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Subject: Re: [boost] boost::directx?
From: Carlos Rafael Giani (e0325834_at_[hidden])
Date: 2009-06-09 07:02:07

joel wrote:
> Christian Schladetsch wrote:
>> That simply isn't true, unfortunately. DirectX and OpenGL have different
>> abstractions for the same hardware, and what's worse is that the hardware
>> itself is changing even faster than the API's that access it.
>> That is far different to the API's that deal with threads. To make
>> matters
>> worse, OpenGL is a few generations behind DirectX (sorry, but it's true),
>> and the gap is only increasing with Geometry Shaders.
>> The reality is that DirectX provides the best API to use hardware, OpenGL
>> wont and can't compete at that level because unlike DirectX, OpenGL is
>> not
>> driving the hardware industry.
> Wasn't that stuff like Ogre3d do somehow.
> That's ages i didn't dip into these so take this question as a real
> naive one for the sake of the
> argument.

Examples are:
- pixel formats supported by one API but not by the other (Direct3D: YUV
textures, OpenGL: latc compression, at least I'm not aware of a D3D
- buffers: OpenGL Buffer Objects and Direct3D Buffers work differently,
and allow for different semantics
- render-to-texture differs significantly between the two (OpenGL FBOs
allow have many more features than their D3D equivalents)
- Direct3D10 unifies all types of buffers, OpenGL 3 doesnt
- Render-To-Texture in D3D understands (0,0) as being the upper left
corner, in D3D it is the lower left one
- Direct3D shaders and OpenGL ones have different, incompatible
approaches (D3D knows no shader linking for example)
- Direct3D uses vertex declarations, OpenGL uses pointers (which
actually are offsets when buffer objects are used)

This is a small excerpt of the differences. There are more subtle ones,
such as locking flags for memory mapping allowing more fine-grained data
transfers in D3D.

The problem is that the only feasible way is a lowest common
denominator, both in terms of features and performance. To use the
graphics hardware best, you must use API specific functions.


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