cesium
Version:
Cesium is a JavaScript library for creating 3D globes and 2D maps in a web browser without a plugin.
285 lines (251 loc) • 10.4 kB
JavaScript
/*global define*/
define([
'./Cartesian3',
'./defined',
'./DeveloperError'
], function(
Cartesian3,
defined,
DeveloperError) {
'use strict';
/**
* Contains functions for operating on 2D triangles.
*
* @exports Intersections2D
*/
var Intersections2D = {};
/**
* Splits a 2D triangle at given axis-aligned threshold value and returns the resulting
* polygon on a given side of the threshold. The resulting polygon may have 0, 1, 2,
* 3, or 4 vertices.
*
* @param {Number} threshold The threshold coordinate value at which to clip the triangle.
* @param {Boolean} keepAbove true to keep the portion of the triangle above the threshold, or false
* to keep the portion below.
* @param {Number} u0 The coordinate of the first vertex in the triangle, in counter-clockwise order.
* @param {Number} u1 The coordinate of the second vertex in the triangle, in counter-clockwise order.
* @param {Number} u2 The coordinate of the third vertex in the triangle, in counter-clockwise order.
* @param {Number[]} [result] The array into which to copy the result. If this parameter is not supplied,
* a new array is constructed and returned.
* @returns {Number[]} The polygon that results after the clip, specified as a list of
* vertices. The vertices are specified in counter-clockwise order.
* Each vertex is either an index from the existing list (identified as
* a 0, 1, or 2) or -1 indicating a new vertex not in the original triangle.
* For new vertices, the -1 is followed by three additional numbers: the
* index of each of the two original vertices forming the line segment that
* the new vertex lies on, and the fraction of the distance from the first
* vertex to the second one.
*
* @example
* var result = Cesium.Intersections2D.clipTriangleAtAxisAlignedThreshold(0.5, false, 0.2, 0.6, 0.4);
* // result === [2, 0, -1, 1, 0, 0.25, -1, 1, 2, 0.5]
*/
Intersections2D.clipTriangleAtAxisAlignedThreshold = function(threshold, keepAbove, u0, u1, u2, result) {
//>>includeStart('debug', pragmas.debug);
if (!defined(threshold)) {
throw new DeveloperError('threshold is required.');
}
if (!defined(keepAbove)) {
throw new DeveloperError('keepAbove is required.');
}
if (!defined(u0)) {
throw new DeveloperError('u0 is required.');
}
if (!defined(u1)) {
throw new DeveloperError('u1 is required.');
}
if (!defined(u2)) {
throw new DeveloperError('u2 is required.');
}
//>>includeEnd('debug');
if (!defined(result)) {
result = [];
} else {
result.length = 0;
}
var u0Behind;
var u1Behind;
var u2Behind;
if (keepAbove) {
u0Behind = u0 < threshold;
u1Behind = u1 < threshold;
u2Behind = u2 < threshold;
} else {
u0Behind = u0 > threshold;
u1Behind = u1 > threshold;
u2Behind = u2 > threshold;
}
var numBehind = u0Behind + u1Behind + u2Behind;
var u01Ratio;
var u02Ratio;
var u12Ratio;
var u10Ratio;
var u20Ratio;
var u21Ratio;
if (numBehind === 1) {
if (u0Behind) {
u01Ratio = (threshold - u0) / (u1 - u0);
u02Ratio = (threshold - u0) / (u2 - u0);
result.push(1);
result.push(2);
if (u02Ratio !== 1.0) {
result.push(-1);
result.push(0);
result.push(2);
result.push(u02Ratio);
}
if (u01Ratio !== 1.0) {
result.push(-1);
result.push(0);
result.push(1);
result.push(u01Ratio);
}
} else if (u1Behind) {
u12Ratio = (threshold - u1) / (u2 - u1);
u10Ratio = (threshold - u1) / (u0 - u1);
result.push(2);
result.push(0);
if (u10Ratio !== 1.0) {
result.push(-1);
result.push(1);
result.push(0);
result.push(u10Ratio);
}
if (u12Ratio !== 1.0) {
result.push(-1);
result.push(1);
result.push(2);
result.push(u12Ratio);
}
} else if (u2Behind) {
