复合canvas叠加显示

Posted 李雷

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<!-- Licensed under a BSD license. See license.html for license -->
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
    <title>WebGL - Fundamentals</title>
     <style>
	 #c {
  background-color: #fff;
  border: 1px solid black;
  position: absolute;
  left: 100px;
  top: 100px;
  /* NOTE: This size is changed if in iframe - see below ‘.iframe canvas‘ */
  width: 400px;
  height: 300px;
  display: block;
}

	 #c2 {
  background-color: transparent;
  border: 1px solid black;
  position: absolute;
  left: 100px;
  top: 100px;
  /* NOTE: This size is changed if in iframe - see below ‘.iframe canvas‘ */
  width: 400px;
  height: 300px;
  display: block;
  
}

	 #c3 {
  background-color: transparent;
  border: 1px solid black;
  position: absolute;
  left: 100px;
  top: 100px;
  /* NOTE: This size is changed if in iframe - see below ‘.iframe canvas‘ */
  width: 400px;
  height: 300px;
  display: block;
  
}

	 #c4 {
  background-color: transparent;
  border: 1px solid black;
  position: absolute;
  left: 100px;
  top: 100px;
  /* NOTE: This size is changed if in iframe - see below ‘.iframe canvas‘ */
  width: 400px;
  height: 300px;
  display: block;
  
}
	 </style>
  </head>
  <body>
    <canvas id="c"></canvas>
	 <canvas id="c2"></canvas><canvas id="c3"></canvas><canvas id="c4"></canvas>
  </body>
</html>
<!--
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 http://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and http://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="resources/webgl-utils.js"></script>
<script src="resources/webgl-lessons-helper.js"></script> <!-- you can and should delete this script. it is only used on the site to help with errors -->
<script id="2d-vertex-shader" type="notjs">

  // an attribute will receive data from a buffer
  attribute vec4 a_position;

  
  varying vec4 v_color;
  
  uniform vec2 u_scale;
  
  // 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 * vec4(u_scale,1,1);
	gl_PointSize = 10.0;
	v_color = gl_Position * vec4(1,1,0.5,1);
  }

</script>

<script id="2d-vertex-shader2" type="notjs">

  // an attribute will receive data from a buffer
  attribute vec4 a_position;

  
  varying vec4 v_color;
  
  uniform vec2 u_scale;
  
  // 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 * vec4(u_scale,1,1);
	gl_PointSize = 10.0;
	v_color = gl_Position * vec4(1,1,0.5,1);
  }

</script>

<script id="2d-fragment-shader" type="notjs">

  // fragment shaders don‘t have a default precision so we need
  // to pick one. mediump is a good default
  precision mediump float;
   varying vec4 v_color;
  void main() {
    // gl_FragColor is a special variable a fragment shader
    // is responsible for setting
    //gl_FragColor = vec4(0, 0, 1, 1); // return redish-purple
	
	gl_FragColor = v_color;
  }

</script>

<script id="2d-fragment-shader2" type="notjs">

  // fragment shaders don‘t have a default precision so we need
  // to pick one. mediump is a good default
  precision mediump float;
  varying vec4 v_color;
  void main() {
    // gl_FragColor is a special variable a fragment shader
    // is responsible for setting
    gl_FragColor = vec4(0, 0, 1, 1); // return redish-purple
	
	//gl_FragColor = v_color;
  }

</script>

<script>
"use strict";

function createShader(gl, type, source) {
  var shader = gl.createShader(type);
  gl.shaderSource(shader, source);
  gl.compileShader(shader);
  var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
  if (success) {
    return shader;
  }

  console.log(gl.getShaderInfoLog(shader));
  gl.deleteShader(shader);
}

function createProgram(gl, vertexShader, fragmentShader) {
  var program = gl.createProgram();
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  var success = gl.getProgramParameter(program, gl.LINK_STATUS);
  if (success) {
    return program;
  }

  console.log(gl.getProgramInfoLog(program));
  gl.deleteProgram(program);
}

function main() {
  // Get A WebGL context
  var canvas = document.getElementById("c");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }
  
  var scale_x = 1;
  var scale_y = 1;

