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Trouble using swt GLCanvas on linux [message #1022304]

Thu, 21 March 2013 12:37

Steven Reynolds
Messages: 2
Registered: March 2013

Junior Member

Hi

I am having trouble using the swt GLCanvas while on linux. If I use the provided Snippet209

http://git.eclipse.org/c/platform/eclipse.platform.swt.git/tree/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet209.java

I get 100% CPU utilization. The code is clearly structured to cause this high utilitzation. It does (from the main method)

display.asyncExec(new Runnable() {
int rot = 0;
public void run() {
// draw stuff
display.asyncExec(this);
}
});

Which means that it busy loops drawing as fast as it can.

When I try to convert the snippet to draw on PaintEvents, the opengl drawing that I do is immediatedly klobbered with something that draws plain black.

Does anyone have any luck using the swt GLCanvas on linux? Busy looping won't work for my application, most of the time, the display should be static and not consume CPU.

I've attached the PaintEvent version as DemoSWT2.

thanks
Steven

Attachment: DemoSWT2.java
(Size: 6.84KB, Downloaded 24 times)

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Re: Trouble using swt GLCanvas on linux [message #1022372 is a reply to message #1022304]

Thu, 21 March 2013 15:10

Steven Reynolds
Messages: 2
Registered: March 2013

Junior Member

Oh, I have a solution. It looks like the swt GLCanvas is doing GTK double buffering. The associated gtk buffer swap hammered my drawing. With the following change, the code seems fine now

retrieving revision 1.7
retrieving revision 1.8
diff -u -r1.7 -r1.8
--- DemoSWT2.java 20 Mar 2013 22:13:41 -0000 1.7
+++ DemoSWT2.java 21 Mar 2013 18:49:58 -0000 1.8
@@ -9,6 +9,7 @@
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Rectangle;
+import org.eclipse.swt.internal.gtk.OS;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.opengl.GLCanvas;
import org.eclipse.swt.opengl.GLData;
@@ -83,7 +84,11 @@
GLData data = new GLData ();
data.doubleBuffer = true;
final GLCanvas canvas = new GLCanvas(comp, SWT.NONE, data);
-
+ if (SWT.getPlatform().equals("gtk")) {
+ System.out.printf("Disabling GTK double buffering\n");
+ // TODO invoke reflectively?
+ OS.gtk_widget_set_double_buffered(canvas.handle,false);
+ }
canvas.setCurrent();
final GLContext context = GLDrawableFactory.getFactory().createExternalGLContext();

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