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R0ger

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Posts posted by R0ger

  1. Posted

    Why mode 4 ? Every color counts, and you use tiles for the map anyway.

    You can still move enemies and objects smoothly, with some extra processing. But you have to do the processing in bitmap mode too. You can merge the enemies with background. Again, it's about the same as with bitmap mode. Character mode eats a bit more DMA, and you will most likely need some DLIs (or many), but the extra color is imho worth it.

     

    Btw. international karate is in character mode. With shifting and background merging (background being the other character). Games like these will never be 50/60 fps, but you don't really need that.

    • Like 1

  2. Posted

    I think emkay talks about what's usually called artifacting. In hires mode, especially when used with black and white, every pixel has slight color tint. On PAL it's not so pronounced, and the logic of it complex, but on NTSC, it's simple. It's based on X coordinate. If it's odd, the pixel is shifted toward cyan, and if it is even, it's shifted toward magenta. And it's pretty strong. If you want to have white color, you have to use two pixels side by side.

     

    As for other differences between PAL and NTSC, PAL has 50Hz and NTSC 60. Both have same horizontal resolution and timing, NTSC simply has less lines visible. VBI is triggered on the same line though. This means, that there is MUCH less time from start of VBI to start of next frame. Generally, you have less time in NTSC, as more time is spent generating video per second. And if your game logic is based on framerate, it will run at different speeds on PAL and NTSC.

    Then there is different palette. More or less NTSC colors are shifted one hue step up, just check Altirra's color editor, you will understand.

    Most games are made for NTSC, and they simply run slower, and have wrong colors on PAL. Some games are designed for PAL, and simply don't run on NTSC at all. And few run on both system at the same speed, with the same colors.

    • Thanks 1

  5. Posted

    There is another problem with all that complexity. At least in my case it was like that. You will only fully understand the limitations by trying to do something. It's so complex, that nothing you will read will give you correct and complete idea about how it works. You will try to do something, it won't work, and only then you will realize that's what that one sentence was talking about. So all I can recommend is maybe less reading, more experimenting. You should be able to setup PMG or two with few pokes in basic, and then try to use every mode and every register, you get hang of it soon.

     

    • Like 4

  8. Posted · Edited by R0ger

    I'd say the most typical mode for Atari games is 160x200, 5 colors, character mode for background and enemies, and PMG for player character.

    But it's really not so simple. Most games use some kind of DLIST / DLI trick. Mixing modes is also common.

     

    Btw. if you use Altirra (and you should), CTRL+F8 shows you what is made from PMG, and color changes (typically done by DLI). Mode changes (hires / lowres) are pretty much visible without any tool. It's also possible to change modes during the line (side by side) but that's more useful for intro screen.

     

    Combinations and tricks are bread and butter. For example, look at my game Sails of Doom: https://atariage.com/forums/topic/283993-sails-of-doom-new-multijoy-game/

     

    The intro screen is horizontal split with hires on left, and lowres on right, with PMG underlay to make the ship silhouette really black (which is otherwise problem in hires). There is also kernel routine (routine which controls hardware registers while the image is being drawn, without returning to main thread), which changes colors every line.

     

    The game start menu is in hires character mode, with PMG used for cursor and player colors.

     

    The game itself is 4 color lowres in bitmap mode. But the stats above and bellow are character mode hires. All ships and shells are SW sprites, 4 color flags are made using PMG, and the next 4 flags are SW sprites, using same colors as ships and islands.

     

    I'd say this is bellow average amount of tricks, at least if you look at modern homebrews. It's not newbie friendly, but I know there are some serious tricks being used on C64 these days, I'm sure you'll be fine. Just analyze everything you see, and don't be afraid to ask.

     

    As for docs, the holly grail is Altirra hardware manual, and for basic info I use standard wikipedia for ANTIC and GTIA. But it's a reference, not guide, and certainly not tutorial. I learned most of the things from my friends, so can't really help you here. Experimenting with G2F should get you started, but it has its own quirks.

