# 2. 实例

// 顶点着色器程序
'attribute vec4 a_Position;\n' + // attribute variable
'attribute vec4 a_Color;\n' +
'uniform mat4 u_MvpMatrix;\n' +
'varying vec4 v_Color;\n' +
'void main() {\n' +
'  gl_Position = u_MvpMatrix * a_Position;\n' + // Set the vertex coordinates of the point
'  v_Color = a_Color;\n' +
'}\n';

// 片元着色器程序
'precision mediump float;\n' +
'varying vec4 v_Color;\n' +
'void main() {\n' +
'  gl_FragColor = v_Color;\n' +
'}\n';

//定义一个矩形体：混合构造函数原型模式
function Cuboid(minX, maxX, minY, maxY, minZ, maxZ) {
this.minX = minX;
this.maxX = maxX;
this.minY = minY;
this.maxY = maxY;
this.minZ = minZ;
this.maxZ = maxZ;
}

Cuboid.prototype = {
constructor: Cuboid,
CenterX: function () {
return (this.minX + this.maxX) / 2.0;
},
CenterY: function () {
return (this.minY + this.maxY) / 2.0;
},
CenterZ: function () {
return (this.minZ + this.maxZ) / 2.0;
},
LengthX: function () {
return (this.maxX - this.minX);
},
LengthY: function () {
return (this.maxY - this.minY);
}
}

var currentAngle = [0.0, 0.0]; // 绕X轴Y轴的旋转角度 ([x-axis, y-axis])
var curScale = 1.0;   //当前的缩放比例

function main() {
// 获取 <canvas> 元素
var canvas = document.getElementById('webgl');

// 获取WebGL渲染上下文
var gl = getWebGLContext(canvas);
if (!gl) {
console.log('Failed to get the rendering context for WebGL');
return;
}

// 初始化着色器
return;
}

// 设置顶点位置
var cuboid = new Cuboid(399589.072, 400469.072, 3995118.062, 3997558.062, 732, 1268);
var n = initVertexBuffers(gl, cuboid);
if (n < 0) {
console.log('Failed to set the positions of the vertices');
return;
}

//注册鼠标事件
initEventHandlers(canvas);

// 指定清空<canvas>的颜色
gl.clearColor(0.0, 0.0, 0.0, 1.0);

// 开启深度测试
gl.enable(gl.DEPTH_TEST);

//绘制函数
var tick = function () {
//设置MVP矩阵
setMVPMatrix(gl, canvas, cuboid);

//清空颜色和深度缓冲区
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

//绘制矩形体
gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);

//请求浏览器调用tick
requestAnimationFrame(tick);
};

//开始绘制
tick();

// 绘制矩形体
gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);
}

//注册鼠标事件
function initEventHandlers(canvas) {
var dragging = false;         // Dragging or not
var lastX = -1, lastY = -1;   // Last position of the mouse

//鼠标按下
canvas.onmousedown = function (ev) {
var x = ev.clientX;
var y = ev.clientY;
// Start dragging if a moue is in <canvas>
var rect = ev.target.getBoundingClientRect();
if (rect.left <= x && x < rect.right && rect.top <= y && y < rect.bottom) {
lastX = x;
lastY = y;
dragging = true;
}
};

//鼠标离开时
canvas.onmouseleave = function (ev) {
dragging = false;
};

//鼠标释放
canvas.onmouseup = function (ev) {
dragging = false;
};

//鼠标移动
canvas.onmousemove = function (ev) {
var x = ev.clientX;
var y = ev.clientY;
if (dragging) {
var factor = 100 / canvas.height; // The rotation ratio
var dx = factor * (x - lastX);
var dy = factor * (y - lastY);
currentAngle[0] = currentAngle[0] + dy;
currentAngle[1] = currentAngle[1] + dx;
}
lastX = x, lastY = y;
};

//鼠标缩放
canvas.onmousewheel = function (event) {
if (event.wheelDelta > 0) {
curScale = curScale * 1.1;
} else {
curScale = curScale * 0.9;
}
};
}

//设置MVP矩阵
function setMVPMatrix(gl, canvas, cuboid) {
// Get the storage location of u_MvpMatrix
var u_MvpMatrix = gl.getUniformLocation(gl.program, 'u_MvpMatrix');
if (!u_MvpMatrix) {
console.log('Failed to get the storage location of u_MvpMatrix');
return;
}

//模型矩阵
var modelMatrix = new Matrix4();
modelMatrix.scale(curScale, curScale, curScale);
modelMatrix.rotate(currentAngle[0], 1.0, 0.0, 0.0); // Rotation around x-axis
modelMatrix.rotate(currentAngle[1], 0.0, 1.0, 0.0); // Rotation around y-axis
modelMatrix.translate(-cuboid.CenterX(), -cuboid.CenterY(), -cuboid.CenterZ());

//投影矩阵
var fovy = 60;
var near = 1;
var projMatrix = new Matrix4();
projMatrix.setPerspective(fovy, canvas.width / canvas.height, 1, 10000);

//计算lookAt()函数初始视点的高度
var angle = fovy / 2 * Math.PI / 180.0;
var eyeHight = (cuboid.LengthY() * 1.2) / 2.0 / angle;

//视图矩阵
var viewMatrix = new Matrix4();  // View matrix
viewMatrix.lookAt(0, 0, eyeHight, 0, 0, 0, 0, 1, 0);

//MVP矩阵
var mvpMatrix = new Matrix4();
mvpMatrix.set(projMatrix).multiply(viewMatrix).multiply(modelMatrix);

//将MVP矩阵传输到着色器的uniform变量u_MvpMatrix
gl.uniformMatrix4fv(u_MvpMatrix, false, mvpMatrix.elements);
}

