03f970652e
working demo of old vs. new git-svn-id: http://skia.googlecode.com/svn/trunk@5209 2bbb7eff-a529-9590-31e7-b0007b416f81
71 lines
1.7 KiB
C++
71 lines
1.7 KiB
C++
#include "QuadraticUtilities.h"
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#include <math.h>
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/*
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Numeric Solutions (5.6) suggests to solve the quadratic by computing
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Q = -1/2(B + sgn(B)Sqrt(B^2 - 4 A C))
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and using the roots
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t1 = Q / A
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t2 = C / Q
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*/
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int quadraticRoots(double A, double B, double C, double t[2]) {
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B *= 2;
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double square = B * B - 4 * A * C;
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if (square < 0) {
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return 0;
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}
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double squareRt = sqrt(square);
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double Q = (B + (B < 0 ? -squareRt : squareRt)) / -2;
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int foundRoots = 0;
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double ratio = Q / A;
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if (ratio > -FLT_EPSILON && ratio < 1 + FLT_EPSILON) {
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if (ratio < FLT_EPSILON) {
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ratio = 0;
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} else if (ratio > 1 - FLT_EPSILON) {
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ratio = 1;
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}
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t[foundRoots++] = ratio;
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}
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ratio = C / Q;
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if (ratio > -FLT_EPSILON && ratio < 1 + FLT_EPSILON) {
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if (ratio < FLT_EPSILON) {
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ratio = 0;
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} else if (ratio > 1 - FLT_EPSILON) {
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ratio = 1;
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}
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t[foundRoots++] = ratio;
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}
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return foundRoots;
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}
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void dxdy_at_t(const Quadratic& quad, double t, double& x, double& y) {
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double a = t - 1;
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double b = 1 - 2 * t;
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double c = t;
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if (&x) {
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x = a * quad[0].x + b * quad[1].x + c * quad[2].x;
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}
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if (&y) {
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y = a * quad[0].y + b * quad[1].y + c * quad[2].y;
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}
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}
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void xy_at_t(const Quadratic& quad, double t, double& x, double& y) {
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double one_t = 1 - t;
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double a = one_t * one_t;
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double b = 2 * one_t * t;
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double c = t * t;
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if (&x) {
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x = a * quad[0].x + b * quad[1].x + c * quad[2].x;
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}
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if (&y) {
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y = a * quad[0].y + b * quad[1].y + c * quad[2].y;
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}
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}
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