桶形畸变

今天，查找了下桶形畸变，特分享如下：

顶点缓冲区

void main(void)
{
    gl_TexCoord[0] = gl_MultiTexCoord0;
    gl_Position = ftransform();
}

片元着色器

uniform sampler2D colorMap;
const float PI = 3.1415926535;
const float BarrelPower = 0.5;  //可调

vec2 Distort(vec2 p )
{
    float theta = atan(p.y, p.x );
    float radius = length(p);
    radius = pow(radius, BarrelPower);
    p.x = radius * cos(theta);
    p.y = radius * sin(theta);
    return 0.5 * ( p+1.0);
}
void main(void)
{
   vec2 xy = 2.0 * gl_TexCoord[0].xy - 1.0;
   vec2 uv;
   float d = length(xy);
   if( d < 1.0 )
   {
 uv = Distort(xy);
   }
   else
   {
 uv = gl_TexCoord[0].xy;
   }
 
   gl_FragColor = texture2D(colorMap, uv );
}