base2/4.html

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
    }
  </style>
</head>

<body>
  <script type="shader-source" id="vertexShader">
    precision mediump float;

    attribute vec2 a_Position;
    attribute vec2 a_Canvas_Size;

    void main(){
      vec2 position = (a_Position / a_Canvas_Size) * 2.0 - 1.0;
      position = position * vec2(1.0,-1.0);
      gl_Position = vec4(position,0,1);
    }

  </script>
  <script type="shader-source" id="fragmentShader">
    precision mediump float;
    uniform vec4 u_Color;
    void main(){
      vec4 color  = u_Color/ vec4(255,255,255,1);
      gl_FragColor = color;
    }

  </script>
  <script src="../util.js"></script>
  <script>
    const canvas = document.createElement('canvas')
    const wWidth = window.innerWidth;
    const wHeight = window.innerHeight;
    canvas.width = wWidth;
    canvas.height = wHeight;
    document.body.appendChild(canvas)
    const gl = canvas.getContext('webgl');
    const program = createSimpleProgram(gl);
    gl.useProgram(program)

    //设置清空画布颜色为黑色。
    gl.clearColor(0.0, 0.0, 0.0, 1.0);
    //用上一步设置的清空画布颜色清空画布。
    gl.clear(gl.COLOR_BUFFER_BIT);

    const u_Color = gl.getUniformLocation(program, 'u_Color')
    const a_Position = gl.getAttribLocation(program, 'a_Position')
    const a_Canvas_Size = gl.getAttribLocation(program, 'a_Canvas_Size')
    gl.vertexAttrib2f(program, wWidth, wHeight);

    const buffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, buffer)
    gl.enableVertexAttribArray(a_Position)

    const size = 2;
    const type = gl.FLOAT;
    const normalize = false;
    const stride = 0;
    const offset = 0;
    gl.vertexAttribPointer(a_Position, size, type, normalize, stride, offset)


    const positionData = [0, 0];

    canvas.onclick = function (e) {
      const color = randomColor();
      gl.uniform4f(u_Color, color.r, color.g, color.b, color.a);
      positionData.push(e.x)
      positionData.push(e.y)
      gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positionData), gl.STATIC_DRAW)
      //设置清空画布颜色为黑色。
      gl.clearColor(0.0, 0.0, 0.0, 1.0);
      //用上一步设置的清空画布颜色清空画布。
      gl.clear(gl.COLOR_BUFFER_BIT);
      gl.drawArrays(gl.LINE_STRIP, 0, positionData.length / 2)
    }
  </script>
</body>

</html>