Hatched Fill

Hatched Fill





A J Renton makes it easy to fill


the Spectrum screen with patterns.





These two machine-code routines provide your 48K Spectrum


with a way of filling in the screen without all the pro-


blems of attributes, i.e. colours overlapping. This is


achieved by filling in the required area with a set pixel


pattern, set up by the user in the first user-defined


graphic.


The main dollop of machine code is in fact a common or


garden fill routine, this particular one by N. Dore -


Your Computer October 1983. The program first fills in the


required area in the usual way, then hatches it.


[The machine code is on "Hatched Fill.tzx" under the


names of "hatch", for the hatching code, and "fill", for


the filling code. The programs originally used to load


these code files are also there, as "hatch data" and


"fill data".]


Listing 3 [on the TZX as "Demo"] demonstrates some of the


possibilities of this routine. How to use this routine is


probably best learned by studying this program but here is


an example of step by step hatching.


1. Create shape to be filled on screen, making sure there


are no gaps along the edges.


2. Define the first UDG (see listing 4 or manual).


[Listing 4 being your usual READ-and-POKE affair; see any


number of programs, the Demo, or, indeed, the manual.]


3. Choose any point inside the shape and type


PLOT INVERSE 1;x,y


where x,y is the chosen point.


4. Type


RANDOMIZE USR 64800


and the area will fill with ink.


5. Type


RANDOMIZE USR 58000


and the area filled will become hatched.


6. If you don't like the pattern, then type


RANDOMIZE USR 58000


redefine the UDG and retype


RANDOMIZE USR 58000


7. If you wish to remove all of the filled area, using


RANDOMIZE USR 58000


revert the hatch pattern to its original all filled in


positino, define the UDG as totally blank and type


RANDOMIZE USR 58000


Hey presto! the filled area disappears.


A final warning: before loading the fill routine, always


type:


CLEAR 57999


or the computer is likely to crash. [Amusingly enough, the


article's own Demo program neglected to do this. The ver-


sion on the TZX does, of course.]