Flash Moves

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\H11\H07\H10\H02\H13\H00 F L A S H M O V E S





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Flash, bang, wallop, what a picture! 20th Century Chris


Somerville takes a look at loading screens and shows you how to


turn them into moving pictures.


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A title page is a great way of adding that extra


professional touch to your programs. Use SCREEN$


to save it and it'll load before the main


program. That way you'll keep up flagging


interest during those long LOADs and raise


expectations for the program ahead. The big snag


(I knew it - there's always a snag! Ed.) is that


it adds considerably to the loading time - a


standard loading screen takes up 6.75K of


memory.


Now, it's possible to design a much simplified


title screen using only the 768 bytes of the


Attribute File. You'll find this reduces the


loading time from around forty-five seconds down


to about five. And it's here that you get the


added bonus - animation throughout the loading.


You can flash words on the screen just like in


Manic Miner - take a look at the demo program to


see how it's done. Or you could extend the


process to cover anything that moves. How about


a ghost that appears and disappears, a see-saw


rising and falling or Troubleshootin' Pete


getting in'n'out of his comfy chair!





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NAME DROPPING


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Our name in lights at last! Pretty flash, eh? These two piccies


show you exactly what you'll get by typing in the listing below.


When you're designing your own screens always think in terms


of two different screens. Draw the first one on squared paper -


graph paper's a good idea - showing all the colours. Remember


these are Paper colours.


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\H10\H01\H11\H01


\H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07


\H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07


\H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07


\H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H02 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H07


\H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07


\H11\H07 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07


\H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07


\H10\H01\H11\H01


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Next, design the screen for stage two, this time on squared


tracing paper, making sure the squares match up with those on


screen one. Then indicate each colour with its initial or code


number - these are all Ink colours. Now, lay the tracing paper


over the graph paper and you should see just what Paper and Ink


you need at every character position when FLASH is set to 1.


There are two ways you can now build up your piccy on screen.


Either POKE the Attribute File with the appropriate numbers or


you can PRINT spaces (CHR$ 32) in the right Paper and Ink


colours.


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\H10\H01\H11\H01


\H11\H07


\H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H02 \H11\H07 \H11\H02 \H11\H02 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02


\H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02


\H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02


\H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02


\H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H02 \H11\H07 \H11\H02 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02 \H11\H02 \H11\H07 \H11\H02 \H11\H07 \H11\H02


\H11\H07


\H10\H01\H11\H01


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This demo program POKEs all the data into the Attribute area of


memory. Every time you enter 191, for example, you're supplying


info about one character square that has FLASH set to 1, PAPER


white and INK white (128+56+7). As the Paper and Ink colours are


the same there'll be no movement or colour change to these areas


of the screen.


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10 REM DEMONSTRATION LOADING


SCREEN


20 REM RUN THIS PROGRAM THEN


SAVE THE RESULTING


SCREEN BY:


SAVE "ys"CODE 22528,768


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Lines 10-20 REMark statements for your info.


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100 DATA 9,191,191,191,191,191,


151,191,191,191,191,191,151


110 DATA 191,191,151,151,191,19


1,151,191,191,151,191,151,151


120 DATA 151,191,191,191,191,19


1,191,186,186,186,191,186,186


130 DATA 151,191,186,186,151,19


1,186,146,191,186,146,186,151


140 DATA 186,186,151,191,146,19


1,186,151,186,191,191,191,186


150 DATA 186,191,191,191,186,19


1,186,151,186,151,191,186,191


160 DATA 151,191,191,146,191,15


1,186,191,146,191,146,191,186


170 DATA 151,186,186,191,186,18


6,191,186,191,191,186,186,191


180 DATA 191,146,186,191,186,19


1,151,191,191,146,191,151,186


190 DATA 186,151,191,146,151,14


6,191,186,191,186,191,186,191


200 DATA 191,186,191,186,191,19


1,191,146,191,191,186,191,151


210 DATA 191,191,146,191,151,18


6,191,146,191,146,191,186,151


220 DATA 186,191,191,191,186,18


6,186,186,191,186,191,191,191


230 DATA 146,186,191,191,186,14


6,191,191,146,191,151,186,191


240 DATA 146,191,146,186,186,15


1,186,191,191,191,186,191,191


250 DATA 191,191,191,191,191,19


1,151,191,191,191,191,191,151


260 DATA 151,191,191,191,151,15


1,191,191,151,191,191,151,191


270 DATA 191,191,191,191,9


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Lines 100-270 The data statements with all the info to be


POKEd into the Attribute area.


