Let QScreen::grabWindow's winId parameter default to 0 and add test

The platform plugins are implemented to grab the entire screen if
no window ID is provided. They do not grab the entire virtual
screen, just the screen the method is called on.

On macOS, the implementation ignored the window parameter, and
always grabbed the entire virtual screen. This change fixes the
cocoa implementation. The test passes in local tests (with two
displays with different dpr). Since grabbing a screen returns an
image with managed colors, we need to convert it to sRGB color
spec first, otherwise displaying a grabbed image will produce
different results. This will need to be changed once Qt supports
a fully color managed flow.

The test does not cover the case where a window spans multiple
displays, since this is generally not supported at least on macOS.
The code that exists in QCocoaScreen to handle that case is
untested, but with the exception of the optimization it is also
unchanged.

Done-with: Morten Sørvig <morten.sorvig@qt.io>
Change-Id: I8ac1233e56d559230ff9e10111abfb6227431e8c
Fixes: QTBUG-84876
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

2 files changed, 77 insertions, 43 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoascreen.h b/src/plugins/platforms/cocoa/qcocoascreen.h
index 5a5d7fc735..ffbb67b677 100644
--- a/src/plugins/platforms/cocoa/qcocoascreen.h
+++ b/src/plugins/platforms/cocoa/qcocoascreen.h
@@ -79,6 +79,7 @@ public:
 
     // ----------------------------------------------------
 
+    static NSScreen *nativeScreenForDisplayId(CGDirectDisplayID displayId);
     NSScreen *nativeScreen() const;
 
     void requestUpdate();
diff --git a/src/plugins/platforms/cocoa/qcocoascreen.mm b/src/plugins/platforms/cocoa/qcocoascreen.mm
index ebf1afb57d..70d02d1a0d 100644
--- a/src/plugins/platforms/cocoa/qcocoascreen.mm
+++ b/src/plugins/platforms/cocoa/qcocoascreen.mm
@@ -592,70 +592,99 @@ QWindow *QCocoaScreen::topLevelAt(const QPoint &point) const
     return window;
 }
 
+/*!
+    \internal
+
+    Coordinates are in screen coordinates if \a view is 0, otherwise they are in view
+    coordiantes.
+*/
 QPixmap QCocoaScreen::grabWindow(WId view, int x, int y, int width, int height) const
 {
-    // Determine the grab rect. FIXME: The rect should be bounded by the view's
-    // geometry, but note that for the pixeltool use case that window will be the
-    // desktop widget's view, which currently gets resized to fit one screen
-    // only, since its NSWindow has the NSWindowStyleMaskTitled flag set.
-    Q_UNUSED(view);
+    /*
+       Grab the grabRect section of the specified display into a pixmap that has
+       sRGB color spec. Once Qt supports a fully color-managed flow and conversions
+       that don't lose the colorspec information, we would want the image to maintain
+       the color spec of the display from which it was grabbed. Ultimately, rendering
+       the returned pixmap on the same display from which it was grabbed should produce
+       identical visual results.
+    */
+    auto grabFromDisplay = [](CGDirectDisplayID displayId, const QRect &grabRect) -> QPixmap {
+        QCFType<CGImageRef> image = CGDisplayCreateImageForRect(displayId, grabRect.toCGRect());
+        const QCFType<CGColorSpaceRef> sRGBcolorSpace = CGColorSpaceCreateWithName(kCGColorSpaceSRGB);
+        if (CGImageGetColorSpace(image) != sRGBcolorSpace) {
+            qCDebug(lcQpaScreen) << "applying color correction for display" << displayId;
+            image = CGImageCreateCopyWithColorSpace(image, sRGBcolorSpace);
+        }
+        QPixmap pixmap = QPixmap::fromImage(qt_mac_toQImage(image));
+        pixmap.setDevicePixelRatio(nativeScreenForDisplayId(displayId).backingScaleFactor);
+        return pixmap;
+    };
+
     QRect grabRect = QRect(x, y, width, height);
     qCDebug(lcQpaScreen) << "input grab rect" << grabRect;
 
-    // Find which displays to grab from, or all of them if the grab size is unspecified
+    if (!view) {
+        // coordinates are relative to the screen
+        if (!grabRect.isValid()) // entire screen
+            grabRect = QRect(QPoint(0, 0), geometry().size());
+        else
+            grabRect.translate(-geometry().topLeft());
+        return grabFromDisplay(displayId(), grabRect);
+    }
+
+    // grab the window; grab rect in window coordinates might span multiple screens
+    NSView *nsView = reinterpret_cast<NSView*>(view);
+    NSPoint windowPoint = [nsView convertPoint:NSMakePoint(0, 0) toView:nil];
+    NSRect screenRect = [nsView.window convertRectToScreen:NSMakeRect(windowPoint.x, windowPoint.y, 1, 1)];
+    QPoint position = mapFromNative(screenRect.origin).toPoint();
+    QSize size = QRectF::fromCGRect(NSRectToCGRect(nsView.bounds)).toRect().size();
+    QRect windowRect = QRect(position, size);
+    if (!grabRect.isValid())
+        grabRect = windowRect;
+    else
+        grabRect.translate(windowRect.topLeft());
+
+    // Find which displays to grab from
     const int maxDisplays = 128;
     CGDirectDisplayID displays[maxDisplays];
     CGDisplayCount displayCount;
-    CGRect cgRect = (width < 0 || height < 0) ? CGRectInfinite : grabRect.toCGRect();
+    CGRect cgRect = grabRect.isValid() ? grabRect.toCGRect() : CGRectInfinite;
     const CGDisplayErr err = CGGetDisplaysWithRect(cgRect, maxDisplays, displays, &displayCount);
     if (err || displayCount == 0)
         return QPixmap();
 
