tmf: Cache the result of gc.getFontMetrics in callstack view

This is a major performance bottleneck on Linux/GTK when a lot of elements are
drawn.

Change-Id: I5259a8910f08b6602801f97fc200b00b7c55c4a1
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/34605
Tested-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/lttng/org.eclipse.linuxtools.tmf.ui/src/org/eclipse/linuxtools/tmf/ui/views/callstack/CallStackPresentationProvider.java b/lttng/org.eclipse.linuxtools.tmf.ui/src/org/eclipse/linuxtools/tmf/ui/views/callstack/CallStackPresentationProvider.java
index 9eb7425da4..0fc2f6b774 100644
--- a/lttng/org.eclipse.linuxtools.tmf.ui/src/org/eclipse/linuxtools/tmf/ui/views/callstack/CallStackPresentationProvider.java
+++ b/lttng/org.eclipse.linuxtools.tmf.ui/src/org/eclipse/linuxtools/tmf/ui/views/callstack/CallStackPresentationProvider.java
@@ -44,6 +44,8 @@ public class CallStackPresentationProvider extends TimeGraphPresentationProvider
 
     private final CallStackView fView;
 
+    private Integer fAverageCharWidth;
+
     private enum State {
         MULTIPLE (new RGB(100, 100, 100)),
         EXEC     (new RGB(0, 200, 0));
@@ -120,7 +122,10 @@ public class CallStackPresentationProvider extends TimeGraphPresentationProvider
 
     @Override
     public void postDrawEvent(ITimeEvent event, Rectangle bounds, GC gc) {
-        if (bounds.width <= gc.getFontMetrics().getAverageCharWidth()) {
+        if (fAverageCharWidth == null) {
+            fAverageCharWidth = gc.getFontMetrics().getAverageCharWidth();
+        }
+        if (bounds.width <= fAverageCharWidth) {
             return;
         }
         if (!(event instanceof CallStackEvent)) {