回答編集履歴
2
法線ベクトルの算出アルゴリズムについてのメモを追加
test
CHANGED
|
@@ -135,3 +135,9 @@
|
|
|
135
135
|
}
|
|
136
136
|
|
|
137
137
|
```
|
|
138
|
+
|
|
139
|
+
|
|
140
|
+
|
|
141
|
+
NOTE:
|
|
142
|
+
|
|
143
|
+
途中で求めた法線ベクトル二つを足して簡易的に2で割っているけれど, 本当はもっと適した算出法があるかもしれない.(この操作が引き起こす実用上の問題は不明)
|
1
コードを追加
test
CHANGED
|
@@ -7,3 +7,131 @@
|
|
|
7
7
|
|
|
8
8
|
|
|
9
9
|
三点から得られたポリゴン面に垂直に立つ法線ベクトルを求め, それを真上から射影すればその方向と傾きが得られる.
|
|
10
|
+
|
|
11
|
+
|
|
12
|
+
|
|
13
|
+
---
|
|
14
|
+
|
|
15
|
+
例えばここを参考としてスクリプトを組んで見る.
|
|
16
|
+
|
|
17
|
+
[http://www.dstorm.co.jp/dsproducts/developers/Technical_Data/CalcNormal.html](http://www.dstorm.co.jp/dsproducts/developers/Technical_Data/CalcNormal.html)
|
|
18
|
+
|
|
19
|
+
```HTML
|
|
20
|
+
|
|
21
|
+
<canvas id="canvas" width="400" height="400" style="background-color:yellow;"></canvas>
|
|
22
|
+
|
|
23
|
+
```
|
|
24
|
+
|
|
25
|
+
```JavaScript
|
|
26
|
+
|
|
27
|
+
"use strict";
|
|
28
|
+
|
|
29
|
+
{
|
|
30
|
+
|
|
31
|
+
function getNormal(a, b){
|
|
32
|
+
|
|
33
|
+
const vec = [
|
|
34
|
+
|
|
35
|
+
a[1] * b[2] - a[2] * b[1],
|
|
36
|
+
|
|
37
|
+
a[2] * b[0] - a[0] * b[2],
|
|
38
|
+
|
|
39
|
+
a[0] * b[1] - a[1] * b[0]
|
|
40
|
+
|
|
41
|
+
];
|
|
42
|
+
|
|
43
|
+
const norm = Math.sqrt(vec.reduce((prev, val) => prev + val * val, 0));
|
|
44
|
+
|
|
45
|
+
return vec.map((val, i) => vec[i] /= norm);
|
|
46
|
+
|
|
47
|
+
}
|
|
48
|
+
|
|
49
|
+
function plot(table){
|
|
50
|
+
|
|
51
|
+
const ctx = canvas.getContext("2d");
|
|
52
|
+
|
|
53
|
+
ctx.strokeStyle = ctx.fillStyle = "red";
|
|
54
|
+
|
|
55
|
+
ctx.lineWidth = 2;
|
|
56
|
+
|
|
57
|
+
const unit = 100, arrow = 50;
|
|
58
|
+
|
|
59
|
+
const marker = new Path2D("M0,-5L5,0 0 5z");
|
|
60
|
+
|
|
61
|
+
const rows = table.length, cols = table[0].length;
|
|
62
|
+
|
|
63
|
+
for(let y = 0; y < rows-1; y++){
|
|
64
|
+
|
|
65
|
+
for(let x = 0; x < cols-1; x++){
|
|
66
|
+
|
|
67
|
+
ctx.save();
|
|
68
|
+
|
|
69
|
+
//ベクトルの描画基準
|
|
70
|
+
|
|
71
|
+
ctx.translate(unit * (x + 0.5), unit * (y + 0.5));
|
|
72
|
+
|
|
73
|
+
//上半三角
|
|
74
|
+
|
|
75
|
+
const normalT = getNormal(
|
|
76
|
+
|
|
77
|
+
[1, 0, table[y][x+1] - table[y][x]],
|
|
78
|
+
|
|
79
|
+
[0, 1, table[y+1][x] - table[y][x]]
|
|
80
|
+
|
|
81
|
+
);
|
|
82
|
+
|
|
83
|
+
//下半三角
|
|
84
|
+
|
|
85
|
+
const normalB = getNormal(
|
|
86
|
+
|
|
87
|
+
[-1, 0, table[y+1][x] - table[y+1][x+1]],
|
|
88
|
+
|
|
89
|
+
[0, -1, table[y][x+1] - table[y+1][x+1]]
|
|
90
|
+
|
|
91
|
+
);
|
|
92
|
+
|
|
93
|
+
//平均
|
|
94
|
+
|
|
95
|
+
const normal = normalT.map((val, i) => (val + normalB[i])/2)
|
|
96
|
+
|
|
97
|
+
ctx.beginPath();
|
|
98
|
+
|
|
99
|
+
ctx.moveTo(0,0);
|
|
100
|
+
|
|
101
|
+
ctx.lineTo(normal[0] * arrow, normal[1] * arrow);
|
|
102
|
+
|
|
103
|
+
ctx.stroke();
|
|
104
|
+
|
|
105
|
+
//marker
|
|
106
|
+
|
|
107
|
+
ctx.translate(normal[0] * arrow, normal[1] * arrow);
|
|
108
|
+
|
|
109
|
+
ctx.rotate(Math.atan2(normal[1], normal[0]));
|
|
110
|
+
|
|
111
|
+
ctx.fill(marker);
|
|
112
|
+
|
|
113
|
+
ctx.restore();
|
|
114
|
+
|
|
115
|
+
}
|
|
116
|
+
|
|
117
|
+
}
|
|
118
|
+
|
|
119
|
+
}
|
|
120
|
+
|
|
121
|
+
plot([
|
|
122
|
+
|
|
123
|
+
[0, 0, 1, 0, 0],
|
|
124
|
+
|
|
125
|
+
[1, 1, 1, 1, 1],
|
|
126
|
+
|
|
127
|
+
[2, 3, 2, 4, 2],
|
|
128
|
+
|
|
129
|
+
[3, 3, 3, 3, 3],
|
|
130
|
+
|
|
131
|
+
[4, 3, 5, 6, 7]
|
|
132
|
+
|
|
133
|
+
]);
|
|
134
|
+
|
|
135
|
+
}
|
|
136
|
+
|
|
137
|
+
```
|