-    // If the grab size is not specified, set it to be the bounding box of all screens,
-    if (width < 0 || height < 0) {
-        QRect windowRect;
-        for (uint i = 0; i < displayCount; ++i) {
-            QRect displayBounds = QRectF::fromCGRect(CGDisplayBounds(displays[i])).toRect();
-            // Only include the screen if it is positioned past the x/y position
-            if ((displayBounds.x() >= x || displayBounds.right() > x) &&
-                (displayBounds.y() >= y || displayBounds.bottom() > y)) {
-                windowRect = windowRect.united(displayBounds);
-            }
-        }
-        if (grabRect.width() < 0)
-            grabRect.setWidth(windowRect.width());
-        if (grabRect.height() < 0)
-            grabRect.setHeight(windowRect.height());
-    }
-
     qCDebug(lcQpaScreen) << "final grab rect" << grabRect << "from" << displayCount << "displays";
 
     // Grab images from each display
-    QVector<QImage> images;
+    QVector<QPixmap> pixmaps;
     QVector<QRect> destinations;
     for (uint i = 0; i < displayCount; ++i) {
         auto display = displays[i];
-        QRect displayBounds = QRectF::fromCGRect(CGDisplayBounds(display)).toRect();
-        QRect grabBounds = displayBounds.intersected(grabRect);
+        const QRect displayBounds = QRectF::fromCGRect(CGDisplayBounds(display)).toRect();
+        const QRect grabBounds = displayBounds.intersected(grabRect);
         if (grabBounds.isNull()) {
             destinations.append(QRect());
-            images.append(QImage());
+            pixmaps.append(QPixmap());
             continue;
         }
-        QRect displayLocalGrabBounds = QRect(QPoint(grabBounds.topLeft() - displayBounds.topLeft()), grabBounds.size());
-        QImage displayImage = qt_mac_toQImage(QCFType<CGImageRef>(CGDisplayCreateImageForRect(display, displayLocalGrabBounds.toCGRect())));
-        displayImage.setDevicePixelRatio(displayImage.size().width() / displayLocalGrabBounds.size().width());
-        images.append(displayImage);
-        QRect destBounds = QRect(QPoint(grabBounds.topLeft() - grabRect.topLeft()), grabBounds.size());
+        const QRect displayLocalGrabBounds = QRect(QPoint(grabBounds.topLeft() - displayBounds.topLeft()), grabBounds.size());
+
+        qCDebug(lcQpaScreen) << "grab display" << i << "global" << grabBounds << "local" << displayLocalGrabBounds;
+        QPixmap displayPixmap = grabFromDisplay(display, displayLocalGrabBounds);
+        // Fast path for when grabbing from a single screen only
+        if (displayCount == 1)
+            return displayPixmap;
+
+        qCDebug(lcQpaScreen) << "grab sub-image size" << displayPixmap.size() << "devicePixelRatio" << displayPixmap.devicePixelRatio();
+        pixmaps.append(displayPixmap);
+        const QRect destBounds = QRect(QPoint(grabBounds.topLeft() - grabRect.topLeft()), grabBounds.size());
         destinations.append(destBounds);
-        qCDebug(lcQpaScreen) << "grab display" << i << "global" << grabBounds << "local" << displayLocalGrabBounds
-                             << "grab image size" << displayImage.size() << "devicePixelRatio" << displayImage.devicePixelRatio();
     }
 
     // Determine the highest dpr, which becomes the dpr for the returned pixmap.
     qreal dpr = 1.0;
     for (uint i = 0; i < displayCount; ++i)
-        dpr = qMax(dpr, images.at(i).devicePixelRatio());
+        dpr = qMax(dpr, pixmaps.at(i).devicePixelRatio());
 
     // Allocate target pixmap and draw each screen's content
     qCDebug(lcQpaScreen) << "Create grap pixmap" << grabRect.size() << "at devicePixelRatio" << dpr;
@@ -664,7 +693,7 @@ QPixmap QCocoaScreen::grabWindow(WId view, int x, int y, int width, int height)
     windowPixmap.fill(Qt::transparent);
     QPainter painter(&windowPixmap);
     for (uint i = 0; i < displayCount; ++i)
-        painter.drawImage(destinations.at(i), images.at(i));
+        painter.drawPixmap(destinations.at(i), pixmaps.at(i));
 
     return windowPixmap;
 }
@@ -754,19 +783,23 @@ QCocoaScreen *QCocoaScreen::get(CFUUIDRef uuid)
     return nullptr;
 }
 
-NSScreen *QCocoaScreen::nativeScreen() const
+NSScreen *QCocoaScreen::nativeScreenForDisplayId(CGDirectDisplayID displayId)
 {
-    if (!m_displayId)
-        return nil; // The display has been disconnected
-
     for (NSScreen *screen in NSScreen.screens) {
-        if (screen.qt_displayId == m_displayId)
+        if (screen.qt_displayId == displayId)
             return screen;
     }
-
     return nil;
 }
 
+NSScreen *QCocoaScreen::nativeScreen() const
+{
+    if (!m_displayId)
+        return nil; // The display has been disconnected
+
+    return nativeScreenForDisplayId(m_displayId);
+}
+
 CGPoint QCocoaScreen::mapToNative(const QPointF &pos, QCocoaScreen *screen)
 {
     Q_ASSERT(screen);