src/com/android/gallery3d/filtershow/imageshow/GeometryMath.java

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.gallery3d.filtershow.imageshow;

import android.graphics.Rect;
import android.graphics.RectF;

public class GeometryMath {

    // Math operations for 2d vectors
    public static float clamp(float i, float low, float high) {
        return Math.max(Math.min(i, high), low);
    }

    public static float[] lineIntersect(float[] line1, float[] line2) {
        float a0 = line1[0];
        float a1 = line1[1];
        float b0 = line1[2];
        float b1 = line1[3];
        float c0 = line2[0];
        float c1 = line2[1];
        float d0 = line2[2];
        float d1 = line2[3];
        float t0 = a0 - b0;
        float t1 = a1 - b1;
        float t2 = b0 - d0;
        float t3 = d1 - b1;
        float t4 = c0 - d0;
        float t5 = c1 - d1;

        float denom = t1 * t4 - t0 * t5;
        if (denom == 0)
            return null;
        float u = (t3 * t4 + t5 * t2) / denom;
        float[] intersect = {
                b0 + u * t0, b1 + u * t1
        };
        return intersect;
    }

    public static float[] shortestVectorFromPointToLine(float[] point, float[] line) {
        float x1 = line[0];
        float x2 = line[2];
        float y1 = line[1];
        float y2 = line[3];
        float xdelt = x2 - x1;
        float ydelt = y2 - y1;
        if (xdelt == 0 && ydelt == 0)
            return null;
        float u = ((point[0] - x1) * xdelt + (point[1] - y1) * ydelt)
                / (xdelt * xdelt + ydelt * ydelt);
        float[] ret = {
                (x1 + u * (x2 - x1)), (y1 + u * (y2 - y1))
        };
        float[] vec = {
                ret[0] - point[0], ret[1] - point[1]
        };
        return vec;
    }

    // A . B
    public static float dotProduct(float[] a, float[] b) {
        return a[0] * b[0] + a[1] * b[1];
    }

    public static float[] normalize(float[] a) {
        float length = (float) Math.sqrt(a[0] * a[0] + a[1] * a[1]);
        float[] b = {
                a[0] / length, a[1] / length
        };
        return b;
    }

    // A onto B
    public static float scalarProjection(float[] a, float[] b) {
        float length = (float) Math.sqrt(b[0] * b[0] + b[1] * b[1]);
        return dotProduct(a, b) / length;
    }

    public static float[] getVectorFromPoints(float[] point1, float[] point2) {
        float[] p = {
                point2[0] - point1[0], point2[1] - point1[1]
        };
        return p;
    }

    public static float[] getUnitVectorFromPoints(float[] point1, float[] point2) {
        float[] p = {
                point2[0] - point1[0], point2[1] - point1[1]
        };
        float length = (float) Math.sqrt(p[0] * p[0] + p[1] * p[1]);
        p[0] = p[0] / length;
        p[1] = p[1] / length;
        return p;
    }

    public static RectF scaleRect(RectF r, float scale) {
        return new RectF(r.left * scale, r.top * scale, r.right * scale, r.bottom * scale);
    }

    // A - B
    public static float[] vectorSubtract(float[] a, float[] b) {
        int len = a.length;
        if (len != b.length)
            return null;
        float[] ret = new float[len];
        for (int i = 0; i < len; i++) {
            ret[i] = a[i] - b[i];
        }
        return ret;
    }

    public static float vectorLength(float[] a) {
        return (float) Math.sqrt(a[0] * a[0] + a[1] * a[1]);
    }

    public static float scale(float oldWidth, float oldHeight, float newWidth, float newHeight) {
        if (oldHeight == 0 || oldWidth == 0)
            return 1;
        return Math.min(newWidth / oldWidth, newHeight / oldHeight);
    }

    public static Rect roundNearest(RectF r) {
        Rect q = new Rect(Math.round(r.left), Math.round(r.top), Math.round(r.right),
                Math.round(r.bottom));
        return q;
    }

}