04.多点绘制

作者: cmd_ts | 来源:发表于2020-03-20 11:12 被阅读0次

04.多点绘制
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通过循环来生成多点

04for.png

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>cmd_webgl_study3</title>
</head>
<body>
<!-- 1.创建webgl标签 -->
<canvas id="webgl" width="500" height="500"></canvas>
<script type="shader" id="vertex">
        attribute vec4 apos;
        attribute float a_PointSize;
        void main(){
            gl_PointSize = a_PointSize;
            gl_Position = apos;
        }
    </script>
<script type="shader" id="fragment">
        precision mediump float;
        uniform vec4 vColor;
        void main(){
            gl_FragColor = vColor;
        }
    </script>
<script src="./libs/webgl_libs.js"></script>
<script>
    // 2.得到canvas element
    let canvas = document.getElementById('webgl');
    // 3.得到上下文对象 context
    let gl = canvas.getContext('webgl');

    //4.编写顶点着色器源代码、实际绘制的代码，GPU：描述一个顶点的大小、位置（3d坐标） 顶点着色器
    let vertex_shader_source = document.getElementById("vertex").innerHTML;

    //5.片元着色器源代码：描述一个点的颜色 片元着色器
    let fragment_shader_source = document.getElementById("fragment").innerHTML;



    let program = create_program(gl,vertex_shader_source,fragment_shader_source);
    console.log('program:',program);

    let apos = gl.getAttribLocation(program,'apos');
    let aPointSize = gl.getAttribLocation(program,'a_PointSize');
    let a_colol = gl.getUniformLocation(program,'vColor');
    console.log('a_color:',a_colol);
   
    gl.vertexAttrib1f(aPointSize,20.0);

    let p = new Float32Array([0.0, 0.0, 1.0,1.0]);
    gl.uniform4fv(a_colol, p);

    // 13.设置背景色
    gl.clearColor(1.0,0.0,0.0,1.0);
    gl.clear(gl.COLOR_BUFFER_BIT);
    // 14.绘制
    for(var i = 0; i<2; i++){//循环添加点
        //将点的位置传递到变量中a_position
        gl.vertexAttrib2f(apos,-0.1*i,-0.1*i);

        //绘制点
        gl.drawArrays(gl.POINTS,0,1);
    }
    

</script>
</body>
</html>