Rotate around a Center Point

Programming Questions

mikifare

in Programming Questions • 2 years ago

Hello I have the following class and what I am trying to do is rotate the circle and square around the center point.

Please help.

class arrow {
float x;
float y;
float a;
float iAlpha;
float scaleUpF = 1.01;
float scaleDownF = 0.99;
float fRotation;
float vx = 0;
arrow (float cX, float cY, float cA, float ciAlpha) {
x= cX;
y= cY;
a= cA;
iAlpha = ciAlpha;
fRotation = 0;
vx = 0;
}
void display () {
pushMatrix();
translate(width/2+x+vx, height/2+x+vx);
fill(170,170,170,iAlpha);
rotate( radians(fRotation) );
rect (x + vx,y ,3*a,a);
ellipse(x + vx, y, 5 ,5 );
// x1 y1, x2 y2, x3 y3
triangle (x+vx+(1.5*a), -a, x+vx+(1.5*a), a, vx+x+4*a, y);
popMatrix();
}
void checkKey()
{
if(keyPressed == true && key == 's' || key == 'S') {
a *= scaleUpF;
}
if(keyPressed == true && key == 'x' || key == 'X') {
a *= scaleDownF;
}
if(keyPressed == true && key == 'a' || key == 'A')
{
iAlpha *= scaleUpF;
}
else if(keyPressed == true && key == 'z' || key == 'Z')
{
iAlpha *= scaleDownF;
}
else if(keyPressed == true && key == CODED && keyCode == LEFT) {
fRotation += scaleUpF;
}
else if(keyPressed == true && key == CODED && keyCode == RIGHT)
{
fRotation -= scaleUpF;
}
else if(keyPressed == true && key == CODED && keyCode == UP)
{
vx += 1;
}
else if(keyPressed == true && key == CODED && keyCode == DOWN)
{
vx -= 1;
}
}
void keyReleased() {
if( vx > 0) vx = 0;
}
}

miki

Replies(1)

cedrickie..

Re: Rotate around a Center Point

2 years ago

for rotating around its centerpoint you need to translate it first back to (0,0) cause thats where the rotation happens.
in your case you need to translate it -x-halfradius and -y-halfRadius to move the center of the ellipse to 0,0. apply the rotation and move it back to its position.
otherwise, use translate(x,y) in the first place and draw the ellipse itself at -halfRadius, - halfRadius.

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