d6176b0dca
This CL is part II of IV (I broke down the 1280 files into 4 CLs). Review URL: https://codereview.appspot.com/6474054 git-svn-id: http://skia.googlecode.com/svn/trunk@5263 2bbb7eff-a529-9590-31e7-b0007b416f81
85 lines
2.7 KiB
C++
85 lines
2.7 KiB
C++
#include "CurveIntersection.h"
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#include "CurveUtilities.h"
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#include "LineParameters.h"
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#include <algorithm> // used for std::swap
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// return false if unable to clip (e.g., unable to create implicit line)
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// caller should subdivide, or create degenerate if the values are too small
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bool bezier_clip(const Cubic& cubic1, const Cubic& cubic2, double& minT, double& maxT) {
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minT = 1;
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maxT = 0;
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// determine normalized implicit line equation for pt[0] to pt[3]
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// of the form ax + by + c = 0, where a*a + b*b == 1
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// find the implicit line equation parameters
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LineParameters endLine;
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endLine.cubicEndPoints(cubic1);
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if (!endLine.normalize()) {
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printf("line cannot be normalized: need more code here\n");
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return false;
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}
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double distance[2];
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endLine.controlPtDistance(cubic1, distance);
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// find fat line
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double top = distance[0];
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double bottom = distance[1];
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if (top > bottom) {
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std::swap(top, bottom);
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}
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if (top * bottom >= 0) {
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const double scale = 3/4.0; // http://cagd.cs.byu.edu/~tom/papers/bezclip.pdf (13)
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if (top < 0) {
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top *= scale;
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bottom = 0;
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} else {
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top = 0;
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bottom *= scale;
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}
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} else {
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const double scale = 4/9.0; // http://cagd.cs.byu.edu/~tom/papers/bezclip.pdf (15)
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top *= scale;
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bottom *= scale;
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}
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// compute intersecting candidate distance
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Cubic distance2y; // points with X of (0, 1/3, 2/3, 1)
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endLine.cubicDistanceY(cubic2, distance2y);
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int flags = 0;
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if (approximately_lesser(distance2y[0].y, top)) {
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flags |= kFindTopMin;
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} else if (approximately_greater(distance2y[0].y, bottom)) {
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flags |= kFindBottomMin;
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} else {
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minT = 0;
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}
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if (approximately_lesser(distance2y[3].y, top)) {
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flags |= kFindTopMax;
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} else if (approximately_greater(distance2y[3].y, bottom)) {
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flags |= kFindBottomMax;
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} else {
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maxT = 1;
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}
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// Find the intersection of distance convex hull and fat line.
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char to_0[2];
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char to_3[2];
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bool do_1_2_edge = convex_x_hull(distance2y, to_0, to_3);
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x_at(distance2y[0], distance2y[to_0[0]], top, bottom, flags, minT, maxT);
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if (to_0[0] != to_0[1]) {
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x_at(distance2y[0], distance2y[to_0[1]], top, bottom, flags, minT, maxT);
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}
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x_at(distance2y[to_3[0]], distance2y[3], top, bottom, flags, minT, maxT);
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if (to_3[0] != to_3[1]) {
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x_at(distance2y[to_3[1]], distance2y[3], top, bottom, flags, minT, maxT);
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}
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if (do_1_2_edge) {
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x_at(distance2y[1], distance2y[2], top, bottom, flags, minT, maxT);
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}
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return minT < maxT; // returns false if distance shows no intersection
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}
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