Page:Calligraphy for computers (Hershey, 1967) (IA DTIC AD0662398).djvu/30

 The decimal format for NORC data is not suitable for STRETCH programming. Inasmuch as the NORC word is 16 decimal digits long and the STRETCH word is 64 binary bits long, there can be a one to one correspondence between the BCD datum word for NORC and the binary datum word for STRETCH. One decimal digit with 9's complements in NORC is mapped into three integer bits and one sign bit in STRETCH. An array of coordinates for dot plotting is recovered from memory by interrogation of a pair of STRAP subroutines.

Replacement of FORTRAN programming by STRAP programming in the character plotting routines has achieved a 7-fold reduction in machine time.

VECTOR DATA

Smooth straight lines are no problem for a vector plotter, but curved lines are approximated by polygons. Small polygons are constructed from short vectors whose components $$\Delta X, \Delta Y$$ have the following integral values

$$

\begin{align} & \left ( \Delta X, \Delta Y \right ) = \left ( 1, 0 \right ) & \left ( \Delta X, \Delta Y \right ) = \left ( 1, 1 \right ) \\ & \left ( \Delta X, \Delta Y \right ) = \left ( 2, 0 \right ) & \left ( \Delta X, \Delta Y \right ) = \left ( 2, 1 \right ) & \left ( \Delta X, \Delta Y \right ) = \left ( 2, 2 \right ) \\ & \left ( \Delta X, \Delta Y \right ) = \left ( 3, 0 \right ) & \left ( \Delta X, \Delta Y \right ) = \left ( 3, 1 \right ) & \left ( \Delta X, \Delta Y \right ) = \left ( 3, 2 \right )\\ & \left ( \Delta X, \Delta Y \right ) = \left ( 4, 0 \right ) & \left ( \Delta X, \Delta Y \right ) = \left ( 4, 1 \right ) \\ & \left ( \Delta X, \Delta Y \right ) = \left ( 5, 0 \right ) \end{align} $$

or have any permutation of magnitude or reversal of sign among these values. 24