How do I move move a sprite that has an x and y velocity, in a circle at a constant speed. Something with vectors??? I am not fimiliar with this type of math.

  int angle = 0;while(true){    angle = (angle+1)%360;    sprite.xpos = 100+100*cos(2*PI*angle/360.0);        sprite.ypos = 100+100*sin(2*PI*angle/360.0);    sprite.render();}  

  int angle = 0;while(true){    angle = (angle+1)%360;    sprite.xpos = 100.0+100.0*cos(2.0*PI*angle/360.0);        sprite.ypos = 100.0+100.0*sin(2.0*PI*angle/360.0);    sprite.render();}  

The Anonymous Poster gave a reasonably good implementation (optimizations lurk, as always). The theory is as follows: imagine a vector reaching out from the center of the circle to its circumference; this vector will move with a constant angular velocity (your increment) and a variable linear acceleration due to the rotation. Say the circle is centered about (x,y) and the vector is of length l . The position (vx,vy) of the sprite - the tip of the vector - is defined by the simple trigonometric opposite and adjacent sides of the right angle triangle formed by the x-axis, the y-axis and the vector itself. Given the angle t in radians :

    vx = l * cos(t);vy = l * sin(t);  

Provided t is measured in the counterclockwise direction from the positive x-axis. Degree to radian angle conversions can be done as

radian = PI * degree / 180;

and sine and cosine values can be precomputed for all integer degree values (0 <= degree < 360). Throw all this into the preceding loop from the Anonymous Poster and voila!

Edited by - Oluseyi on June 8, 2001 8:45:37 PM