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Posted By

Mad
on 2016-10-12
14:46:16
 Re: Back in the day...

Just my two cent, since I plan to convert my current plus/4 experiment to the c64, too. The C64 and the plus/4 do have almost the same graphic modes.

There is one difference: If you have multicolor bitmap mode, then the plus/4 supports 2 free colors per 4x8 block and 2 solid ones for the entire image. On the C64 you have in this mode 3 free colors per 4x8 block and 1 solid color (backgroundcolor) for the entire image.

If you port from the C64 to the plus/4 it's also pretty easy to convert the colors, since the plus/4 has some (of the 121) colors which are somehow close to the 16 ones of the C64.

However what's really bad about the C64 is, that you can't have real doublebuffering, because the colormatrix is always at the same location (the screenmatrix can be changed, though). On plus/4 you can change screenmatrix and colormatrix to reside in every location you want (of the 64kb).

I don't know anything about sprite handling back in the days, however it is pretty hard to code a fast routine which uses low memory (both at once). You can do very fast sprites if you stick to just one color for the sprite. And you can even do very fast sprites if you consume a lot of memory, however memory is a resource you should handle wisely, so perhaps do some (a little) slower sprites.

If it comes to sprite colors, the plus4 is sadly a little of. You could do sprites with their own colors, but you must somehow handle color clashing then or choose the location of the sprites in the level wisely (e.g. no background graphics). The easiest approach is to reserve some colors for the sprites (for instance 2 in bitmap mode, which would be the same for the entire image), you could use these 2 colors also for the background, but you will have to somehow make sure the sprite is not vanishing because of indistinguable colors (between the sprite and the background). So my assumption would be, that plus/4 games always would have less colourful sprites than their c64 pendandts, or you just have no background graphics behind them.

I didn't mention, that the c64 can use the same code like the plus/4, because it's the same "processor family". However the plus/4 should be a little faster. But as Krill pointed out, in reality it seems a little slower because of more graphics updates per frame. You can make the plus/4 really faster, by disabling graphics output after some screen line, though.

I think porting games without sprites to the plus/4 is not that big of a deal. If it gets to sprites, then it somehow gets complicated. Soundtechnically I just have no clue, but there are sid converters as far as I know and it seems, that most of the people own a SIDCard, too. If you use a SIDCard than the porting is done by just changing some adresses in the code, as far as I know!

Hope this helps a little, and perhaps some other people also do have some (perhaps opposing) points..


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