Webgl Shadertoy

2022-09-07 约 601 字预计阅读 2 分钟

gl_FragCoord的使用

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    gl_FragColor = vec4(fract(gl_FragCoord.xy/50.0), 0, 1);

gl_FragCoord 是像素坐标，取值范围是canvas的高和宽,如果gl_FragCoord.x 为 75. 75 / 50 = 1.5， fract(1.5) = 0.5,每50个像素，他们的值一直在0-1之间变化

一个简单的VertexShader 代码片段

CSS:

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body {
  margin: 0;
}
canvas {
  width: 100vw;
  height: 100vh;
  display: block;
}

HTML:

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<canvas id="canvas"></canvas>
<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="https://webglfundamentals.org/webgl/resources/webgl-utils.js"></script>

JS:

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"use strict";

function main() {
  // Get A WebGL context
  /** @type {HTMLCanvasElement} */
  const canvas = document.querySelector("#canvas");
  const gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }

  const vs = `
    // an attribute will receive data from a buffer
    attribute vec4 a_position;

    // all shaders have a main function
    void main() {

      // gl_Position is a special variable a vertex shader
      // is responsible for setting
      gl_Position = a_position;
    }
  `;

  const fs = `
    precision highp float;
    void main() {
      // gl_FragColor is a special variable a fragment shader
      // is responsible for setting

//       gl_FragColor = vec4(1, 0, 0.5, 1); // return reddish-purple
    gl_FragColor = vec4(fract(gl_FragCoord.xy/50.0), 0, 1);

    }
  `;

  // setup GLSL program
  const program = webglUtils.createProgramFromSources(gl, [vs, fs]);

  // look up where the vertex data needs to go.
  const positionAttributeLocation = gl.getAttribLocation(program, "a_position");

  // Create a buffer to put three 2d clip space points in
  const positionBuffer = gl.createBuffer();

  // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  // fill it with a 2 triangles that cover clipspace
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
    -1, -1,  // first triangle
     1, -1,
    -1,  1,
    -1,  1,  // second triangle
     1, -1,
     1,  1,
  ]), gl.STATIC_DRAW);

  webglUtils.resizeCanvasToDisplaySize(gl.canvas);

  // Tell WebGL how to convert from clip space to pixels
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  // Tell it to use our program (pair of shaders)
  gl.useProgram(program);

  // Turn on the attribute
  gl.enableVertexAttribArray(positionAttributeLocation);

  // Bind the position buffer.
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  // Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
  gl.vertexAttribPointer(
      positionAttributeLocation,
      2,          // 2 components per iteration
      gl.FLOAT,   // the data is 32bit floats
      false,      // don't normalize the data
      0,          // 0 = move forward size * sizeof(type) each iteration to get the next position
      0,          // start at the beginning of the buffer
  );

  gl.drawArrays(
      gl.TRIANGLES,
      0,     // offset
      6,     // num vertices to process
  );
}

main();

运行结果:

目录

Webgl Shadertoy

gl_FragCoord的使用

一个简单的VertexShader 代码片段