How to check if point is inside the rectangle around a diagonal line?

Question

First of all: I know I can calc the distance from a point to a line to check if the point was on the line. This is what I do for detecting clicks (with an offset) on a line.

But before that, I want to apply a general check around the diagonal line. The line itself with Start and End point defines a rectangular area:

Pstart(sx, sy), Pend(ex, ey).

I can use boundary check to determine if the Point(px, py) was inside that rectangle:

sx <= px && ex >= px && sy <= px && ey >= py

But this only applies if the line goes from top left to bottom right. If it goes a different direction I have to modify the algorithm. How could I use my formula above regardless of the line direction?

How can I get the formula to respect the direction accordingly?

Check co-ordinate sizes and swap? – Boris the Spider Mar 25 '13 at 14:51 — Boris the Spider, Mar 25 '13 at 14:51

score 3 · Accepted Answer · answered Mar 25 '13 at 14:50

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Just compare for Math.min(sx, ex) <= px <= Math.max(sx, ex) and likewise for the y dimension.

answered Mar 25 '13 at 14:50

Alnitak

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score 0 · Answer 2 · answered Mar 25 '13 at 14:52

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Line2D.ptSegDist(x1, y1, x2, y2, xP, yP) returns 0.0 iff the point (xP, yP) is on the line segment from (x1, y1) to (x2, y2). Line2D.ptLineDist does the same thing for the infinite line.

answered Mar 25 '13 at 14:52

Parth Soni

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That's what I do for deeper analysis, but I want to include a precheck to not having to run the ptSegDist algorithm against all my lines, but only the lines that lie inside the defined rectangle of the line start and end points. – membersound Mar 25 '13 at 14:57
@membersound: i think [this](http://stackoverflow.com/questions/2752725/finding-whether-a-point-lies-inside-a-rectangle-or-not) may help you for that :) – Parth Soni Mar 25 '13 at 15:05

How to check if point is inside the rectangle around a diagonal line?

2 Answers2