Christmas Diamonds
stars.s
Author: Nesu
Category: Christmas Challenge
System: Amstrad CPC
Language: Assembler, using firmware calls (SDCC assembler, as used in CPCtelera)
Len source code: 1034 bytes (commented code)
Len exe file: 27 bytes + header info
Len code only: 27 bytes
Instructions:
-Normal loading:
Insert the provided dsk file in any emulator and type:
memory&2a06:load"stars",&2a06:cls:call&2a06
-Easy loading:
Previous command is included in a provided basic loader, just type:
run"loader
-Detailed loading:
In order to properly work, the routine must be placed at adress &2a06. However, by default
Basic prevents us from using this address, so first we have to use the memory command:
memory &2a06
Then we can normally load the code into memory:
load "stars",&2a06
The program does not clear the screen before drawing, so before calling the program it is
recommended to scroll down until the "Ready" message disappears from screen. Then the
program can be called with:
call &2a06
Description:
Stars in paralel lines of stars (lines going up or lines going down) are at a constant
horizontal distance distance of 6 units one from another. So the program simply decrements
by 6 the X coordinate to get the next star position. When the end of the line is reached,
the horizontal value is fixed and line is decremented, exiting the program if there are no
more lines remaining. In each star position a star is placed and a vertically mirrored star
is also placed. Then the process repeats.
Comments:
In order to save bytes the program draws each star 128 times, so it takes about 50 seconds
to complete the drawing.
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