Impact of planes size

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KanedaFr
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Impact of planes size

Post by KanedaFr » Wed Jun 17, 2015 8:39 pm

Hi,

I'm currently rewriting my map scroll engine.
One of the alternatives is to use large planes to 3x3 viewport idea

If I use it, i'll need to use large plane size (64x64 or 128x128)

So here comes my question :
is there any direct impact on
- memory (tiles available on VRAM?)
- performance (slower to scroll ?)
?

apart the problem linked to DMA, I don't remember reading any line about diff between 32x32 and 128x128 plane size...
Did I miss a post ? ;)

Mask of Destiny
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Post by Mask of Destiny » Wed Jun 17, 2015 11:26 pm

Plane size impacts the amount of RAM needed for the name table. You need 2 bytes per cell so a 32x32 plane takes 2KB, 64x32 takes 4KB and so on. Due to a limitation in the way the VDP handles addresses the name table is limited to a max of 8KB in size so you can't have a 128x128 table. 128x64 or 64x128 is as big as you can go.

Scrolling performance is the same for all sizes apart from the amount of time needed to fill the name table in the first place.

ob1
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Post by ob1 » Thu Jun 18, 2015 11:28 am

Mask of Destiny wrote:Due to a limitation in the way the VDP handles addresses the name table is limited to a max of 8KB in size so you can't have a 128x128 table. 128x64 or 64x128 is as big as you can go.
I think it would be 128 x 32, 64 x 64, or 32 x 128.

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Post by Mask of Destiny » Fri Jun 19, 2015 1:28 am

Ah, you're correct there. I thought 128x128 was the only invalid size, but 8KB appears to be the number I'm using in BlastEm and indeed 128x64 would be 16KB. Apologies for the error.

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Post by KanedaFr » Fri Jun 19, 2015 7:58 pm

thanks, exactly what I was looking for ;)

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