平视显示器（head up display）简称HUD，最早用于飞机驾驶。平视显示器将一些重要信息投射到飞机驾驶舱前方的一块玻璃上，飞行员能够将外界的影像和这些重要的信息融合在一起，而不用频繁低头观察仪表盘。三维图形程序，尤其是游戏，也经常在三维场景中叠加文本或二维图形信息，以达到HUD的效果。
思路：
（1）html中添加两个标签，一个用于显示模型的，另一个获取getContext("2d")，来显示文本相关内容。
（2）然后给前面的添加一个draw2D()的方法用于绘制相关内容。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport"
content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Title</title>
<style>
body {
margin: 0;
}
#canvas,#hud {
margin: 0;
display: block;
position: absolute;
}
#canvas{
z-index: 0;
}
#hud{
z-index: 1;
}
</style>
</head>
<body onload="main()">
<canvas id="canvas" height="800" width="1200"></canvas>
<canvas id="hud"></canvas>
</body>
<script src="webgl/webgl-utils.js"></script>
<script src="webgl/webgl-debug.js"></script>
<script src="webgl/cuon-utils.js"></script>
<script src="webgl/cuon-matrix.js"></script>
<script>
//设置WebGL全屏显示
var canvas = document.getElementById("canvas");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
//设置显示hud的canvas全屏显示
var hud = document.getElementById("hud");
hud.width = window.innerWidth;
hud.height = window.innerHeight;
//顶点着色器
var vertexShaderSource = "" +
"attribute vec4 a_Position;\n" +
"attribute vec4 a_Color;\n" +
"attribute float a_Face;\n" +//表面编号，不是用int类型
"uniform mat4 u_MvpMatrix;\n" +
"uniform int u_PickedFace;\n" + //被选中的表面编号
"varying vec4 v_Color;\n" +
"void main (){\n" +
" gl_Position = u_MvpMatrix * a_Position;\n" +
" int face = int(a_Face);\n" +
" vec3 color = (face == u_PickedFace) ? vec3(1.0) : a_Color.rgb;\n" +
" if(u_PickedFace == 0){\n" +
" v_Color = vec4(color, a_Face/255.0);\n" +
" }else{\n" +
" v_Color = vec4(color, a_Color.a);\n" +
" }\n" +
"}\n";
//片元着色器
var fragmentShaderSource = "" +
"#ifdef GL_ES\n" +
"precision mediump float;\n" +
"#endif\n" +
"varying vec4 v_Color;\n" +
"void main(){\n" +
" gl_FragColor = v_Color;\n" +
"}\n";
function main() {
//获取WebGL对象
var gl = getWebGLContext(canvas);
var ctx = hud.getContext("2d");
//初始化着色器
initShaders(gl, vertexShaderSource, fragmentShaderSource);
//将数据存入缓冲区
var n = initVertexBuffers(gl);
if (n < 0) {
console.log("数据存入缓冲区失败");
return;
}
//设置背景色和开启层级关系
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.enable(gl.DEPTH_TEST);
//获取uniform变量的存储位置
var u_MvpMatrix = gl.getUniformLocation(gl.program, "u_MvpMatrix");
var u_PickedFace = gl.getUniformLocation(gl.program, "u_PickedFace");
if (!u_MvpMatrix || !u_PickedFace) {
console.log("无法获取相关的存储位置");
return;
}
//设置视点和投影矩阵
var viewProjectionMatrix = new Matrix4();
viewProjectionMatrix.setPerspective(30.0, canvas.width / canvas.height, 1.0, 100.0);
viewProjectionMatrix.lookAt(0.0, 0.0, 7.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
//设置一个自动转圈的变量
var currentAngle = 0.0;
// 初始化被选中的表面的变量
gl.uniform1i(u_PickedFace, -1);
hud.onmousedown = function (e) {
//鼠标按下时，将u_PickedFace修改为0，然后重新绘制场景
gl.uniform1i(u_PickedFace, 0);
draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix);
//因为绘制的场景将代表下标的存入了a的值内，所以需要获取颜色来获取下标
var pixels = new Uint8Array(4); //存储获取的颜色的变量
gl.readPixels(e.offsetX, window.innerHeight - e.offsetY, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
//给u_PickedFace赋值然后交给顶点着色器判断是否相同
gl.uniform1i(u_PickedFace, pixels[3]);
draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix);
};
//定时绘制页面
var tick = function () {
currentAngle = animate(currentAngle);
draw2D(ctx, currentAngle);
draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix);
requestAnimationFrame(tick);
};
tick();
}
//修改currentAngle的值
var last = +new Date();
var angleStep = 20.0;//每次旋转的速度
function animate(currentAngle) {
var now = +new Date();
var elapsed = now - last;
last = now;
//这里是为了保证旋转保证匀速旋转
var newAngle = currentAngle + (angleStep * elapsed) / 1000;
return newAngle % 360;
}
//设置顶点数据和将数据存入缓冲区
