a8r8g8b8 mode non available on my video card

a8r8g8b8 mode non available on my video card

Post by <mcdougalljonat.. » Fri, 15 Nov 2002 12:36:24



Hi, I am trying to use transparency with textures and I just read that I
need to use alpha blending, which is (if I understand correctly) not a
possibility on my computer, since it accepts only r5g6b5 mode.  I was using
color keying with ddraw and it worked well, is there a way with d3d8 to go
around alpha blending?

Thank you,

Jonathan Mcdougall
Montreal, Quebec

 
 
 

a8r8g8b8 mode non available on my video card

Post by Rich [Microsoft Direct3D MV » Fri, 15 Nov 2002 13:18:10


[Please do not mail me a copy of your followup]



Quote:>Hi, I am trying to use transparency with textures and I just read that I
>need to use alpha blending, which is (if I understand correctly) not a
>possibility on my computer, since it accepts only r5g6b5 mode.

What does caps viewer show for supported buffer formats?
What kind of card do you have?

You don't need alpha in the display mode in order to do alpha
blending.  You only need alpha in the render target if you intend to
use destination alpha as part of your blending.  Caps viewer will also
show you supported blending factors for source and destination blends.

Unless your card is really old, it supports basic alpha blending.
Everything supports ONE:ZERO blends, because this is equivalent to
just writing the source pixels into the frame buffer and performing
no blending.  (ONE:ZERO refers to the src:dest blend factors.)

Even old cards support ONE:ONE or {ONE,SRCALPHA}:INVSRCALPHA blends
which lets you do basic "a over b" compositing.  Newer cards support
all the blend modes, typically.
--
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  Direct3D Book <http://www.xmission.com/~legalize/book/>
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1. --- PETITION for a MODERN BASIC VIDEO MODE on PC VIDEO CARDS ---

     How nice is graphics programming on PC video cards ! a lot of modes, no
norm but the old VGA, and only the black and white easy to use or the VESA
with its interrupts and BIOS extensions. And if we want to do protected mode
video graphics without BIOS ?

          COMPUTER SCIENTISTS LET US ASK MANUFACTURERS FOR A BASIC MODERN
VIDEO MODE !!

     I propose the following very simple thing :

     Card manufacturers ! give us a memory mapped 1024x768 256 colours mode
with customizable base address and full data bus width addressing.

It is very simple :

     We keep the DACs registers on ports h3C6, h3C7, h3C8 and h3C9 to
manipulate the palette.
     And you give us a Video RAM Base Register (VRBR) accessed through a
world wide standard byte port (the VRBR Address Port, VRBR_AP) at a standard
free port address (h3CA if it is free ? ) and whose functionning is :
     * after reset the VRBR is all 0 and the card is its usual reset video
mode, the VRBR_AP byte port points to the least significant byte (LSB) of
the VRBR.
     * To program the BASIC MODE, we first write each byte of the VRAM base
address to the byte port which increments toward more significant bytes (so
that if we have 64 bits addresses someday, it will just be enough to enlarge
th VRBR, if any body needs to put the video buffer out of 4 Gb ! ).
     * To activate the BASIC MODE we read the VRBR_AP, which also returns
the VRBR_AP to point on the VRBR LSB.

     Return to every other mode is done by classical means for those who
want.

     That will not cost a lot, it will not compete with powerful 3D hardware
modes, but it will considerably facilitate the programming of simple video
tasks. It will be a considerable plus for the manufacturers choosing such a
basic service as it allows for quick alternate system developments making
the PC platform a real de facto computer hardware standard known of
everybody. At present the lack of standard basic video makes the PC hardware
non universal and that restrains the market.
     256 colours on 16 millions is enough for simple video, and each pixel
is naturally aligned.

     I propose to discuss this demand, and once a good group of people
agrees on a basic video service, we contact the manufacturers, and we make a
list of responses, lack of responses etc on the network.

     Every comment is welcome.


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