skia2/experimental/Intersection/LineIntersection.cpp
caryclark@google.com 45a8fc6a8b shape ops work in progress
git-svn-id: http://skia.googlecode.com/svn/trunk@7738 2bbb7eff-a529-9590-31e7-b0007b416f81
2013-02-14 15:29:11 +00:00

339 lines
12 KiB
C++

/*
* Copyright 2012 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "CurveIntersection.h"
#include "Intersections.h"
#include "LineIntersection.h"
#include "LineUtilities.h"
/* Determine the intersection point of two lines. This assumes the lines are not parallel,
and that that the lines are infinite.
From http://en.wikipedia.org/wiki/Line-line_intersection
*/
void lineIntersect(const _Line& a, const _Line& b, _Point& p) {
double axLen = a[1].x - a[0].x;
double ayLen = a[1].y - a[0].y;
double bxLen = b[1].x - b[0].x;
double byLen = b[1].y - b[0].y;
double denom = byLen * axLen - ayLen * bxLen;
SkASSERT(denom);
double term1 = a[1].x * a[0].y - a[1].y * a[0].x;
double term2 = b[1].x * b[0].y - b[1].y * b[0].x;
p.x = (term1 * bxLen - axLen * term2) / denom;
p.y = (term1 * byLen - ayLen * term2) / denom;
}
static int computePoints(const _Line& a, int used, Intersections& i) {
i.fPt[0] = xy_at_t(a, i.fT[0][0]);
if ((i.fUsed = used) == 2) {
i.fPt[1] = xy_at_t(a, i.fT[0][1]);
}
return i.fUsed;
}
/*
Determine the intersection point of two line segments
Return FALSE if the lines don't intersect
from: http://paulbourke.net/geometry/lineline2d/
*/
int intersect(const _Line& a, const _Line& b, Intersections& i) {
double axLen = a[1].x - a[0].x;
double ayLen = a[1].y - a[0].y;
double bxLen = b[1].x - b[0].x;
double byLen = b[1].y - b[0].y;
/* Slopes match when denom goes to zero:
axLen / ayLen == bxLen / byLen
(ayLen * byLen) * axLen / ayLen == (ayLen * byLen) * bxLen / byLen
byLen * axLen == ayLen * bxLen
byLen * axLen - ayLen * bxLen == 0 ( == denom )
*/
double denom = byLen * axLen - ayLen * bxLen;
double ab0y = a[0].y - b[0].y;
double ab0x = a[0].x - b[0].x;
double numerA = ab0y * bxLen - byLen * ab0x;
double numerB = ab0y * axLen - ayLen * ab0x;
bool mayNotOverlap = (numerA < 0 && denom > numerA) || (numerA > 0 && denom < numerA)
|| (numerB < 0 && denom > numerB) || (numerB > 0 && denom < numerB);
numerA /= denom;
numerB /= denom;
if ((!approximately_zero(denom) || (!approximately_zero_inverse(numerA)
&& !approximately_zero_inverse(numerB))) && !sk_double_isnan(numerA)
&& !sk_double_isnan(numerB)) {
if (mayNotOverlap) {
return 0;
}
i.fT[0][0] = numerA;
i.fT[1][0] = numerB;
i.fPt[0] = xy_at_t(a, numerA);
return computePoints(a, 1, i);
}
/* See if the axis intercepts match:
ay - ax * ayLen / axLen == by - bx * ayLen / axLen
axLen * (ay - ax * ayLen / axLen) == axLen * (by - bx * ayLen / axLen)
axLen * ay - ax * ayLen == axLen * by - bx * ayLen
*/
// FIXME: need to use AlmostEqualUlps variant instead
if (!approximately_equal_squared(axLen * a[0].y - ayLen * a[0].x,
axLen * b[0].y - ayLen * b[0].x)) {
return 0;
}
const double* aPtr;
const double* bPtr;
if (fabs(axLen) > fabs(ayLen) || fabs(bxLen) > fabs(byLen)) {
aPtr = &a[0].x;
bPtr = &b[0].x;
} else {
aPtr = &a[0].y;
bPtr = &b[0].y;
}
double a0 = aPtr[0];
double a1 = aPtr[2];
double b0 = bPtr[0];
double b1 = bPtr[2];
// OPTIMIZATION: restructure to reject before the divide
// e.g., if ((a0 - b0) * (a0 - a1) < 0 || abs(a0 - b0) > abs(a0 - a1))
// (except efficient)
double aDenom = a0 - a1;
if (approximately_zero(aDenom)) {
if (!between(b0, a0, b1)) {
return 0;
}
i.fT[0][0] = i.fT[0][1] = 0;
} else {
double at0 = (a0 - b0) / aDenom;
