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Thread: Algorithm efficiency

  1. #1
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    Default 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!


  2. #2
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    Default Re: Algorithm efficiency

    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

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    Default Re: Algorithm efficiency

    Quote Originally Posted by copeg View Post
    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?

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    Administrator copeg's Avatar
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    Default Re: Algorithm efficiency

    Quote Originally Posted by lozbritt View Post
    Could it be the drawing?
    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

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    Default Re: Algorithm efficiency

    Quote Originally Posted by copeg View Post
    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.

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    Default Re: Algorithm efficiency

    Have you tried isolating the problem further than at your methods level?
    There are two calls to the Canvas drawLine() method. Try commenting them both out, then one then the other.
    If you don't understand my answer, don't ignore it, ask a question.

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