Optimiz5.Txt

        This text file is the fifth in a guide for use by QB/QBASIC
programmers to help optimize the program code for greater efficiency and/or
give a program a more professional look..  If you have any quetions, contact
VirtuaSoft at gump@gnt.net.  Address to Danny.

        (Note: This is not for the beginning programmer.  A strong
        background in QB/QBASIC programming is highly recommended.)

        5. SPRITES
                a. What is a sprite?
                b. Making a sprite routine

5. SPRITES

        a. What is a sprite?
                A sprite is basically any image in a program that is not
        the background or foreground.  Moving images are sprites.  Some
        examples would be Mario or MegaMan.  

        b. Making a sprite routine (in screen 13H)
                Before you read any further, be sure that you have read
        the tutorials on POKEing and PEEKing and INTEGERs for efficiency.
                Since we are not using the Commodore 128 with its built-in
        sprite routines, we need to go through the trouble of designing our
        own.  QB's GET and PUT either leave black boxes around the images
        (PSET) or don't show the black but distort the colors (XOR), so that
        won't work.  To make a transparent sprite (doesn't draw black), you
        need to draw it pixel-by-pixel, checking for black before each plot.
                The easiest way to do this would be to save the image in
        GET-PUT format with each element as an INTEGER
        (ex. DIM picture(32001) as INTEGER).  Below is the format for INTEGER
        GET-PUT arrays:

                array%(0) = width of image in bits
                array%(1) = height of image in pixels
                array%(2)
                ...       = listing of pixel values (2 per element)
                array%(n)

                To get the image's width in pixels, simply divide array-
        element 0 by 8 (ex. width%=array%(0)\8).  The image's height equals
        array element 1.  To start drawing your sprite, you must define the
        array's memory segment (ex. DEF SEG=VARSEG(array%(0)) ).  This is
        because you will be PEEKing the pixel values directly from the array.
        Let's say the black value on your palette is color # 0, so this
        sprite routine should be set to not draw any pixel it encounters
        with the value 0.
                So basically what was set up, above, is the beginning of the
        sprite routine and all the needed values.  You are now ready to begin
        making your sprite.  Below is an example of the finished sprite
        routine that is included in VirtuaSoft's graphics library...

                SUB sprite (x%, y%, file$)

                DIM picture(32001) AS INTEGER
                DEF SEG = VARSEG(picture(0))
                BLOAD file$, VARPTR(picture(0))
                FOR tempx% = 0 TO picture(0) \ 8 - 1
                   FOR tempy% = 0 TO picture(1) - 1
                      temp% = PEEK(VARPTR(picture(2)) + tempx% + (picture(0) \ 8&) * tempy%)
                      IF temp% > 0 AND tempx% + x% >= 0 AND tempx% + x% < 320 AND tempy% + y% >= 0 AND tempy% + y% < 200 THEN
                         PSET (x% + tempx%, y% + tempy%), temp%
                      END IF
                   NEXT
                NEXT
                DEF SEG = &HA000

                END SUB

                (x% and y% are the values passed to the sub that tell where
        the top-left of the sprite will be, and file$ is the file that holds
        the array.)
                If you decide to use this code in a program, remember to cite
        VirtuaSoft in the credits and e-mail a copy of the file to
        gump@gnt.net so that VirtuaSoft can feel proud that it's programs and
        tutorials have helped someone.

               ... This concludes the lesson ...