vis.js is a dynamic, browser-based visualization library
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/**
* Calculate the forces the nodes apply on eachother based on a repulsion field.
* This field is linearly approximated.
*
* @private
*/
exports._calculateNodeForces = function () {
var dx, dy, distance, fx, fy,
repulsingForce, node1, node2, i, j;
var nodes = this.calculationNodes;
var nodeIndices = this.calculationNodeIndices;
// repulsing forces between nodes
var nodeDistance = this.constants.physics.hierarchicalRepulsion.nodeDistance;
// we loop from i over all but the last entree in the array
// j loops from i+1 to the last. This way we do not double count any of the indices, nor i == j
for (i = 0; i < nodeIndices.length - 1; i++) {
node1 = nodes[nodeIndices[i]];
for (j = i + 1; j < nodeIndices.length; j++) {
node2 = nodes[nodeIndices[j]];
// nodes only affect nodes on their level
if (node1.level == node2.level) {
dx = node2.x - node1.x;
dy = node2.y - node1.y;
distance = Math.sqrt(dx * dx + dy * dy);
var steepness = 0.05;
if (distance < nodeDistance) {
repulsingForce = -Math.pow(steepness*distance,2) + Math.pow(steepness*nodeDistance,2);
}
else {
repulsingForce = 0;
}
// normalize force with
if (distance == 0) {
distance = 0.01;
}
else {
repulsingForce = repulsingForce / distance;
}
fx = dx * repulsingForce;
fy = dy * repulsingForce;
node1.fx -= fx;
node1.fy -= fy;
node2.fx += fx;
node2.fy += fy;
}
}
}
};
/**
* this function calculates the effects of the springs in the case of unsmooth curves.
*
* @private
*/
exports._calculateHierarchicalSpringForces = function () {
var edgeLength, edge, edgeId;
var dx, dy, fx, fy, springForce, distance;
var edges = this.edges;
var nodes = this.calculationNodes;
var nodeIndices = this.calculationNodeIndices;
for (var i = 0; i < nodeIndices.length; i++) {
var node1 = nodes[nodeIndices[i]];
node1.springFx = 0;
node1.springFy = 0;
}
// forces caused by the edges, modelled as springs
for (edgeId in edges) {
if (edges.hasOwnProperty(edgeId)) {
edge = edges[edgeId];
if (edge.connected) {
// only calculate forces if nodes are in the same sector
if (this.nodes.hasOwnProperty(edge.toId) && this.nodes.hasOwnProperty(edge.fromId)) {
edgeLength = edge.customLength ? edge.length : this.constants.physics.springLength;
// this implies that the edges between big clusters are longer
edgeLength += (edge.to.clusterSize + edge.from.clusterSize - 2) * this.constants.clustering.edgeGrowth;
dx = (edge.from.x - edge.to.x);
dy = (edge.from.y - edge.to.y);
distance = Math.sqrt(dx * dx + dy * dy);
if (distance == 0) {
distance = 0.01;
}
// the 1/distance is so the fx and fy can be calculated without sine or cosine.
springForce = this.constants.physics.springConstant * (edgeLength - distance) / distance;
fx = dx * springForce;
fy = dy * springForce;
if (edge.to.level != edge.from.level) {
edge.to.springFx -= fx;
edge.to.springFy -= fy;
edge.from.springFx += fx;
edge.from.springFy += fy;
}
else {
var factor = 0.5;
edge.to.fx -= factor*fx;
edge.to.fy -= factor*fy;
edge.from.fx += factor*fx;
edge.from.fy += factor*fy;
}
}
}
}
}
// normalize spring forces
var springForce = 1;
var springFx, springFy;
for (i = 0; i < nodeIndices.length; i++) {
var node = nodes[nodeIndices[i]];
springFx = Math.min(springForce,Math.max(-springForce,node.springFx));
springFy = Math.min(springForce,Math.max(-springForce,node.springFy));
node.fx += springFx;
node.fy += springFy;
}
// retain energy balance
var totalFx = 0;
var totalFy = 0;
for (i = 0; i < nodeIndices.length; i++) {
var node = nodes[nodeIndices[i]];
totalFx += node.fx;
totalFy += node.fy;
}
var correctionFx = totalFx / nodeIndices.length;
var correctionFy = totalFy / nodeIndices.length;
for (i = 0; i < nodeIndices.length; i++) {
var node = nodes[nodeIndices[i]];
node.fx -= correctionFx;
node.fy -= correctionFy;
}
};