棋盘图案基本模式

                                                    Box filtered checkerboard

float checkers( in vec2 p, in vec2 dpdx, in vec2 dpdy )

{

    vec2 w = max(abs(dpdx), abs(dpdy));

    vec2 i = 2.0*(abs(fract((p-0.5*w)*0.5)-0.5)-

                  abs(fract((p+0.5*w)*0.5)-0.5))/w;

    return 0.5 - 0.5*i.x*i.y;                 

}

                                                                    Box filtered grid

float grid( in vec2 p, in vec2 dpdx, in vec2 dpdy )

{

    const float N = 10.0; // grid ratio

    vec2 w = max(abs(dpdx), abs(dpdy));

    vec2 a = p + 0.5*w;                       

    vec2 b = p - 0.5*w;         

    vec2 i = (floor(a)+min(fract(a)*N,1.0)-

              floor(b)-min(fract(b)*N,1.0))/(N*w);

    return (1.0-i.x)*(1.0-i.y);

}

                                                            Box filtered squares

float squaresid( in vec2 p, in vec2 dpdx, in vec2 dpdy )

{

    const float N = 3.0;

    vec2 w = max(abs(dpdx), abs(dpdy));

    vec2 a = p + 0.5*w;                       

    vec2 b = p - 0.5*w;         

    vec2 i = (floor(a)+min(fract(a)*N,1.0)-

              floor(b)-min(fract(b)*N,1.0))/(N*w);

    return 1.0-i.x*i.y;

}

                                                        

Box filtered crosses

float crosses( in vec2 p, in vec2 dpdx, in vec2 dpdy )

{

    const float N = 3.0;

    vec2 w = max(abs(dpdx), abs(dpdy));

    vec2 a = p + 0.5*w;                       

    vec2 b = p - 0.5*w;         

    vec2 i = (floor(a)+min(fract(a)*N,1.0)-

              floor(b)-min(fract(b)*N,1.0))/(N*w);

    return 1.0-i.x-i.y+2.0*i.x*i.y;

}