227 lines
7.9 KiB
C#
227 lines
7.9 KiB
C#
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// -----------------------------------------------------------------------
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// <copyright file="IntersectionHelper.cs" company="">
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// Triangle.NET code by Christian Woltering, http://triangle.codeplex.com/
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// </copyright>
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// -----------------------------------------------------------------------
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namespace UnityEngine.U2D.Animation.TriangleNet
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.Tools
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{
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using Animation.TriangleNet.Geometry;
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internal static class IntersectionHelper
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{
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/// <summary>
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/// Compute intersection of two segments.
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/// </summary>
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/// <param name="p0">Segment 1 start point.</param>
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/// <param name="p1">Segment 1 end point.</param>
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/// <param name="q0">Segment 2 start point.</param>
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/// <param name="q1">Segment 2 end point.</param>
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/// <param name="c0">The intersection point.</param>
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/// <remarks>
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/// This is a special case of segment intersection. Since the calling algorithm assures
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/// that a valid intersection exists, there's no need to check for any special cases.
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/// </remarks>
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internal static void IntersectSegments(Point p0, Point p1, Point q0, Point q1, ref Point c0)
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{
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double ux = p1.x - p0.x;
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double uy = p1.y - p0.y;
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double vx = q1.x - q0.x;
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double vy = q1.y - q0.y;
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double wx = p0.x - q0.x;
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double wy = p0.y - q0.y;
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double d = (ux * vy - uy * vx);
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double s = (vx * wy - vy * wx) / d;
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// Intersection point
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c0.x = p0.X + s * ux;
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c0.y = p0.Y + s * uy;
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}
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/// <summary>
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/// Intersect segment with a bounding box.
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/// </summary>
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/// <param name="rect">The clip rectangle.</param>
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/// <param name="p0">Segment endpoint.</param>
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/// <param name="p1">Segment endpoint.</param>
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/// <param name="c0">The new location of p0.</param>
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/// <param name="c1">The new location of p1.</param>
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/// <returns>Returns true, if segment is clipped.</returns>
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/// <remarks>
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/// Based on Liang-Barsky function by Daniel White:
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/// http://www.skytopia.com/project/articles/compsci/clipping.html
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/// </remarks>
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internal static bool LiangBarsky(Rectangle rect, Point p0, Point p1, ref Point c0, ref Point c1)
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{
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// Define the x/y clipping values for the border.
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double xmin = rect.Left;
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double xmax = rect.Right;
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double ymin = rect.Bottom;
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double ymax = rect.Top;
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// Define the start and end points of the line.
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double x0 = p0.X;
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double y0 = p0.Y;
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double x1 = p1.X;
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double y1 = p1.Y;
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double t0 = 0.0;
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double t1 = 1.0;
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double dx = x1 - x0;
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double dy = y1 - y0;
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double p = 0.0, q = 0.0, r;
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for (int edge = 0; edge < 4; edge++)
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{
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// Traverse through left, right, bottom, top edges.
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if (edge == 0) { p = -dx; q = -(xmin - x0); }
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if (edge == 1) { p = dx; q = (xmax - x0); }
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if (edge == 2) { p = -dy; q = -(ymin - y0); }
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if (edge == 3) { p = dy; q = (ymax - y0); }
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r = q / p;
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if (p == 0 && q < 0) return false; // Don't draw line at all. (parallel line outside)
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if (p < 0)
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{
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if (r > t1) return false; // Don't draw line at all.
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else if (r > t0) t0 = r; // Line is clipped!
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}
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else if (p > 0)
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{
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if (r < t0) return false; // Don't draw line at all.
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else if (r < t1) t1 = r; // Line is clipped!
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}
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}
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c0.X = x0 + t0 * dx;
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c0.Y = y0 + t0 * dy;
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c1.X = x0 + t1 * dx;
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c1.Y = y0 + t1 * dy;
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return true; // (clipped) line is drawn
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}
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/// <summary>
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/// Intersect a ray with a bounding box.
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/// </summary>
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/// <param name="rect">The clip rectangle.</param>
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/// <param name="p0">The ray startpoint (inside the box).</param>
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/// <param name="p1">Any point in ray direction (NOT the direction vector).</param>
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/// <param name="c1">The intersection point.</param>
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/// <returns>Returns false, if startpoint is outside the box.</returns>
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internal static bool BoxRayIntersection(Rectangle rect, Point p0, Point p1, ref Point c1)
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{
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return BoxRayIntersection(rect, p0, p1.x - p0.x, p1.y - p0.y, ref c1);
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}
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/// <summary>
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/// Intersect a ray with a bounding box.
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/// </summary>
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/// <param name="rect">The clip rectangle.</param>
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/// <param name="p">The ray startpoint (inside the box).</param>
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/// <param name="dx">X direction.</param>
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/// <param name="dy">Y direction.</param>
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/// <returns>Returns false, if startpoint is outside the box.</returns>
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internal static Point BoxRayIntersection(Rectangle rect, Point p, double dx, double dy)
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{
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var intersection = new Point();
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if (BoxRayIntersection(rect, p, dx, dy, ref intersection))
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{
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return intersection;
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}
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return null;
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}
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/// <summary>
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/// Intersect a ray with a bounding box.
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/// </summary>
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/// <param name="rect">The clip rectangle.</param>
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/// <param name="p">The ray startpoint (inside the box).</param>
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/// <param name="dx">X direction.</param>
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/// <param name="dy">Y direction.</param>
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/// <param name="c">The intersection point.</param>
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/// <returns>Returns false, if startpoint is outside the box.</returns>
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internal static bool BoxRayIntersection(Rectangle rect, Point p, double dx, double dy, ref Point c)
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{
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double x = p.X;
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double y = p.Y;
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double t1, x1, y1, t2, x2, y2;
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// Bounding box
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double xmin = rect.Left;
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double xmax = rect.Right;
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double ymin = rect.Bottom;
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double ymax = rect.Top;
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// Check if point is inside the bounds
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if (x < xmin || x > xmax || y < ymin || y > ymax)
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{
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return false;
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}
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// Calculate the cut through the vertical boundaries
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if (dx < 0)
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{
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// Line going to the left: intersect with x = minX
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t1 = (xmin - x) / dx;
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x1 = xmin;
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y1 = y + t1 * dy;
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}
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else if (dx > 0)
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{
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// Line going to the right: intersect with x = maxX
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t1 = (xmax - x) / dx;
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x1 = xmax;
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y1 = y + t1 * dy;
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}
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else
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{
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// Line going straight up or down: no intersection possible
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t1 = double.MaxValue;
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x1 = y1 = 0;
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}
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// Calculate the cut through upper and lower boundaries
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if (dy < 0)
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{
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// Line going downwards: intersect with y = minY
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t2 = (ymin - y) / dy;
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x2 = x + t2 * dx;
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y2 = ymin;
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}
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else if (dy > 0)
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{
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// Line going upwards: intersect with y = maxY
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t2 = (ymax - y) / dy;
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x2 = x + t2 * dx;
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y2 = ymax;
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}
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else
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{
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// Horizontal line: no intersection possible
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t2 = double.MaxValue;
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x2 = y2 = 0;
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}
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if (t1 < t2)
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{
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c.x = x1;
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c.y = y1;
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}
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else
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{
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c.x = x2;
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c.y = y2;
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}
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return true;
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}
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}
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}
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