本教程的主题是利用HTML5技术在2D和3D图形之间搭一座互通的桥梁（通过WebGL方式）。今天我将展示如何使用一个多边形网格绘制一个三维对象。
一个多边形网格或非结构化网格是一个集合的顶点,边缘和面孔,在3
d电脑图像和实体建模定义了一个多面体的对象的形状。通常由三角形的面孔,四边形或其他简单凸多边形,因为这样可以简化渲染,但也可能是由更一般的凹多边
形,或多边形的洞。
为了演示,我们准备了简单的三维物体——一个多维数据集和多维领域
HTML CODE
通常我们会在canvas里做一个简单的标记
Triangle mesh for 3D objects in HTML5 | Script Tutorials
<script><br> //var obj = new cube();<br> //var obj = new sphere(6);<br> var obj = new sphere(16);<br> </script>
Please use Up / Down keys to change opacity
<script><br> //var obj = new cube();<br> //var obj = new sphere(6);<br> var obj = new sphere(16);<br></script>
// get random color
function getRandomColor() {
var letters = '0123456789ABCDEF'.split('');
var color = '#';
for (var i = 0; i color += letters[Math.round(Math.random() * 15)];
}
return color;
}
// prepare object
function prepareObject(o) {
o.colors = new Array();
// prepare normals
o.normals = new Array();
for (var i = 0; i o.normals[i] = [0, 0, 0];
o.colors[i] = getRandomColor();
}
// prepare centers: calculate max positions
o.center = [0, 0, 0];
for (var i = 0; i o.center[0] += o.points[i][0];
o.center[1] += o.points[i][1];
o.center[2] += o.points[i][2];
}
// prepare distances
o.distances = new Array();
for (var i = 1; i o.distances[i] = 0;
}
// calculate average center positions
o.points_number = o.points.length;
o.center[0] = o.center[0] / (o.points_number - 1);
o.center[1] = o.center[1] / (o.points_number - 1);
o.center[2] = o.center[2] / (o.points_number - 1);
o.faces_number = o.faces.length;
o.axis_x = [1, 0, 0];
o.axis_y = [0, 1, 0];
o.axis_z = [0, 0, 1];
}
// Cube object
function cube() {
// prepare points and faces for cube
this.points=[
[0,0,0],
[100,0,0],
[100,100,0],
[0,100,0],
[0,0,100],
[100,0,100],
[100,100,100],
[0,100,100],
[50,50,100],
[50,50,0],
];
this.faces=[
[0,4,5],
[0,5,1],
[1,5,6],
[1,6,2],
[2,6,7],
[2,7,3],
[3,7,4],
[3,4,0],
[8,5,4],
[8,6,5],
[8,7,6],
[8,4,7],
[9,5,4],
[9,6,5],
[9,7,6],
[9,4,7],
];
prepareObject(this);
}
// Sphere object
function sphere(n) {
var delta_angle = 2 * Math.PI / n;
// prepare vertices (points) of sphere
var vertices = [];
for (var j = 0; j for (var i = 0; i vertices[j * n + i] = [];
vertices[j * n + i][0] = 100 * Math.sin((j + 1) * delta_angle) * Math.cos(i * delta_angle);
vertices[j * n + i][1] = 100 * Math.cos((j + 1) * delta_angle);
vertices[j * n + i][2] = 100 * Math.sin((j + 1) * delta_angle) * Math.sin(i * delta_angle);
}
}
vertices[(n / 2 - 1) * n] = [];
vertices[(n / 2 - 1) * n + 1] = [];
vertices[(n / 2 - 1) * n][0] = 0;
vertices[(n / 2 - 1) * n][1] = 100;
vertices[(n / 2 - 1) * n][2] = 0;
vertices[(n / 2 - 1) * n + 1][0] = 0;
vertices[(n / 2 - 1) * n + 1][1] = -100;
vertices[(n / 2 - 1) * n + 1][2] = 0;
this.points = vertices;
// prepare faces
var faces = [];
for (var j = 0; j for (var i = 0; i faces[j * 2 * n + i] = [];
faces[j * 2 * n + i + n] = [];
faces[j * 2 * n + i][0] = j * n + i;
faces[j * 2 * n + i][1] = j * n + i + 1;
faces[j * 2 * n + i][2] = (j + 1) * n + i + 1;
faces[j * 2 * n + i + n][0] = j * n + i;
faces[j * 2 * n + i + n][1] = (j + 1) * n + i + 1;
faces[j * 2 * n + i + n][2] = (j + 1) * n + i;
}
faces[j * 2 * n + n - 1] = [];
faces[2 * n * (j + 1) - 1] = [];
faces[j * 2 * n + n - 1 ][0] = (j + 1) * n - 1;
faces[j * 2 * n + n - 1 ][1] = (j + 1) * n;
faces[j * 2 * n + n - 1 ][2] = j * n;
faces[2 * n * (j + 1) - 1][0] = (j + 1) * n - 1;
faces[2 * n * (j + 1) - 1][1] = j * n + n;
faces[2 * n * (j + 1) - 1][2] = (j + 2) * n - 1;
}
for (var i = 0; i faces[n * (n - 4) + i] = [];
faces[n * (n - 3) + i] = [];
faces[n * (n - 4) + i][0] = (n / 2 - 1) * n;
faces[n * (n - 4) + i][1] = i;
faces[n * (n - 4) + i][2] = i + 1;
faces[n * (n - 3) + i][0] = (n / 2 - 1) * n + 1;
faces[n * (n - 3) + i][1] = (n / 2 - 2) * n + i + 1;
faces[n * (n - 3) + i][2] = (n / 2 - 2) * n + i;
