c682590538
git-svn-id: http://skia.googlecode.com/svn/trunk@3141 2bbb7eff-a529-9590-31e7-b0007b416f81
35 lines
1.2 KiB
C++
35 lines
1.2 KiB
C++
#include "CurveIntersection.h"
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/* This rejects coincidence with two muls, two adds, and one cmp.
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Coincident candidates will take another four muls and two adds, but may still
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fail if they don't overlap. (The overlap test isn't performed here.)
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*/
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bool implicit_matches(const _Line& one, const _Line& two) {
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_Point oneD, twoD;
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tangent(one, oneD);
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tangent(two, twoD);
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/* See if the slopes match, i.e.
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dx1 / dy1 == dx2 / dy2
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(dy1 * dy2) * dx1 / dy1 == (dy1 * dy2) * dx2 / dy2
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dy2 * dx1 == dy1 * dx2
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*/
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if (!approximately_equal(oneD.x * twoD.y, twoD.x * oneD.y)) {
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return false;
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}
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/* See if the axis intercepts match, i.e.
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y0 - x0 * dy / dx == y1 - x1 * dy / dx
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dx * (y0 - x0 * dy / dx) == dx * (y1 - x1 * dy / dx)
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dx * y0 - x0 * dy == dx * y1 - x1 * dy
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*/
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if (!approximately_equal(oneD.x * one[0].y - oneD.y * one[0].x,
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oneD.x * two[0].y - oneD.y * two[0].x)) {
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return false;
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}
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return true;
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}
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void tangent(const _Line& line, _Point& result) {
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result.x = line[0].x - line[1].x;
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result.y = line[0].y - line[1].y;
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}
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