Re: Sinclair jump started programming in Europe
LDIR (repeating block load with increment) was the most inefficient way to clear the Spectrum screen space when it comes to T states. The code is one of the shortest in terms of memory bytes used though. Disassembling Ultimate Play the Game titles from Ashby Computers and Graphics ltd, I came across a much lengthier piece of code using simpler instructions (a RISC approach) that cleared the screen far, far, faster than using LDIR. Not surprisingly this technique was used in their isometric games and I recall they even wrote their game screen to part of the speccys high memory area and used an interrupt to dump the content to the speccy screen memory space. Another aspect of the code was that it wrote to the speccy screen from bottom right to top left which I assume was to avoid a clash with the PAL screen refresh and thus avoiding major flickering on the display. The bible of the day was Programming the Z80 by Rodney Zaks http://www.z80.info/zip/zaks_book.pdf
Biting the hand that feeds IT
