# Rotation matrices

• 01-07-2003
gazsux
Rotation matrices
I'm currently doing a programming project and decided to leave the easiest bit till last. however, im having some trouble with it ;). im sure im missing something simple.

All i want to do is take some inputted points for a triangle, and rotate them. Is the following code correct?

matrix((vertex[count][X]-mX), (vertex[count][Y]-mY));

the call is that ^

The theory is to minus the triangle mid-point (mX,mY) from the existing entered points (vertex[count][X], vertex[count][Y]). Then rotate by the matrices. Then shift back.

DEG2RAD is just the conversion factor from degrees to radians needed for sin/cos etc
Code:

```void matrix(float tempx, float tempy) { int count; float matrix[4]={cos(5*DEG2RAD), sin(5*DEG2RAD), -sin(5*DEG2RAD), cos(5*DEG2RAD)}; for(count=0; count<=3; count++)         {         vertex[count][X]=(matrix[0]*tempx)+(matrix[2]*tempx)+mX;         vertex[count][Y]=(matrix[1]*tempy)+(matrix[3]*tempx)+mY;         } return; }```
Its in opengl but im not allowed to use any preritten functions for the rotation or anything

Code tags added by Hammer
• 01-07-2003
no-one
this site explains matrix translation, rotation, and the like.

http://www.geocities.com/SiliconVall.../matrices.html
• 01-07-2003
gazsux
cool i'll take a look, although i did look at some sites like mathworld but the scope goes a little beyond what i wanted... cheers :)
• 01-07-2003
gazsux
yep sorry just seen the post about adding code tags, i'll remember that :) :\$