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ShikariSohanShikariSohan
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Add line clipping algorithms (#5580)
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‎src/main/java/com/thealgorithms/lineclipping/CohenSutherland.java

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package com.thealgorithms.lineclipping;
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import com.thealgorithms.lineclipping.utils.Line;
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import com.thealgorithms.lineclipping.utils.Point;
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/**
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* @author shikarisohan
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* @since 10/4/24
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* Cohen-Sutherland Line Clipping Algorithm
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*
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* This algorithm is used to clip a line segment to a rectangular window.
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* It assigns a region code to each endpoint of the line segment, and
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* then efficiently determines whether the line segment is fully inside,
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* fully outside, or partially inside the window.
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*
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* Reference:
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* https://en.wikipedia.org/wiki/Cohen%E2%80%93Sutherland_algorithm
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*
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* Clipping window boundaries are defined as (xMin, yMin) and (xMax, yMax).
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* The algorithm computes the clipped line segment if it's partially or
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* fully inside the clipping window.
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*/
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public class CohenSutherland {
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// Region codes for the 9 regions
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private static final int INSIDE = 0; // 0000
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private static final int LEFT = 1; // 0001
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private static final int RIGHT = 2; // 0010
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private static final int BOTTOM = 4; // 0100
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private static final int TOP = 8; // 1000
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// Define the clipping window
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double xMin;
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double yMin;
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double xMax;
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double yMax;
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public CohenSutherland(double xMin, double yMin, double xMax, double yMax) {
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this.xMin = xMin;
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this.yMin = yMin;
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this.xMax = xMax;
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this.yMax = yMax;
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}
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// Compute the region code for a point (x, y)
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private int computeCode(double x, double y) {
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int code = INSIDE;
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if (x < xMin) // to the left of rectangle
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{
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code |= LEFT;
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} else if (x > xMax) // to the right of rectangle
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{
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code |= RIGHT;
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}
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if (y < yMin) // below the rectangle
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{
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code |= BOTTOM;
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} else if (y > yMax) // above the rectangle
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{
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code |= TOP;
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}
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return code;
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}
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// Cohen-Sutherland algorithm to return the clipped line
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public Line cohenSutherlandClip(Line line) {
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double x1 = line.start.x;
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double y1 = line.start.y;
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double x2 = line.end.x;
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double y2 = line.end.y;
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int code1 = computeCode(x1, y1);
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int code2 = computeCode(x2, y2);
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boolean accept = false;
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while (true) {
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if ((code1 == 0) && (code2 == 0)) {
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// Both points are inside the rectangle
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accept = true;
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break;
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} else if ((code1 & code2) != 0) {
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// Both points are outside the rectangle in the same region
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break;
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} else {
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// Some segment of the line is inside the rectangle
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double x = 0;
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double y = 0;
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// Pick an endpoint that is outside the rectangle
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int codeOut = (code1 != 0) ? code1 : code2;
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// Find the intersection point using the line equation
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if ((codeOut & TOP) != 0) {
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// Point is above the rectangle
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x = x1 + (x2 - x1) * (yMax - y1) / (y2 - y1);
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y = yMax;
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} else if ((codeOut & BOTTOM) != 0) {
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// Point is below the rectangle
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x = x1 + (x2 - x1) * (yMin - y1) / (y2 - y1);
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y = yMin;
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} else if ((codeOut & RIGHT) != 0) {
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// Point is to the right of the rectangle
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y = y1 + (y2 - y1) * (xMax - x1) / (x2 - x1);
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x = xMax;
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} else if ((codeOut & LEFT) != 0) {
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// Point is to the left of the rectangle
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y = y1 + (y2 - y1) * (xMin - x1) / (x2 - x1);
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x = xMin;
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}
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// Replace the point outside the rectangle with the intersection point
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if (codeOut == code1) {
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x1 = x;
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y1 = y;
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code1 = computeCode(x1, y1);
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} else {
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x2 = x;
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y2 = y;
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code2 = computeCode(x2, y2);
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}
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}
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}
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if (accept) {
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return new Line(new Point(x1, y1), new Point(x2, y2));
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} else {
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return null; // The line is fully rejected
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}
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}
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}

