关键点：
<!--实现原理：要保证这两个canvas相互重叠;z-index表示了两个画布的上下层关系--> <!--是WEBGL的三维图形Canvas（主要用于绘制三维场景）--> <canvas id="webgl" width="400" height="400" style="position: absolute; z-index: 0"> Please use a browser that supports "canvas" </canvas> <!--二维的HUD的canvas（主要用于绘制HUD信息）--> <canvas id="hud" width="400" height="400" style="position: absolute; z-index: 1"></canvas>
js核心代码：
// HUD.js (c) 2012 matsuda // Vertex shader program var VSHADER_SOURCE = 'attribute vec4 a_Position;\n' + 'attribute vec4 a_Color;\n' + 'uniform mat4 u_MvpMatrix;\n' + 'uniform bool u_Clicked;\n' + // Mouse is pressed 'varying vec4 v_Color;\n' + 'void main() {\n' + ' gl_Position = u_MvpMatrix * a_Position;\n' + ' if (u_Clicked) {\n' + // Draw in red if mouse is pressed ' v_Color = vec4(1.0, 0.0, 0.0, 1.0);\n' + ' } else {\n' + ' v_Color = a_Color;\n' + ' }\n' + '}\n'; // Fragment shader program var FSHADER_SOURCE = '#ifdef GL_ES\n' + 'precision mediump float;\n' + '#endif\n' + 'varying vec4 v_Color;\n' + 'void main() {\n' + ' gl_FragColor = v_Color;\n' + '}\n'; var ANGLE_STEP = 20.0; // Rotation angle (degrees/second) function main() { // Retrieve <canvas> element var canvas = document.getElementById('webgl'); var hud = document.getElementById('hud'); if (!canvas || !hud) { console.log('Failed to get HTML elements'); return false; } // Get the rendering context for WebGL var gl = getWebGLContext(canvas); // Get the rendering context for 2DCG var ctx = hud.getContext('2d'); if (!gl || !ctx) { console.log('Failed to get rendering context'); return; } // Initialize shaders if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) { console.log('Failed to intialize shaders.'); return; } // Set the vertex information var n = initVertexBuffers(gl); if (n < 0) { console.log('Failed to set the vertex information'); return; } // Set the clear color and enable the depth test gl.clearColor(0.0, 0.0, 0.0, 1.0); gl.enable(gl.DEPTH_TEST); // Get the storage locations of uniform variables var u_MvpMatrix = gl.getUniformLocation(gl.program, 'u_MvpMatrix'); var u_Clicked = gl.getUniformLocation(gl.program, 'u_Clicked'); if (!u_MvpMatrix || !u_Clicked) { console.log('Failed to get the storage location of uniform variables'); return; } // Calculate the view projection matrix var viewProjMatrix = new Matrix4(); viewProjMatrix.setPerspective(30.0, canvas.width / canvas.height, 1.0, 100.0); viewProjMatrix.lookAt(0.0, 0.0, 7.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); gl.uniform1i(u_Clicked, 0); // Pass false to u_Clicked var currentAngle = 0.0; // Current rotation angle // 鼠标在HUD画布中如果有动作将就响应 hud.onmousedown = function(ev) { // Mouse is pressed var x = ev.clientX, y = ev.clientY; var rect = ev.target.getBoundingClientRect(); if (rect.left <= x && x < rect.right && rect.top <= y && y < rect.bottom) { // If pressed position is inside <canvas>, check if it is above object var x_in_canvas = x - rect.left, y_in_canvas = rect.bottom - y; var picked = check(gl, n, x_in_canvas, y_in_canvas, currentAngle, u_Clicked, viewProjMatrix, u_MvpMatrix); if (picked) alert('The cube was selected! '); } } var tick = function() { // Start drawing currentAngle = animate(currentAngle); //重复绘制二维图形（不断更新角度值） draw2D(ctx, currentAngle); // Draw 2D draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix); requestAnimationFrame(tick, canvas); }; tick(); } function initVertexBuffers(gl) { // Create a cube // v6----- v5 // /| /| // v1------v0| // | | | | // | |v7---|-|v4 // |/ |/ // v2------v3 var vertices = new Float32Array([ // Vertex coordinates 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 0.2, 0.58, 0.82, 0.2, 0.58, 0.82, 0.2, 0.58, 0.82, 0.2, 0.58, 0.82, // 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 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, // v0-v5-v6-v1 up 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, // v1-v6-v7-v2 left 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, // 