//
function initVertexBuffers(gl, cuboid) {
// Create a cube
//    v6----- v5
//   /|      /|
//  v1------v0|
//  | |     | |
//  | |v7---|-|v4
//  |/      |/
//  v2------v3
// 顶点坐标和颜色
var verticesColors = new Float32Array([
cuboid.maxX, cuboid.maxY, cuboid.maxZ, 1.0, 1.0, 1.0,  // v0 White
cuboid.minX, cuboid.maxY, cuboid.maxZ, 1.0, 0.0, 1.0,  // v1 Magenta
cuboid.minX, cuboid.minY, cuboid.maxZ, 1.0, 0.0, 0.0,  // v2 Red
cuboid.maxX, cuboid.minY, cuboid.maxZ, 1.0, 1.0, 0.0,  // v3 Yellow
cuboid.maxX, cuboid.minY, cuboid.minZ, 0.0, 1.0, 0.0,  // v4 Green
cuboid.maxX, cuboid.maxY, cuboid.minZ, 0.0, 1.0, 1.0,  // v5 Cyan
cuboid.minX, cuboid.maxY, cuboid.minZ, 0.0, 0.0, 1.0,  // v6 Blue
cuboid.minX, cuboid.minY, cuboid.minZ, 1.0, 0.0, 1.0   // v7 Black
]);

//顶点索引
var indices = new Uint8Array([
0, 1, 2, 0, 2, 3,    // 前
0, 3, 4, 0, 4, 5,    // 右
0, 5, 6, 0, 6, 1,    // 上
1, 6, 7, 1, 7, 2,    // 左
7, 4, 3, 7, 3, 2,    // 下
4, 7, 6, 4, 6, 5     // 后
]);

//
var FSIZE = verticesColors.BYTES_PER_ELEMENT;   //数组中每个元素的字节数

// 创建缓冲区对象
var vertexColorBuffer = gl.createBuffer();
var indexBuffer = gl.createBuffer();
if (!vertexColorBuffer || !indexBuffer) {
console.log('Failed to create the buffer object');
return -1;
}

// 将缓冲区对象绑定到目标
gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorBuffer);
// 向缓冲区对象写入数据
gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW);

//获取着色器中attribute变量a_Position的地址
var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
if (a_Position < 0) {
console.log('Failed to get the storage location of a_Position');
return -1;
}
// 将缓冲区对象分配给a_Position变量
gl.vertexAttribPointer(a_Position, 3, gl.FLOAT, false, FSIZE * 6, 0);

// 连接a_Position变量与分配给它的缓冲区对象
gl.enableVertexAttribArray(a_Position);

//获取着色器中attribute变量a_Color的地址
var a_Color = gl.getAttribLocation(gl.program, 'a_Color');
if (a_Color < 0) {
console.log('Failed to get the storage location of a_Color');
return -1;
}
// 将缓冲区对象分配给a_Color变量
gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 6, FSIZE * 3);
// 连接a_Color变量与分配给它的缓冲区对象
gl.enableVertexAttribArray(a_Color);

// 将顶点索引写入到缓冲区对象
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);

return indices.length;
}


## 2.1. 重绘刷新

//绘制函数
var tick = function () {
//设置MVP矩阵
setMVPMatrix(gl, canvas, cuboid);

//清空颜色和深度缓冲区
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

//绘制矩形体
gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);

//请求浏览器调用tick
requestAnimationFrame(tick);
};

//开始绘制
tick();


## 2.2. 鼠标事件调整参数

var currentAngle = [0.0, 0.0]; // 绕X轴Y轴的旋转角度 ([x-axis, y-axis])
var curScale = 1.0;   //当前的缩放比例

//设置MVP矩阵
function setMVPMatrix(gl, canvas, cuboid) {
//...

//模型矩阵
var modelMatrix = new Matrix4();
modelMatrix.scale(curScale, curScale, curScale);
modelMatrix.rotate(currentAngle[0], 1.0, 0.0, 0.0); // Rotation around x-axis
modelMatrix.rotate(currentAngle[1], 0.0, 1.0, 0.0); // Rotation around y-axis
modelMatrix.translate(-cuboid.CenterX(), -cuboid.CenterY(), -cuboid.CenterZ());

//...
}


currentAngle和curScale是预先定义的全局变量，它们在函数initEventHandlers中被设置。在initEventHandlers函数中，注册了画布元素canvas的鼠标事件。当鼠标在画布视图中拖动的时候，currentAngle根据鼠标在X、Y方向上位移变化而变化：

//鼠标按下
canvas.onmousedown = function (ev) {
var x = ev.clientX;
var y = ev.clientY;
// Start dragging if a moue is in <canvas>
var rect = ev.target.getBoundingClientRect();
if (rect.left <= x && x < rect.right && rect.top <= y && y < rect.bottom) {
lastX = x;
lastY = y;
dragging = true;
}
};

//...

//鼠标移动
canvas.onmousemove = function (ev) {
var x = ev.clientX;
var y = ev.clientY;
if (dragging) {
var factor = 100 / canvas.height; // The rotation ratio
var dx = factor * (x - lastX);
var dy = factor * (y - lastY);
currentAngle[0] = currentAngle[0] + dy;
currentAngle[1] = currentAngle[1] + dx;
}
lastX = x, lastY = y;
};


//鼠标缩放
canvas.onmousewheel = function (event) {
if (event.wheelDelta > 0) {
curScale = curScale * 1.1;
} else {
curScale = curScale * 0.9;
}
};


currentAngle和curScale的变化使得模型矩阵发生改变，而每绘制一帧就会重新设置MVP矩阵，这就使得三维场景随着鼠标操作而变化，从而完成交互操作。

# 4. 参考

posted @ 2019-10-06 22:48  charlee44  阅读(2844)  评论(0编辑  收藏  举报