Help with API needed: Drawing meshes

[Rastar]

Somehow I can't find the right API calls for what I would like to do:

 

1) Define a couple of vertex and index buffers. These are used as generic patches for a displacement mapped terrain. I therefore only need 2D vecs, but of course 3D vecs are OK as well.

2) Draw these several times during a frame update, each with a different position and/or scale.

 

The only place I could find to define vertex and index buffers is the Surface class. But if I use it as part of a model (created by Model::AddSurface() ) I don't know how to reuse the patches. If I try to use stand-alone Surfaces (Surface::Create() ) without adding them to a model, my program crashes.

 

Is there a way to do this?

[shadmar]

Something like this would create a 2 triangle plane:

 

local patch = Model:Create()

local surface = patch:AddSurface()

surface:AddVertex(-0.5,-0.5,0, 0,0,-1)

surface:AddVertex(0.5,-0.5,0, 0,0,-1)

surface:AddVertex(0.5,0.5,0, 0,0,-1)

surface:AddVertex(-0.5,0.5,0, 0,0,-1)

surface:AddTriangle(2,1,0)

surface:AddTriangle(0,3,2)

 

patch:SetColor(1,1,0)

 

Then maybe instance more of them and rescale them :

 

local patch2 = patch:Instance()

patch2:SetScale(2)

patch2:SetColor(1,0,0)

[Rastar]

Ah, thanks, I wasn't aware of the Instance() member. But will this actually create a second vertex and index buffer? I like to draw the same set of vertices several times, since they're only the regular mesh to be displaced in the shader.

[shadmar]

No, this would be the same mesh since it instanced from the first one. (not a copy, but an instanced one)

You can do the same using a loaded mesh, and just instance it several times, then use a vertex shader to displace height.

[Admin]

This is pretty much exactly what the built-in terrain system does.

[Rastar]

Is an instancing call expensive? I need many of those patches, can I instance them each frame update, or should I store the instances ( which would make the code less elegant)?

[Admin]

Creating instances will be faster because they will be rendered in a batch. This is one of the tricks Leadwerks uses for terrain...the landscape is split into identical patches and the heightmap texture is used to control the height offset.

[Rastar]

Yes, but do create the instances in the Draw() call, or do you create them during initialization and store them in an array?

[Admin]

Create them once, ahead of time!