Implementing rotation function like glRotate

[SummertimeClothes]

I am trying to implement my own rotation function in OpenGL on C++, i.e. something like glRotate. My code for rotating around y looks like this:

    void do_rotateY(GLdouble angle)
    {
    	//rotate around y axis
    	GLdouble s = angle;
    	GLdouble c[4][4];
    	c[1][1] = c[3][3]= 1.0;
    	c[0][0] = c[2][2] = cos(s);
    	c[2][0] = sin(s);
    	c[0][2] = -c[2][0];
    	glMultMatrixd(*c);
    }

When I'm doing a call like:

    glPushMatrix();
    do_rotateY(100);
    ...draw something...
    glPopMatrix();

nothing appears on the screen. When I replace do_rotateY(...) with glRotatef(...) I can see everything correctly.

Thanks for your help!

[uwi2k2]

Hi,

taken from a ES-Framework, this may help you:

void ESUTIL_API
esRotate(ESMatrix *result, GLfloat angle, GLfloat x, GLfloat y, GLfloat z)
{
   GLfloat sinAngle, cosAngle;
   GLfloat mag = sqrtf(x * x + y * y + z * z);
 
   sinAngle = sinf ( angle * PI / 180.0f );
   cosAngle = cosf ( angle * PI / 180.0f );
   if ( mag > 0.0f )
   {
      GLfloat xx, yy, zz, xy, yz, zx, xs, ys, zs;
      GLfloat oneMinusCos;
      ESMatrix rotMat;
 
      x /= mag;
      y /= mag;
      z /= mag;
 
      xx = x * x;
      yy = y * y;
      zz = z * z;
      xy = x * y;
      yz = y * z;
      zx = z * x;
      xs = x * sinAngle;
      ys = y * sinAngle;
      zs = z * sinAngle;
      oneMinusCos = 1.0f - cosAngle;
 
      rotMat.m[0][0] = (oneMinusCos * xx) + cosAngle;
      rotMat.m[0][1] = (oneMinusCos * xy) - zs;
      rotMat.m[0][2] = (oneMinusCos * zx) + ys;
      rotMat.m[0][3] = 0.0F; 
 
      rotMat.m[1][0] = (oneMinusCos * xy) + zs;
      rotMat.m[1][1] = (oneMinusCos * yy) + cosAngle;
      rotMat.m[1][2] = (oneMinusCos * yz) - xs;
      rotMat.m[1][3] = 0.0F;
 
      rotMat.m[2][0] = (oneMinusCos * zx) - ys;
      rotMat.m[2][1] = (oneMinusCos * yz) + xs;
      rotMat.m[2][2] = (oneMinusCos * zz) + cosAngle;
      rotMat.m[2][3] = 0.0F; 
 
      rotMat.m[3][0] = 0.0F;
      rotMat.m[3][1] = 0.0F;
      rotMat.m[3][2] = 0.0F;
      rotMat.m[3][3] = 1.0F;
 
      esMatrixMultiply( result, &rotMat, result );
   }
}

cu
uwi

[Dan Bartlett]

You need to zero out the terms of c that are meant to contain zero, because local variables aren't initialized so will contain garbage.