Question

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Extend a line segment a specific distance

Ok for some reason I’m drawing a blank on this. I know the two points of a line segment, and I want to extend that line segment by a known distance. So, I know the starting point for the extension, I know the slope of the extension, I know the length of the extension…how do I find the ending coordinates of that extension?

I’m doing this for a billiards game and I’m trying to figure out at what point the cueball has to hit the object ball in order to sink it into the object pocket. The line segment that I have already is the line from the pocket to the middle of the object ball. The ending point of the line segment extension will be the coordinates that I have to send the cueball to in order to hit the object ball at the correct angle to sink it. I hope that makes sense. I’m using Java, by the way. Thanks for any help.

Answer 1

lengthAB = sqrt((a.x - b.x)^2 + (a.y - b.y)^2) 
c.x = b.x + (b.x - a.x) / lengthAB * length;
c.y = b.y + (b.y - a.y) / lengthAB * length;

*Pulled and consolidated from this answer: Extend a line segment a specific distance