Loop through tiles

sx = max( 0 , min( player_x - fx / 2 , width - fx ) );
sy = max( 0 , min( player_y - fy / 2 , height - fy ) );
for(i=sx;i<sx+fx;i=i+1)
for(j=sy;j<sy+fy;j=j+1)
{
//somehow i is getting greater then width, don't know about j
}