u20Ratio = (threshold - u2) / (u0 - u2);
u21Ratio = (threshold - u2) / (u1 - u2);
result.push(0);
result.push(1);
if (u21Ratio !== 1.0) {
result.push(-1);
result.push(2);
result.push(1);
result.push(u21Ratio);
}
if (u20Ratio !== 1.0) {
result.push(-1);
result.push(2);
result.push(0);
result.push(u20Ratio);
}
}
} else if (numBehind === 2) {
if (!u0Behind && u0 !== threshold) {
u10Ratio = (threshold - u1) / (u0 - u1);
u20Ratio = (threshold - u2) / (u0 - u2);
result.push(0);
result.push(-1);
result.push(1);
result.push(0);
result.push(u10Ratio);
result.push(-1);
result.push(2);
result.push(0);
result.push(u20Ratio);
} else if (!u1Behind && u1 !== threshold) {
u21Ratio = (threshold - u2) / (u1 - u2);
u01Ratio = (threshold - u0) / (u1 - u0);
result.push(1);
result.push(-1);
result.push(2);
result.push(1);
result.push(u21Ratio);
result.push(-1);
result.push(0);
result.push(1);
result.push(u01Ratio);
} else if (!u2Behind && u2 !== threshold) {
u02Ratio = (threshold - u0) / (u2 - u0);
u12Ratio = (threshold - u1) / (u2 - u1);
result.push(2);
result.push(-1);
result.push(0);
result.push(2);
result.push(u02Ratio);
result.push(-1);
result.push(1);
result.push(2);
result.push(u12Ratio);
}
} else if (numBehind !== 3) {
// Completely in front of threshold
result.push(0);
result.push(1);
result.push(2);
}
// else Completely behind threshold
return result;
};
/**
* Compute the barycentric coordinates of a 2D position within a 2D triangle.
*
* @param {Number} x The x coordinate of the position for which to find the barycentric coordinates.
* @param {Number} y The y coordinate of the position for which to find the barycentric coordinates.
* @param {Number} x1 The x coordinate of the triangle's first vertex.
* @param {Number} y1 The y coordinate of the triangle's first vertex.
* @param {Number} x2 The x coordinate of the triangle's second vertex.
* @param {Number} y2 The y coordinate of the triangle's second vertex.
* @param {Number} x3 The x coordinate of the triangle's third vertex.
* @param {Number} y3 The y coordinate of the triangle's third vertex.
* @param {Cartesian3} [result] The instance into to which to copy the result. If this parameter
* is undefined, a new instance is created and returned.
* @returns {Cartesian3} The barycentric coordinates of the position within the triangle.
*
* @example
* var result = Cesium.Intersections2D.computeBarycentricCoordinates(0.0, 0.0, 0.0, 1.0, -1, -0.5, 1, -0.5);
* // result === new Cesium.Cartesian3(1.0 / 3.0, 1.0 / 3.0, 1.0 / 3.0);
*/
Intersections2D.computeBarycentricCoordinates = function(x, y, x1, y1, x2, y2, x3, y3, result) {
//>>includeStart('debug', pragmas.debug);
if (!defined(x)) {
throw new DeveloperError('x is required.');
}
if (!defined(y)) {
throw new DeveloperError('y is required.');
}
if (!defined(x1)) {
throw new DeveloperError('x1 is required.');
}
if (!defined(y1)) {
throw new DeveloperError('y1 is required.');
}
if (!defined(x2)) {
throw new DeveloperError('x2 is required.');
}
if (!defined(y2)) {
throw new DeveloperError('y2 is required.');
}
if (!defined(x3)) {
throw new DeveloperError('x3 is required.');
}
if (!defined(y3)) {
throw new DeveloperError('y3 is required.');
}
//>>includeEnd('debug');
var x1mx3 = x1 - x3;
var x3mx2 = x3 - x2;
var y2my3 = y2 - y3;
var y1my3 = y1 - y3;
var inverseDeterminant = 1.0 / (y2my3 * x1mx3 + x3mx2 * y1my3);
var ymy3 = y - y3;
var xmx3 = x - x3;
var l1 = (y2my3 * xmx3 + x3mx2 * ymy3) * inverseDeterminant;
var l2 = (-y1my3 * xmx3 + x1mx3 * ymy3) * inverseDeterminant;
var l3 = 1.0 - l1 - l2;
if (defined(result)) {
result.x = l1;
result.y = l2;
result.z = l3;
return result;
} else {
return new Cartesian3(l1, l2, l3);
}
};
return Intersections2D;
});