Polygon rotation is too fast compared to objects rotation

manderin87 · 2012-11-30T19:11:32

I am designing a game in android and I have a problem when updating a polygon that is used for collision detection. When the objects update method is called it rotates the object by .5 and then updates the polygon by rotating it by the same amount. The problem is on the screen the polygon is rotating faster than the object when drawn. The polygon is rotating so fast that it looks like a star, eventually it slows down and then speeds up again. It will not stay in step with the objects rotation. This is the rotation code for the polygon. public void rotate(float x0, float y0, double angle) { for(int i = 0; i < mOrigins.size(); i++) { Point point = mOrigins.get(i); float x = (float) (x0 + (point.x - x0) * Math.cos(Utilities.toRadians(angle)) - (point.y - y0) * Math.sin(Utilities.toRadians(angle))); float y = (float) (y0 + (point.x - x0) * Math.sin(Utilities.toRadians(angle)) + (point.y - y0) * Math.cos(Utilities.toRadians(angle))); Point npoint = mPoints.get(i); npoint.x = x; npoint.y = y; mPoints.set(i, npoint); } } This is the update method for the object public void update(float deltaTime) { mAccumulatedTime += deltaTime; while(mAccumulatedTime > FIXED_FRAME_TIME) { mAccumulatedTime -= FIXED_FRAME_TIME; if(isActive()) { rotate(); mBounding.rotate(mPosition.x, mPosition.y, mDegree); drawBounding(); } } } Trying to limit the time has no effect on the polygon and it continues to speed up and slow down. Can anyone please identify the error or lead me in the right direction to fix this? thanks

For Beginners

Started by manderin87 November 29, 2012 03:32 PM

35 comments, last by manderin87 11 years, 4 months ago

manderin87

130

Author

November 30, 2012 12:38 AM

Its the same thing... my Utilities.toRadians() calls Math.toRadians()

Khatharr

8,814

November 30, 2012 03:00 AM

Does SpriteBatch::draw() want degrees or radians?

void hurrrrrrrr() {__asm sub [ebp+4],5;}

There are ten kinds of people in this world: those who understand binary and those who don't.

Khatharr

8,814

November 30, 2012 03:04 AM

This method is better for fixing the degree but it didnt change the behavior that I am experiencing

if(mDegree >= 360) { mDegree -= 360; } else if(mDegree < 0) { mDegree += 360; }

Try:
[source lang="java"]
while(mDegree >= 360) {mDegree -= 360;}
while(mDegree < 0) {mDegree += 360;}
[/source]

Edit - Aagh, derp. Sorry for double post.

void hurrrrrrrr() {__asm sub [ebp+4],5;}

There are ten kinds of people in this world: those who understand binary and those who don't.

manderin87

130

Author

November 30, 2012 03:04 AM

Does SpriteBatch::draw() want degrees or radians?

Degrees

manderin87

130

Author

November 30, 2012 03:11 AM

while(mDegree >= 360) {mDegree -= 360;}
while(mDegree < 0) {mDegree += 360;}

Didnt fix it. I know it has to be something wrong with the polygone rotation, its not working correctly. Ive stared at it for hours and i dont know what the problem is. Ive checked several places and the algorithm seems to be correct, but its not rotating correctly.

Khatharr

8,814

November 30, 2012 03:12 AM

Okay, looking back over the whole thread, can you post the whole code path for this thing? Seems like it'll be faster than everyone guessing at it.

Didnt fix it. I know it has to be something wrong with the polygone rotation, its not working correctly. Ive stared at it for hours and i dont know what the problem is. Ive checked several places and the algorithm seems to be correct, but its not rotating correctly.

Yeah, that wasn't intended as a fix. Just a more complete solution for rotating something into range without modulation.

void hurrrrrrrr() {__asm sub [ebp+4],5;}

There are ten kinds of people in this world: those who understand binary and those who don't.

manderin87

130

Author

November 30, 2012 07:11 PM

Ive rechecked everything... The rotation code was the problem.... I made two lists to keep track of the points... the original points and the rotated points. Both were pointing to the same object, i thought they were seperate, but they were not... so I just made both lists create a new point when adding to the list. The rotation is now correct.

Here is the polygon constructor



public Polygon(Point... points) {

  if(points.length < 3) {

   throw new IllegalArgumentException("polygons must contain at least 3 points.");

  }



  for(Point p : points) {

   mRotatedPoints.add(new Point(p));

   mOriginalPoints.add(new Point(p));

  }

}

And the rotation code.



public void rotate(float x0, float y0, float degree) {

  for(int i = 0; i < mOriginalPoints.size(); i++) {

   Point point = mOriginalPoints.get(i);



   float x = (float) (x0 + (point.x - x0) * Math.cos(Utilities.toRadians(degree)) -

				  (point.y - y0) * Math.sin(Utilities.toRadians(degree)));

   float y = (float) (y0 + (point.x - x0) * Math.sin(Utilities.toRadians(degree)) +

			(point.y - y0) * Math.cos(Utilities.toRadians(degree)));



   Point p = mRotatedPoints.get(i);

   p.x = x;

   p.y = y;

  }

thanks everyone for the help and forgive my idiocy for not noticing they were they same instead of being seperate.

Polygon rotation is too fast compared to objects rotation

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Polygon rotation is too fast compared to objects rotation

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