Bug 484729: [GTK3] Eclipse IDE consumes CPU when idle

Bug 479998 introduced a call to getClientArea() in Composite.gtk_draw().
This calls forceResize() in both the Composite and the parent Control,
which causes unnecessary overhead. It also causes a paint loop in
CTabFolder, with never ending calls to
gdk_cairo_region_create_from_surface(). The looped system calls to GDK
cause high CPU usage.

To remedy this we can use a GtkAllocation instead of calling
getClientArea(): this is far more efficient and does not trigger any
additional SWT machinery.

Tested on GTK3.18.6, 3.14, and 2.24. AllNonBrowser JUnit tests pass on
GTK3 and GTK2.

Change-Id: Ib1e5900e5c9339e9c0555a9436e8b2a9949b6372
Signed-off-by: Eric Williams <ericwill@redhat.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Composite.java b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Composite.java
index 4aef32c917..f45f78e801 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Composite.java
+++ b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Composite.java
@@ -355,9 +355,14 @@ void createHandle (int index, boolean fixed, boolean scrolled) {
 @Override
 long /*int*/ gtk_draw (long /*int*/ widget, long /*int*/ cairo) {
 	if (OS.GTK_VERSION >= OS.VERSION(3, 16, 0)) {
-		Rectangle area = getClientArea();
 		long /*int*/ context = OS.gtk_widget_get_style_context(widget);
-		OS.gtk_render_background(context, cairo, area.x, area.y, area.width, area.height);
+		GtkAllocation allocation = new GtkAllocation();
+		OS.gtk_widget_get_allocation (widget, allocation);
+		int width = (state & ZERO_WIDTH) != 0 ? 0 : allocation.width;
+		int height = (state & ZERO_HEIGHT) != 0 ? 0 : allocation.height;
+		// We specify a 0 value for x & y as we want the whole widget to be
+		// colored, not some portion of it.
+		OS.gtk_render_background(context, cairo, 0, 0, width, height);
 	}
 	return super.gtk_draw(widget, cairo);
 }