Subject: Additive on Macs 2004-02-27 - By Neto
Back
Maybe using a screen capture xtra could allow automatic detection at least
in projectors?
-- -- Original Message -- --
From: "noisecrime" <noise@(protected)>
To: <dir3d-l@(protected)>
Sent: Friday, February 27, 2004 12:19 PM
Subject: Re: [Dir3d-l] Additive on Macs
> Hi Mal,
>
> First to those who are interested, the artcile and source to the demo Mal
> posted can be found here.
> http://www.noisecrime.com/develop/tutorials/additiveblend/
>
> To recap
> To date no PC running in DX5 has failed to produce additive blending using
> maxTextureUnits+1 to place the additive texture into.
>
> On a PC, any card that supports 8 texture units will not be able to
produce
> additive blending in DX7
>
> On a Mac additive blending is supported in openGL as long as the card has
> less than 8 texture units. However the gethardware() command is unreliable
> and does not return the correct maxTextureUnits.
>
> When getting the image of the sw3d member on a mac, you always get back a
> software openGL version (not software), which invalidates automatic
> checking.
>
> This means on a Mac, there is no automatic way of determing if it supports
> additive blending, you have to ask the user, and basically cycle through
> which texture unit to place the additive texture into.
>
> Most Mac cards, if not all will support aditive belnding, its just the
> developer has no gauranteed method of knowing which layer to place the
> additive texture. One idea was to use the cards name as a look up into a
> database where you would store the known maxTextureUnits. Sadly though
> naming appears in consistant and so is not gauranteed to work.
>
> Basically then Macs are a bit of a bugger for additive blending. It will
> work, but you need to invent some method of getting the user to identify
> which layer provides the belnding affect. My outlook on this was that
> additive benldning would be off by default on macs, and the user had to
turn
> it on through a preference screen. This screen would display a
pre-generated
> additive blend of some scene or object, and then the w3d trying to
implement
> additive blending. They have a simple 'yes' 'no' decision to make if the
> images match or not. If they don't match move onto the next texturelayer,
if
> they do, then you can stop because you know which texture layer to use.
>
> Two tips
> Firstly don't forget the user may have overriden the renderer API in the
SW
> preferences
> Secondly that the num of texture units is API dependant. So if running in
> DX5 you will always get 1 for the maxtextureunits.
>
> I've got another 50-75 results that I'll try and add to the tutorial
results
> over the weekend.
>
> Hope this helps
>
> Noisecrime 2004
>
>
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