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POAndroid/Java how to check if a Rectangle and a line segment intersect without line2d
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<p>in my game for Android I need to check for intersection between a rectangle and a line segment. I cannot use <a href="http://docs.oracle.com/javase/6/docs/api/java/awt/geom/Line2D.html" rel="nofollow noreferrer">line2d</a> as android does not support that. I have looked at similar questions dealing with lines and tried to modify them and failed. I also realize this <a href="https://stackoverflow.com/questions/4823789/how-to-check-if-any-point-or-part-of-a-line-is-inside-or-touches-a-rectangle">Q/A</a> which is basically what I want, however I have failed. For an example here is my code for a Line class that includes my attempt at intersection. The results have been some non-intersections returning true and some intersections returning false. EDIT: Oli Charlesworth helped me and here is working code for any googlers out there.</p> <pre><code> package com.example.HelloAndroid; import android.graphics.Rect; public class Segment { int x1; int y1; int x2; int y2; double m; double b; boolean ishoriz; boolean isvert; public Segment(int x1s, int y1s, int x2s, int y2s) { if (x1s > x2s) { this.x1 = x2s; this.x2 = x1s; } else { this.x1 = x1s; this.x2 = x2s; } if (y1s > y2s) { this.y1 = y2s; this.y2 = y1s; } else { this.y1 = y1s; this.y2 = y2s; } int ydif = y2s - y1s; int xdif = x2s - x1s; if (ydif == 0) { this.ishoriz = true; this.m = 0; this.b = x1s; } else if (xdif == 0) { this.isvert = true; } else { this.m = (double) ydif / xdif; double r = (double) ydif / xdif; this.b = y1s - (r * x1s); this.isvert = false; this.ishoriz = false; } } public final boolean intersected(Segment s, Segment s2) { if (s.ishoriz && s2.ishoriz) { //parallel return false; } if (s.isvert && s2.isvert) { //parallel return false; } if (s.isvert) { //x is constant see if the x is on the other line int x = s.x1; //add 2 for round-off error if (s2.x1 <= x + 2 && s2.x2 + 2 >= x) { //solve and check if y is on both segments int y = (int) ((s.m * x) + s.b); if(s.y1<=y+2&&s.y2+2>=y) { if(s2.y1<=y+2&&s2.y2+2>=y) { return true;} } } return false; } if (s2.isvert) { //x is constant see if the x is on the other line int x = s2.x1; //add 2 for round-off error if (s.x1 <= x + 2 && s.x2 + 2 >= x) { //solve and check if y is on both segments int y = (int) ((s.m * x) + s.b); if(s.y1<=y+2&&s.y2+2>=y) { if(s2.y1<=y+2&&s2.y2+2>=y) { return true;} } } return false; } if (s.ishoriz) { //y is constant see if the y is on the other line int y = s.y1; //add 2 for round-off error if (s2.y1 <= y + 2 && s2.y2 + 2 >= y) { //solve and check if x is on both segments int x=(int) ((y-s.b)/s.m); if(s.x1<=x+2&&s.x2+2>=x) { if(s2.x1<=x+2&&s2.x2+2>=x) return true;} return false; }} if (s2.ishoriz) { //y is constant see if the y is on the other line int y = s2.y1; //add 2 for round-off error if (s.y1 <= y + 2 && s.y2 + 2 >= y) { //solve and check if x is on both segments int x=(int) ((y-s.b)/s.m); if(s.x1<=x+2&&s.x2+2>=x) { if(s2.x1<=x+2&&s2.x2+2>=x) return true;} } return false; } if (s.m == s2.m) { //parallel return false; } // use substitution // (s.m-s2.m)x=s2.b-s.b int x = (int) (s.m - s2.m); x = (int) ((s2.b - s.b) / x); // find y int y = (int) ((x * s.m) + s.b); //check if the values are in between for both lines //add 2 for round-off error if (s.y1 <= y + 2) { if (s.y2 + 2 >= y) { if (s2.y1 <= y + 2) { if (s2.y2 + 2 >= y) { if (s.x1 <= x + 2) { if (s.x2 + 2 >= x) { if (s2.x1 <= x + 2) { if (s2.x2 + 2 >= x) { return true; } } } } } } } } return false; } public final boolean intersects2(Segment s, Rect r) { //created lines of the rect Segment top = new Segment(r.left, r.top, r.right, r.top); Segment left = new Segment(r.left, r.top, r.left, r.bottom); Segment bottom = new Segment(r.left, r.bottom, r.right, r.bottom); Segment right = new Segment(r.right, r.top, r.right, r.bottom); boolean topp = s.intersected(s, top); if (topp) { return true; } boolean leftp = s.intersected(s, left); if (leftp) { return true; } boolean bottomp = s.intersected(s, bottom); if (bottomp) { return true; } boolean rightp = s.intersected(s, right); if (rightp) { return true; } else { return false; } } </code></pre> <p>}</p>
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<java><android><intersection><lines>
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Android/Java how to check if a Rectangle and a line segment intersect without line2d
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