介绍

网上很多文章都是介绍OpenGLES着色器语言的，所介绍的内置变量是GLES语言的标准内置变量，但是Three.js有默认的自定义的变量，这里介绍下：

发送到顶点着色器和片元着色器的GLSL程序的构造函数， 包含默认的变量(uniforms)和属性

内置的变量(uniforms)和属性

顶点着色器(无条件的):

// = object.matrixWorld
uniform mat4 modelMatrix;

// = camera.matrixWorldInverse * object.matrixWorld
uniform mat4 modelViewMatrix;

// = camera.projectionMatrix
uniform mat4 projectionMatrix;

// = camera.matrixWorldInverse
uniform mat4 viewMatrix;

// = inverse transpose of modelViewMatrix
uniform mat3 normalMatrix;

// = camera position in world space
uniform vec3 cameraPosition;
// default vertex attributes provided by Geometry and BufferGeometry
attribute vec3 position;
attribute vec3 normal;
attribute vec2 uv;

注意，可以通过以下方式计算顶点着色器中顶点的位置：
```javascript
gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

或者也可以这样：

gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4( position, 1.0 );

顶点着色器(有条件的):

#if defined( USE_COLOR_ALPHA )
	// vertex color attribute with alpha
	attribute vec4 color;
#elif defined( USE_COLOR )
	// vertex color attribute
	attribute vec3 color;
#endif
#ifdef USE_MORPHTARGETS
	attribute vec3 morphTarget0;
	attribute vec3 morphTarget1;
	attribute vec3 morphTarget2;
	attribute vec3 morphTarget3;
	#ifdef USE_MORPHNORMALS
		attribute vec3 morphNormal0;
		attribute vec3 morphNormal1;
		attribute vec3 morphNormal2;
		attribute vec3 morphNormal3;
	#else
		attribute vec3 morphTarget4;
		attribute vec3 morphTarget5;
		attribute vec3 morphTarget6;
		attribute vec3 morphTarget7;
	#endif
#endif
#ifdef USE_SKINNING
	attribute vec4 skinIndex;
	attribute vec4 skinWeight;
#endif

片元着色器:

uniform mat4 viewMatrix;
uniform vec3 cameraPosition;