Wait, Builderboy might've messed something up...let me give my (i think) fixed code with explanation

Code: [Select]

{{r2/8*W+   // get tile row, multiply by width
(r1/8)+   //get tile column
L1}*8+  // now we have the value of the tile you are in, then multiply by 8 because 8 bytes per sprite
(r2^8)+      //get pixel row # with respect to the tile you are in
Str1}    //we add this to the pointer to the mask table, thus returning the exact byte of the sprite mask
e r1    // and now we check if the appropriate pixel is lit or not in the given row
Return
Where r1 is your X position, r2 is your Y position, W is the width of your tilemap (in tiles), L1 is the location of your matrix data buffer, and Str1 is the start of your Mask Sprite table.