OpenGL 内置函数 和 unity3d 内置函数对照表

修改一下，来个完整的

 #define ivec2 int2
 #define ivec3 int3
 #define ivec4 int4


 #define vec2 float2
 #define vec3 float3
 #define vec4 float4
 #define mat2 float2x2
 #define mat3 float3x3
 #define mat4 float4x4
 #define mat4x4 float4x4
 #define iGlobalTime _Time.y
 #define mod fmod
 #define mix lerp
 #define inversesqrt rsqrt
 #define fract frac
 #define texture2D tex2D
 #define texture tex2D
 #define textureProj tex2Dproj
 #define iResolution _ScreenParams
 #define gl_FragCoord ((_iParam.scrPos.xy/_iParam.scrPos.w) * _ScreenParams.xy)
 #define PI2 6.28318530718
 #define pi 3.14159265358979
 #define halfpi (pi * 0.5)
 #define oneoverpi (1.0 / pi)
 #define samplerCube samplerCUBE