WEBGL（3）：鼠标动态绘制点

1 实现思路

• 绘制单个点
• 鼠标事件监听点击事件
• 将点推送到数组中
• 绘制数组中所有点

2 实现代码

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="js/glMatrix-0.9.6.min.js"></script>
    <script>
        let vertexstring = `
        attribute vec3 a_position;
        uniform     mat4    proj;


        void main(void){
            gl_Position = vec4(a_position,1.0)  ;
            gl_PointSize=60.0;

        }
        `;
        let fragmentstring = `
        precision mediump float;
        void main(void){
          gl_FragColor = vec4(0.0,0.0,1.0,1.0);
        }
        `;
        var projMat4 = mat4.create();
        var webgl;
        function init() {
            initWebgl();
            initShader();
            initBuffer();
            draw();
        }
        function initWebgl() {
            let webglDiv = document.getElementById('myCanvas');
            webgl = webglDiv.getContext("webgl");
            webgl.viewport(0, 0, webglDiv.clientWidth, webglDiv.clientHeight);
            mat4.ortho(0, webglDiv.clientWidth, webglDiv.clientHeight, 0, -1.0, 1.0, projMat4)
        }
        function initShader() {

            let vsshader = webgl.createShader(webgl.VERTEX_SHADER);
            let fsshader = webgl.createShader(webgl.FRAGMENT_SHADER);

            webgl.shaderSource(vsshader, vertexstring);
            webgl.shaderSource(fsshader, fragmentstring);

            webgl.compileShader(vsshader);
            webgl.compileShader(fsshader);
            if (!webgl.getShaderParameter(vsshader, webgl.COMPILE_STATUS)) {
                var err = webgl.getShaderInfoLog(vsshader);
                alert(err);
                return;
            }
            if (!webgl.getShaderParameter(fsshader, webgl.COMPILE_STATUS)) {
                var err = webgl.getShaderInfoLog(fsshader);
                alert(err);
                return;
            }
            let program = webgl.createProgram();
            webgl.attachShader(program, vsshader);
            webgl.attachShader(program, fsshader)

            webgl.linkProgram(program);
            webgl.useProgram(program);

            webgl.program = program
        }
        var points = [];
        var colors=[];
        function initBuffer() {
            let aPsotion = webgl.getAttribLocation(webgl.program, "a_position");
            
            document.addEventListener("mousedown", function (e) {
                debugger
                let x = e.clientX;
                let y = e.clientY;
                let rect = e.target.getBoundingClientRect();
                let pointx = ((x - rect.left) - 512) / 512;
                //let pointy = -((y - rect.top) - 350) / 350;
                let pointy = (350 - (y - rect.top)) / 350;
                points.push(pointx);
                points.push(pointy);
                points.push(0);
              
                let pointPosition = new Float32Array(points);
                //创建缓冲区
                let pointBuffer = webgl.createBuffer();
                webgl.bindBuffer(webgl.ARRAY_BUFFER, pointBuffer);
                webgl.bufferData(webgl.ARRAY_BUFFER, pointPosition, webgl.STATIC_DRAW);
                webgl.enableVertexAttribArray(aPsotion);
                webgl.vertexAttribPointer(aPsotion, 3, webgl.FLOAT, false, 0, 0);

                webgl.clearColor(0.0, 0.0, 0.0, 1.0);
                webgl.clear(webgl.COLOR_BUFFER_BIT | webgl.DEPTH_BUFFER_BIT);
                webgl.drawArrays(webgl.POINTS, 0, points.length / 3);
            })



            let uniformProj = webgl.getUniformLocation(webgl.program, "proj");
            webgl.uniformMatrix4fv(uniformProj, false, projMat4);
        }
        function draw() {
            webgl.clearColor(0.0, 0.0, 0.0, 1.0);
            webgl.clear(webgl.COLOR_BUFFER_BIT | webgl.DEPTH_BUFFER_BIT);

        }
    </script>
</head>

<body onload="init()">
    <canvas id='myCanvas' width="1024" height='700'></canvas>
</body>

</html>

3 实现效果

鼠标点击加载图像