Double Low Resolution Library for the Apple II

May 7, 2020

Posted by A.P.P.L.E.

A.P.P.L.E. member Dr. Marc A. Golombeck has developed a Double Low Resolution graphics amper-library for the Apple IIe Enhanced, IIc, and the IIgs. This library allows users to perform many advanced graphics functions in Double Lo-Res mode (80 x 48 pixels in 16 color mode) with simple to use amper routines all based in Applesoft BASIC.

The Double Low-Resolution Amper Library includes a host of routines including:

&GR: switches to double LORES mode and clears the screen
&TEXT: returns to 40-column text mode
&COLOR=: sets the plotting color (range: 0..15)
&PLOT X,Y[,COLOR]:plots a pixel at X,Y. The parameter COLOR is optional.
&SCRN(X,Y,C%): reads out MAIN or AUX memory depending on the given coordinates and returns the color value C% of the selected pixel (range: $00..$0F / 0..15)
&VLIN Y1,Y2,X[,COLOR]: plots a vertical line from Y1 to Y2 at column X. The parameter COLOR is optional.
&HLIN X1,X2,Y[,COLOR]: plots a horizontal line from X1 to X2 at row Y. The parameter COLOR is optional.

With these routines, you can write Applesoft programs like the following program which prints a kaleidoscope of colors to the display screen:

10  REM  DOLORES KALEIDOSCOPE 
15  REM  LOAD DLCOREAMP FIRST! 
20  E = - 16384
30  & GR 
40  FOR W = 3 TO 50:
      W1 = W / 73:
      FOR I = 1 TO 19:
        W2 = I * W1:
        I1 = 3 / (I + 3):
        FOR J = 0 TO 19:
          K = I + J
45        IF PEEK (E) > 128 THEN 
            300
50        C = J * I1 + W2
60        & PLOT 20 + I,3 + K,C:
          & PLOT 20 + K,3 + I,C:
          & PLOT 60 - I,43 - K,C:
          & PLOT 60 - K,43 - I,C
70        & PLOT 20 + K,43 - I,C:
          & PLOT 60 - I,3 + K,C:
          & PLOT 20 + I,43 - K,C:
          & PLOT 60 - K,3 + I,C
80  NEXT J,I,W
90  GOTO 40: REM   RESTART
300 & TEXT : END

The resulting image on the Apple II display screen with the library loaded and the program run will look something like this: