!!FP1.0
#here compute the normal of a vector which in a 2d Texture
#add all elements together into ONE element

#HERE Texture Unit----RECT, just ONE channel
DECLARE TexOffset ={0,0,0,0};

#sample the current position (i,j)
TEX R0, f[WPOS], TEX0, RECT;

#sample the (i+1,j)
ADD R1, f[WPOS], {1,0,0,0};
TEX R1, R1, TEX0, RECT;
ADD R0, R0, R1;

#sample the (i,j+1)
ADD R1, f[WPOS], {0,1,0,0};
TEX R1, R1, TEX0, RECT;
ADD R0, R1, R0;

#sample the (i+1, j+1)
ADD R1, f[WPOS], {1,1,0,0};
TEX R1, R1, TEX0, RECT;

#sum 4 positions together in 1 channel
#ADD o[COLR], R1, R0;

#If in 4 Channels, we need to sum RGBA components together
ADD R2, R1, R0;
ADD R2.x, R2.x, R2.y;
ADD R2.x, R2.x, R2.z;
ADD o[COLR], R2.x, R2.w;

 
END