Checks whether the line and the cubic curve intersect. - Java java.lang

Java examples for java.lang:Math Curve

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Description

Checks whether the line and the cubic curve intersect.

Demo Code



public class Main{
    /**/*w  ww .  j a va 2 s. c o  m*/
     * Checks whether the line (x1, y1) - (x2, y2) and the cubic curve (cx1, cy1) - (cx2, cy2) -
     * (cx3, cy3) - (cx4, cy4) intersect. The points of intersection are saved to {@code points}.
     * Therefore {@code points} must be of length at least 6.
     *
     * @return the numbers of roots that lie in the defined interval.
     */
    public static int intersectLineAndCubic(float x1, float y1, float x2,
            float y2, float cx1, float cy1, float cx2, float cy2,
            float cx3, float cy3, float cx4, float cy4, float[] params) {
        float[] eqn = new float[4];
        float[] t = new float[3];
        float[] s = new float[3];
        float dy = y2 - y1;
        float dx = x2 - x1;
        int quantity = 0;
        int count = 0;

        eqn[0] = (cy1 - y1) * dx + (x1 - cx1) * dy;
        eqn[1] = -3 * (cy1 - cy2) * dx + 3 * (cx1 - cx2) * dy;
        eqn[2] = (3 * cy1 - 6 * cy2 + 3 * cy3) * dx
                - (3 * cx1 - 6 * cx2 + 3 * cx3) * dy;
        eqn[3] = (-3 * cy1 + 3 * cy2 - 3 * cy3 + cy4) * dx
                + (3 * cx1 - 3 * cx2 + 3 * cx3 - cx4) * dy;

        if ((count = Crossing.solveCubic(eqn, t)) == 0) {
            return 0;
        }

        for (int i = 0; i < count; i++) {
            if (dx != 0) {
                s[i] = (cubic(t[i], cx1, cx2, cx3, cx4) - x1) / dx;
            } else if (dy != 0) {
                s[i] = (cubic(t[i], cy1, cy2, cy3, cy4) - y1) / dy;
            } else {
                s[i] = 0f;
            }
            if (t[i] >= 0 && t[i] <= 1 && s[i] >= 0 && s[i] <= 1) {
                params[2 * quantity] = t[i];
                params[2 * quantity + 1] = s[i];
                ++quantity;
            }
        }

        return quantity;
    }
    public static float cubic(float t, float x1, float x2, float x3,
            float x4) {
        return x1 * (1f - t) * (1f - t) * (1f - t) + 3f * x2 * (1f - t)
                * (1f - t) * t + 3f * x3 * (1f - t) * t * t + x4 * t * t
                * t;
    }
}

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