Question

您好我正在关注Edward Angel的交互式3D图形简介。我想做一个递归迷宫，但首先我需要能够做一个基本的方块。我在书籍脚本上为sierpinski垫片建模了这个脚本。我已经花了好几个小时，只是看不出我做错了什么。 HTML页面只显示一行。我尝试了不同类型的顶点连接器，如LINES LINE_LOOP POLYGON，但我似乎无法让它工作。请帮助我，我觉得我疯了。这是脚本：

<!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>

Answer 1

2个问题

假设flatten的标准实现，它返回一个JavaScript本机数组，但gl.bufferData需要一个类型化数组。所以我把它改成了
```
gl.bufferData(..., new Float32Array(flatten(...)), ...
```
gl.LINES绘制每一对点。你只传了4分，这意味着2线。你不会得到一个正方形。您可以使用gl.LINE_LOOP连接所有4个点，也可以使用最后一个连接到第一个点。

另外，当我运行你的代码时，我在JavaScript控制台中遇到了错误，这帮助我找到了问题。您应该始终检查JavaScript控制台是否有错误和警告。

＆＃13;

//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();

＆＃13;

<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>

＆＃13;

使用Javascript，WebGL和HTML绘制正方形

1 个答案: