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Old 03-27-10, 03:07 AM   #1
MaXThReAT
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Default Are Geometry Shaders and Tessellation the same thing?

It appears to me as though they are the same thing. Maybe slightly different techniquies but the same damn thing in the end programming wise.
I was watching the Nvidia medusa demo and noticed it describes the geometry shader effect. They say, "Geometry shaders create new surface geometry on the fly to propagate the creeping stone effect." Sounds a lot like tessellation right?
Seems to me this is the exact same thing as our now so called "DX11 ONLY" tessellation. Just so everyone knows tessellation has been used on consoles already. I didn't know they had DX11 GPUs? MMMMM Maybe there is something special about those GPU cores like they aren't labeled DX this and that but they seem to run everything fine. Seems like just another BS reason to dump cash on a card. I not even going to talk about Crysis DX9 vs DX10 cuz thatís just a joke. Same thing all over again. I bet in reality (NDA) a 7900gt could do DX10 and DX11 shaders, probably not as fast but it could do it at lower setting.
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Old 03-27-10, 06:37 AM   #2
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Default Re: Are Geometry Shaders and Tessellation the same thing?

You can use GS to split up geometry and tessellate objects, but the reason why that never picked up with DX10 was due to that way not being very fast or efficient.
DX11 HW dont just pick it up and run it on the shader units as GS code.

tessellation has been done even earlier then the consoles, the TruForm thing ATi had back on the 8500 did a form of tessellation.
But without the ability to read a heightmap and deform it, IE do displacement mapping, itīs just making things rounder, and thats not always a desired result, unless you can spec and retain hard edges where they should be.
Like the rounded Balloon-like weapons TruForm would give in Counter-Strike.
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Old 03-27-10, 06:48 AM   #3
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Default Re: Are Geometry Shaders and Tessellation the same thing?

I think devs were able to mark objects as Truform or not but since they didn't everything went rounded?

It was a missed opportunity for sure.
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Old 03-27-10, 06:52 AM   #4
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Default Re: Are Geometry Shaders and Tessellation the same thing?

Quote:
Originally Posted by MaXThReAT View Post
It appears to me as though they are the same thing. Maybe slightly different techniquies but the same damn thing in the end programming wise.
I was watching the Nvidia medusa demo and noticed it describes the geometry shader effect. They say, "Geometry shaders create new surface geometry on the fly to propagate the creeping stone effect." Sounds a lot like tessellation right?
Seems to me this is the exact same thing as our now so called "DX11 ONLY" tessellation. Just so everyone knows tessellation has been used on consoles already. I didn't know they had DX11 GPUs? MMMMM Maybe there is something special about those GPU cores like they aren't labeled DX this and that but they seem to run everything fine. Seems like just another BS reason to dump cash on a card. I not even going to talk about Crysis DX9 vs DX10 cuz thatís just a joke. Same thing all over again. I bet in reality (NDA) a 7900gt could do DX10 and DX11 shaders, probably not as fast but it could do it at lower setting.
Not really the same thing. The xbox 360 has a hardware tesselator as does all of the DX11 gpus. You could do tesselation via the geometry shader, but that is way too inefficient to ever be considered a viable option in today's games.

Quote:
The hull shader takes control points for a patch as an input. Note that this is the first appearance of patch-based data used in DirectX. The output of the hull shader essentially tells the tessellator stage how much to tessellate. The tessellator itself is a fixed function unit, taking the outputs from the hull shader and generating the added geometry. The domain shader calculates the vertex positions from the tessellation data, which is passed to the geometry shader.
From the MSDN Direct3D 10 FAQ:

Quote:
Geometry Shader

Should I use the geometry shader to tessellate my (insert anything here)?
No. The geometry shader should NOT be used for tessellation.
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Old 03-27-10, 09:42 PM   #5
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Default Re: Are Geometry Shaders and Tessellation the same thing?

Okay so what I've read since writing this and from your posts; it's kind of the same thing on a basic programming level but true tessellation should include the heightmap. DX11 GPUs have a dedicated hardware section for tessellation only and because DX10 GPUs do not it comes at too high of a performance cost, I would guess because of the complex shaders that are run along with the other shaders running not to mention attempting to write in the heightmap into a DX10 geometry shader calculation, if it's even possible, hence we now have a dedicated hardware section. Learned a lot thanks, I'm trying to catch on current...stuff.
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