display enable/disable and invert on pcw

Started by arnoldemu, 14:14, 27 August 12

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is there any effect for changing these more than 1 time on a line?
is it possible to create a scroller as we can do with R8/R6 on CPC?

Just wondering how much of this stuff has been tested... 

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I read it uses roller ram so perhaps it is possible. But it rolls vertically, so if you want a vertical scroller you're laughing...


Not sure about invert, but I noticed an effect in some PCW games - Head over Heels comes to mind - that may be the display enable/disable switch.

Unfortunately, if it is, this takes much too long for manipulation within a scan line. It's literally turning the display off and then on again with the display stabilising within the blink of an eye. Picture the old CRT TVs after having warmed up. When you switch them off and immediately on again, the picture is there almost instantly and is shown completely but takes a noticeable amount of time to "grow" into the full sized rectangle of the stable picture.

For vertical scrolling roller ram is fastest - there's a nice effect in the main menu of Starglider PCW. The title picture (looks like the one on the CPC) rotates smoothly and fast around the middle vertical axis a couple of times.

(BTW, off topic, but you may be interested in it, arnoldemu, Starglider PCW uses a simple depth cue algorithm. Objects that are far away are drawn with a dotted instead of a full line, and appear darker to the eye.)

On horizontal scrolling: Much like on the CPC, you probably can implement horizontal pixel scrolling by switching between various screens which are all shifted by 1 or 2 pixel. If what I've been reading is correct, a full 128k can be utilised as video ram. A full picture of a PCW is 22k, so bitwise scrolling is out of the question. But this may not be bad, because by shifting 2 pixels and grouping them horizontally in pairs one can implement shades of grey (as is done in games).
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