VDP1 sprites priority

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paul_met

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Hello. I wondered how to make the sprites that VDP1 draws translucent on top of VDP2 layers. I got it on the example of the game Device Reign. But almost all sprites become translucent at once. Although there are exceptions (character panel with a portrait and statistics). It seems that individual sprites are somehow given their own priority. But I don’t know whether to change the order of the sprites in such a way as to make only specific ones translucent.
 

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antime

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Transparency depends on the pixel data in the VDP1 frame buffer, and how VDP2 is configured to interpret it. By setting the CMDCOLR word of the sprite drawing command, you can select different priority and color calculation settings for each sprite. Chapter 9 of the VDP2 manual explains it, but it's not the easiest read.

This thread also discussed sprite modes and color banks.
 

mrkotfw

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Identify the command table that corresponds to the in-game characters. In the word that @antime described, it should tell you whether it's actual color bank code, or a CLUT which could contain color bank codes. From that, find what sprite type the VDP2 is set to. From there you can figure out which bits correspond to what in the color bank code.

You won't see the effect outright. The effect is done, I believe when the VDP2 merges the result frame buffer from the VDP1.
 

vexatious

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Not sure how you're imposing transparent sprites but usually it involves a color table with lookup table. Don't know too much about Saturn compared to Mars but...

Double buffering is also used for a more advanced method. Some programmers might call this "copy to buffer". This way usually solves most problems if you impose it only when necessary and only on required sprites-tiles-layers so as not to lose memory or waste it. This has the benefit of many other special effects possible like: shading, lighting, blending, motion blur, and etc. Don't confuse dual VDPs with double buffering; I think you want double buffering only on VDP1.

By the way what game is that first picture?

Edit: Oh wait nevermind. Didn't know "Device Reign" was a catalog.
 
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