Vintage Computing Christmas Challenge 2025 Entry
Author: Matt Shepcar
Category: Christmas Challenge
System: BBC Micro
Language: 6502 Assembler
Len source code: 520
Len exe file: 56
Len code only: 56
Instructions:
Drop the SSD file into https://bbc.xania.org/ and press shift+f12 to boot.
B-em is another good emulator. https://b-em.bbcmicro.com/
Description:
This works by taking the negative absolute value of coordinates X-10 and Y-10 and looking up what to draw in a bitmap with special cases for the middle row/column.
Comments:
Entry can also be viewed using this link
https://bbcmic.ro/#%7B%22v%22%3A1%2C%22program%22%3A%22REM%20VCCC2025%20entry%20by%20Matt%20Shepcar%5Cnstart%3D%2659%3Aoswrch%3D%26FFEE%3Acursorx%3D%26318%5CnFORO%3D0TO3STEP3%3AP%25%3Dstart%3A%5BOPTO%5CnEQUD%2672305102%3A.nine%3AEQUD%2649920409%3A.bitmap%5Cn.nextch%3AJSRabs%3ABEQstar%3ATAY%5Cn.entrypoint%3A.ldarow%3ALDA%2319%3AJSRabs%5CnCPY%23256-9%20%5C%5Cclear%20carry%20if%20past%20end%20of%20line%5Cn.nextrow%3ATAX%3ABEQstar%5CnLDAbitmap%2CX%3A.lsr%3ALSRA%3AINY%3ABNElsr%5Cn.star%3ALDA%23ASC%5C%22*%5C%22%3ABCSwrch%3A.space%3ALDA%23ASC%5C%22%20%5C%22%5Cn.wrch%3AJSRoswrch%3ALDAcursorx%3ABNEnextch%5CnDECldarow%2B1%3AEQUB%26D0%3A%5C%5CBNEnextrow%5Cn.abs%3ASBCnine%3ABMIneg%3A%5C%5CEOR%26430%2CX%5CnEOR%23255%3AADC%230%3A.neg%3ARTS%5Cn%5DNEXT%3ACALLentrypoint%5CnPRINT'%3BP%25-start%3B%5C%22%20bytes%20of%206502%5C%22%22%7D
