# WebGL示例


## 效果
<style>

	canvas{
		width:100%;
		height:300px;
	}

</style>
<canvas  id = "my_Canvas"></canvas>

<script id="vertex-shader" type="shader">
  attribute vec3 coordinates;
  
  void main(void) {
    gl_Position = vec4(coordinates, 1.0);
  }
</script>
<script id="fragment-shader" type="shader">
  void main(void) {
    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
  }
</script>

<script>

         /*============== Creating a canvas ====================*/
         var canvas = document.getElementById('my_Canvas');
         gl = canvas.getContext('experimental-webgl');
      
         /*======== Defining and storing the geometry ===========*/

         var vertices = [
            -0.5,0.5,0.0,
            -0.5,-0.5,0.0,
            0.5,-0.5,0.0, 
         ];
         
         indices = [0,1,2];
         
         // Create an empty buffer object to store vertex buffer
         var vertex_buffer = gl.createBuffer();

         // Bind appropriate array buffer to it
         gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);
         
         // Pass the vertex data to the buffer
         gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

         // Unbind the buffer
         gl.bindBuffer(gl.ARRAY_BUFFER, null);

         // Create an empty buffer object to store Index buffer
         var Index_Buffer = gl.createBuffer();

         // Bind appropriate array buffer to it
         gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, Index_Buffer);

         // Pass the vertex data to the buffer
         gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indices), gl.STATIC_DRAW);
         
         // Unbind the buffer
         gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);

         /*================ Shaders ====================*/
         
         // Create a vertex shader object
         var vertShader = gl.createShader(gl.VERTEX_SHADER);

         // Attach vertex shader source code
         gl.shaderSource(vertShader, document.querySelector('#vertex-shader').textContent);

         // Compile the vertex shader
         gl.compileShader(vertShader);

         // Create fragment shader object
         var fragShader = gl.createShader(gl.FRAGMENT_SHADER);

         // Attach fragment shader source code
         gl.shaderSource(fragShader, document.querySelector('#fragment-shader').textContent); 
         
         // Compile the fragmentt shader
         gl.compileShader(fragShader);

         // Create a shader program object to store
         // the combined shader program
         var shaderProgram = gl.createProgram();

         // Attach a vertex shader
         gl.attachShader(shaderProgram, vertShader);

         // Attach a fragment shader
         gl.attachShader(shaderProgram, fragShader);

         // Link both the programs
         gl.linkProgram(shaderProgram);

         // Use the combined shader program object
         gl.useProgram(shaderProgram);

         /*======= Associating shaders to buffer objects =======*/

         // Bind vertex buffer object
         gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);

         // Bind index buffer object
         gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, Index_Buffer);
         
         // Get the attribute location
         var coord = gl.getAttribLocation(shaderProgram, "coordinates");

         // Point an attribute to the currently bound VBO
         gl.vertexAttribPointer(coord, 3, gl.FLOAT, false, 0, 0); 
         
         // Enable the attribute
         gl.enableVertexAttribArray(coord);

         /*=========Drawing the triangle===========*/

         // Clear the canvas
         gl.clearColor(0., 0., 0., 0.9);

         // Enable the depth test
         gl.enable(gl.DEPTH_TEST);

         // Clear the color buffer bit
         gl.clear(gl.COLOR_BUFFER_BIT);

         // Set the view port
         gl.viewport(0,0,canvas.width,canvas.height);

         // Draw the triangle
         gl.drawElements(gl.TRIANGLES, indices.length, gl.UNSIGNED_SHORT,0);

</script>

## 代码

```js
<style>

	canvas{
		width:100%;
		height:300px;
	}

</style>
<canvas  id = "my_Canvas"></canvas>

<script id="vertex-shader" type="shader">
  attribute vec3 coordinates;
  
  void main(void) {
    gl_Position = vec4(coordinates, 1.0);
  }
</script>
<script id="fragment-shader" type="shader">
  void main(void) {
    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
  }
</script>

<script>

         /*============== Creating a canvas ====================*/
         var canvas = document.getElementById('my_Canvas');
         gl = canvas.getContext('experimental-webgl');
      
         /*======== Defining and storing the geometry ===========*/

         var vertices = [
            -0.5,0.5,0.0,
            -0.5,-0.5,0.0,
            0.5,-0.5,0.0, 
         ];
         
         indices = [0,1,2];
         
         // Create an empty buffer object to store vertex buffer
         var vertex_buffer = gl.createBuffer();

         // Bind appropriate array buffer to it
         gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);
         
         // Pass the vertex data to the buffer
         gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

         // Unbind the buffer
         gl.bindBuffer(gl.ARRAY_BUFFER, null);

         // Create an empty buffer object to store Index buffer
         var Index_Buffer = gl.createBuffer();

         // Bind appropriate array buffer to it
         gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, Index_Buffer);

         // Pass the vertex data to the buffer
         gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indices), gl.STATIC_DRAW);
         
         // Unbind the buffer
         gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);

         /*================ Shaders ====================*/
         
         // Create a vertex shader object
         var vertShader = gl.createShader(gl.VERTEX_SHADER);

         // Attach vertex shader source code
         gl.shaderSource(vertShader, document.querySelector('#vertex-shader').textContent);

         // Compile the vertex shader
         gl.compileShader(vertShader);

         // Create fragment shader object
         var fragShader = gl.createShader(gl.FRAGMENT_SHADER);

         // Attach fragment shader source code
         gl.shaderSource(fragShader, document.querySelector('#fragment-shader').textContent); 
         
         // Compile the fragmentt shader
         gl.compileShader(fragShader);

         // Create a shader program object to store
         // the combined shader program
         var shaderProgram = gl.createProgram();

         // Attach a vertex shader
         gl.attachShader(shaderProgram, vertShader);

         // Attach a fragment shader
         gl.attachShader(shaderProgram, fragShader);

         // Link both the programs
         gl.linkProgram(shaderProgram);

         // Use the combined shader program object
         gl.useProgram(shaderProgram);

         /*======= Associating shaders to buffer objects =======*/

         // Bind vertex buffer object
         gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);

         // Bind index buffer object
         gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, Index_Buffer);
         
         // Get the attribute location
         var coord = gl.getAttribLocation(shaderProgram, "coordinates");

         // Point an attribute to the currently bound VBO
         gl.vertexAttribPointer(coord, 3, gl.FLOAT, false, 0, 0); 
         
         // Enable the attribute
         gl.enableVertexAttribArray(coord);

         /*=========Drawing the triangle===========*/

         // Clear the canvas
         gl.clearColor(0., 0., 0., 0.9);

         // Enable the depth test
         gl.enable(gl.DEPTH_TEST);

         // Clear the color buffer bit
         gl.clear(gl.COLOR_BUFFER_BIT);

         // Set the view port
         gl.viewport(0,0,canvas.width,canvas.height);

         // Draw the triangle
         gl.drawElements(gl.TRIANGLES, indices.length, gl.UNSIGNED_SHORT,0);

</script>
```