AllocBitMap vs AllocBitMapTags

	Bottom Previous Topic Next Topic
Register To Post

« 1 (2)

Hypex

Re: AllocBitMap vs AllocBitMapTags

Posted on: 2023/2/28 4:37 #21

Not too shy to talk

@FlynnTheAvatar

Quote:

No, the values are correct. BMA_ISRTG, BMA_BYTESPERPIXEL, BMA_BITSPERPIXEL, and BMA_PIXELFORMAT are only on AmigaOS 4.1, and are only filled when you have a RTG bitmap.

Still, I would have expected them to be filled, if they are called from OS4. Zero bits per pixel is impossible with any bitmap format, so if it understand the tags, then returning a null value is simply wrong. They shouldn't rely on BMA_ISRTG being true since they apply to bitplanes as well.

Hypex

Re: AllocBitMap vs AllocBitMapTags

Posted on: 2023/2/28 4:56 #22

Not too shy to talk

@joerg

Quote:

Maybe it's surprising but 8 bit RGB modes really did exist in the 80s/90s, IIRC the Amiga Zorro III Merlin GFX card did support an R2G3B2 mode while all other (Amiga) gfx cards from that time were limited to CLUT (all supported 8 bit chunky modes, some additionally 8 bit planar modes) and YUV for <= 8 bits.

That is surprising! Interesting but limited. Easier to manage than HAM though HAM6 could offer more colour resolution in places. It would be a max 128 colour high colour mode. With red and blue in 2 bits and green in 3 I imagine it would look harsh. Another combination would be R3G2B3 to max out the 8 bits by reducing green instead.

There is also YUV-planar common. But I think it can be described as more of a hybrid mode with colour channel or YUV on a plane. The RGB-planar on AAA, had it came out, would be similar with RGB on a plane.

VGA is almost similar since it's based on an RGB colour model like CGA and EGA but instead can be organised as pixel planar where columns of pixels have their own plane.
Quote:

But there never ever was any 1 bit RBG gfx card

Not for RGB but it can be for CLUT. So 1 bit chunky or 1 bit packed.

Though it could work for RGB, 0 would be black (00,00,00) and 1 would be all white (FF,FF,FF), with no palette needed.

Quote:

The RGB8 formats are irrelevant nowadays, only still required for MSX and Sega emulators maybe.

And rare.

Quote:

Except for such rare exceptions and YUV, no matter if it's planar or chunky, with <= 8 bits/pixel it's always a palette based mode with CLUT.

Makes sense.

Register To Post	« 1 (2)
	Top Previous Topic Next Topic

Currently Active Users Viewing This Thread: 1 ( 0 members and 1 Anonymous Users )