How do I move a point's y coordinate to intersect with a line?

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I have point c, which represents the center of a circle. After I drag the circle, I want its y coordinate hmm to snap to a line that's drawn between point a and b. How do I solve for hmm?

So far I've been able to find the midway y value between points a and b. However, it's not taking into account point c's x value.:

const snapYToLine = (aY, bY) => {
  const yDist = bY - aY;
  return aY + (yDist * 0.5);
}

const a = { x: 10, y: 10 };
const b = { x: 50, y: 30 };
const c = { x: 20, y: 0 }; // not doing anything with this yet...

const hmm = snapYToLine(a.y, b.y); // will need to include c.x here...
console.log(hmm);
geometry javascript
1 Answers

X coordinate of C depends on where you drag it, but Y coordinate should be so point stays on line between A and B?

The equation of line between 2 points (A and B): (x - Xa) / (Xa - Xb) = (y - Ya) / (Ya - Yb).

So hmm = (x - Xa) * (Ya - Yb) / (Xa - Xb) + Ya.

Because it's equation of line you can drag point C over A/B X coordinates and still find corresponsive Y value.

Hope I've understood your question right.

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