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Atari coding BBS
Re: Overscan+rasters
Posted by: ggn May,03.2017-08:20 

(Just to get the ball rolling until the people that wrote these formats step forward and explain better)

First of all, when you say "rasters" do you mean a single palette change per scanline or multiple (like MPP or PCS does)?

The first is really simple: you get 16 unique colours per line, so you can plan your image to work with this.

The second is a more complex subject: yes you do get more than 16 colours per scanline but there is a big limitation: you cannot have a stable amount of colours throughout the line.

To get technical for a moment, it has to do with the CPU being unable to reload all palette colours instantly. Which means that you might get palette index 3 (for example) quite early at the left side of the line, reusing it with another colour will take a fixed amount of time (which depends on the format you use).

So what this boils down to is: you can use a single colour inside a fixed window. So for index 1 this will be (again, this is an example - actual figures will vary depending on the format you use) pixels 16 to 80, index 2 pixels 32 to 96, index 3 pixels 64 to 112. So think of it as a sliding window.

Of course you probably don't have much control over this since you will probably use a converter to this format that does all the colour scheduling automatically for you. But I think that if you follow the above rule of thumb you can make its life much easier.

Finally if you want to see this in action try painting a bit with spectrum 512 and watch it as it reschedules palettes and stuff in real time as you lay down many cols per line - plus it's not a bad drawing program really :D.

Hope this helps, any multi palette format author is free to chip in this thread and completely shoot the above down if I'm wrong :).

[All messages in this thread]

Topic Posted by  Date 
Overscan+rasters mic/dune May,02.2017-12:38
  Re: Overscan+rasters leonard May,02.2017-14:29
    Re: Overscan+rasters mic/dune May,02.2017-23:39
      Re: Overscan+rasters ggn May,03.2017-08:20
        Re: Overscan+rasters dml May,03.2017-12:22
          Re: Overscan+rasters Troed May,26.2017-07:48
      Re: Overscan+rasters mic/dune May,03.2017-18:25
        Re: Overscan+rasters leonard May,03.2017-22:49
          Re: Overscan+rasters mic/dune May,04.2017-07:44
          Re: Overscan+rasters evil May,05.2017-20:26
            Re: Overscan+rasters mic/dune May,05.2017-22:54

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