double at1 = (a0 - b1) / aDenom;
if ((at0 < 0 && at1 < 0) || (at0 > 1 && at1 > 1)) {
return 0;
}
i.fT[0][0] = SkTMax(SkTMin(at0, 1.0), 0.0);
i.fT[0][1] = SkTMax(SkTMin(at1, 1.0), 0.0);
}
double bDenom = b0 - b1;
if (approximately_zero(bDenom)) {
i.fT[1][0] = i.fT[1][1] = 0;
} else {
int bIn = aDenom * bDenom < 0;
i.fT[1][bIn] = SkTMax(SkTMin((b0 - a0) / bDenom, 1.0), 0.0);
i.fT[1][!bIn] = SkTMax(SkTMin((b0 - a1) / bDenom, 1.0), 0.0);
}
bool second = fabs(i.fT[0][0] - i.fT[0][1]) > FLT_EPSILON;
SkASSERT((fabs(i.fT[1][0] - i.fT[1][1]) <= FLT_EPSILON) ^ second);
return computePoints(a, 1 + second, i);
}
int horizontalIntersect(const _Line& line, double y, double tRange[2]) {
double min = line[0].y;
double max = line[1].y;
if (min > max) {
SkTSwap(min, max);
}
if (min > y || max < y) {
return 0;
}
if (AlmostEqualUlps(min, max)) {
tRange[0] = 0;
tRange[1] = 1;
return 2;
}
tRange[0] = (y - line[0].y) / (line[1].y - line[0].y);
return 1;
}
// OPTIMIZATION Given: dy = line[1].y - line[0].y
// and: xIntercept / (y - line[0].y) == (line[1].x - line[0].x) / dy
// then: xIntercept * dy == (line[1].x - line[0].x) * (y - line[0].y)
// Assuming that dy is always > 0, the line segment intercepts if:
// left * dy <= xIntercept * dy <= right * dy
// thus: left * dy <= (line[1].x - line[0].x) * (y - line[0].y) <= right * dy
// (clever as this is, it does not give us the t value, so may be useful only
// as a quick reject -- and maybe not then; it takes 3 muls, 3 adds, 2 cmps)
int horizontalLineIntersect(const _Line& line, double left, double right,
double y, double tRange[2]) {
int result = horizontalIntersect(line, y, tRange);
if (result != 1) {
// FIXME: this is incorrect if result == 2
return result;
}
double xIntercept = line[0].x + tRange[0] * (line[1].x - line[0].x);
if (xIntercept > right || xIntercept < left) {
return 0;
}
return result;
}
int horizontalIntersect(const _Line& line, double left, double right,
double y, bool flipped, Intersections& intersections) {
int result = horizontalIntersect(line, y, intersections.fT[0]);
switch (result) {
case 0:
break;
case 1: {
double xIntercept = line[0].x + intersections.fT[0][0]
* (line[1].x - line[0].x);
if (xIntercept > right || xIntercept < left) {
return 0;
}
intersections.fT[1][0] = (xIntercept - left) / (right - left);
break;
}
case 2:
#if 0 // sorting edges fails to preserve original direction
double lineL = line[0].x;
double lineR = line[1].x;
if (lineL > lineR) {
SkTSwap(lineL, lineR);
}
double overlapL = SkTMax(left, lineL);
double overlapR = SkTMin(right, lineR);
if (overlapL > overlapR) {
return 0;
}
if (overlapL == overlapR) {
result = 1;
}
intersections.fT[0][0] = (overlapL - line[0].x) / (line[1].x - line[0].x);
intersections.fT[1][0] = (overlapL - left) / (right - left);
if (result > 1) {
intersections.fT[0][1] = (overlapR - line[0].x) / (line[1].x - line[0].x);
intersections.fT[1][1] = (overlapR - left) / (right - left);
}
#else
double a0 = line[0].x;
double a1 = line[1].x;
double b0 = flipped ? right : left;
double b1 = flipped ? left : right;
// FIXME: share common code below
double at0 = (a0 - b0) / (a0 - a1);
double at1 = (a0 - b1) / (a0 - a1);
if ((at0 < 0 && at1 < 0) || (at0 > 1 && at1 > 1)) {
return 0;
}
intersections.fT[0][0] = SkTMax(SkTMin(at0, 1.0), 0.0);
intersections.fT[0][1] = SkTMax(SkTMin(at1, 1.0), 0.0);
int bIn = (a0 - a1) * (b0 - b1) < 0;
intersections.fT[1][bIn] = SkTMax(SkTMin((b0 - a0) / (b0 - b1),
1.0), 0.0);
