webgl example1

<!doctype html>

<html lang="en">

  <head>

    <meta charset="utf-8">

    <title>WebGL Demo</title>

    <link rel="stylesheet" href="../webgl.css" type="text/css">

  </head>

  <body>

    <canvas id="glcanvas" width="640" height="480"></canvas>

  </body>

</html>

main();

function main() {

  const canvas = document.querySelector('#glcanvas');

  const gl = canvas.getContext('webgl');

  if (!gl) {

    alert('Unable to initialize WebGL. Your browser or machine may not support it.');

    return;

  }

  // 顶点着色器代码

  const vsSource = `

    attribute vec4 aVertexPosition;

    uniform mat4 uModelViewMatrix;

    uniform mat4 uProjectionMatrix;

    void main() {

      gl_Position = uProjectionMatrix * uModelViewMatrix * aVertexPosition;

    }

  `;

  // 版本着色器代码

  const fsSource = `

    void main() {

      gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);

    }

  `;

  // 生成着色器

  const shaderProgram = initShaderProgram(gl, vsSource, fsSource);

  // 着色器需要的数据

  const programInfo = {

    program: shaderProgram,

    attribLocations: {

      vertexPosition: gl.getAttribLocation(shaderProgram, 'aVertexPosition'),

    },

    uniformLocations: {

      projectionMatrix: gl.getUniformLocation(shaderProgram, 'uProjectionMatrix'),

      modelViewMatrix: gl.getUniformLocation(shaderProgram, 'uModelViewMatrix'),

    },

  };

  const buffers = initBuffers(gl);

  drawScene(gl, programInfo, buffers);

}

// 初始化buff数据

function initBuffers(gl) {

  const positionBuffer = gl.createBuffer();

  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  const positions = [

     1.0,  1.0,

    -1.0,  1.0,

     1.0, -1.0,

    -1.0, -1.0,

  ];

  gl.bufferData(gl.ARRAY_BUFFER,

                new Float32Array(positions),

                gl.STATIC_DRAW);

  return {

    position: positionBuffer,

  };

}

function drawScene(gl, programInfo, buffers) {

  gl.clearColor(0.0, 0.0, 0.0, 1.0);  // Clear to black, fully opaque

  gl.clearDepth(1.0);                 // Clear everything

  gl.enable(gl.DEPTH_TEST);           // Enable depth testing

  gl.depthFunc(gl.LEQUAL);            // Near things obscure far things

  // Clear the canvas before we start drawing on it.

  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  // Create a perspective matrix, a special matrix that is

  // used to simulate the distortion of perspective in a camera.

  // Our field of view is 45 degrees, with a width/height

  // ratio that matches the display size of the canvas

  // and we only want to see objects between 0.1 units

  // and 100 units away from the camera.

  const fieldOfView = 45 * Math.PI / 180;   // in radians

  const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;

  const zNear = 0.1;

  const zFar = 100.0;

  const projectionMatrix = mat4.create();

  // note: glmatrix.js always has the first argument

  // as the destination to receive the result.

  mat4.perspective(projectionMatrix,

                   fieldOfView,

                   aspect,

                   zNear,

                   zFar);

  // Set the drawing position to the "identity" point, which is

  // the center of the scene.

  const modelViewMatrix = mat4.create();

  // Now move the drawing position a bit to where we want to

  // start drawing the square.

  mat4.translate(modelViewMatrix,     // destination matrix

                 modelViewMatrix,     // matrix to translate

                 [-0.0, 0.0, -6.0]);  // amount to translate

  // Tell WebGL how to pull out the positions from the position

  // buffer into the vertexPosition attribute.

  {

    const numComponents = 2;

    const type = gl.FLOAT;

    const normalize = false;

    const stride = 0;

    const offset = 0;

    gl.bindBuffer(gl.ARRAY_BUFFER, buffers.position);

    gl.vertexAttribPointer(

        programInfo.attribLocations.vertexPosition,

        numComponents,

        type,

        normalize,

        stride,

        offset);

    gl.enableVertexAttribArray(

        programInfo.attribLocations.vertexPosition);

  }

  // Tell WebGL to use our program when drawing

  gl.useProgram(programInfo.program);

  // Set the shader uniforms

  gl.uniformMatrix4fv(

      programInfo.uniformLocations.projectionMatrix,

      false,

      projectionMatrix);

  gl.uniformMatrix4fv(

      programInfo.uniformLocations.modelViewMatrix,

      false,

      modelViewMatrix);

  {

    const offset = 0;

    const vertexCount = 4;

    gl.drawArrays(gl.TRIANGLE_STRIP, offset, vertexCount);

  }

}


// 编译着色器
function initShaderProgram(gl, vsSource, fsSource) {

  const vertexShader = loadShader(gl, gl.VERTEX_SHADER, vsSource);

  const fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fsSource);

  // Create the shader program

  const shaderProgram = gl.createProgram();

  gl.attachShader(shaderProgram, vertexShader);

  gl.attachShader(shaderProgram, fragmentShader);

  gl.linkProgram(shaderProgram);

  // If creating the shader program failed, alert

  if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {

    alert('Unable to initialize the shader program: ' + gl.getProgramInfoLog(shaderProgram));

    return null;

  }

  return shaderProgram;

}

// 编译某种类型着色器

function loadShader(gl, type, source) {

  const shader = gl.createShader(type);

  // Send the source to the shader object

  gl.shaderSource(shader, source);

  // Compile the shader program

  gl.compileShader(shader);

  // See if it compiled successfully

  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {

    alert('An error occurred compiling the shaders: ' + gl.getShaderInfoLog(shader));

    gl.deleteShader(shader);

    return null;

  }

  return shader;

}
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webgl example1

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