在本章中,我们将举例说明如何使用WebGL修改三角形的比例.
缩放是只是增加或减少对象的大小.例如,如果三角形具有大小为[a,b,c]的顶点,则具有顶点[2a,2b,2c]的三角形将是其大小的两倍.因此,要缩放三角形,必须将每个顶点与缩放系数相乘.您还可以缩放特定顶点.
要缩放三角形,在程序的顶点着色器中,我们创建一个统一矩阵并将坐标值与此矩阵相乘.之后,我们传递一个4×4对角矩阵,在对角线位置(最后一个对角线位置1)具有x,y,z坐标的比例因子.
创建用于缩放三角形的WebGL应用程序需要执行以下步骤.
步骤1 : 去;准备画布并获取WebGL渲染上下文
在此步骤中,我们使用 getContext()获取WebGL渲染上下文对象.
第2步和第2步;定义几何并将其存储在缓冲区对象中
由于我们绘制三角形,我们必须传递三角形的三个顶点,并将它们存储在缓冲区中.
var vertices = [-0.5,0.5,0.0,-0.5,-0.5,0.0,0.5,-0.5,0.0,];
第3步和第3步;创建和编译着色器程序
在此步骤中,您需要编写顶点着色器和片段着色器程序,编译它们,并通过链接这两个程序来创建组合程序.
顶点着色器 : 在程序的顶点着色器中,我们定义了一个矢量属性来存储3D坐标.与此同时,我们定义一个统一矩阵来存储缩放因子,最后,我们将这两个值相乘并将其分配给 gl_position ,它保存顶点的最终位置.
var vertCode = 'attribute vec4 coordinates;' + 'uniform mat4 u_xformMatrix;' + 'void main(void) {' + ' gl_Position = u_xformMatrix * coordinates;' + '}';
片段着色器 : 在片段着色器中,我们只是将片段颜色分配给 gl_FragColor 变量.
var fragCode ='void main(void){'+'gl_FragColor = vec4(1,0.5,0.0,1);'+'}';
步骤4 : 将着色器程序与缓冲区对象相关联
在此步骤中,我们将缓冲区对象与着色器程序相关联.
第5步 : 绘制必需对象
由于我们使用索引绘制三角形,因此我们使用 drawArrays()方法.对于这种方法,我们必须传递要考虑的顶点/元素的数量.由于我们绘制一个三角形,我们将传递3作为参数.
gl.drawArrays(gl.TRIANGLES, 0, 3);
<!doctype html> <html> <body> <canvas width = "300" height = "300" id = "my_Canvas"></canvas> <script> /*=================Creating a canvas=========================*/ var canvas = document.getElementById('my_Canvas'); gl = canvas.getContext('experimental-webgl'); /*===========Defining and storing the geometry==============*/ var vertices = [ -0.5,0.5,0.0, -0.5,-0.5,0.0, 0.5,-0.5,0.0, ]; //Create an empty buffer object and store vertex data var vertex_buffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer); gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW); gl.bindBuffer(gl.ARRAY_BUFFER, null); /*========================Shaders============================*/ //Vertex shader source code var vertCode = 'attribute vec4 coordinates;' + 'uniform mat4 u_xformMatrix;' + 'void main(void) {' + ' gl_Position = u_xformMatrix * coordinates;' + '}'; //Create a vertex shader program object and compile it var vertShader = gl.createShader(gl.VERTEX_SHADER); gl.shaderSource(vertShader, vertCode); gl.compileShader(vertShader); //fragment shader source code var fragCode = 'void main(void) {' + ' gl_FragColor = vec4(0.0, 0.0, 0.0, 0.1);' + '}'; //Create a fragment shader program object and compile it var fragShader = gl.createShader(gl.FRAGMENT_SHADER); gl.shaderSource(fragShader, fragCode); gl.compileShader(fragShader); //Create and use combiened shader program var shaderProgram = gl.createProgram(); gl.attachShader(shaderProgram, vertShader); gl.attachShader(shaderProgram, fragShader); gl.linkProgram(shaderProgram); gl.useProgram(shaderProgram); /*===================scaling==========================*/ var Sx = 1.0, Sy = 1.5, Sz = 1.0; var xformMatrix = new Float32Array([ Sx, 0.0, 0.0, 0.0, 0.0, Sy, 0.0, 0.0, 0.0, 0.0, Sz, 0.0, 0.0, 0.0, 0.0, 1.0 ]); var u_xformMatrix = gl.getUniformLocation(shaderProgram, 'u_xformMatrix'); gl.uniformMatrix4fv(u_xformMatrix, false, xformMatrix); /* ===========Associating