使用Javascript, WebGL和HTML绘制正方形

Drawing a square using Javascript, WebGL and HTML

本文关键字：HTML 绘制 正方形 WebGL Javascript 使用      更新时间：2023-09-26

大家好，我正在学习Edward Angel的《互动3D图形导论》。我想做一个递归迷宫但首先我需要做一个基本的正方形。我在书的脚本上建模了这个脚本，用于一个sierpinski垫圈。我已经在这几个小时，只是不知道我做错了什么。HTML页面将只显示一行。我尝试了不同类型的顶点joiner，如LINES LINE_LOOP POLYGON，但我似乎不能让它工作。请帮帮我，我觉得我快疯了。脚本如下:

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" >
<title>Maze Sierpinski Gasket</title>

<script id="vertex-shader" type="x-shader/x-vertex">
attribute vec4 vPosition;

void
main()
{
    gl_Position = vPosition;
}
</script>
<script id="fragment-shader" type="x-shader/x-fragment">
precision mediump float;
void
main()
{
    gl_FragColor = vec4( 1.0, 0.0, 0.0, 1.0 );
}
</script>
<script type="text/javascript" src="../Common/webgl-utils.js"></script>
<script type="text/javascript" src="../Common/initShaders.js"></script>
<script type="text/javascript" src="../Common/MV.js"></script>
<script>
//goal: try and draw just a square.
var canvas;
var gl;
var points = [];

window.onload = function init()
{
    canvas = document.getElementById( "gl-canvas" );
    gl = WebGLUtils.setupWebGL( canvas );
    if ( !gl ) { alert( "WebGL isn't available" ); }
   //enter new script 
var vertices = [
  vec2(-1.0,-1.0),
  vec2(-1.0,1.0),
  vec2(1.0,1.0),
  vec2(1.0,-1.0)
];
square(vertices[0],vertices[1],vertices[2],vertices[3]);
//
    //  Configure WebGL
    //
    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.clearColor( 1.0, 1.0, 1.0, 1.0 );
    //  Load shaders and initialize attribute buffers
    var program = initShaders( gl, "vertex-shader", "fragment-shader" );
    gl.useProgram( program );
    // Load the data into the GPU
    var bufferId = gl.createBuffer();
    gl.bindBuffer( gl.ARRAY_BUFFER, bufferId );
    gl.bufferData( gl.ARRAY_BUFFER, flatten(points), gl.STATIC_DRAW );
    // Associate out shader variables with our data buffer
    var vPosition = gl.getAttribLocation( program, "vPosition" );
    gl.vertexAttribPointer( vPosition, 2, gl.FLOAT, false, 0, 0 );
    gl.enableVertexAttribArray( vPosition );
    render();
};
function square(a,b,c,d)
{
points.push(a);
points.push(b);
points.push(c);
points.push(d);
}

function render(){
    gl.clear( gl.COLOR_BUFFER_BIT );
    gl.drawArrays(gl.LINES, 0, points.length);
}
</script>
</head>   
<body>
<canvas id="gl-canvas" width="512" height="512">
Oops ... your browser doesn't support the HTML5 canvas element
</canvas>
</body>
</html>

2 issue

  1. 假设flatten的标准实现返回JavaScript原生数组，但gl.bufferData需要类型数组。我把它改成

    gl.bufferData(..., new Float32Array(flatten(...)), ...

  2. gl.LINES绘制每对点。你只进了4个点，也就是2条线。你不会得到一个正方形。您可以使用gl.LINE_LOOP将所有4个点以及最后一个点连接到第一个点。

另外，当我运行你的代码时，我在JavaScript控制台得到了错误，这帮助我找到了问题。你应该经常检查JavaScript控制台是否有错误和警告。

//goal: try and draw just a square.
var canvas;
var gl;
var points = [];
function init()
{
    canvas = document.getElementById( "gl-canvas" );
    gl = WebGLUtils.setupWebGL( canvas );
    if ( !gl ) { alert( "WebGL isn't available" ); }
   //enter new script 
var vertices = [
  vec2(-1.0,-1.0),
  vec2(-1.0,1.0),
  vec2(1.0,1.0),
  vec2(1.0,-1.0)
];
square(vertices[0],vertices[1],vertices[2],vertices[3]);
//
    //  Configure WebGL
    //
    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.clearColor( 1.0, 1.0, 1.0, 1.0 );
    //  Load shaders and initialize attribute buffers
    var program = initShaders( gl, "vertex-shader", "fragment-shader" );
    gl.useProgram( program );
    // Load the data into the GPU
    var bufferId = gl.createBuffer();
    gl.bindBuffer( gl.ARRAY_BUFFER, bufferId );
    gl.bufferData( gl.ARRAY_BUFFER, new Float32Array(flatten(points)), gl.STATIC_DRAW );
    // Associate out shader variables with our data buffer
    var vPosition = gl.getAttribLocation( program, "vPosition" );
    gl.vertexAttribPointer( vPosition, 2, gl.FLOAT, false, 0, 0 );
    gl.enableVertexAttribArray( vPosition );
    render();
};
function square(a,b,c,d)
{
points.push(a);
points.push(b);
points.push(c);
points.push(d);
}
function render(){
    gl.clear( gl.COLOR_BUFFER_BIT );
    gl.drawArrays(gl.LINE_LOOP, 0, points.length);
}
// ---------------[ missing functions ] ---------
var WebGLUtils = {
  setupWebGL: function(canvas) {
    return canvas.getContext("webgl");
  },
};
function initShaders(gl, vs, fs) {
  return twgl.createProgramFromScripts(gl, [vs, fs]);
}
function vec2(x, y) {
  return [x, y];
}
function flatten(arrayOfArrays) {
  var flattened =  arrayOfArrays.reduce(function(a, b) {
    return a.concat(b);
  }, []);
  return flattened;
}
  
init();
<script id="vertex-shader" type="x-shader/x-vertex">
attribute vec4 vPosition;
void
main()
{
    gl_Position = vPosition;
}
</script>
<script id="fragment-shader" type="x-shader/x-fragment">
precision mediump float;
void
main()
{
    gl_FragColor = vec4( 1.0, 0.0, 0.0, 1.0 );
}
</script>
<script src="https://twgljs.org/dist/twgl.min.js"></script>
<canvas id="gl-canvas" width="512" height="512">
Oops ... your browser doesn't support the HTML5 canvas element
</canvas>

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