  // Get the strings for our GLSL shaders
  var vertexShaderSource = document.getElementById("2d-vertex-shader").text;

  var fragmentShaderSource = document.getElementById("2d-fragment-shader").text;

  // create GLSL shaders, upload the GLSL source, compile the shaders
  var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
  
  console.log(vertexShader)
  
  var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);

  // Link the two shaders into a program
  var program = createProgram(gl, vertexShader, fragmentShader);

  

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

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

  var ps = []
  
  var positions = [
    0, 0,
    0, 0.8,
    0.7, 0,
  ];
  
  ps.push(positions);
  
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

  // code above this line is initialization code.
  // code below this line is rendering code.

  webglUtils.resizeCanvasToDisplaySize(gl.canvas);

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

  // Clear the canvas
  gl.clearColor(0, 0, 0, 0);
  gl.clear(gl.COLOR_BUFFER_BIT);

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

  // look up where the vertex data needs to go.
  var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
  
  // 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)
  var size = 2;          // 2 components per iteration
  var type = gl.FLOAT;   // the data is 32bit floats
  var normalize = false; // don‘t normalize the data
  var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
  var offset = 0;        // start at the beginning of the buffer
  gl.vertexAttribPointer(
      positionAttributeLocation, size, type, normalize, stride, offset)
	  
	  
	// look up uniform locations
  var resolutionUniformLocation = gl.getUniformLocation(program, "u_scale");  
  gl.uniform2f(resolutionUniformLocation, scale_x, scale_y);
  // draw
  //POINTS
  //LINES
  //LINE_LOOP
  //LINE_STRIP
  //TRIANGLES
  var primitiveType = gl.LINE_STRIP;
  var offset = 0;
  var count = 3;
  gl.drawArrays(primitiveType, offset, count);

}

main();



function main2() {
  // Get A WebGL context
  var canvas = document.getElementById("c2");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }
  
  var scale_x = 1;
  var scale_y = 1;

  // Get the strings for our GLSL shaders
  var vertexShaderSource = document.getElementById("2d-vertex-shader").text;

  var fragmentShaderSource = document.getElementById("2d-fragment-shader").text;

  // create GLSL shaders, upload the GLSL source, compile the shaders
  var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
  
  console.log(vertexShader)
  
  var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);

  // Link the two shaders into a program
  var program = createProgram(gl, vertexShader, fragmentShader);

  

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

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

  var ps = []
  
  var positions = [
    0, 0,
    0, -0.8,
    0.7, 0,
  ];
  
  ps.push(positions);
  
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

  // code above this line is initialization code.
  // code below this line is rendering code.

  webglUtils.resizeCanvasToDisplaySize(gl.canvas);

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

  // Clear the canvas
  gl.clearColor(0, 0, 0, 0);
  gl.clear(gl.COLOR_BUFFER_BIT);

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

  // look up where the vertex data needs to go.
  var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
  
  // 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)
  var size = 2;          // 2 components per iteration
  var type = gl.FLOAT;   // the data is 32bit floats
  var normalize = false; // don‘t normalize the data
  var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
  var offset = 0;        // start at the beginning of the buffer
  gl.vertexAttribPointer(
      positionAttributeLocation, size, type, normalize, stride, offset)
	  
	  
	// look up uniform locations
  var resolutionUniformLocation = gl.getUniformLocation(program, "u_scale");  
  gl.uniform2f(resolutionUniformLocation, scale_x, scale_y);
  // draw
  //POINTS
  //LINES
  //LINE_LOOP
  //LINE_STRIP
  //TRIANGLES
  var primitiveType = gl.TRIANGLES;
  var offset = 0;
  var count = 3;
  gl.drawArrays(primitiveType, offset, count);

}

main2();



function main3() {
  // Get A WebGL context
  var canvas = document.getElementById("c3");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }
  
  var scale_x = 1;
  var scale_y = 1;

