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my app contains an object moving on a surfaceview. I am able to move it around via accelerometer. Here's the movement code of the player object: 

if(x + mx*speed > 0 && x + mx*speed < GameView.WIDTH) {
        x += mx*speed;
    }
if(y+ my*speed > 0 && y+ my*speed < GameView.HEIGHT) {
        y+=my*speed;
    }

x and y are the player's coordinates

mx is the value the player gets from the accelerometer, for example: when tilting to the left, mx is -2, when tilting more, mx is -4, -5, -6 etc. --> my is the same for the y-axis

the speed is a variable to modify and play around when i want to have a faster movement.

as you can see I tried to limit the movement to only move when the player is inside of the view.

Now my problem is: when tilting the device intensively to the right, mx turns to something like 6. speed is set to 5. This means, when the player's position + 6 * 5 is bigger than the game view it should not move any more. But this results in the player stopping pixels in front of the right side of the view... when tilting lightly to the right, the object stops perfectly at the border of the view...

Now how should i change the code to achieve an object that stops it's movement perfectly at borders of the screen?

Image with intensively use of accelerometer

On this picture you can see the circle not stopping quite at the bottom, as there are some pixels between the circle and the bottom border. when going slightly back with the accelerometer, the circle aligns itself to the bottom of the screen:

bottom of the screen

But now, i can only reach the screen borders when moving slowly, which means with a low mx or my.

the screenshots you can see the mY values. On the first picture my = ca. 8 and on the second ca. 6.

Any ideas?

Thanks in advance

Machavity
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user2410644
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  • A screen shot or two might help clarify your question. – D-Dᴙum Feb 13 '14 at 17:24
  • added two screenshots – user2410644 Feb 13 '14 at 18:43
  • Some babbling about collision detection can be found in Android Breakout (https://code.google.com/p/android-breakout/). Note in particular the comments at the top of `findFirstCollision()` in GameState.java -- the game steps the ball forward in small increments, checking at each step. You don't need this -- you only have the four walls to worry about, so algebra will provide the answer -- but if you add more objects to collide with you may need something similar. (It also gets more complicated if the collision happens at the edge of the object rather than the center.) – fadden Feb 14 '14 at 01:18

1 Answers1

2

Try to instead cap the value to the border like so

x = Math.max(Math.min(x + mx*speed, GameView.WIDTH), 0.0f));
y = Math.max(Math.min(y + my*speed, GameView.HEIGHT, 0.0f));
vidstige
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  • Going to try that out, thanks! EDIT: Works great! But sadly it only works on the right and the bottom of the screen... Have you got a suggestion how to implement these two sides as well? – user2410644 Feb 13 '14 at 19:07
  • sure. I've added some code that should handle this. A bit hacky though. At this point you might want to create your own method called `cap` or something like that. – vidstige Feb 13 '14 at 19:16
  • Works like a charm! Thank you! (Totally wasn't thinking of Math.min or Math.max) – user2410644 Feb 13 '14 at 20:01
  • @user2410644 the problem with your code before was that close to the edge, you didn't change the position at all leaving the object at a small distance from the wall. With `Math.min` you'll update the position close to the edge, but never travel over it. – vidstige Feb 14 '14 at 08:35