图1. 流网络示意图

代码

//parameters
float w=800;
float h=600;
PVector [] nodes = {};
PVector [] weights = {};
Arrow [] arrows;

//data
float[][] pos =   {{1*w/6, h/2},{2*w/6, h/2},{3*w/6, 2*h/6},
                   {3*w/6, 4*h/6},{4*w/6, 2*h/6},{4*w/6, 4*h/6},
                   {5*w/6, h/2}
                   };  
                   
int[][] edges = {{0,1,80},{1,2,50},{1,3,30},
                {3,2,10},{2,4,20},{2,5,30},
                {4,5,10},{5,3,5},{2,6,10},
                {4,6,10},{3,6,25},{5,6,35}}; 

void setup(){
  
  size(int(w),int(h));
  background(255);
  smooth();
  
  //initialize nodes
  for (int i = 0; i < pos.length; i++){
    nodes = (PVector[]) append(nodes, new PVector(int(pos[i][0]),int(pos[i][1])));
  }
  
  // initialize weights and arrows
  arrows = new Arrow[edges.length];
  for (int i = 0; i < edges.length; i++) {
    int start = int(edges[i][0]);
    int end = int(edges[i][1]);
    float x1=nodes[start].x; 
    float y1=nodes[start].y;
    float x2=nodes[end].x; 
    float y2=nodes[end].y;
    float dx=x2-x1;
    float dy=y2-y1;
    float r=sqrt(sq(dx)+sq(dy));
    arrows[i] = new Arrow(x1+20*dx/r, y1+20*dy/r, x2-20*dx/r, y2-20*dy/r, color(100));
    weights = (PVector[]) append(weights, new PVector(x1+dx/2,y1+dy/2,edges[i][2]));
  }
  
   // plot nodes, labels, weights, and arrows
  for (int i = 0; i < nodes.length; i++) {
    //nodes
    noFill();
    stroke(200);
    ellipseMode(RADIUS);
    ellipse(nodes[i].x,nodes[i].y,20,20);
    //labels
    fill(50);
    textSize(16);
    textAlign(CENTER);
    text(str(i),nodes[i].x,nodes[i].y+5);
  }  
  
  //weights
  for (int i = 0; i < weights.length; i++) {
    fill(50);
    textSize(10);
    text(nf(weights[i].z,0,0),weights[i].x-20,weights[i].y);
  }
  
  //plot arrows
    for (int j = 0; j < arrows.length; j++) {
    arrows[j].draw();
  }
 
 //save the figure
 saveFrame("/Users/csid/Documents/Processing/experiments/exampleFlowNetwork/pngs/line-######.png");
}

class Arrow {
  float x1, y1, x2, y2;
  color lineColor, arrowColor;
  // Contructor
  Arrow(float x1Temp, float y1Temp, float x2Temp, float y2Temp, color cTemp1) {
    x1 = x1Temp;
    y1 = y1Temp;
    x2 = x2Temp;
    y2 = y2Temp;
    lineColor = cTemp1;
  }
  // Custom method for drawing the object
  void draw() {
    arrowLine(x1,y1, x2, y2, 0, radians(10), true, lineColor);
  }
}

// arrowline function copied from http://www.openprocessing.org/sketch/7029
void arrowLine(float x0, float y0, float x1, float y1,
  float startAngle, float endAngle, boolean solid, color lineColor)
{
  stroke(lineColor);
  line(x0, y0, x1, y1);
  if (startAngle != 0)
  {
    arrowhead(x0, y0, atan2(y1 - y0, x1 - x0), startAngle, solid, lineColor);
  }
  if (endAngle != 0)
  {
    arrowhead(x1, y1, atan2(y0 - y1, x0 - x1), endAngle, solid, lineColor);
  }
}
 
/*
 * Draws an arrow head at given location
 * x0 - arrow vertex x-coordinate
 * y0 - arrow vertex y-coordinate
 * lineAngle - angle of line leading to vertex (radians)
 * arrowAngle - angle between arrow and line (radians)
 * solid - true for a solid arrow, false for an "open" arrow
 */
void arrowhead(float x0, float y0, float lineAngle,
  float arrowAngle, boolean solid, color arrowColor)
{
  float phi;
  float x2;
  float y2;
  float x3;
  float y3;
  final float SIZE = 20;
  x2 = x0 + SIZE * cos(lineAngle + arrowAngle);
  y2 = y0 + SIZE * sin(lineAngle + arrowAngle);
  x3 = x0 + SIZE * cos(lineAngle - arrowAngle);
  y3 = y0 + SIZE * sin(lineAngle - arrowAngle);
  if (solid)
  {
    noStroke();
    fill(arrowColor);
    triangle(x0, y0, x2, y2, x3, y3);
  }
  else
  {
    line(x0, y0, x2, y2);
    line(x0, y0, x3, y3);
  } 
}