  // Get the strings for our GLSL shaders
  var vertexShaderSource = document.getElementById("2d-vertex-shader").text;

  var fragmentShaderSource = document.getElementById("2d-fragment-shader").text;

  // create GLSL shaders, upload the GLSL source, compile the shaders
  var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
  
  console.log(vertexShader)
  
  var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);

  // Link the two shaders into a program
  var program = createProgram(gl, vertexShader, fragmentShader);

  

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

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

  var ps = []
  
  var positions = [
    0, 0,
    0, -0.8,
    -0.7, 0,
  ];
  
  ps.push(positions);
  
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

  // code above this line is initialization code.
  // code below this line is rendering code.

  webglUtils.resizeCanvasToDisplaySize(gl.canvas);

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

  // Clear the canvas
  gl.clearColor(0, 0, 0, 0);
  gl.clear(gl.COLOR_BUFFER_BIT);

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

  // look up where the vertex data needs to go.
  var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
  
  // 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)
  var size = 2;          // 2 components per iteration
  var type = gl.FLOAT;   // the data is 32bit floats
  var normalize = false; // don‘t normalize the data
  var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
  var offset = 0;        // start at the beginning of the buffer
  gl.vertexAttribPointer(
      positionAttributeLocation, size, type, normalize, stride, offset)
	  
	  
	// look up uniform locations
  var resolutionUniformLocation = gl.getUniformLocation(program, "u_scale");  
  gl.uniform2f(resolutionUniformLocation, scale_x, scale_y);
  // draw
  //POINTS
  //LINES
  //LINE_LOOP
  //LINE_STRIP
  //TRIANGLES
  var primitiveType = gl.LINE_STRIP;
  var offset = 0;
  var count = 3;
  gl.drawArrays(primitiveType, offset, count);

}

main3();


function main4() {
  // Get A WebGL context
  var canvas = document.getElementById("c4");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }
  
  var scale_x = 1;
  var scale_y = 1;

  // Get the strings for our GLSL shaders
  var vertexShaderSource = document.getElementById("2d-vertex-shader").text;

  var fragmentShaderSource = document.getElementById("2d-fragment-shader").text;

  // create GLSL shaders, upload the GLSL source, compile the shaders
  var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
  
  console.log(vertexShader)
  
  var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);

  // Link the two shaders into a program
  var program = createProgram(gl, vertexShader, fragmentShader);

  

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

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

  var ps = []
  
  var positions = [
    0, 0,
    0, 0.8,
    -0.7, 0,
  ];
  
  ps.push(positions);
  
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

  // code above this line is initialization code.
  // code below this line is rendering code.

  webglUtils.resizeCanvasToDisplaySize(gl.canvas);

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

  // Clear the canvas
  gl.clearColor(0, 0, 0, 0);
  gl.clear(gl.COLOR_BUFFER_BIT);

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

  // look up where the vertex data needs to go.
  var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
  
  // 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)
  var size = 2;          // 2 components per iteration
  var type = gl.FLOAT;   // the data is 32bit floats
  var normalize = false; // don‘t normalize the data
  var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
  var offset = 0;        // start at the beginning of the buffer
  gl.vertexAttribPointer(
      positionAttributeLocation, size, type, normalize, stride, offset)
	  
	  
	// look up uniform locations
  var resolutionUniformLocation = gl.getUniformLocation(program, "u_scale");  
  gl.uniform2f(resolutionUniformLocation, scale_x, scale_y);
  // draw
  //POINTS
  //LINES
  //LINE_LOOP
  //LINE_STRIP
  //TRIANGLES
  var primitiveType = gl.TRIANGLES;
  var offset = 0;
  var count = 3;
  gl.drawArrays(primitiveType, offset, count);
  
  var flag = false;
  
  document.onclick = function(){
  
	if (!flag){
		gl.clearColor(0, 0, 0, 0);
		gl.clear(gl.COLOR_BUFFER_BIT);
		flag = true;
	}else{
		gl.drawArrays(primitiveType, offset, count);
		flag = false;
	}
	
  }
  

}

main4();

</script>

  

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