[news.eclipse.platform.swt] Question about PaintSurface.

[irum@xxxxxxxxxx (Irum Godil)]

Hi, 

I am working with the SWT PaintSurface class. I am extending it to provide 
capability to set an image in the background and then draw some unfilled 
rectangles on top of it. To this end, I have changed the code in the 
"PaintSurface's" 'addPaintListener' API. I have attached the code at the 
end of this email. \n

I am facing 2 problems as follows: \n

1) The rectangle that comes up generally only comes with 2 edges and not 
all 4. \n

2) If I bring up another application in the foreground and switch back to 
the Paint view, all the rectangles that I had drawn disappear. \n

In the code below, importedImage is the image I am importing for the 
background image, and I have also copied code to set it. If someone can 
please take a look at this code and suggest what is going wrong I will 
really appreciate. \n

I could also send you my entire project if needed or snapshots to see what 
to do here. \n

I will really appreciate your help on this. \n

Inside PaintSurface \n:

paintCanvas.addPaintListener(new PaintListener() {
			public void paintControl(PaintEvent event) {
				if (rubberband.isEmpty()) {
				// Nothing to merge, so we check if there is an image to show or we 
just refresh
					if (importedImage != null) {
					    showImportedImage(event.gc);
					}
					else {
						event.gc.drawImage(image,
								displayFDC.xOffset + event.x, displayFDC.yOffset + event.y, 
event.width, event.height,
								event.x, event.y, event.width, event.height);
					}
				} else {
					/*
					 * Avoid flicker when merging overlayed objects by constructing the 
image on
					 * a backbuffer first, then blitting (cp from memory to screen) it to 
the screen.
					 */
					// Check that the backbuffer is large enough, if not, dispose it
					if (paintImage != null) {
						Rectangle rect = paintImage.getBounds();
						if ((event.width + event.x > rect.width) ||
							(event.height + event.y > rect.height)) {
							paintFDC.gc.dispose();
							paintImage.dispose();
							paintImage = null;
						}
					}
					if (paintImage == null) {
						// get the paintSurface's display
						Display display = getDisplay();
						// rect - rectangle that can display data
						Rectangle rect = display.getClientArea();
						// construct image of needed size
						paintImage = new Image(display,
							Math.max(rect.width, event.width + event.x),
							Math.max(rect.height, event.height + event.y));
						paintFDC.gc = new GC(paintImage);
					}
					// Setup clipping and the FDC
					Region clipRegion = new Region();
					// set clipRegion to the current clipping region of event.gc
					event.gc.getClipping(clipRegion);	
					// sets displayable area of paintFDC.gc to clip region of event.gc
					paintFDC.gc.setClipping(clipRegion);
					clipRegion.dispose();

					// sets offsets and scales of paintFDC to that of displayFDC
					paintFDC.xOffset = displayFDC.xOffset;
					paintFDC.yOffset = displayFDC.yOffset;
					paintFDC.xScale = displayFDC.xScale;
					paintFDC.yScale = displayFDC.yScale;
					
					// Merge the overlayed objects into the image, then blit (cp form 
memory to screen)
					// draw image that we had before to paintFDC.gc
					paintFDC.gc.drawImage(image,
						displayFDC.xOffset + event.x, displayFDC.yOffset + event.y, 
event.width, event.height,
						event.x, event.y, event.width, event.height);
					// calls draw from Figure for each object in rubber band
					rubberband.draw(paintFDC);
					// draw the new object
					event.gc.drawImage(paintImage,
						event.x, event.y, event.width, event.height,
						event.x, event.y, event.width, event.height);
				}
			}
		});



\n

/* Show image function function */
	private void showImportedImage(GC gc) {
		// get rid of all figures up to now
		this.clearRubberbandSelection();
		
		// clientRect is the size of displayable area
		Rectangle clientRect = paintCanvas.getClientArea(); /* Canvas' painting 
area */
		// sets the area of gc that can be changed (by drawing) to clientRect
		gc.setClipping(clientRect);
		// fills clientRect by backgrnd color (white)
		gc.fillRectangle(clientRect);
		
		// clear the gc of the imageFDC
		imageFDC.gc.setClipping(clientRect);
		imageFDC.gc.fillRectangle(clientRect);
		
		// draw the image to gc
		gc.drawImage(importedImage, 0, 0);
	}