openGL之API学习（一二二）smoothstep

该函数用于求解两个值之间的Hermite样条插值。

float smoothstep(float edge0, float edge1, float x)  
vec2 smoothstep(vec2 edge0, vec2 edge1, vec2 x)  
vec3 smoothstep(vec3 edge0, vec3 edge1, vec3 x)  
vec4 smoothstep(vec4 edge0, vec4 edge1, vec4 x)
vec2 smoothstep(float edge0, float edge1, vec2 x)  
vec3 smoothstep(float edge0, float edge1, vec3 x)  
vec4 smoothstep(float edge0, float edge1, vec4 x)

smoothstep函数的背后计算等同于如下计算：

genType t;
t = clamp((x - edge0) / (edge1 - edge0), 0.0, 1.0);
return (3.0 - 2.0 * t) * t * t;