shaders to buffer objects============*/ gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer); var coordinatesVar = gl.getAttribLocation(shaderProgram, "coordinates"); gl.vertexAttribPointer(coordinatesVar, 3, gl.FLOAT, false, 0, 0); gl.enableVertexAttribArray(coordinatesVar); /*=================Drawing the Quad========================*/ gl.clearColor(0.5, 0.5, 0.5, 0.9); gl.enable(gl.DEPTH_TEST); gl.clear(gl.COLOR_BUFFER_BIT); gl.viewport(0,0,canvas.width,canvas.height); gl.drawArrays(gl.TRIANGLES, 0, 3); </script> </body> </html>
<html> <body> <canvas width = "300" height = "300" id = "my_Canvas"></canvas> <script> /*=================Creating a canvas=========================*/ var canvas = document.getElementById('my_Canvas'); gl = canvas.getContext('experimental-webgl'); /*===========Defining and storing the geometry==============*/ var vertices = [ -0.5,0.5,0.0, -0.5,-0.5,0.0, 0.5,-0.5,0.0, ]; //Create an empty buffer object and store vertex data var vertex_buffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer); gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW); gl.bindBuffer(gl.ARRAY_BUFFER, null); /*========================Shaders============================*/ //Vertex shader source code var vertCode = 'attribute vec4 coordinates;' + 'uniform mat4 u_xformMatrix;' + 'void main(void) {' + ' gl_Position = u_xformMatrix * coordinates;' + '}'; //Create a vertex shader program object and compile it var vertShader = gl.createShader(gl.VERTEX_SHADER); gl.shaderSource(vertShader, vertCode); gl.compileShader(vertShader); //fragment shader source code var fragCode = 'void main(void) {' + ' gl_FragColor = vec4(0.0, 0.0, 0.0, 0.1);' + '}'; //Create a fragment shader program object and compile it var fragShader = gl.createShader(gl.FRAGMENT_SHADER); gl.shaderSource(fragShader, fragCode); gl.compileShader(fragShader); //Create and use combiened shader program var shaderProgram = gl.createProgram(); gl.attachShader(shaderProgram, vertShader); gl.attachShader(shaderProgram, fragShader); gl.linkProgram(shaderProgram); gl.useProgram(shaderProgram); /*===================scaling==========================*/ var Sx = 1.0, Sy = 1.5, Sz = 1.0; var xformMatrix = new Float32Array([ Sx, 0.0, 0.0, 0.0, 0.0, Sy, 0.0, 0.0, 0.0, 0.0, Sz, 0.0, 0.0, 0.0, 0.0, 1.0 ]); var u_xformMatrix = gl.getUniformLocation(shaderProgram, 'u_xformMatrix'); gl.uniformMatrix4fv(u_xformMatrix, false, xformMatrix); /* ===========Associating shaders to buffer objects============*/ gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer); var coordinatesVar = gl.getAttribLocation(shaderProgram, "coordinates"); gl.vertexAttribPointer(coordinatesVar, 3, gl.FLOAT, false, 0, 0); gl.enableVertexAttribArray(coordinatesVar); /*=================Drawing the Quad========================*/ gl.clearColor(0.5, 0.5, 0.5, 0.9); gl.enable(gl.DEPTH_TEST); gl.clear(gl.COLOR_BUFFER_BIT); gl.viewport(0,0,canvas.width,canvas.height); gl.drawArrays(gl.TRIANGLES, 0, 3); </script> </body> </html>