WebGL中的OpenGL点功能 [英] OpenGL Point Functionality in WebGL

问题描述

在OpenGL中，您可以绘制定义这样的点:

In OpenGL you can draw define points like this:

glBegin(GL_POINTS);
for(float theta=0, radius=60.0; radius>1.0; theta+=0.1, radius-=0.3){
   glColor3f(radius/60.0,0.3,1-(radius/60.0));
   glVertex2i(200+radius*cos(theta),200+radius*sin(theta));
}
glEnd();

您如何在WebGL中实现相同的功能?

How do you accomplish this same functionality in WebGL?

推荐答案

您编写的代码除了定义一些要点外，实际上并没有做什么用.在WebGL中可以做到这一点

The code you wrote really doesn't do much except define some points. To do that in WebGL could do it like this

var colors = [];
var verts = [];
var theta=0 
for(var radius=60.0; radius>1.0; radius-=0.3) {
  colors.push(radius/60.0, 0.3, 1-(radius/60.0));
  verts.push(200+radius*Math.cos(theta),200+radius*Math.sin(theta));
  theta+=0.1;
}
var numPoints = colors.length / 3;

这将产生2个JavaScript数组.然后，您需要将它们放入WebGLBuffers

That would make 2 JavaScript arrays. You'd then need to put them to WebGLBuffers

var colorBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);

var vertBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(verts), gl.STATIC_DRAW);

在那之后，尽管您需要编写一个着色器并进行设置.着色器是一个巨大的话题.对于您的特定数据，我猜想这些着色器会做

After that though you need to write a shader and set it up. Shaders are a huge topic. For your particular data I'm guessing these shader would do

顶点着色器

uniform mat4 u_matrix;
attribute vec4 a_vertex;
attribute vec4 a_color;
varying vec4 v_color;

void main() {
  // Set the size of the point
  gl_PointSize = 3.0;

  // multiply each vertex by a matrix.
  gl_Position = u_matrix * a_vertex;

  // pass the color to the fragment shader
  v_color = a_color;
}

片段着色器

precision mediump float;
varying vec4 v_color;
void main() {
  gl_FragColor = v_color;
}

接下来，您需要初始化着色器和参数.我假设我将着色器放在脚本标签中，它们的ID为"vshader"和"fshader"，并且

Next you need to initialize the shaders and parameters. I'm going to assume I put the shaders in script tags with ids "vshader" and "fshader" and use this boilerplate code to load them.

var program = createProgramFromScriptTags(gl, "vshader", "fshader");
gl.useProgram(program);

// look up the locations for the inputs to our shaders.
var u_matLoc = gl.getUniformLocation(program, "u_matrix");
var colorLoc = gl.getAttribLocation(program, "a_color");
var vertLoc = gl.getAttribLocation(program, "a_vertex");

// Set the matrix to some that makes 1 unit 1 pixel.
gl.uniformMatrix4fv(u_matLoc, false, [
  2 / width, 0, 0, 0,
  0, 2 / height, 0, 0,
  0, 0, 1, 0,
  0, 0, 0, 1
]);

// Tell the shader how to get data out of the buffers.
gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
gl.vertexAttribPointer(colorLoc, 3, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(colorLoc);
gl.bindBuffer(gl.ARRAY_BUFFER, vertBuffer);
gl.vertexAttribPointer(vertLoc, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(vertLoc);

最后画点

gl.drawArrays(gl.POINTS, 0, numPoints);

这是一个片段

var canvas = document.getElementById("c");
var gl = canvas.getContext("webgl");
if (!gl) {
    alert("no WebGL");
    //return;
}

var colors = [];
var verts = [];
var theta=0 
for(var radius=160.0; radius>1.0; radius-=0.3) {
    colors.push(radius/160.0, 0.3, 1-(radius/160.0));
    verts.push(radius*Math.cos(theta),radius*Math.sin(theta));
    theta+=0.1;
}
var numPoints = colors.length / 3;

var colorBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);

var vertBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(verts), gl.STATIC_DRAW);

var program = twgl.createProgramFromScripts(gl, ["vshader", "fshader"]);
gl.useProgram(program);

// look up the locations for the inputs to our shaders.
var u_matLoc = gl.getUniformLocation(program, "u_matrix");
var colorLoc = gl.getAttribLocation(program, "a_color");
var vertLoc = gl.getAttribLocation(program, "a_vertex");

function draw() {
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.clearColor(1.0, 1.0, 1.0, 1.0);
    
 // Set the matrix to some that makes 1 unit 1 pixel.
gl.uniformMatrix4fv(u_matLoc, false, [
    2 / canvas.width, 0, 0, 0,
    0, -2 / canvas.height, 0, 0,
    0, 0, 1, 0,
    0, 0, 0, 1
]);
    
    gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
    gl.vertexAttribPointer(colorLoc, 3, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(colorLoc);
    gl.bindBuffer(gl.ARRAY_BUFFER, vertBuffer);
    gl.vertexAttribPointer(vertLoc, 2, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(vertLoc);
    
    gl.drawArrays(gl.POINTS, 0, numPoints);
    
    requestAnimationFrame(draw, canvas);
}

draw();

canvas { border: 1px solid black; }

<script src="https://twgljs.org/dist/3.x/twgl.min.js"></script>
<script id="vshader" type="whatever">
    uniform mat4 u_matrix;
    attribute vec4 a_vertex;
    attribute vec4 a_color;
    varying vec4 v_color;

    void main() {
      // Set the size of the point
      gl_PointSize = length(a_vertex) * 0.1;
    
      // multiply each vertex by a matrix.
      gl_Position = u_matrix * a_vertex;

      // pass the color to the fragment shader
      v_color = a_color;
    }    
</script>
<script id="fshader" type="whatever">
precision mediump float;
varying vec4 v_color;
void main() {
    gl_FragColor = v_color;
}
</script>
<canvas id="c" width="400" height="400"></canvas>

您可能会发现这些WebGL教程很有帮助.

这篇关于WebGL中的OpenGL点功能的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！