‎src/main/java/com/thealgorithms/lineclipping/LiangBarsky.java

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package com.thealgorithms.lineclipping;
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import com.thealgorithms.lineclipping.utils.Line;
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import com.thealgorithms.lineclipping.utils.Point;
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/**
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* @author shikarisohan
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* @since 10/5/24
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*
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* * The Liang-Barsky line clipping algorithm is an efficient algorithm for
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* * line clipping against a rectangular window. It is based on the parametric
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* * equation of a line and checks the intersections of the line with the
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* * window boundaries. This algorithm calculates the intersection points,
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* * if any, and returns the clipped line that lies inside the window.
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* *
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* * Reference:
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* * https://en.wikipedia.org/wiki/Liang%E2%80%93Barsky_algorithm
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*
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* Clipping window boundaries are defined as (xMin, yMin) and (xMax, yMax).
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* The algorithm computes the clipped line segment if it's partially or
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* fully inside the clipping window.
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*/
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public class LiangBarsky {
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// Define the clipping window
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double xMin;
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double xMax;
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double yMin;
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double yMax;
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public LiangBarsky(double xMin, double yMin, double xMax, double yMax) {
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this.xMin = xMin;
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this.yMin = yMin;
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this.xMax = xMax;
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this.yMax = yMax;
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}
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// Liang-Barsky algorithm to return the clipped line
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public Line liangBarskyClip(Line line) {
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double dx = line.end.x - line.start.x;
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double dy = line.end.y - line.start.y;
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double[] p = {-dx, dx, -dy, dy};
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double[] q = {line.start.x - xMin, xMax - line.start.x, line.start.y - yMin, yMax - line.start.y};
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double[] resultT = clipLine(p, q);
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if (resultT == null) {
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return null; // Line is outside the clipping window
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}
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return calculateClippedLine(line, resultT[0], resultT[1], dx, dy);
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}
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// clip the line by adjusting t0 and t1 for each edge
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private double[] clipLine(double[] p, double[] q) {
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double t0 = 0.0;
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double t1 = 1.0;
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for (int i = 0; i < 4; i++) {
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double t = q[i] / p[i];
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if (p[i] == 0 && q[i] < 0) {
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return null; // Line is outside the boundary
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} else if (p[i] < 0) {
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if (t > t1) {
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return null;
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} // Line is outside
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if (t > t0) {
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t0 = t;
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} // Update t0
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} else if (p[i] > 0) {
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if (t < t0) {
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return null;
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} // Line is outside
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if (t < t1) {
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t1 = t;
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} // Update t1
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}
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}
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return new double[] {t0, t1}; // Return valid t0 and t1
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}
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// calculate the clipped line based on t0 and t1
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private Line calculateClippedLine(Line line, double t0, double t1, double dx, double dy) {
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double clippedX1 = line.start.x + t0 * dx;
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double clippedY1 = line.start.y + t0 * dy;
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double clippedX2 = line.start.x + t1 * dx;
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double clippedY2 = line.start.y + t1 * dy;
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return new Line(new Point(clippedX1, clippedY1), new Point(clippedX2, clippedY2));
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}
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}

‎src/main/java/com/thealgorithms/lineclipping/utils/Line.java

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package com.thealgorithms.lineclipping.utils;
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import java.util.Objects;
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/**
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* @author moksedursohan
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* @since 10/4/24
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*/
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public class Line {
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public Point start;
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public Point end;
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public Line() {
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}
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public Line(Point start, Point end) {
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this.start = start;
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this.end = end;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) {
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return true;
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}
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if (!(o instanceof Line line)) {
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return false;
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}
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return Objects.equals(start, line.start) && Objects.equals(end, line.end);
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}
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@Override
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public int hashCode() {
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return Objects.hash(start, end);
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}
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@Override
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public String toString() {
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return "Line from " + start + " to " + end;
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}
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}

‎src/main/java/com/thealgorithms/lineclipping/utils/Point.java

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package com.thealgorithms.lineclipping.utils;
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import java.util.Objects;
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/**
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* @author moksedursohan
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* @since 10/4/24
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*/
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public class Point {
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public double x;
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public double y;
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public Point() {
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}
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public Point(double x, double y) {
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this.x = x;
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this.y = y;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) {
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return true;
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}
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if (!(o instanceof Point point)) {
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return false;
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}
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return Double.compare(x, point.x) == 0 && Double.compare(y, point.y) == 0;
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}
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@Override
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public int hashCode() {
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return Objects.hash(x, y);
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}
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@Override
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public String toString() {
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return "(" + x + ", " + y + ")";
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}
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}

‎src/test/java/com/thealgorithms/lineclipping/CohenSutherlandTest.java

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package com.thealgorithms.lineclipping;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNotNull;
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import static org.junit.jupiter.api.Assertions.assertNull;
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import com.thealgorithms.lineclipping.utils.Line;
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import com.thealgorithms.lineclipping.utils.Point;
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import org.junit.jupiter.api.Test;
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/**
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* @author shikarisohan
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* @since 10/4/24
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*/
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class CohenSutherlandTest {
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// Define the clipping window (1.0, 1.0) to (10.0, 10.0)
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CohenSutherland cs = new CohenSutherland(1.0, 1.0, 10.0, 10.0);
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@Test
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void testLineCompletelyInside() {
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// Line fully inside the clipping window
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Line line = new Line(new Point(2.0, 2.0), new Point(8.0, 8.0));
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Line clippedLine = cs.cohenSutherlandClip(line);
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assertNotNull(clippedLine, "Line should not be null.");
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assertEquals(line, clippedLine, "Line inside the window should remain unchanged.");
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}
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@Test
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void testLineCompletelyOutside() {
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// Line completely outside and above the clipping window
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Line line = new Line(new Point(11.0, 12.0), new Point(15.0, 18.0));
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Line clippedLine = cs.cohenSutherlandClip(line);
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assertNull(clippedLine, "Line should be null because it's completely outside.");
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}
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@Test
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void testLinePartiallyInside() {
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// Line partially inside the clipping window
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Line line = new Line(new Point(5.0, 5.0), new Point(12.0, 12.0));
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Line expectedClippedLine = new Line(new Point(5.0, 5.0), new Point(10.0, 10.0)); // Clipped at (10, 10)
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Line clippedLine = cs.cohenSutherlandClip(line);
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assertNotNull(clippedLine, "Line should not be null.");
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assertEquals(expectedClippedLine, clippedLine, "Line should be clipped correctly.");
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}
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@Test
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void testLineOnBoundary() {
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// Line exactly on the boundary of the clipping window
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Line line = new Line(new Point(1.0, 5.0), new Point(10.0, 5.0));
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Line clippedLine = cs.cohenSutherlandClip(line);
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assertNotNull(clippedLine, "Line should not be null.");
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assertEquals(line, clippedLine, "Line on the boundary should remain unchanged.");
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}
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@Test
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void testDiagonalLineThroughClippingWindow() {
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// Diagonal line crossing from outside to outside through the window
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Line line = new Line(new Point(0.0, 0.0), new Point(12.0, 12.0));
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Line expectedClippedLine = new Line(new Point(1.0, 1.0), new Point(10.0, 10.0)); // Clipped at both boundaries
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Line clippedLine = cs.cohenSutherlandClip(line);
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assertNotNull(clippedLine, "Line should not be null.");
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assertEquals(expectedClippedLine, clippedLine, "Diagonal line should be clipped correctly.");
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}
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@Test
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void testVerticalLineClipping() {
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// Vertical line crossing the top and bottom of the clipping window
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Line line = new Line(new Point(5.0, 0.0), new Point(5.0, 12.0));
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Line expectedClippedLine = new Line(new Point(5.0, 1.0), new Point(5.0, 10.0)); // Clipped at yMin and yMax
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Line clippedLine = cs.cohenSutherlandClip(line);
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assertNotNull(clippedLine, "Line should not be null.");
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assertEquals(expectedClippedLine, clippedLine, "Vertical line should be clipped correctly.");
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}
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}

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