Cocoa: impl. performance boost for dnd

It turns out that registering drag types for each NSView that can
receive drop events is _really_ slow. And many widget in Qt
subscribe for DnD (QTextEdit, QScrollArea, etc), so the result is
an application that will spend startup time preparing for DnD. For
some edge cases, we're talking several seconds!
This patch removes this overhead by moving drag type registering
out of NSView, and into NSWindow (that is, QCocoaWindow and
QCocoaPanel).

Task-number: QT-1586
Reviewed-by: Prasanth

1 files changed, 126 insertions, 0 deletions

diff --git a/src/gui/kernel/qcocoasharedwindowmethods_mac_p.h b/src/gui/kernel/qcocoasharedwindowmethods_mac_p.h
index f347240..8dd03aa 100644
--- a/src/gui/kernel/qcocoasharedwindowmethods_mac_p.h
+++ b/src/gui/kernel/qcocoasharedwindowmethods_mac_p.h
@@ -54,8 +54,31 @@
 QT_BEGIN_NAMESPACE
 extern Qt::MouseButton cocoaButton2QtButton(NSInteger buttonNum); // qcocoaview.mm
 extern QPointer<QWidget> qt_button_down; //qapplication_mac.cpp
+extern const QStringList& qEnabledDraggedTypes(); // qmime_mac.cpp
+
+Q_GLOBAL_STATIC(QPointer<QWidget>, currentDragTarget);
+
 QT_END_NAMESPACE
 
+- (id)initWithContentRect:(NSRect)contentRect
+    styleMask:(NSUInteger)windowStyle
+    backing:(NSBackingStoreType)bufferingType
+    defer:(BOOL)deferCreation
+{
+    self = [super initWithContentRect:contentRect styleMask:windowStyle
+        backing:bufferingType defer:deferCreation];
+    if (self) {
+        currentCustomDragTypes = 0;
+    }
+    return self;
+}
+
+- (void)dealloc
+{
+    delete currentCustomDragTypes;
+    [super dealloc];
+}
+
 - (BOOL)canBecomeKeyWindow
 {
     QWidget *widget = [self QT_MANGLE_NAMESPACE(qt_qwidget)];
@@ -185,3 +208,106 @@ QT_END_NAMESPACE
     return [super frameViewClassForStyleMask:styleMask];
 }
 
+-(void)registerDragTypes
+{
+    // Calling registerForDraggedTypes below is slow, so only do
+    // it once for each window, or when the custom types change.
+    QMacCocoaAutoReleasePool pool;
+    const QStringList& customTypes = qEnabledDraggedTypes();
+    if (currentCustomDragTypes == 0 || *currentCustomDragTypes != customTypes) {
+        if (currentCustomDragTypes == 0)
+            currentCustomDragTypes = new QStringList();
+        *currentCustomDragTypes = customTypes;
+        const NSString* mimeTypeGeneric = @"com.trolltech.qt.MimeTypeName";
+        NSMutableArray *supportedTypes = [NSMutableArray arrayWithObjects:NSColorPboardType,
+                       NSFilenamesPboardType, NSStringPboardType,
+                       NSFilenamesPboardType, NSPostScriptPboardType, NSTIFFPboardType,
+                       NSRTFPboardType, NSTabularTextPboardType, NSFontPboardType,
+                       NSRulerPboardType, NSFileContentsPboardType, NSColorPboardType,
+                       NSRTFDPboardType, NSHTMLPboardType, NSPICTPboardType,
+                       NSURLPboardType, NSPDFPboardType, NSVCardPboardType,
+                       NSFilesPromisePboardType, NSInkTextPboardType,
+                       NSMultipleTextSelectionPboardType, mimeTypeGeneric, nil];
+        // Add custom types supported by the application.
+        for (int i = 0; i < customTypes.size(); i++) {
+           [supportedTypes addObject:reinterpret_cast<const NSString *>(QCFString::toCFStringRef(customTypes[i]))];
+        }
+        [self registerForDraggedTypes:supportedTypes];
+    }
+}
+
+- (QWidget *)dragTargetHitTest:(id <NSDraggingInfo>)sender
+{
+    // Do a hittest to find the NSView under the
+    // mouse, and return the corresponding QWidget:
+    NSPoint windowPoint = [sender draggingLocation];
+    NSView *candidateView = [[self contentView] hitTest:windowPoint];
+    if (![candidateView isKindOfClass:[QT_MANGLE_NAMESPACE(QCocoaView) class]])
+        return 0;
+    return [static_cast<QT_MANGLE_NAMESPACE(QCocoaView) *>(candidateView) qt_qwidget];
+}
+
+- (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender
+{
+    // The user dragged something into the window. Send a draggingEntered message
+    // to the QWidget under the mouse. As the drag moves over the window, and over
+    // different widgets, we will handle enter and leave events from within 
+    // draggingUpdated below. The reason why we handle this ourselves rather than
+    // subscribing for drag events directly in QCocoaView is that calling 
+    // registerForDraggedTypes on the views will severly degrade initialization time
+    // for an application that uses a lot of drag subscribing widgets.
+
+    QWidget *target = [self dragTargetHitTest:sender];
+    if (!target)
+        return [super draggingEntered:sender];
+    if (target->testAttribute(Qt::WA_DropSiteRegistered) == false)
+        return NSDragOperationNone;
+
+    *currentDragTarget() = target;
+    return [reinterpret_cast<NSView *>((*currentDragTarget())->winId()) draggingEntered:sender];
+ }
+
+- (NSDragOperation)draggingUpdated:(id < NSDraggingInfo >)sender
+{
+    QWidget *target = [self dragTargetHitTest:sender];
+    if (!target)
+        return [super draggingUpdated:sender];
+
+    if (target == *currentDragTarget()) {
+        // The drag continues to move over the widget that we have sendt
+        // a draggingEntered message to. So just update the view:
+        return [reinterpret_cast<NSView *>((*currentDragTarget())->winId()) draggingUpdated:sender];
+    } else {
+        // The widget under the mouse has changed.
+        // So we need to fake enter/leave events:
+        if (*currentDragTarget())
+            [reinterpret_cast<NSView *>((*currentDragTarget())->winId()) draggingExited:sender];
+        if (target->testAttribute(Qt::WA_DropSiteRegistered) == false) {
+            *currentDragTarget() = 0;
+            return NSDragOperationNone;
+        }
+        *currentDragTarget() = target;
+        return [reinterpret_cast<NSView *>((*currentDragTarget())->winId()) draggingEntered:sender];
+    }
+}
+
+- (void)draggingExited:(id < NSDraggingInfo >)sender
+{
+    if (*currentDragTarget())
+        [reinterpret_cast<NSView *>((*currentDragTarget())->winId()) draggingExited:sender];
+    else
+        [super draggingExited:sender];
+    *currentDragTarget() = 0;
+}
+
+- (BOOL)performDragOperation:(id < NSDraggingInfo >)sender
+{
+    BOOL dropAccepted = NO;
+    if (*currentDragTarget())
+        dropAccepted = [reinterpret_cast<NSView *>((*currentDragTarget())->winId()) performDragOperation:sender];
+    else
+        return [super performDragOperation:sender];
+    *currentDragTarget() = 0;
+    return dropAccepted;
+}
+