Re: [stella] Gas gauge - revisited

Subject: Re: [stella] Gas gauge - revisited
From: Manuel Polik <manuel.polik@xxxxxxxxxxx>
Date: Tue, 13 Mar 2001 11:30:17 +0100
Joe Grand wrote:

> I am trying to make the gauge two-color (e.g. red underneath and green for
> the actual "time remaining"). With playfield graphics only, I was thinking
> of just drawing the red data on one frame and the green data on the next
> frame and alternate that way - I wouldn't assume the eye would see a
> flicker. 

You'd definitely see it flicker, since you can see the colors only on
50% of the viewing time. It doesn't help that they're not overlayed.

> I started to try this on the airplane last night but my battery
> died before I could finish. Is this worth pursuing, or would there be an
> easier way?

The easiest way would be faking it with the background color, like Chris

Let's say, you'd do a defined background color change during a scannline
like this:

<-- Green --><--------- normal BG color ------------>
          Cycle X

Now, you'd always change the background color at the beginning of a
scannline and again on cycle X. Now you can easily draw a growing red PF
bar within the green bar.

> The gauge doesn't have to have very high-resolution, but it would be nice
> if it was a little higher than standard playfield graphics. I'm using both
> P0 and P1 to draw the "SCSISIDE" logo on the same lines that I hope to have
> the gauge. Maybe I could use playfield graphics for the red and draw the
> green data "on top" using missle?

The above way will work with your logo too and don't interfere with it.
Adding a missile for a higher resolution would be possible too, I think.
This adds two more color changes though, so you'd have to produce very
tight code here. But I'd say it could work.

> Although not currently very exciting, I will post source of my playfield
> graphics (which is just a modified version of J.V. "Matt" Matthews demo of
> asymmetric playfield drawing from October 1996) if people are interested (I
> can't do it now since it is on my laptop which isn't with me)

Go ahead & post it.


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