm(), fd, alloc);
     mBuffer = wl_shm_pool_create_buffer(mShmPool,0, size.width(), size.height(),
                                        stride, WL_SHM_FORMAT_ARGB8888);
@@ -101,8 +103,10 @@ QWaylandShmBuffer::~QWaylandShmBuffer(void)
     wl_shm_pool_destroy(mShmPool);
 }
 
-QImage *QWaylandShmBuffer::imageInsideMargins(const QMargins &margins)
+QImage *QWaylandShmBuffer::imageInsideMargins(const QMargins &marginsIn)
 {
+    QMargins margins = marginsIn * int(mImage.devicePixelRatio());
+
     if (!margins.isNull() && margins != mMargins) {
         if (mMarginsImage) {
             delete mMarginsImage;
@@ -112,6 +116,7 @@ QImage *QWaylandShmBuffer::imageInsideMargins(const QMargins &margins)
         int b_s_width = mImage.size().width() - margins.left() - margins.right();
         int b_s_height = mImage.size().height() - margins.top() - margins.bottom();
         mMarginsImage = new QImage(b_s_data, b_s_width,b_s_height,mImage.bytesPerLine(),mImage.format());
+        mMarginsImage->setDevicePixelRatio(mImage.devicePixelRatio());
     }
     if (margins.isNull()) {
         delete mMarginsImage;
@@ -228,7 +233,7 @@ void QWaylandShmBackingStore::flush(QWindow *window, const QRegion &region, cons
 
     if (damageAll) {
         //need to damage it all, otherwise the attach offset may screw up
-        waylandWindow()->damage(QRect(QPoint(0,0),mFrontBuffer->size()));
+        waylandWindow()->damage(QRect(QPoint(0,0), window->size()));
     } else {
         QVector<QRect> rects = region.rects();
         for (int i = 0; i < rects.size(); i++) {
@@ -249,7 +254,8 @@ void QWaylandShmBackingStore::resize(const QSize &size, const QRegion &)
 void QWaylandShmBackingStore::resize(const QSize &size)
 {
     QMargins margins = windowDecorationMargins();
-    QSize sizeWithMargins = size + QSize(margins.left()+margins.right(),margins.top()+margins.bottom());
+    int scale = waylandWindow()->scale();
+    QSize sizeWithMargins = (size + QSize(margins.left()+margins.right(),margins.top()+margins.bottom())) * scale;
 
     QImage::Format format = QPlatformScreen::platformScreenForWindow(window())->format();
 
@@ -260,7 +266,7 @@ void QWaylandShmBackingStore::resize(const QSize &size)
         delete mBackBuffer; //we delete the attached buffer when we flush
     }
 
-    mBackBuffer = new QWaylandShmBuffer(mDisplay, sizeWithMargins, format);
+    mBackBuffer = new QWaylandShmBuffer(mDisplay, sizeWithMargins, format, scale);
 
     if (windowDecoration() && window()->isVisible())
         windowDecoration()->update();
@@ -354,7 +360,7 @@ void QWaylandShmBackingStore::done(void *data, wl_callback *callback, uint32_t t
             delete window->attached();
         }
         window->attachOffset(self->mFrontBuffer);
-        window->damage(QRect(QPoint(0,0),self->mFrontBuffer->size()));
+        window->damage(QRect(QPoint(0,0),window->geometry().size()));
         window->commit();
     }
 }

src/plugins/platforms/wayland/qwaylandshmbackingstore_p.h

@@ -57,9 +57,10 @@ class QWaylandWindow;
 class Q_WAYLAND_CLIENT_EXPORT QWaylandShmBuffer : public QWaylandBuffer {
 public:
     QWaylandShmBuffer(QWaylandDisplay *display,
-           const QSize &size, QImage::Format format);
+           const QSize &size, QImage::Format format, int scale = 1);
     ~QWaylandShmBuffer();
     QSize size() const { return mImage.size(); }
+    int scale() const Q_DECL_OVERRIDE { return int(mImage.devicePixelRatio()); }
     QImage *image() { return &mImage; }
 
     QImage *imageInsideMargins(const QMargins &margins);

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -126,6 +126,12 @@ QWaylandWindow::QWaylandWindow(QWindow *window)
         mShellSurface->setTopLevel();
     }
 
+    // Enable high-dpi rendering. Scale() returns the screen scale factor and will
+    // typically be integer 1 (normal-dpi) or 2 (high-dpi). Call set_buffer_scale()
+    // to inform the compositor that high-resolution buffers will be provided.
+    if (mDisplay->compositorVersion() >= 3)
+        set_buffer_scale(scale());
+
     setOrientationMask(window->screen()->orientationUpdateMask());
     setWindowFlags(window->flags());
     setGeometry_helper(window->geometry());
@@ -369,7 +375,6 @@ void QWaylandWindow::requestResize()
 void QWaylandWindow::attach(QWaylandBuffer *buffer, int x, int y)
 {
     mBuffer = buffer;
-
     if (mBuffer)
         attach(mBuffer->buffer(), x, y);
     else
@@ -707,6 +712,16 @@ bool QWaylandWindow::isExposed() const
     return QPlatformWindow::isExposed();
 }
 
+int QWaylandWindow::scale() const
+{
+    return screen()->scale();
+}
+
+qreal QWaylandWindow::devicePixelRatio() const
+{
+    return screen()->devicePixelRatio();
+}
+
 bool QWaylandWindow::setMouseGrabEnabled(bool grab)
 {
     if (window()->type() != Qt::Popup) {

src/plugins/platforms/wayland/qwaylandwindow_p.h

@@ -142,6 +142,9 @@ public:
 
     void setMask(const QRegion &region) Q_DECL_OVERRIDE;
 
+    int scale() const;
+    qreal devicePixelRatio() const Q_DECL_OVERRIDE;
+
     void requestActivateWindow() Q_DECL_OVERRIDE;
     bool isExposed() const Q_DECL_OVERRIDE;
     void unfocus();