     

     

     

    • Thanks 1

  9. Posted

    That reminds me when I was making my own mindlink for Amiga. It used operational amplifiers, with +12 and -12 V from the Amiga.

    Since then I know, that when you apply what's basically 24V difference over moist electrodes to your forehead, you will see nice flashes. Without pain or any sensation at all on the skin itself !

     

    • Like 3
    • Haha 5

  15. Posted

    6 hours ago, foft said:

    I think this particular case still needs work?

     

     I tried to download the latest altirra 3.2 to check but had config issues (crash on boot with any os), so not sure.

     

    I think the trace on here is from that, but not 100%. Pokey vs EclaireXL in that case.

     

    http://www.64kib.com/redmine/issues/67

    Interesting. You have to reset Altirra settings sadly. I had the same issue.

  17. Posted

    2 hours ago, Synthpopalooza said:

    What if you use that timer reset trick pavros discovered for $Cx mod 3 bass?

    Pavros syncs timers to polynomial generators. For full control over PWM with filter you need something different. You need to sync 2 channels to each other. Typically you will sync 1 and 3, and use "high-pass" filter on those.

    You can use STIMER, or setting frequency to 0 for some time. That time can be greatly decreased by setting channel 1 and 3 to 1.79MHz source. That can't be done with channels 2 and 4 though.

    After you reset both channels, you set them them to different frequencies for some defined time. During that time the phases of the two channels will gradually shift away from each other. You can control how much by the frequency difference and the time. Then you set them to the same frequencies.

     

  20. Posted

    2 minutes ago, Synthpopalooza said:

    Normal 16-bit filter ($10 in AUDCTL) silences channel 0.  Channel 1 plays the music.  This is usually accompanied by a 1.79 clock ($40 AUDCTL) on 0 to transpose the channels up into a playable range. 

     

    Reverse 16 bit filter is same settings, but instead channel 1 is silenced and 0 is played.  This may or may not require the 1.79 mhz clock depending on distortion usage.  This changes the timbre of the sound.

    $10 in AUDCTL is not really a filter. It just merges channels 1 and 2 into one 16 bit counter. You are right though, it does create special sound.

     

    Whenever the low byte goes to 0, it flips channel 1. And when the whole 16 bit number hits zero, the channel is reset. So basically if you set frequency $140 ($40 in audf0 and $1 in audf1) you will get one pulse of length $40 and another pulse of length $100.

    The low byte controls length of the first pulse, the high byte controls number of $100 long pulses after that. With $A0 distortion it's best used with normal 64k. Not sure how it can be useful in music, but it might add some flavor to the bass. Can't see how RMT could be easily hacked to test it though. I need 16 bit tables for 64kHz, and different AUDC settings, compared to what RMT normally uses.

  22. Posted

    5 hours ago, drpeter said:

    What 'fiddles' do you have set up?

    The most important are:

    view / filter mode / bilinear

    system / configure system / video / scalines

    system / configure system / video / pal artifacting (low is cleaner, high is more realistic, and needed for phase artifact effects)

     

    Then view / adjust screen effects.

    Scanline intensity I set to 0, distortions to 0.

    Bloom is the magic option IMHO. Start with 0 treshold, 0.5 radius, 0.5 direct and 0.5 indirect. Increase treshold to make dark areas darker, mix direct and indirect to achieve desired sharpness.

     

    It's also good idea to adjust colors in view / adjust colors. Like boosting contrast and saturation a bit, or adjusting gamma.

     

     

    • Like 1

  25. Posted

    10 hours ago, Kyle22 said:

    Could we reset the poly counter, then rapidly sample the bytes to use as an encryption key? A variable amount of time between the reset and the sampling would shift he key numbers.

    Am I on to anything, or is it just BS?

     

    What would it be good for ? What you asking is basically pseudo random number generator. Pokey's RNG is hard to predict, that's it's main feature. Predictable RNG can be easily made in software.

    Or as anti-piracy measure ? That could work. But then Altirra can emulate even that, and if it can't at the moment, Phareon will eventually fix it :-D

    And these days you want your games to be able to run on emulators anyway.

     

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