geometry shader

[keith]

I have difficulty understanding how a vertex and geometry shader
interact. Does a geometry shader get the out variables of the vertex
shader? Can both a geometry and fragment shader get them? Also, can both
3 of them share uniforms, or is it impossible?

[fungus]

On Dec 18, 4:11 pm, keith <johndoe64...@yahoo.com> wrote:
> I have difficulty understanding how a vertex and geometry shader
> interact.

They don't. They're completely separated.

> Does a geometry shader get the out variables of the vertex
> shader?

Yes.

> Can both a geometry and fragment shader get them? Also, can both
> 3 of them share uniforms, or is it impossible?

The geometry shader can pass values via (eg.) texture coordintes.

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[keith]

fungus pravi:

> On Dec 18, 4:11 pm, keith <johndoe64...@yahoo.com> wrote:
>> I have difficulty understanding how a vertex and geometry shader
>> interact.
> They don't. They're completely separated.

Well, apparently they can communicate.

>> Does a geometry shader get the out variables of the vertex
>> shader?
> Yes.

Is this scheme then correct?

vertex shader -> geometry shader
-> fragment shader

Both get the out variables of the vertex shader then? Can both gs and fs
consume the same out variables?

>> Can both a geometry and fragment shader get them? Also, can both
>> 3 of them share uniforms, or is it impossible?
> The geometry shader can pass values via (eg.) texture coordintes.

You mean the built-in or user variables? How about the uniforms? Can
they be shared among the shaders?

[Wojciech "Spook" Sura]

keith wrote:
> vertex shader -> geometry shader
> -> fragment shader

I know only vertex and fragment shader. What's the difference between vertex
and geometry shader?

Best regards -- Spook.

[Timo Kunze]

Wojciech "Spook" Sura schrieb:

> keith wrote:
>> vertex shader -> geometry shader
>> -> fragment shader
>
> I know only vertex and fragment shader. What's the difference between vertex
> and geometry shader?

Vertex shader can modify existing geometry, geometry shader can produce
new geometry (e.g. new triangles).

Timo
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[Timo Kunze]

keith schrieb:

> Is this scheme then correct?
>
> vertex shader -> geometry shader
> -> fragment shader

No, it's not. It's more like:
VS -> GS -> FS
with the GS being optional.

> Both get the out variables of the vertex shader then? Can both gs and fs
> consume the same out variables?

No. If you specify a GS, the out variables of the VS go to the GS. The
out variables of the GS go to the FS. The syntax for varying variables
has been extended for the GS: Use "varying in" for in variables and
"varying out" for out variables of the GS. The in variables of the GS
obviously are the out variables of the VS and the out variables of the
GS are the in variables of the FS.
Uniforms are the same for all shaders anyway.