}
faces[n * (n - 3) - 1] = [];
faces[n * (n - 2) - 1] = [];
faces[n * (n - 3) - 1][0] = (n / 2 - 1) * n;
faces[n * (n - 3) - 1][1] = n - 1;
faces[n * (n - 3) - 1][2] = 0;
faces[n * (n - 2) - 1][0] = (n / 2 - 1) * n + 1;
faces[n * (n - 2) - 1][1] = (n / 2 - 2) * n;
faces[n * (n - 2) - 1][2] = (n / 2 - 2) * n + n - 1;
this.faces=faces;
prepareObject(this);
}
// inner variables
var canvas, ctx;
var vAlpha = 0.5;
var vShiftX = vShiftY = 0;
var distance = -700;
var vMouseSens = 0.05;
var iHalfX, iHalfY;
// initialization
function sceneInit() {
// prepare canvas and context objects
canvas = document.getElementById('scene');
ctx = canvas.getContext('2d');
iHalfX = canvas.width / 2;
iHalfY = canvas.height / 2;
// initial scale and translate
scaleObj([3, 3, 3], obj);
translateObj([-obj.center[0], -obj.center[1], -obj.center[2]],obj);
translateObj([0, 0, -1000], obj);
// attach event handlers
document.onkeydown = handleKeydown;
canvas.onmousemove = handleMousemove;
// main scene loop
setInterval(drawScene, 25);
}
// onKeyDown event handler
function handleKeydown(e) {
kCode = ((e.which) || (e.keyCode));
switch (kCode) {
case 38: vAlpha = (vAlpha case 40: vAlpha = (vAlpha >= 0.2) ? (vAlpha - 0.1) : vAlpha; break; // Down key
}
}
// onMouseMove event handler
function handleMousemove(e) {
var x = e.pageX - canvas.offsetLeft;
var y = e.pageY - canvas.offsetTop;
if ((x > 0) && (x 0) && (y vShiftY = vMouseSens * (x - iHalfX) / iHalfX;
vShiftX = vMouseSens * (y - iHalfY) / iHalfY;
}
}
// draw main scene function
function drawScene() {
// clear canvas
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
// set fill color, stroke color, line width and global alpha
ctx.strokeStyle = 'rgb(0,0,0)';
ctx.lineWidth = 0.5;
ctx.globalAlpha= vAlpha;
// vertical and horizontal rotate
var vP1x = getRotationPar([0, 0, -1000], [1, 0, 0], vShiftX);
var vP2x = getRotationPar([0, 0, 0], [1, 0, 0], vShiftX);
var vP1y = getRotationPar([0, 0, -1000], [0, 1, 0], vShiftY);
var vP2y = getRotationPar([0, 0, 0], [0, 1, 0], vShiftY);
rotateObj(vP1x, vP2x, obj);
rotateObj(vP1y, vP2y, obj);
// recalculate distances
for (var i = 0; i obj.distances[i] = Math.pow(obj.points[i][0],2) + Math.pow(obj.points[i][1],2) + Math.pow(obj.points[i][2], 2);
}
// prepare array with face triangles (with calculation of max distance for every face)
var iCnt = 0;
var aFaceTriangles = new Array();
for (var i = 0; i var max = obj.distances[obj.faces[i][0]];
for (var f = 1; f if (obj.distances[obj.faces[i][f]] > max)
max = obj.distances[obj.faces[i][f]];
}
aFaceTriangles[iCnt++] = {faceVertex:obj.faces[i], faceColor:obj.colors[i], distance:max};
}
aFaceTriangles.sort(sortByDistance);
// prepare array with projected points
var aPrjPoints = new Array();
for (var i = 0; i aPrjPoints[i] = project(distance, obj.points[i], iHalfX, iHalfY);
}
// draw an object (surfaces)
for (var i = 0; i
ctx.fillStyle = aFaceTriangles[i].faceColor;
// begin path
ctx.beginPath();
// face vertex index
var iFaceVertex = aFaceTriangles[i].faceVertex;
// move to initial position
ctx.moveTo(aPrjPoints[iFaceVertex[0]][0], aPrjPoints[iFaceVertex[0]][1]);
// and draw three lines (to build a triangle)
for (var z = 1; z ctx.lineTo(aPrjPoints[iFaceVertex[z]][0], aPrjPoints[iFaceVertex[z]][1]);
}
// close path, strole and fill a triangle
ctx.closePath();
ctx.stroke();
ctx.fill();
}
}
// sort function
function sortByDistance(x, y) {
return (y.distance - x.distance);
}
// initialization
if (window.attachEvent) {
window.attachEvent('onload', sceneInit);
} else {
if (window.onload) {
var curronload = window.onload;
var newonload = function() {
curronload();
sceneInit();
};
window.onload = newonload;
} else {
window.onload = sceneInit;
}
}
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