2d intersection between lines and circle, how to?

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secondsky

2d intersection between lines and circle, how to?

in General Discussion • Other • 7 months ago

Hello everyone, I would like to know if there was a library or a method that makes easy to calculate the intersections between planar figures, and in particular I would like to find it among a series of lines and a circle.

thanks

Replies(2)

tfguy44

Re: 2d intersection between lines and circle, how to?

7 months ago

To find the exact intersection points you'd need to have the equations for both the circle and the line, and then solve that system of equations to find the point(s) at which they intersect.

To determine if they just intersect, you can use:

void setup() {
size(400, 400);
}
void draw() {
background(0);
stroke(255);
line(0, 0, width, height);
if ( circleLineIntersect(0, 0, width, height, mouseX, mouseY, 20) ) {
stroke( 255, 0, 0);
}
else {
stroke(0, 255, 0);
}
noFill();
ellipse(mouseX, mouseY, 40, 40);
}
boolean circleLineIntersect(float x1, float y1, float x2, float y2, float cx, float cy, float cr ) {
float dx = x2 - x1;
float dy = y2 - y1;
float a = dx * dx + dy * dy;
float b = 2 * (dx * (x1 - cx) + dy * (y1 - cy));
float c = cx * cx + cy * cy;
c += x1 * x1 + y1 * y1;
c -= 2 * (cx * x1 + cy * y1);
c -= cr * cr;
float bb4ac = b * b - 4 * a * c;
return (bb4ac>=0);
}

But keep in mind that this checks for a LINE, not a LINE SEGMENT.

secondsky

Re: 2d intersection between lines and circle, how to?

7 months ago

It is a nice example, but i think i need the first case: findindng the points in order to obtain the intersected segment.

What I'm trying to get is a circular paragraph of text.

So, i would like to dispose the characters on a series of lines inside a circle.

I know there are many way to reach it, trigonometric equations for example.

But i'm not very good in mats, and for me is more easy think in graphical terms.

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