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Archive Magazine 1996
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spriteplot
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SPRITEBITS
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Text File
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1989-03-16
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5KB
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151 lines
06601010101800
1
2 #
F0110030
9[........................................................]001
üANIMATED SPRITESÇ
By Ian Smith
There have been many articles relating to the use of Sprites on the
Archimedes. These have covered the use of PLOT &ED,X,Y to display a
Sprite in its defined colours at point (X,Y) and the use of a Mask to
allow a background to appear through the 'unused' parts of a sprite.
They have also shown the use of Exclusive OR plotting using GCOL 11,0 to
allow the sprite to be moved over any coloured background.
The EOR solution to this last problem, of moving a multi-coloured sprite
over a multicoloured background, works BUT unless a great deal of
thought is given to palette selection the sprite DOES NOT retain its
defined colour during movement.
Many games will require the facility to define a sprite in specified
colours, with a mask, and to move it STILL retaining those colours
rather than those produced by EOR.
A solution is to use the standard Move/Display/Erase in a loop BUT NOT
to use EOR. The following Algorithm does this :
1 Define the sprite 'MySprite' WITH a MASK (using SEDIT on the
Welcome Disk).
2 Determine the size of 'MySprite'.
This may be known BUT a SYS call does it for you.
LOOP
3 Determine the position where 'MySprite' is to be plotted.
4 GRAB a sprite 'Temp' from the screen at this position the
same size as 'MySprite'.
5 PLOT 'MySprite' with the mask.
6 PLOT the grabbed sprite 'Temp' to ERASE 'Mysprite'.
ENDLOOP
The following program demonstrates this :
Ç
10 REM > SpritePlot
20 REM Copyright Ian Smith
30 REM March 1989
40
50 REM An example program to show the use of sprites moving
60 REM across a multi coloured background by grabbing an area
70 REM of screen as a sprite and then using it to overwrite the
80 REM moving sprite.
90
100 MODE 15 : REM Works in others modes
110 T$="Temp" : REM Will be the sprite grabbed from screen
120 M$="MySprite" : REM A masked sprite created with SEDIT
130 *SLOAD !Sprites
140
150 SYS &2E,40,,T$ TO ,,,W,H : REM Find size of sprite to grab
160 : REM W)idth and H)eight
170 PROCDrawBackground : REM Draw a Multicoloured background
180 PROCTitle : REM and put titles on
190
200 REPEAT
210 REM ****** MOVE ******
220 MOUSE X,Y,B
230 SYS &2E,16,,T$,1,X,Y,X+W*2,Y+H*4 : REM Grab sprite from screen
240
250 OSCLI("SCHOOSE " + M$ ) : REM Select original sprite
260
270 REM ****** DISPLAY ******
280 GCOL 8,0 : REM Now plot it with its mask
290 PLOT &ED, X,Y : REM at the mouse position
300 PLOT &ED,900,800 : REM and display it in rectangle
310
320 WAIT:WAIT : REM Synchronise output
330
340 OSCLI("SCHOOSE " + T$) : REM Now plot the grabbed sprite
350
360 REM ****** ERASE ******
370 GCOL 0,0
380 PLOT &ED,X,Y : REM at the same place
390 PLOT &ED,1000,800 : REM and in its rectangle
400 UNTIL B=7 : REM 3 buttons terminates
410 END
420
430 DEF PROCDrawBackground
440 GCOL 3 : RECTANGLE FILL 0,0,300,300 : REM Just a couple of
450 GCOL 4 : RECTANGLE FILL 50,50,50,50 : REM rectangles and
460 GCOL 12: CIRCLE FILL 800,400,200 : REM circle
470 GCOL 5 : CIRCLE FILL 600,300,100
480 OSCLI("SCHOOSE " + M$)
490 PLOT &ED,75,90 : REM and the sprite
500 ENDPROC
510
520 DEF PROCTitle
530 GCOL 1
540 RECTANGLE 900-2,800-4,W*2+4,H*4+8 : REM Draw rectangles
550 RECTANGLE 1000-2,800-4,W*2+4,H*4+8 : REM in which sprires
560 PRINT TAB(53,2);"S P R I T E S" : REM are displayed
570 PRINT TAB(52,3);"original grabbed"
580 PRINT TAB(0,1);"SPRITE DEMONSTRATION : use mouse to move sprite"
590 ENDPROC
ÇComments on the program :
PROCDrawBackgound sets up a background to move over.
PROCTitle Simply puts Text and a couple of rectangles on the screen
150 Uses a SYS call to find the Width and Height of 'MySprite'
This is needed so that the right size 'Temp' can be grabbed.
(See Programmers Reference Manual pp 429,433)
230 Grabs the sprite from the screen using a SYS call.
Note the *2 and *4 to compensate for screen MODE 15
You'll need to change this for other resolution modes.
250 Selects 'MySprite'
280 Selects the Mask Plot option GCOL 8.
290 Plots the sprite at the Mouse selected point
300 Plots the sprite in a rectangle to show its original colours.
340 Selects 'Temp'
380 Plots 'Temp' effectively erasing 'MySprite'
390 Plots 'Temp' in its rectangle.
The effect of 390 has an interesting side-effect.
When you run the program move the sprite over the rectangle ! See what
happens !
The program 'SpritePlot' and Sprite File '!Sprites' are on this month's
disk BUT you can use the program by keying it in AND ALSO CREATING A
MASKED SPRITE IN MODE 15 USING SEDIT SAVED AS !SPRITES.
The program can obviously be modified to run in other Modes.
The flicker on the Sprite can be removed by modifying the program to
plot ONLY if the mouse has been moved.
