Rotating ellipse around its own Y axis

Isackender

Hi! I'm trying to rotate a circle around its own Y axis, but the rotation is not symmetric. It's driving me crazy and AFAIK everything is well written.

Check it out:

color myWhite = 250;
color myBlack = 13;
int centerX = 440;
int centerY = 220;

float angle=-90;

void setup(){
  size(880,440,P3D);
  background(myBlack);
  stroke(myWhite);
  strokeWeight(1);
  noFill();
}

void draw(){
  background(myBlack);
  pushMatrix();
  translate(centerX, centerY, 0); 
  rotateY(radians(angle));
  ellipse(0,0,200,200);
  popMatrix();

  angle+=2; // speed
  if (angle>=360) {
    angle=0; // keep in degree
  }

  line(centerX, 0, centerX, 440);
  line(0, centerY, 880, centerY);
  line(centerX-100, 0, centerX-100, 880);
  line(centerX+100, 0, centerX+100, 880);
}

As you can see, the top and bottom part of the circle are not cut by the central guideline simmetrically.

What I'm doing wrong?

P.S. I've taken the rotation code from here (thanks @Chrisir).

Chrisir

You are doing it wrong.

Chrisir

ellipse(-100,-100,200,200);

Basically draw the thing centered on the origin of the Matrix which is 0,0

hence -100

Also

ellipseMode (CENTER);

or is this the default?

Isackender

Hmm... If I use ellipse(-100,-100,200,200); it will rotate around the line of the center. I don't want that. I want the circle to rotate around it's own axis.

Yeah ellipseMode (CENTER) is the default mode.

Chrisir

Say again what you mean

Isackender

I want this.

It does this.

As you can see, the rotation is not symmetrical.

Chrisir

Minimal difference....

Was it as good before the change I proposed?

I think it is a small offset on the z-axis.....?

Try making the lines with 6 parameters each (Z)

Otherwise I can't help you

Isackender

ellipse(-100,-100,200,200); (image)

Yeah it's minimal, but it really bothers me haha. Also yes, it looks like it's pushed a little on the Z axis.

It's the same with 6-parameter lines:

line(centerX, 0, 0, centerX, 440, 0); // Vertical axis
line(0, centerY, 0, 880, centerY, 0); // Horizontal axis
line(centerX-100, 0, 0, centerX-100, 880, 0); // Left line
line(centerX+100, 0, 0, centerX+100, 880, 0); // Right line

EDIT

If I change the ellipse for a sphere, it works fine. Completely symmetrical.

Chrisir

Optical issue - not in code

Isackender

Ok =/

Thanks for your help anyway Chrisir, appreciate it.

EDIT

Made this:

void draw(){
  background(myBlack);

  if (w<=200 && w>0 && desc) {
    w=w-2;
  } else {
    w=w+2;
    if(w==200){
      desc = true;
    } else {
      desc = false;
    }
  }

  ellipse(centerX,centerY,w,200);

  line(centerX, 0, 0, centerX, 440, 0); // Vertical axis
  line(0, centerY, 0, 880, centerY, 0); // Horizontal axis

  line(centerX-100, 0, 0, centerX-100, 880, 0); // Left line
  line(centerX+100, 0, 0, centerX+100, 880, 0); // Right line
}

I'm not sure if I like it, but at least looks fine.

kfrajer

Hi

I think it has to do with the camera view point. Try setting in your setup function:

camera(0,0,0,0,0,0,0,0,0);

Check the Processing3's reference : camera()

I hope this helps,

Kf

koogs

Those settings make no sense. First 3 are camera position. 2nd three are where the camera is looking, 3rd three are the up vector. Having them all the same will cause real confusion.

Try 0, 0, -10, 0, 0, 0, 0, 1, 0 instead (camera on z axis, looking at origin, y is up)

Isackender

@kfrajer @koogs With those settings it wouldn't work because of the translate(centerX, centerY, 0); command.

I've modified camera settings for this:

camera(centerX,centerY,300,centerX,centerY,0,0.0,1.0,0.0);

But the result is the same.

P.S. If I delete the translate command and change the camera to camera(0, 0, 300, 0, 0, 0, 0.0, 1.0, 0.0); I get the same error.

koogs

Optical issue - not in code

i am increasingly convinced it is this.

add another couple of smaller ellipses inside and you'll see.

might be a perspective trick, might be something along the lines of affine texture mapping problem (google image search...)

Isackender

Yeah @Crhisir said so. I guess you're both right!

More circles

koogs

(i was quoting chrisir's answer)