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RUSH #01
29 мая 1999 |
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Spectrum programming - Mirroring bytes and restoration of the background buffer.
Hi everyone! Today I would like to
tell you about two things to know about that
will, I think, helpful to those who are engaged
toys.
First: Mirroring bytes
(Of course, what is it for?). The algorithm does not
my, I should say. I found it in
DIZZY-XX demo by VAV / MEGACODE. C address
multiple of 256 (eg # 8000)
is a table (256 bytes)
SLR bytes (for 0 is # 00 for # 01
is # 80, etc). When we need
mirror-bytes, for example, to 1, then do
as follows: ...
LD A, 1
LD E, A
LD D, # 80
LD A, (DE); A = # 80, if the table
formed correctly ...
Second: the restoration of the background from the buffer
(Printing sprites with a mask). During
save the background before each line
images retain the address where she
displayed. The working buffer
increase by (window height * 2), however,
recovery rate of increase for
account that will not have to calculate
the next screen line. Example procedure
Recovery:
LD HL, BUFER
LD A, HIGH; height M1 LD E, (HL)
INC HL
LD D, (HL)
INC HL
LDI
LDI
LDI; width of 3 bytes
DEC A
JR NZ, M1
RET
Speed can count themselves.
That's probably all for today. See
you later! Bye!
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