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1000 CLS : RESTORE


1010 READ a


1020 FOR i=22528 TO 22687: POKE


i,a: NEXT i


1030 FOR i=22688 TO 22911: READ


a: POKE i,a: NEXT i


1040 READ a: FOR i=22912 TO 2329


5: POKE i,a: NEXT i


1050 STOP


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Lines 1000-1050 This part of the program POKEs the data into


the Attribute area.


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9999 PAUSE 300: INK 7: CLS : LIS


T


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Line 9999 This line halts the program for a few seconds,


then lists it.


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NAILING THE FILES


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So, how's it done? First off, let's have a look


at the two areas of the Spectrum's memory that


cover screen pictures, the Display and Attribute


files. The first covers shapes, such as lines,


circles and so on, whilst the second's concerned


with the quality of those shapes, their colour,


brightness and whether or not they're flashing.


If you're into the technical details, the


Display File starts at address 16384 and ends at


22527, that's 6143 bytes; and the Attribute File


runs from 22528 to 23295, or 768 bytes.


Now, the reason that the Display File's so


much longer is because a shape can be drawn to


pixel definition but when you assign attributes


you can only do it for blocks of eight by eight


pixels. Say you were to design a picture that


didn't use shapes, only squares of colour. Then


you wouldn't need to save the Display File or


any of its 6143 bytes at all.


The Attribute File holds its info in a pretty


straightforward way, as it follows the normal


PRINT AT position of the screen. So, the file's


address (22528) is equivalent to the first PRINT


position on screen (Line 0, Column 0), the


second address (22529) to the next PRINT posi-


tion (Line 0, Column 1) and so on. You can POKE


into the Attribute File with the Ink colour


number plus eight times the Paper colour number.


Then add 128 to this number if you want the


square to flash or for a bright square add 64.


To give it a go, try:


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POKE 22592,186: REM (7*8)+2+128


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That'll give exactly the same results as:


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PRINT PAPER 7; INK 2; FLASH 1;


AT 2,0; CHR$ 32


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In both cases you'll get a red and white flash-


ing square to the left of the screen three lines


down.


Of course, you can also use the ATTR function


to discover the Attributes at any character


position. You'll see that PRINT ATTR(2,0) gives


the same result as PRINT PEEK 22592. You can


save the screens you've created in this way, not


by SCREEN$, but by:


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SAVE "picture" CODE 22528,32*22


: REM 32 columns, 22 lines


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then load it back with:


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LOAD ""CODE 22528


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In just five seconds your title screen will have


loaded.





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ON THE MOVE


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From here, you can start adding animation. It's


a doddle to do and the devil to describe. It all


hangs on the way FLASH operates. When FLASH is


on, each of the character squares alternates


between the Paper colour and the Ink colour of


that square. So, if you design using, say, red


Paper with yellow Ink and keep the surrounding


area set to yellow Paper with yellow Ink, then


your picture alternately appears and disappears.


That's because the effects of the FLASH become


invisible as soon as you have the same Ink and


Paper colours.


It's not far from making a design appear and


disappear to changing from one design to


another. And that's the basis of all animation.


Walt Disney eat your heart out!





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MOVING PICTURE PAINTER


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Here's the easy way to create your animated loading screens - an


on-screen editor that lets you create two independent attribute


pictures before mixing them together.


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10 REM TWIN SCREEN PAINTPAD


20 CLS : PRINT "Build your fir


st Screen by using the CURS


OR KEYS (5 to 8). You can change


COLOUR at any time by pressi


ng C and entering a colour numbe


r (0 to 7). Press F when F


INISHED."


