FilesExpand file tree

 master

/

draw_layout.js

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

103 lines (90 loc) · 3.25 KB

 master

/

draw_layout.js

Copy path

Top

File metadata and controls

• Code
• Blame

103 lines (90 loc) · 3.25 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

// The familiar Vec type.

class Vec {

constructor(x, y) {

this.x = x; this.y = y;

}

plus(other) {

return new Vec(this.x + other.x, this.y + other.y);

}

minus(other) {

return new Vec(this.x - other.x, this.y - other.y);

}

times(factor) {

return new Vec(this.x * factor, this.y * factor);

}

get length() {

return Math.sqrt(this.x * this.x + this.y * this.y);

}

}

// Since we will want to inspect the layouts our code produces, let's

// first write code to draw a graph onto a canvas. Since we don't know

// in advance how big the graph is, the `Scale` object computes a

// scale and offset so that all nodes fit onto the given canvas.

const nodeSize = 8;

function drawGraph(graph) {

let canvas = document.querySelector("canvas");

if (!canvas) {

canvas = document.body.appendChild(document.createElement("canvas"));

canvas.width = canvas.height = 400;

}

let cx = canvas.getContext("2d");

cx.clearRect(0, 0, canvas.width, canvas.height);

let scale = new Scale(graph, canvas.width, canvas.height);

// Draw the edges.

cx.strokeStyle = "orange";

cx.lineWidth = 3;

for (let i = 0; i < graph.length; i++) {

let origin = graph[i];

for (let target of origin.edges) {

if (graph.indexOf(target) <= i) continue;

cx.beginPath();

cx.moveTo(scale.x(origin.pos.x), scale.y(origin.pos.y));

cx.lineTo(scale.x(target.pos.x), scale.y(target.pos.y));

cx.stroke();

}

}

// Draw the nodes.

cx.fillStyle = "purple";

for (let node of graph) {

cx.beginPath();

cx.arc(scale.x(node.pos.x), scale.y(node.pos.y), nodeSize, 0, 7);

cx.fill();

}

}

// The function starts by drawing the edges, so that they appear

// behind the nodes. Since the nodes on _both_ side of an edge refer

// to each other, and we don't want to draw every edge twice, edges

// are only drawn then the target comes _after_ the current node in

// the `graph` array.

// When the edges have been drawn, the nodes are drawn on top of them

// as purple discs. Remember that the last argument to `arc` gives the

// rotation, and we have to pass something bigger than 2π to get a

// full circle.

// Finding a scale at which to draw the graph is done by finding the

// top left and bottom right corners of the area taken up by the

// nodes. The offset at which nodes are drawn is based on the top left

// corner, and the scale is based on the size of the canvas divided by

// the distance between those corners. The function reserves space

// along the sides of the canvas based on the `nodeSize` variable, so

// that the circles drawn around nodes’ center points don't get cut off.

class Scale {

constructor(graph, width, height) {

let xs = graph.map(node => node.pos.x);

let ys = graph.map(node => node.pos.y);

let minX = Math.min(...xs);

let minY = Math.min(...ys);

let maxX = Math.max(...xs);

let maxY = Math.max(...ys);

this.offsetX = minX; this.offsetY = minY;

this.scaleX = (width - 2 * nodeSize) / (maxX - minX);

this.scaleY = (height - 2 * nodeSize) / (maxY - minY);

}

// The `x` and `y` methods convert from graph coordinates into

// canvas coordinates.

x(x) {

return this.scaleX * (x - this.offsetX) + nodeSize;

}

y(y) {

return this.scaleY * (y - this.offsetY) + nodeSize;

}

}