Thread: Algorithm efficiency

Hi all,

I am making an android racing game. I have a method that draws the track to the screen, the map is bigger than the screen so i clip the bitmap and draw it to the screen hence to draw the track I have to get the visible track points and then draw them. I have noticed that when I enable drawing the track the game lags quite a bit but when i disable it is smooth as expected the code is below if anyone can see any obvious efficiency problems.

	public void drawTrack(Canvas canvas) {
 
		if (this.trackPoints != null && this.trackPoints.size() > 0) {
 
			// get points, convert back to screen coords and add them to array,
			// then
			// use that arraylist<point> below
			getCurrentVisibleTrack();
 
			counter++;
 
			if (this.visibleTrackPoints.size() > 0) {
 
				// draw lines
				Point previousPoint = visibleTrackPoints.get(0);
				Point nextPoint;
				// draw track line
				for (int i = 1; i < visibleTrackPoints.size(); i++) {
					this.p.setColor(Color.BLACK);
					this.p.setStrokeWidth(100);
					nextPoint = visibleTrackPoints.get(i);
					canvas.drawLine(previousPoint.x, previousPoint.y,
							nextPoint.x, nextPoint.y, p);
 
					if (i % 2 == 0) { // draw outer track
						this.p.setColor(Color.WHITE);
						this.p.setStrokeWidth(5);
						canvas.drawLine(previousPoint.x, previousPoint.y,
								nextPoint.x, nextPoint.y, p);
					}
 
					previousPoint = nextPoint;
				}
 
			}
		}
	}
 
	public void getCurrentVisibleTrack() {
 
		// clear all elements
		this.visibleTrackPoints.clear();
 
		// loop track array
		Point point;
		for (int i = 0; i < this.trackPoints.size(); i++) {
			point = this.trackPoints.get(i);
			// if that piece of track is on the screen currently then add to
			// array
			this.visibleTrackPoints.add(new Point((int) (point.x - this.mapx),
					(int) (point.y - this.mapy)));
		}
	}

Thanks in advance!

Originally Posted by copeg

Perhaps I'm missing something, but I don't see any clipping going on - seems all the points in trackPoints is being placed in visibleTrackPoints in the getCurrentVisibleTrack() method. If things seem to be slowing down, I recommend profiling the code using println's and timing (System.currentTimeMillis()) to see how long things actually take for particular steps in the program - helps pinpointing the bottlenecks

Thanks for the reply, I do the clipping in an updateCamera() method which is seperate from this. I wrote this along time ago but it looks like I am moving every track point by -map.x (map.x being the fullsize map) so every point will be translated to my screen coordinates. Ther is only about 30 trackpoints or so, so I don't think this will slow it down. Could it be the drawing?

Originally Posted by copeg

Again, profile the code. There is no use optimizing something that doesn't need optimizing - find the bottleneck first, then work on optimizing. My post above gives advice on how to go about finding the bottleneck

yes but as I said i commented those 2 functions and it speeds up drastically so its something in there thats why im asking i know that method is the bottle neck.