Vertices position from shader

is it possible to retrieve the position of vertices after they ve been modified inside a vertex shader effect ?
I dug in the code but at the moment it seems like a bit of no-sense and I d like to know wheteher it is even possible or the only way to go is to recreate the effect in a “CPU” manner.
For the sake of it, I am looking right now at the Tentacles Phong Directional shader, but I am interested in the whole idea of being able to retrieve that data.


hi Simone,
In directX 9 there’s no way to bring back vertices data to CPU domain after they are processed in GPU.
From dx10 it’s possible to retrieve data after the Geometry shader, just before pixel shader. so we have to wait until devvvvs will upgrade the dx version.
for now you have to work in cpu, by creating dynamic meshes. you can use mesh-(ex9.geometry-join) and vertexbuffer-(ex9.geometry-join) nodes to build your mesh.

thanks for the quick answer, i know how to deal with those node and how to modify a mesh. What I don t know (for the moment being) is how to extrapolate the HLSL to vvvv friendly maths calculation, I guess the first thing to do would be to learn some basic HLSL, what do you guys advice?


everything depends on what you need. you have to study the hlsl code and understand very well how it works… (wich shader is?). btw everything you do in hlsl can be done in vvvv, so… buon lavoro! :)

We are talking about the Tentacles Phong Directional (aka pulpo shader or shader a la romana) (in the Vertex Noise pack), basically I d like to create a dynamic rose stem, with the prickles being all tiny tentacles with origin in a certain amount of the main tentacle´s body.
So it may be possible to create the main tentacle via CPU, then add all the small prickles with the shader.


hmm quite strange use of that shader ;]

i’d say logically easier would be to put pickles inside shader…
so why don’t you give a try to tex2lod so you will have pickles displaced from stem

one solution that comes to my mind:
-create a central spline that moves like the main tentacle.
-create a grid of control points wrapped on that spline as a cylinder (with different radius at the beginning and the end…basically it’s a cone).
-use B-Spline_surface_constrain.rar (6.07 Kb) to place little tentacles where you want, using the wrapped grid as control points .
(little tentacles are in tentacle/fritto misto shader)

ths doc! quite nice modula