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Lines 10-20 Here are the (brief) instructions - practice'll


show you just what you can and can't create.


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30 RESTORE : FOR i=USR "a" TO


USR "a"+7: READ x: POKE i,x: NEX


T i


40 DATA 170,85,170,85,170,85,1


70,85


50 PRINT '"Press a letter to s


tart"


60 PAUSE 0


70 FOR j=1 TO 2


80 PAPER 7: INK 0: CLS


90 FOR k=0 TO 20 STEP 2: FOR l


=0 TO 31 STEP 2: PRINT AT k,l; I


NK 0;CHR$ 143;CHR$ 144;AT k+1,l;


CHR$ 144;CHR$ 143: NEXT l: NEXT


k


100 LET x=0: LET y=0: LET o=0:


LET p=0


110 PRINT #1;"CURSOR COLOUR =";


p


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Lines 30-110 Set up the initial routines. Lines 30 and 40,


for example, set up a UDG character for the


checkerboard screen pattern that'll help when


you're working from squared paper.


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120 PRINT FLASH 1; OVER o; INK


p;AT y,x;CHR$ 143


130 LET i$=INKEY$: IF i$="" THE


N GO TO 130


140 IF CODE i$<53 OR CODE i$>56


AND i$<>"c" AND i$<>"f" THEN G


O TO 130


150 IF i$="c" THEN INPUT "Colo


ur ? ";p$: IF CODE p$<48 OR CODE


p$>56 OR LEN p$>1 THEN GO TO 1


50


160 IF i$="c" THEN LET p=VAL p


$: PRINT #1;"CURSOR COLOUR = ";p


170 IF i$="5" THEN PRINT AT y,


x; OVER o; INK p;CHR$ 143: LET x


=x-1: IF x<=-1 THEN LET x=31: L


ET y=y+(1 AND y<21)-(y AND y>=21


)


180 IF i$="f" THEN PRINT AT y,


x; FLASH 0; INK p;CHR$ 143: GO T


O 240


190 IF i$="8" THEN PRINT AT y,


x; OVER o; INK p;CHR$ 143: LET x


=x+1: IF x>=32 THEN LET x=0: LE


T y=y+(1 AND y<21)-(y AND y>=21)


200 IF i$="6" THEN PRINT AT y,


x; OVER o; INK p;CHR$ 143: LET y


=y+1 AND y<21


210 IF i$="7" THEN PRINT AT y,


x; OVER o; INK 0+(p AND o=0)+((A


TTR (y,x))-56 AND o=1);CHR$ 143:


LET y=y-1 AND y>0


220 PRINT AT y,x; FLASH 1; OVER


o; INK p;CHR$ 143


230 PAUSE 20: GO TO 130


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Lines 120-230 This is the main loop of the program.


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240 IF j=2 THEN GO TO 310


250 INPUT "": PRINT #1;"PLEASE


WAIT A MOMENT"


260 DIM a(704): FOR i=22528 TO


22528+703: LET x=PEEK i: LET x=(


x-56)*8: LET a(i-22527)=x


270 NEXT i


280 CLS : PRINT AT 10,1;"PRESS


ANY LETTER TO BUILD YOUR


SECOND SCREEN"


290 PAUSE 0


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Lines 240-290 This part of the program stores the first


screen ready for you to start on the second.


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300 NEXT j


310 FOR i=1 TO 704: LET x=PEEK


(i+22527): LET x=x-56: LET x=x+a


(i): LET x=x+128: POKE (i+22527)


,x: NEXT i


320 INPUT "": PRINT #1;"Press S


to SAVE your picture"


330 IF INKEY$<>"" THEN GO TO 3


30


340 LET i$=INKEY$: IF i$="" THE


N GO TO 340


350 IF i$<>"s" THEN STOP


360 INPUT "ENTER PICTURE TITLE"


;p$


370 SAVE p$CODE 22528,704


380 STOP


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Lines 300-380 The final part of the program mixes the two


screens and then saves your creation to tape.


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from Your Spectrum #16 (Jul.1985)


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