Polar Coordinates Question (n00b)

Programming Questions

tonyhat

Polar Coordinates Question (n00b)

in Programming Questions • 2 years ago

I always sucked at trig and I am currently trying to teach myself polar coordinates (and PVectors). I had an idea to build a line that rotates around a point but will always rotate towards the mouse. However, I think my implementation is probably pretty scrappy (the whole prev/curr angle thing) and the sketch jitters a great deal.

See the sketch here

Any suggestions on how I could clean this up?

PVector mos;
PVector lin;
float originX, originY, x, y, r, currAngle, prevAngle;;
float theta = 0;
float rev = TWO_PI/500; //revolution rate in radians/frame
void setup() {
size(400, 400);
originX = width/2;
originY = height/2;
r = width/2;
prevAngle = PI;
}
void draw() {
background(255);
//get cartesian from polar
x = r * cos(theta);
y = r * sin(theta);
mos = new PVector(mouseX-originX, mouseY-originY);
lin = new PVector(x,y);
//compare angle between two vectors
currAngle = PVector.angleBetween(mos,lin);
//if it is greater than previous frame, the line is
//moving away - reverse the rotation.
if(currAngle > prevAngle){
rev *= -1;
}
//update previous angle
prevAngle = currAngle;
//modify angle by rotation amount
theta += rev;
//draw out line
drawVector(lin);
}
void drawVector(PVector v) {
pushMatrix();
translate(originX, originY);
line(0, 0, v.x, v.y);
popMatrix();
}

Replies(2)

allonestr..

Re: Polar Coordinates Question (n00b)

2 years ago

I think that it's stuttering as it can never point _exactly_ at the mouse. You might consider adding a trap for pointing within 1 degree of the mouse, say. If so, stop the rotataion.

quarks

Re: Polar Coordinates Question (n00b)

2 years ago

In addition to comment from allonestring you also want to avoid creating new PVector objects in the draw method better to create them once by changing lines 2 & 3 to

PVector mos = new PVector();
PVector lin = new PVector();

and re-use them by changing lines 24 & 25 to

mos.x = mouseX-originX;
mos.y = mouseY-originY;
lin.x = x;
lin.y = y;

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