function initVertexBuffers(gl) {
// Create a cube
// v6----- v5
// /| /|
// v1------v0|
// | | | |
// | |v7---|-|v4
// |/ |/
// v2------v3
var vertices = new Float32Array([ // Vertex coordinates 顶点的位置数据
1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0, 1.0, // v0-v1-v2-v3 front
1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0, // v0-v3-v4-v5 right
1.0, 1.0, 1.0, 1.0, 1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0, // v0-v5-v6-v1 up
-1.0, 1.0, 1.0, -1.0, 1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, // v1-v6-v7-v2 left
-1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, -1.0, -1.0, 1.0, // v7-v4-v3-v2 down
1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, -1.0 // v4-v7-v6-v5 back
]);
var colors = new Float32Array([ // Colors 顶点的颜色数据
0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, // v0-v1-v2-v3 front
0.5, 0.41, 0.69, 0.5, 0.41, 0.69, 0.5, 0.41, 0.69, 0.5, 0.41, 0.69, // v0-v3-v4-v5 right
0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, // v0-v5-v6-v1 up
0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, // v1-v6-v7-v2 left
0.27, 0.58, 0.82, 0.27, 0.58, 0.82, 0.27, 0.58, 0.82, 0.27, 0.58, 0.82, // v7-v4-v3-v2 down
0.73, 0.82, 0.93, 0.73, 0.82, 0.93, 0.73, 0.82, 0.93, 0.73, 0.82, 0.93 // v4-v7-v6-v5 back
]);
var faces = new Uint8Array([ // Faces 顶点的面的数据
1, 1, 1, 1, // v0-v1-v2-v3 front
2, 2, 2, 2, // v0-v3-v4-v5 right
3, 3, 3, 3, // v0-v5-v6-v1 up
4, 4, 4, 4, // v1-v6-v7-v2 left
5, 5, 5, 5, // v7-v4-v3-v2 down
6, 6, 6, 6 // v4-v7-v6-v5 back
]);
var indices = new Uint8Array([ // Indices of the vertices 顶点的索引数据
0, 1, 2, 0, 2, 3, // front
4, 5, 6, 4, 6, 7, // right
8, 9, 10, 8, 10, 11, // up
12, 13, 14, 12, 14, 15, // left
16, 17, 18, 16, 18, 19, // down
20, 21, 22, 20, 22, 23 // back
]);
//存入缓冲区
if (!initArrayBuffer(gl, vertices, gl.FLOAT, 3, "a_Position")) {
return -1;
}
if (!initArrayBuffer(gl, colors, gl.FLOAT, 3, "a_Color")) {
return -1;
}
if (!initArrayBuffer(gl, faces, gl.UNSIGNED_BYTE, 1, "a_Face")) {
return -1;
}
//创建索引缓冲区
var indexBuffer = gl.createBuffer();
if (indexBuffer < 0) {
console.log("无法创建缓冲区");
return -1;
}
//取消ARRAY_BUFFER中的绑定
gl.bindBuffer(gl.ARRAY_BUFFER, null);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);
return indices.length;
}
function initArrayBuffer(gl, data, type, num, attribute) {
var buffer = gl.createBuffer();
if (!buffer) {
console.log("无法创建缓冲区对象");
return;
}
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);
var a_attribute = gl.getAttribLocation(gl.program, attribute);
if (a_attribute < 0) {
console.log("无法获取变量的存储位置" + attribute);
return false;
}
gl.vertexAttribPointer(a_attribute, num, type, false, 0, 0);
gl.enableVertexAttribArray(a_attribute);
return true;
}
//绘制
var matrix = new Matrix4();
function draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix) {
matrix.set(viewProjectionMatrix);
matrix.rotate(currentAngle, 1.0, 0.0, 0.0);
matrix.rotate(currentAngle, 0.0, 1.0, 0.0);
matrix.rotate(currentAngle, 0.0, 0.0, 1.0);
gl.uniformMatrix4fv(u_MvpMatrix, false, matrix.elements);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);
}
//绘制hud
function draw2D(ctx, currentAngle) {
ctx.clearRect(0, 0, 400, 400); // 清除 <hud>
// 用白色的线绘制三角形
ctx.beginPath(); // 开始绘制
ctx.moveTo(120, 10); ctx.lineTo(200, 150); ctx.lineTo(40, 150);
ctx.closePath();
ctx.strokeStyle = 'rgba(255, 255, 255, 1)'; // 设置线条的颜色
ctx.stroke(); // 用白色的线条绘制三角形
// 绘制白色的文本
ctx.font = '18px "Times New Roman"';
ctx.fillStyle = 'rgba(255, 255, 255, 1)'; // 设置文本颜色
ctx.fillText('HUD: 头部上方显示', 40, 180);
ctx.fillText('三角形是通过canvas2d绘制', 40, 200);
ctx.fillText('立方体是通过WebGL接口绘制', 40, 220);
ctx.fillText('实时旋转角度: '+ Math.floor(currentAngle), 40, 240);
}
</script>
</html>