Java-Gaming.org Hi !
 Featured games (90) games approved by the League of Dukes Games in Showcase (769) Games in Android Showcase (230) games submitted by our members Games in WIP (855) games currently in development
 News: Read the Java Gaming Resources, or peek at the official Java tutorials
Pages: [1]
 ignore  |  Print
 Corners of rotated rectangle wrong  (Read 3037 times) 0 Members and 1 Guest are viewing this topic.

Junior Newbie

Exp: 1 year

 « Posted 2014-03-01 19:32:42 »

I have a problem calculating the corners of a rotated rectangle.
For the calculation I use a rotation matrix but there is somewhere a little mistake in my code.

As you can see the corners have a wrong positions but were rotated correctly.
Code:

 1  2  3  4 `corners[0] = translatePoint(x, y);corners[1] = translatePoint(x + width, y);corners[2] = translatePoint(x + width, y + height);corners[3] = translatePoint(x, y + height);`

 1  2  3  4  5 `private Point translatePoint(double x, double y) {        double xNew = (x * Math.cos(getAngleInRadians()) - y * Math.sin(getAngleInRadians()));        double yNew = (x * Math.sin(getAngleInRadians()) + y * Math.cos(getAngleInRadians()));        return new Point(xNew, yNew);}`

(x,y) is the left top corner of the unrotated rectangle.

lcass
 « Reply #1 - Posted 2014-03-01 19:44:59 »

are you translating the object afterwards?
Troubleshoots

JGO Knight

Medals: 36
Exp: 7-9 months

Damn maths.

 « Reply #2 - Posted 2014-03-01 20:26:22 »

That's not actually a rotation matrix. These are the three axis rotation matrices.

You'll want to use the last one. You have to find matrix (dot) vector.
What you're doing currently should work though; just make sure you're translating after you're rotating.

Why are all OpenGL tutorials written in Brainf**k?

Junior Newbie

Exp: 1 year

 « Reply #3 - Posted 2014-03-01 21:04:07 »

After a few tries I noticed that even if the angle is 0 the rotation is wrong.

But I have no idea why
lcass
 « Reply #4 - Posted 2014-03-01 21:13:33 »

 1  2  3  4  5  6  7  8 `              dy = (ty * cosx) - (tz * sinex);         dz = (tz * cosx) + (ty * sinex);         // yrot         mz = (dz * cosy) - (tx * siny);         dx = (tx * cosy) + (dz * siny);         // zrot         mx = (dx * cosz) - (dy * sinz);         my = (dy * cosz) + (dx * sinz);`

This is the code I use when performing transformations, make sure that you use the previous variable. Note , TZ is simply the position of the vertex minus the position of the camera.
DrZoidberg

JGO Coder

Medals: 21

 « Reply #5 - Posted 2014-03-01 23:40:27 »

There is no error in the code you posted.
If getAngleInRadians returns 0, then translatePoint will always return the same point that was put in.
So there must be somthing wrong elsewhere in your code.

Junior Newbie

Exp: 1 year

 « Reply #6 - Posted 2014-03-02 10:12:21 »

Ok I found the wrong line