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 ]); // Indices of the vertices var indices = new Uint8Array([ 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 ]); // Write the vertex property to buffers (coordinates and normals) if (!initArrayBuffer(gl, vertices, 3, gl.FLOAT, 'a_Position')) return -1; // Coordinates if (!initArrayBuffer(gl, colors, 3, gl.FLOAT, 'a_Color')) return -1; // Color Information // Create a buffer object var indexBuffer = gl.createBuffer(); if (!indexBuffer) { return -1; } // Write the indices to the buffer object gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer); gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW); return indices.length; } function check(gl, n, x, y, currentAngle, u_Clicked, viewProjMatrix, u_MvpMatrix) { var picked = false; gl.uniform1i(u_Clicked, 1); // Pass true to u_Clicked(Draw cube with red) draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix); // Read pixel at the clicked position var pixels = new Uint8Array(4); // Array for storing the pixel value gl.readPixels(x, y, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixels); if (pixels[0] == 255) // If red = 255, clicked on cube picked = true; gl.uniform1i(u_Clicked, 0); // Pass false to u_Clicked(Draw cube with specified color) draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix); return picked; } var g_MvpMatrix = new Matrix4(); // Model view projection matrix function draw(gl, n, currentAngle, viewProjMatrix, u_MvpMatrix) { // Caliculate The model view projection matrix and pass it to u_MvpMatrix g_MvpMatrix.set(viewProjMatrix); g_MvpMatrix.rotate(currentAngle, 1.0, 0.0, 0.0); // Rotate appropriately g_MvpMatrix.rotate(currentAngle, 0.0, 1.0, 0.0); g_MvpMatrix.rotate(currentAngle, 0.0, 0.0, 1.0); gl.uniformMatrix4fv(u_MvpMatrix, false, g_MvpMatrix.elements); gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT); // Clear buffers (color and depth) gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0); // Draw } //实现二维图形的绘制工作 function draw2D(ctx, currentAngle) { //传入左上角坐标，宽度和高度，清空绘图区 ctx.clearRect(0, 0, 400, 400); // Clear <hud> // Draw triangle with white lines ctx.beginPath(); // Start drawing ctx.moveTo(120, 10); ctx.lineTo(200, 150); ctx.lineTo(40, 150); ctx.closePath(); ctx.strokeStyle = 'rgba(255, 255, 255, 1)'; // Set white to color of lines ctx.stroke(); // Draw Triangle with white lines // Draw white letters ctx.font = '18px "Times New Roman"'; ctx.fillStyle = 'rgba(255, 255, 255, 1)'; // Set white to the color of letters ctx.fillText('HUD: Head Up Display', 40, 180); ctx.fillText('Triangle is drawn by Canvas 2D API.', 40, 200); ctx.fillText('Cube is drawn by WebGL API.', 40, 220); //Math.floor截掉了小数部分（这里也需要重绘） ctx.fillText('Current Angle: '+ Math.floor(currentAngle), 40, 240); } var last = Date.now(); // Last time that this function was called function animate(angle) { var now = Date.now(); // Calculate the elapsed time var elapsed = now - last; last = now; // Update the current rotation angle (adjusted by the elapsed time) var newAngle = angle + (ANGLE_STEP * elapsed) / 1000.0; return newAngle % 360; } function initArrayBuffer (gl, data, num, type, attribute) { // Create a buffer object var buffer = gl.createBuffer(); if (!buffer) { console.log('Failed to create the buffer object'); return false; } // Write date into the buffer object gl.bindBuffer(gl.ARRAY_BUFFER, buffer); gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW); // Assign the buffer object to the attribute variable var a_attribute = gl.getAttribLocation(gl.program, attribute); if (a_attribute < 0) { console.log('Failed to get the storage location of ' + attribute); return false; } gl.vertexAttribPointer(a_attribute, num, type, false, 0, 0); // Enable the assignment of the buffer object to the attribute variable gl.enableVertexAttribArray(a_attribute); // Unbind the buffer object gl.bindBuffer(gl.ARRAY_BUFFER, null); return true; }