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  A little bit of math - Rotation  (Read 1874 times)
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Offline Kronos

Junior Devvie

Medals: 1

« Posted 2013-02-27 13:07:31 »

Hey guys,

I never listened to our maths teacher back in school time, now I could kick myself in the a** Sad.

I got a laserbeam and at the end a burst (in this case a dot). This laserbeam is rotating from the center to all the edges and so on.
How can I calculate the new coordinates for the end of the beam, where should be displayed an image of a typical laser burst.

My first attempt (thought) was to use some Math.sin and cos. But I really do not know how to use them properly. Wikipedia couldn't help me neither, it's not game dev related enough. I hope you guys are patient and could help me with this, hopefully trivial, question.

Thanks in advance. Smiley

Offline Kronos

Junior Devvie

Medals: 1

« Reply #1 - Posted 2013-02-27 13:30:47 »

I was to quick writing this thread Sad

I added a g.resetTransform(); before the burst image even could rotate...
however... is there an idiot secure mini tutorial for wanne-be game developers regarding cos(), sin() and PI, which you would recommend?
Offline vbrain
« Reply #2 - Posted 2013-02-27 15:12:28 »

Here's something I just whipped up.

public float angle;
public void update()
   angle += 0.5; //increase the degrees by 0.5 each update
   if (angle >= 360)
      angle = 0;

public void draw(Graphics g)
   //if the width is longer than the height, use this, otherwise switch to
   //screenHeight and centerY
   int radiusOfScreen = screenWidth - centerX;

   //convert degrees into radians to use with cos and sin
   int endX = (int)(centerX + radiusOfScreen * Math.cos(Math.toRadians(angle)));
   int endY = (int)(centerY + radiusOfScreen * Math.sin(Math.toRadians(angle)));
   g.drawLine(centerX, centerY, endX, endY)
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Offline Kronos

Junior Devvie

Medals: 1

« Reply #3 - Posted 2013-02-27 18:21:49 »

Thanks vbrain.

I came up with a new problem. How can I manage stop increasing my laser's beam width when it collidates with the frame bounds (or objetcs flying around). I do not know how to calculate the ending point of my Rectangle, when it is rotated. The beam currently goes endlessly into the wide nothing (out of frame)....



I think I made it. It looks good so far.

endPos.set((float)(x + width * Math.cos(Math.toRadians(rotation))), (float)(y + width * Math.sin(Math.toRadians(rotation))));

width is the radius. This gives me a Point of the "circle" -> my rotation. for those who had the same problem, or will have the same problem in the future.

I am a one man show Cheesy
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