intersections.fT[1][!bIn] = SkTMax(SkTMin((b0 - a1) / (b0 - b1),
1.0), 0.0);
bool second = fabs(intersections.fT[0][0] - intersections.fT[0][1])
> FLT_EPSILON;
SkASSERT((fabs(intersections.fT[1][0] - intersections.fT[1][1])
<= FLT_EPSILON) ^ second);
return computePoints(line, 1 + second, intersections);
#endif
break;
}
if (flipped) {
// OPTIMIZATION: instead of swapping, pass original line, use [1].x - [0].x
for (int index = 0; index < result; ++index) {
intersections.fT[1][index] = 1 - intersections.fT[1][index];
}
}
return computePoints(line, result, intersections);
}
static int verticalIntersect(const _Line& line, double x, double tRange[2]) {
double min = line[0].x;
double max = line[1].x;
if (min > max) {
SkTSwap(min, max);
}
if (min > x || max < x) {
return 0;
}
if (AlmostEqualUlps(min, max)) {
tRange[0] = 0;
tRange[1] = 1;
return 2;
}
tRange[0] = (x - line[0].x) / (line[1].x - line[0].x);
return 1;
}
int verticalIntersect(const _Line& line, double top, double bottom,
double x, bool flipped, Intersections& intersections) {
int result = verticalIntersect(line, x, intersections.fT[0]);
switch (result) {
case 0:
break;
case 1: {
double yIntercept = line[0].y + intersections.fT[0][0]
* (line[1].y - line[0].y);
if (yIntercept > bottom || yIntercept < top) {
return 0;
}
intersections.fT[1][0] = (yIntercept - top) / (bottom - top);
break;
}
case 2:
#if 0 // sorting edges fails to preserve original direction
double lineT = line[0].y;
double lineB = line[1].y;
if (lineT > lineB) {
SkTSwap(lineT, lineB);
}
double overlapT = SkTMax(top, lineT);
double overlapB = SkTMin(bottom, lineB);
if (overlapT > overlapB) {
return 0;
}
if (overlapT == overlapB) {
result = 1;
}
intersections.fT[0][0] = (overlapT - line[0].y) / (line[1].y - line[0].y);
intersections.fT[1][0] = (overlapT - top) / (bottom - top);
if (result > 1) {
intersections.fT[0][1] = (overlapB - line[0].y) / (line[1].y - line[0].y);
intersections.fT[1][1] = (overlapB - top) / (bottom - top);
}
#else
double a0 = line[0].y;
double a1 = line[1].y;
double b0 = flipped ? bottom : top;
double b1 = flipped ? top : bottom;
// FIXME: share common code above
double at0 = (a0 - b0) / (a0 - a1);
double at1 = (a0 - b1) / (a0 - a1);
if ((at0 < 0 && at1 < 0) || (at0 > 1 && at1 > 1)) {
return 0;
}
intersections.fT[0][0] = SkTMax(SkTMin(at0, 1.0), 0.0);
intersections.fT[0][1] = SkTMax(SkTMin(at1, 1.0), 0.0);
int bIn = (a0 - a1) * (b0 - b1) < 0;
intersections.fT[1][bIn] = SkTMax(SkTMin((b0 - a0) / (b0 - b1),
1.0), 0.0);
intersections.fT[1][!bIn] = SkTMax(SkTMin((b0 - a1) / (b0 - b1),
1.0), 0.0);
bool second = fabs(intersections.fT[0][0] - intersections.fT[0][1])
> FLT_EPSILON;
SkASSERT((fabs(intersections.fT[1][0] - intersections.fT[1][1])
<= FLT_EPSILON) ^ second);
return computePoints(line, 1 + second, intersections);
#endif
break;
}
if (flipped) {
// OPTIMIZATION: instead of swapping, pass original line, use [1].y - [0].y
for (int index = 0; index < result; ++index) {
intersections.fT[1][index] = 1 - intersections.fT[1][index];
}
}
return computePoints(line, result, intersections);
}
// from http://www.bryceboe.com/wordpress/wp-content/uploads/2006/10/intersect.py
// 4 subs, 2 muls, 1 cmp
static bool ccw(const _Point& A, const _Point& B, const _Point& C) {
return (C.y - A.y) * (B.x - A.x) > (B.y - A.y) * (C.x - A.x);
}
// 16 subs, 8 muls, 6 cmps
bool testIntersect(const _Line& a, const _Line& b) {
return ccw(a[0], b[0], b[1]) != ccw(a[1], b[0], b[1])
&& ccw(a[0], a[1], b[0]) != ccw(a[0], a[1], b[1]);
}