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what does 'w' mean in shader assembler


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#21 Jason Z   Crossbones+   -  Reputation: 4843

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Posted 14 June 2013 - 04:30 PM

 

Out of all of the conjecture and philosophical discussion (which is also important...) nobody answered the original question from the OP.  He wants to know why his w value is initialized to 1 when he only has a XYZ format for his vertex information.  Its been really long since I worked with D3D9, so I couldn't say off the top of my head why that is.  Can you describe how you managed to determine that the value is 1?

The original question isn't really very clear.

I would guess that it may be about this: If you have a vertex declaration entry for vertex position (D3DDECLUSAGE_POSITION) with the type D3DDECLTYPE_FLOAT3 and your vertex shader input parameter for position is float4, then w is automatically filled with w = 1, because that's what points need. I don't know whether for normal it would put 0 there, but I guess it would.

Anyway, I personaly have always been consistent in this and with D3DDECLTYPE_FLOAT3 I use float3 in shaders. And I add w manually.

 

 

That seems like prudent advice - can the original poster chime in about that?  Are you using all four components of a vector without initializing them?  It could be that since he is using an assembly shader, that the full register is initialized regardless of if he declares 3 or 4 components.



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#22 Icebone1000   Members   -  Reputation: 1016

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Posted 14 June 2013 - 07:41 PM

Its just me who thinks wikipedia entries on any math subject are terrible? I never learned anything about math on wikipedia, but I did learned a trick: try searching on really early versions of the entry, before some calculus freak made his version full of weird notations and explanations nobody really cares, helps a lot, since early version focus on things ppl are actually more concerned, instead of those versions full of history and names.






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