How to Rotate a 3D "Line" like a 2D "Line"

nelsitorocks

Hello I am trying to get a 3D "Line" (the "line" is really a box() but you get the idea) I am drawing to rotate around one end the same way a 2D line does. In the example below you can see that the red line which is your standard line() object rotates around one of its points. I would like to get my box() object which is in green to rotate the same way as the red line. Any advice would be greatly appreciated.

void setup()
{
  size(640,360,P3D);

}
float n=0;
void draw(){
background(255);
//GREEN LINE
pushMatrix();
stroke(0,255,0);
translate(width/2, height/2);
rotate(n);
box(90,1,1);
popMatrix();

//RED LINE
pushMatrix();
stroke(255,0,0);
translate(width/2, height/2);
rotate(n);
line(0,0,-95,100);
popMatrix();
n=n+0.01;
}

TfGuy44

float n=0;

void setup() {
  size(640, 360, P3D);
}

void draw() {
  background(255);

  //GREEN BOX
  pushMatrix();
  stroke(0, 255, 0);
  translate(width/2, height/2);
  rotate(n);
  translate(45, 0, 0);
  box(90, 1, 1);
  popMatrix();

  //RED LINE
  pushMatrix();
  stroke(255, 0, 0);
  translate(width/2, height/2);
  rotate(n);
  line(0, 0, -95, 100);
  popMatrix();

  n=n+0.01;
}

nelsitorocks

Thanks!! TfGuy44 that really helped. So if I understand this correctly the second call of translate moves the center of rotation of the line 45 units in the x direction? so I must first translate the line to the center of the screen and then translate it again in order to rotate it?

TfGuy44

The first translate moves the (0,0,0) point so that it is in the middle of the screen. When you call rotate(), you're actually calling rotateZ(), which rotates space around the Z-axis. The second call to translate() then moves the (0,0,0) point along the (now) ROTATED X-axis. It moves the origin 45 units away from where we rotated, which makes it look like a 90-units long box is now spinning about the center of the screen.

The important thing to realize is that your call to rotate() is changing the direction that the X-axis points!

Chrisir

There is also a version of line with 6 parameters

It's a 3d line

void setup() {
  size(640, 360, P3D);
}

void draw() {
  background(0);
  lights();
  depth(260);
}

void depth(float z1) {

  pushMatrix();

  // A vector that points to the mouse location
  PVector mouse = new PVector(mouseX, mouseY, 0);
  stroke(255);
  line(220, 220, -220, 
    mouse.x, mouse.y, mouse.z );

  popMatrix();
}
// 

Also look at my turtle code, there is a function drawLine iirc

Which gives you a thin rect as a line

Use it with lights();

void setup() {
  size(640, 360, P3D);
}

void draw() {
  background(0);
  lights();
  depth(260);
}

void depth(float z1) {

  pushMatrix();

  // A vector that points to the mouse location
  PVector mouse = new PVector(mouseX, mouseY, 0);
  stroke(255);
  drawLine(220, 220, -220, 
    mouse.x, mouse.y, mouse.z, 
    22, 
    color(255, 0, 0));

  popMatrix();
}
// 

// -----------------------------------------------

void drawLine(float x1, float y1, float z1, 
  float x2, float y2, float z2, 
  float weight, 
  color strokeColour)
  // was called drawLine; programmed by James Carruthers
  // see http : // 
  // processing.org/discourse/yabb2/YaBB.pl?num=1262458611/0#9
{
  PVector p1 = new PVector(x1, y1, z1);
  PVector p2 = new PVector(x2, y2, z2);
  PVector v1 = new PVector(x2-x1, y2-y1, z2-z1);
  float rho = sqrt(pow(v1.x, 2)+pow(v1.y, 2)+pow(v1.z, 2));
  float phi = acos(v1.z/rho);
  float the = atan2(v1.y, v1.x);
  v1.mult(0.5);

  pushMatrix();
  translate(x1, y1, z1);
  translate(v1.x, v1.y, v1.z);
  rotateZ(the);
  rotateY(phi);
  noStroke();
  fill(strokeColour);
  // box(weight,weight,p1.dist(p2)*1.2);
  box(weight, weight, p1.dist(p2)*1.0);
  popMatrix();
}

//

Chrisir

I posted some additional code above