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Genesis limitations for arcade ports

racketboy - Oct 23, 2003

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		it290		Oct 27, 2003
			Yup. I wish I could find my Digi-Paint 3 manual, because it has a concise technical description of HAM mode. It's completely useless for games and the like because you can't just throw 4096 colors on the screen- if you want to go from one color to a very dissimilar one, it takes like three or four pixels to get there (depending on the difference in RGB values). So you couldn't move a sprite across the screen in HAM mode without getting some funky looking color bars. If you use Digi-Paint 3 or Deluxe Paint in HAM mode, you can see this when using the menus.

		it290		Oct 27, 2003
			RadSil, no, they don't have to be completely different colors because you don't have to change the entire palette. So for example you could keep the palette for your sprites the same (and normally would), but you could create a vertical gradient in the background displaying more colors than normally possible using this technique. I think each time you do this takes a little CPU time, so the Sega CD probably handles it by using one processor to do this technique while using the other for the main game logic. But you couldn't have 256 different colors on the same horizontal line, for example.

ExCyber

Oct 27, 2003

	
	
		
		
			When you're running in 40 cell mode the VDP has a higher clock so it can render more sprites.

i.e. read more VRAM, which is what I was getting at; I imagine it's loading up timed shift registers (edit: probably closer to a FIFO array than a simple bank of shift registers, but the principle is the same) rather than, say, drawing into a linebuffer (though the latter is certainly possible).

		M3d10n		Oct 28, 2003
			Another trick to get more colors in the genny is to use the shadow/hilite effects. You can get up to 190 or so colors in that way, to a certain extent, since you can have the base palette, and the same colors at twice and half the luminance. Some games are said to use it to get extra colors, Ecco II being one of them. But you need to be pretty clever when designing the palettes and placing the shadow and hilite masks to get all 190+ colors.

		Mask of Destiny		Oct 28, 2003
			The biggest problem with shadow hilight mode is that the priority bit effects whether or not a tile is shown in shadow or hilight also sets the priority of the tile and most games need things set to a certain priority in order for things to draw in the right order. This makes it difficult (though not impossible) to use for much other than stills or very simple games. It should also be noted that shadow/hilight doesn't halve/double the intensity of the color. Pure black (RGB 0, 0, 0) becomes a light grey in hilight which suggests an addition since 0 times anything is still 0.

		fonzievoltonov		Aug 21, 2004
			Old topic but I noticed something important for the genny dev'er (with the S/H use). ---------------------> On gens, when you put a area with highlight (using sprite), the other sprites under are highlighted. On real hardware, the sprites under aren't drawed. I investigated and this is due to the fallowing thing: To increase the drawing speed for sprites, the VDP draws sprites from the upper one (foreground>1st in list) to the under one (background>Last in list). That means that the VDP "ONLY" draws if the under-color is transparent (0coded). But hightlight/shadow uses the color code 14 and 15, so the VDP dont draw under shadow/highlight pixels from sprites . Be carefull with this .... PS: This problem isn't present with planes (since the sprites are drawed separately). ------------------------- BTW: I took a look at Eternal Champion and the maximum color i was able to count (using a screen shot) are 50-70 (not 256) :lol: . A game that might use more color is Samurai Showdown (i noticed raster dots on real hardware > Raster effect with colors). Bye and hope it will help.

		it290		Aug 21, 2004
			I believe Ranger-X is supposed to use some tricks to achieve more colors as well; you might want to check that one out. That game is an astounding programming feat - and really fun!

		fonzievoltonov		Aug 22, 2004
			Yeah, rangerx is pretty cool . I made a demo to get 3*512-2 colors using all the availables techniques: -Raster effect -Shadow -Highlight But seems there is a bug because i only get 1467 colors ^^ :huh. PS: Seems that this post is more a dev post ^^.

		antime		Aug 22, 2004
			The colour ranges are probably overlapping when using shadow/highlight. (Is the exact method used to modify the colours known? AFAIK all emulators use a "close enough" way.)

		Kaneda		Aug 23, 2004
			charles McDonald already made a demo like this...

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