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Index › Programming Questions & Help › Syntax Questions › Centered, equilateral triangle - math help
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Centered, equilateral triangle - math help (Read 946 times)
endasf
Centered, equilateral triangle - math help
Jan 6th, 2010, 11:16am  
Hi there,

I saw this thread:
http://processing.org/discourse/yabb2/num_1252373090.html
and it is very useful, except I would like to know how to do 3 things:
1. draw the triangle so that your cursor is in the middle of it and it moves
2. depict orientation of the triangle (left/right/up/down) somehow
3. specify the distance from the CURSOR to each of the points (or even the length of the sides)
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...endasf...
 
abel
Re: Centered, equilateral triangle - math help
Reply #1 - Jan 6th, 2010, 12:41pm  
Here is some math:
if the triangle has the bottom line in direction of the x-achsis, an the lenght of a side is c, you add a vector to the left bottom point
with x-component c/2 and an y-component -c/sqrt(3). Thats the middle.
From here you get the distance to the three points with the dist()-function.
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endasf
Re: Centered, equilateral triangle - math help
Reply #2 - Jan 6th, 2010, 1:31pm  
Hm; OK.  For a second let's just forget about the mouse.
How about a way to just draw the triangle?  I don't want to use all of the built-in functions; I'm really looking to learn more about the math involved.

I'm not looking for someone to do this for me, but I really thought it would be something closer to:

Code:
float prevx, prevy, nextx, nexty, radius, angle;
int deg, midx, midy;

void setup()
{
  size(400,400);
  fill(200);
  midx = width/2;
  midy = height/2;
  radius = 80;

}

void draw()
{
  background(100); 
  translate(midx, midy);
  
  beginShape();
  for(deg = 0; deg < 360; deg += 120)
  {
    angle = deg * PI / 180;
    nextx = cos(angle) * radius;
    nexty = sin(angle) * radius;
    vertex(nextx, nexty);
  }
  endShape(CLOSE);
}


... but I want the triangle to sit pointing directly upwards (north).
For ex., if I add the code...

Code:
  rotate(radians(30));


...after the shape has been ended, it seems to be sorta straight; but I know that there is more to this; I would like to know what I need to do to have the for loop draw the correct vertices...  

Thanks
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...endasf...
 
abel
Re: Centered, equilateral triangle - math help
Reply #3 - Jan 7th, 2010, 2:12pm  
I had a very similar idea after my first reply. I did the rotation by adding a multiple of 90°-angles to the 120-degrees.
This is my  code:
Code:
void setup() {
  size(600,400);
  smooth();
}
float angle=2*PI/3;  //120 Degrees
float angle_rect=PI/2;
float d=50;
float centerx=200;
float centery=200;

void draw() {

  stroke(0);

}

void draw_shape(float x, float y, int b){

  beginShape();
  for(int i=0;i<3;i++){
    vertex(x+d*sin(angle*i+b*angle_rect),y+d*cos(angle*i+b*angle_rect));
  }
  endShape();

}


void keyPressed() {
  background(200);
  switch(key){
  case '0':
    draw_shape(centerx,centery,0);
    break;
  case '1':
    draw_shape(centerx,centery,1);
    break;
  case '2':
    draw_shape(centerx,centery,2);
    break;

  case '3':
    draw_shape(centerx,centery,3);
    break;
  }

}
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