Animation on SPECTRUM - Sprites and masks...

SPRIES AND MASKS        
                                
   So, let's say y us yes   
background (Fig. 1), and sprite (Fig. 2). B
as an example we took them from
BATMAN program, which is
is a brilliant example of three-dimensional
no animation, bypassed
almost all are eight-bit
computers - ENTERPRISE, COMMO-
DORE 64, ATARI, SCHNEIDER, SPEC-
TRUM 48/128 and others.               
                                
        
             
             
        
             
             
             
             
             
                                
    If we just forward
sprite on the screen, we get this
such a picture (Fig. 3). Main
part of the forwarding program
the sprite on the screen may look like
something like this:                   
LD A,(DE) ;in DE - address in     
             memory             
LD (HL),A; in HL - address on    
             screen             
    To prevent the sprite window from closing
Ralo background, you can only turn on
those bits that match c
background bits, then we get
such a picture (Fig. 4). That is,
now the background shows through
sprite. Forwarding program every
How many bytes of sprite may look like
do it like this:                       
LD A,(DE)                      
AND (HL)                        
LD(HL),A                      
                                
      
         
         
         
         
         
         
         
         
                                
    Thus, we need
maybe not everything will shine through
sprite window, but not the place
occupied by a BATMAN figurine.  Here
This is where a mask comes in handy
(Fig. 5), repeating the contour of the volume
project that should not npocbe-
chivat. First through logical
“And” (AND) is applied to the background
mask, then apply the same
in the same place sprite and in
As a result, we get the following picture:
nku (Fig. 6)                     
    Of course it's not the only one
a way to overlay a sprite on a background,
there can be a lot of options -
go, with this example we only want to
decided to demonstrate his own
principle                           
                                
      B next chapter we      
let's look at ways to move
sprite vertically pixel by pixel
 and horizontally.       
                                
      to be continued.      
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