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24-bit with ddraw


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#1 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 24 December 1999 - 06:49 AM

I'm having problems with trying to use 24-bit mode. When I initialize direct draw (I'm using version 7), I get an error when putting in 24 for the bpp the screen res should use. Do I need to say 32 and not use the alpha channel? I know my video card can support 24- and 32-bit.

-Densun


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#2 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 22 December 1999 - 05:39 PM

I have the same problem (using visual basic btw)... It works fine with 16-bit mode, but if I change the bpp parameter to 24bit, DDraw returns the noexclusivemode errorcode.

David


#3 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 22 December 1999 - 05:50 PM

Well, I'm not sure if this is the problem, but I have had trouble in the past (on my old Diamond Stealth 3D 2000) switching into exclusive fullscreen mode when the desired mode has a different bpp then the one that Windows is curently running in (ie, if you're in 16 bpp mode in Windows, the driver might not let you switch to 24 bpp in your program). I would think that any decent card wouldn't have that drawback anymore, but who knows.

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Posted 23 December 1999 - 07:09 AM

I switched windows into 32-bit mode (it won't allow 24-bit) and ddraw still wouldn't switch into 24-bit mode, in fullscreen or windowed. Seems like 32-bit is the only answer.

-Densun


#5 +AA_970+   Members   -  Reputation: 122

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Posted 23 December 1999 - 08:12 AM

Some video cards don't support 24 bit color, it the card does not support it then direct draw will not let you use it.

If windows won't let you switch into 24 bpp its likely your card dosen't support it.


#6 null_pointer   Members   -  Reputation: 289

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Posted 24 December 1999 - 06:49 AM

Aren't 24- and 32-bit color modes mutually exclusive? Besides, since 32-bit color is actually 24-bit color with an extra 8 bits, why not use 32-bit instead? (Except for performance reasons of course. 32-bit vs. 24-bit makes the memory required about 33% greater. However, depending on what you are doing with the surface memory, it might be faster with 32-bit because the memory is DWORD-aligned.)

I heard that although some cards support both, it's only because the driver really supports one, and just maps the other to it (i.e., the card supports 24-bit, but can also use 32-bit by ignoring the alpha information). Some cards use the alpha information (the upper 8 bits of the 32) and that's why they don't function with 24-bit modes. Perhaps it has a lot to do with the particular chipset the board uses and performance reasons. I think that several companies haved either added or dropped support for certain color depths from one driver release to the next because of performance gain/loss.

Anyway, I am not trying to sound like an authority on the situation; just raising some interesting questions in the hopes that someone will answer them.

- null_pointer

[This message has been edited by null_pointer (edited December 24, 1999).]





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