27accef223
Review URL: https://codereview.appspot.com/5576043 git-svn-id: http://skia.googlecode.com/svn/trunk@3087 2bbb7eff-a529-9590-31e7-b0007b416f81
123 lines
4.1 KiB
C++
123 lines
4.1 KiB
C++
#include "DataTypes.h"
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#include "LineIntersection.h"
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#include "LineParameters.h"
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static bool no_intersection(_Point* result) {
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result->x = 0;
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result->y = 0;
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return false;
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}
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/*
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Determine the intersection point of two line segments
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Return FALSE if the lines don't intersect
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from: http://paulbourke.net/geometry/lineline2d/
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min: 8 subs, 4 muls, 4 cmps
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*/
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bool lineIntersect(const _Line& a, const _Line& b, _Point* result) {
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LineParameters paramsA, paramsB;
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double axLen = a[1].x - a[0].x;
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double ayLen = a[1].y - a[0].y;
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double bxLen = b[1].x - b[0].x;
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double byLen = b[1].y - b[0].y;
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double denom = byLen * axLen - ayLen * bxLen;
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if (approximately_zero_squared(denom)) { // is either 'a' or 'b' a point?
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bool aIsPoint = approximately_zero(axLen) && approximately_zero(ayLen);
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bool bIsPoint = approximately_zero(bxLen) && approximately_zero(byLen);
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if (aIsPoint & bIsPoint) {
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if (!approximately_equal(a[0].x, b[0].x)
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|| !approximately_equal(a[0].y, b[0].y)) {
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return no_intersection(result);
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}
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} else {
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double ptToLineDistance;
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if (aIsPoint) {
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paramsB.lineEndPoints(b);
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ptToLineDistance = paramsB.pointDistance(a[0]);
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} else {
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paramsA.lineEndPoints(a);
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ptToLineDistance = paramsA.pointDistance(b[0]);
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}
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if (!approximately_zero(ptToLineDistance)) {
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return no_intersection(result);
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}
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}
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if (aIsPoint) {
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result->x = a[0].x;
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result->y = a[0].y;
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} else {
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result->x = b[0].x;
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result->y = b[0].y;
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}
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return true;
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}
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double ab0y = a[0].y - b[0].y;
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double ab0x = a[0].x - b[0].x;
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double numerA = ab0y * bxLen - byLen * ab0x;
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double numerB;
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if (numerA < 0 && denom > numerA || numerA > 0 && denom < numerA) {
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return no_intersection(result);
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}
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numerB = ab0y * axLen - ayLen * ab0x;
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if (numerB < 0 && denom > numerB || numerB > 0 && denom < numerB) {
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return no_intersection(result);
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}
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/* Are the line coincident? See if they overlap */
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// FIXME: allow returning range of coincidence, instead of or in
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// addition to midpoint
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paramsA.lineEndPoints(a);
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double b0dist = paramsA.pointDistance(b[0]);
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bool b0on = approximately_zero_squared(b0dist);
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double b1dist = paramsA.pointDistance(b[1]);
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bool b1on = approximately_zero_squared(b1dist);
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if (b0on | b1on) {
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if (b0on & b1on) {
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result->x = (b[0].x + b[1].x) / 2;
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result->y = (b[0].y + b[1].y) / 2;
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return true;
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}
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paramsB.lineEndPoints(b);
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double a0dist = paramsB.pointDistance(a[0]);
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bool a0on = approximately_zero_squared(a0dist);
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double a1dist = paramsB.pointDistance(a[1]);
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bool a1on = approximately_zero_squared(a1dist);
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if (a0on | a1on) {
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if (a0on & a1on) {
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result->x = (a[0].x + a[1].x) / 2;
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result->y = (a[0].y + a[1].y) / 2;
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return true;
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}
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const _Point& aPt = a0on ? a[0] : a[1];
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const _Point& bPt = b0on ? b[0] : b[1];
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if (aPt.approximatelyEqual(bPt)) {
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*result = aPt;
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return true;
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}
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result->x = (aPt.x + bPt.x) / 2;
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result->y = (aPt.y + bPt.y) / 2;
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return true;
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}
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}
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/* Is the intersection along the the segments */
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double mua = numerA / denom;
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result->x = a[0].x + mua * (a[1].x - a[0].x);
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result->y = a[0].y + mua * (a[1].y - a[0].y);
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return true;
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}
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// from http://www.bryceboe.com/wordpress/wp-content/uploads/2006/10/intersect.py
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// 4 subs, 2 muls, 1 cmp
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static bool ccw(const _Point& A, const _Point& B, const _Point& C) {
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return (C.y - A.y) * (B.x - A.x) > (B.y - A.y) * (C.x - A.x);
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}
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// 16 subs, 8 muls, 6 cmps
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bool testIntersect(const _Line& a, const _Line& b) {
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return ccw(a[0], b[0], b[1]) != ccw(a[1], b[0], b[1])
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&& ccw(a[0], a[1], b[0]) != ccw(a[0], a[1], b[1]);
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}
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