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Flipper

320C/320D may actually have uses?

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On 6/15/2019 at 11:48 AM, Synthpopalooza said:

So ... does anyone have specs on 320D regarding palette layout, which colors are in which columns, etc.?  It will help me know what I have to work with.

 

EricBall broke down the modes, including 320D, in this post.

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On 6/16/2019 at 6:40 PM, RevEng said:

 

EricBall broke down the modes, including 320D, in this post.

Thanks.

 

Based on the information shown, we're looking at a fully functional 7 color, 4 colors per char mode, no placement limitations, 320A DMA, but 2x the memory needed for fonts, using my flipping technique.  I will work up something this week.

 

I think this one is more promising than 320C.  It would work well for actual games, just needs to be seen if the flicker is going to be manageable.

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So, just to clarify:

320D means that even columns get the 3 colors from palette 0 plus background, and odd columns get the 3 colors from palette 4 plus background.  Is that correct?

 

I am also seeing the same in 320C but from across differing palettes.  Is that correct as well?

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5 hours ago, Synthpopalooza said:

So, just to clarify:

320D means that even columns get the 3 colors from palette 0 plus background, and odd columns get the 3 colors from palette 4 plus background.  Is that correct?

 

No.  Whether the 320D sprite uses palette 0 or 4 depends upon P2.  P1 & P0 selects which colors are used for the graphics bit combinations.  You get 3 colors + background & transparent from 2 palettes

 

5 hours ago, Synthpopalooza said:

I am also seeing the same in 320C but from across differing palettes.  Is that correct as well?

 

320C uses C2 from palettes 0-3 or 4-7 depending upon P2.  So you get 4 colors + background & transparent from 2 "palettes".

 

Note: this is better shown in the spreadsheet as it breaks down the exact pixel colors for each graphics & palette bit combination. 

 

Don't forget that all 320 modes are subject to color aliasing for adjacent pixels with different Y values.

 

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So ... with my interlacing technique, we can get a full 4 colors per character, and two palettes in 320D. Here's how

 

Set P0=1 ... this makes BG and C2 in column 1, C1 and C3 in column 2.

Set c1 to the same color as BG.  C2 and C3 will be unique colors.

 

Swap out between 2 character sets each frame, and also exchange color values for C2 and C3.  This will make the same colors appear in alternate columns each frame.

 

The result is 4 colors per character cell 8x8 pixels:  BG, C2+BG, C3+BG ,C2+C3.  The interlacing effect will happen over vertical 320 pixel width lines and should not be distracting.  This should produce a color mode equivalent to 320B but with the DMA overhead of 320A 

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320C is less potentially useful.  Using my technique you can get a 10 + BG color mode per character at 80 pixel resolution.  Add in another 10 colors for the second palette.  Add in another 4 colors when you factor in blending the component colors with the BG but there are limitations on where they can be used.  Each pixel pair is restricted to a 4 colors palette.  And with the DMA overhead I am not sure how useful it would be.

 

 

 

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