使用canvas 和 webgl2制作界面系统（一）

1 canvas 基础 2 webgl2 基础

画如下的三角形

2.1 使用getcontext webgl2

webgl2 必须使用webgl2 字符串

var gl = canvas.getContext("webgl2");
if (!gl) {
     console.error("WebGL 2 not available");
     document.body.innerHTML = "need WebGL 2 which is unavailable on this system."
}
gl.clearColor(0, 0, 0, 1);

2.2 顶点着色器和片元着色器

把顶点着色器和片元着色器的代码都放到javascript里面， 给script 加上id，在程序里面找到id以后读取字符串即可

  
        #version 300 es
        
        layout (location=0) in vec4 position;
        layout (location=1) in vec3 color;
        
        out vec3 vColor;

        void main() {

            vColor = color;
            gl_Position = position;
        }
    
    
        #version 300 es
        precision highp float;
        
        in vec3 vColor;
        out vec4 fragColor;

        void main() {
            fragColor = vec4(vColor, 1.0);
        }
    

   var vsSource = document.getElementById("vs").text.trim();
   var fsSource = document.getElementById("fs").text.trim();

整体代码如下

DOCTYPE html>


    WebGL 2 Example
    
     


    
        WebGL 2 Example: 三角形
        
            Features: 顶点数组
        

    
    
        #version 300 es
        
        layout (location=0) in vec4 position;
        layout (location=1) in vec3 color;
        
        out vec3 vColor;

        void main() {

            vColor = color;
            gl_Position = position;
        }
    
    
        #version 300 es
        precision highp float;
        
        in vec3 vColor;
        out vec4 fragColor;

        void main() {
            fragColor = vec4(vColor, 1.0);
        }
    
    
    
        var canvas = document.getElementById("webgl-canvas");
        canvas.width = window.innerWidth;
        canvas.height = window.innerHeight;

        var gl = canvas.getContext("webgl2");
        if (!gl) {
            console.error("WebGL 2 not available");
            document.body.innerHTML = "This example requires WebGL 2 which is unavailable on this system."
        }

        gl.clearColor(0, 0, 0, 1);

        /
        // SET UP PROGRAM
        /

        var vsSource = document.getElementById("vs").text.trim();
        var fsSource = document.getElementById("fs").text.trim();

        var vertexShader = gl.createShader(gl.VERTEX_SHADER);
        gl.shaderSource(vertexShader, vsSource);
        gl.compileShader(vertexShader);

        if (!gl.getShaderParameter(vertexShader, gl.COMPILE_STATUS)) {
            console.error(gl.getShaderInfoLog(vertexShader));
        }

        var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
        gl.shaderSource(fragmentShader, fsSource);
        gl.compileShader(fragmentShader);

        if (!gl.getShaderParameter(fragmentShader, gl.COMPILE_STATUS)) {
            console.error(gl.getShaderInfoLog(fragmentShader));
        }

        var program = gl.createProgram();
        gl.attachShader(program, vertexShader);
        gl.attachShader(program, fragmentShader);
        gl.linkProgram(program);

        if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
            console.error(gl.getProgramInfoLog(program));
        }

        gl.useProgram(program);

        /
        // 创造三角形
        /
        
        var triangleArray = gl.createVertexArray();
        gl.bindVertexArray(triangleArray);

        var positions = new Float32Array([
            -0.5, -0.5, 0.0,
            0.5, -0.5, 0.0,
            0.0, 0.5, 0.0
        ]);

        var positionBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, positions, gl.STATIC_DRAW);
        gl.vertexAttribPointer(0, 3, gl.FLOAT, false, 0, 0);
        gl.enableVertexAttribArray(0);

        var colors = new Float32Array([
            1.0, 0.0, 0.0,
            0.0, 1.0, 0.0,
            0.0, 0.0, 1.0
        ]);

        var colorBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, colors, gl.STATIC_DRAW);
        gl.vertexAttribPointer(1, 3, gl.FLOAT, false, 0, 0);
        gl.enableVertexAttribArray(1);

        
        // DRAW
        
        gl.clear(gl.COLOR_BUFFER_BIT);
        gl.drawArrays(gl.TRIANGLES, 0, 3);
    

后面我们就直接使用webgl2 和 canvas 来画这些新的界面