Radiating vector issues

Programming Questions

vtalessi

in Programming Questions • 1 year ago

Is there any way to take a star with 10 vector points and radiate them from the center without using the scale function? I've been beating my head against the wall with int loops and multiplying each point by float commands to increase all the points in size equally. here is the example I have; (i've been tweaking wit the left star)

size (800,400);

background (255);

noFill();

strokeWeight (13);

line (400,0,400,400);

rect (6.5,6.5,790,390);

for (float p=.9; p<10; p+=.1){//p is stand-in for i

pushMatrix();

translate (-372.5,-433);

noFill();

strokeWeight(13);

beginShape();

vertex(115*p,460*p);//1

vertex(460*p,460*p);//2

vertex(575*p,115*p);//3

vertex(690*p,460*p);//4

vertex(1035*p,460*p);//5

vertex(747.5*p,690*p);//6

vertex(862.5*p,1035*p);//7

vertex(575*p,805*p);//8

vertex(285.5*p,1035*p);//9

vertex(402.5*p,690*p);//10

endShape(CLOSE);

popMatrix();

}

This ends up giving me the desired scaling up of size but no pushMatrix can have me shift the progression of size to radiate from the center of the shape. And that is my issue. Does anyone have any tips/ideas? I can't afford to keep buying plaster to fill the holes in the walls.

Replies(2)

allonestr..

Re: Radiating vector issues

1 year ago

I haven't run your code, nor examined the numbers carefully enough to see if you're drawing a regular star, but am assuming that you are.

Let's look at a circle centred at the origin (0, 0). The (x, y) co-ordinates for each point on the circumference are

(radius * cos(rotationAngle), radius * sin(rotationAngle).

And if the circle is centred at (cx, cy), the co-ordinates are

(cx + radius * cos(rotationAngle), cy + radius * sin(rotationAngle).

So to provide the vertices to draw a circle (or an approximation of one) we could use the code

for(int angle = 0; angle < 360; angle++)

{

vertex(cx + radius * cos(radians(angle)), cy + radius * sin(radians(angle));

}

To draw a decagon, we need to divide the 360 degrees in a whole circle by 10, so 36:

for(int angle = 0; angle < 360; angle+=36)

{

vertex(cx + radius * cos(radians(angle)), cy + radius * sin(radians(angle));

}

All you have to do to change the size or position is to change radius or (cx, cy).

If you are drawing a star, then you need to look at two circles, with radii bigRadius and smallRadius. We'll say that the first point is on the big circle, the second on the small and so on. We need to add an if to our loop - if it's the first, third, fifth ... point put it on the big circle, otherwise put it on the small circle. In other words, put the odd numbered points on the big circle and the even ones on the small.

We can do this using modulo %. 7 % 4 = 3, 7 divided by 4 gives a remainder of 3.

So we can find odd numbers by saying that if someInteger % 2 == 1 it's odd.

So our loop becomes

for(int angle = 0; angle < 360; angle+=36)

{

if(angle % 2 == 1)

{

vertex(cx + bigRadius * cos(radians(angle)), cy + bigRadius * sin(radians(angle));

}

else

{

vertex(cx + smallRadius * cos(radians(angle)), cy + smallRadius * sin(radians(angle));

}

for a 10/2 = 5 pointed star. Change the angle increment for a different number of points.

PhiLho

Re: Radiating vector issues

1 year ago

You need to make the translation proportional too.
After some trial and errors, I got that:
You need some tweaking of the constants of translate() to get it right.
I added a scale() call because the star was too big for the surface, and reduced the max p for the same reason.

size(800, 400);
background(255);
noFill();
strokeWeight(13);
line(400, 0, 400, 400);
rect(6.5, 6.5, 790, 390);
scale(0.1);
for (float p = 0.9; p < 5; p += 0.1)
{
pushMatrix();
translate (472.5 - 520 * p, 533 - 520 * p);
noFill();
strokeWeight(13);
stroke(50 * p); // Just to distinguish the stars
beginShape();
vertex(115*p, 460*p);//1
vertex(460*p, 460*p);//2
vertex(575*p, 115*p);//3
vertex(690*p, 460*p);//4
vertex(1035*p, 460*p);//5
vertex(747.5*p, 690*p);//6
vertex(862.5*p, 1035*p);//7
vertex(575*p, 805*p);//8
vertex(285.5*p, 1035*p);//9
vertex(402.5*p, 690*p);//10
endShape(CLOSE);
popMatrix();
}

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