to rotate the circle (top, left, width, height) around some point p (x, y) by angle phi:
// obtain center of circlecenterx = left + width / 2;centery = top + height / 2;// rotate center of circle around p by phix = p.x + (centerx - p.x) * cos(phi);y = p.y + (centery - p.y) * sin(phi);// calculate new top left point for drawOvaltopleft.x = (x - width / 2);topleft.y = (y - height / 2);fillOval(topleft.x, topleft.y, width, height);
This of course assumes, your world coordinates are same as screen coordinates, with x coordinate increasing from left to right, and y coordinate increasing top to bottom.
If you want to rotate the circle by using points, as mentioned above, you do not change the points. You just translate them. fillOval assumes axis-aligned rectangle.
So to apply the above method to your actual coordinates:
// pointsPoint a; // Top leftPoint b; // Top rightPoint c; // Bottom rightPoint d; // Bottom left// obtain center of circlecenterx = (a.x + b.x) / 2;centery = (a.y + c.y) / 2;// rotate the centerx = p.x + (centerx - p.x) * cos(phi);y = p.y + (centery - p.y) * sin(phi);// do this for every point a,b,c,da.x = x + (a.x - centerx);a.y = y + (a.y - centery);b.x = x + (b.x - centerx);b.y = y + (b.y - centery);// and so on for c,d
It does get rather ugly, so some better representation of circle for this purpose is a better way to go.
I define the width by subracting the x component of the point at (2,2) from the x component of (-2,2) - giving 4
And the height by subtract the y component of the point at (2,2) from the y compnent of (2,-2) - again giving 4.
The centre of the car is defined by the centre of the body of the car. To rotate i translate all the points to the origin and then do the rotations. This is where the problem occurs when trying to rotate the circle. I don't think i can explain it very well so hopefully this picture will help you understand:
I realise the problem is the way i am working out the height and width of the circle for use with the fillOval function - however i can't for the life of me think how to do this properly. I am thinking something to do with holding the radius of the circle - but i am not very maths minded at all and can't get any further than this.
Any advice would be greatly appreciated.
Thanks :)
