Hi!

I am currently programming a little engine for terrain rendering with trees and plants.
I´ve just built in trees and grass already. But i have a huge problem with alpha blended objects(both grass and trees needs them).

Are there any techniques to sort the object by the distance to the camera so I can draw them from back to front? If, are there any helpfull render states or do i have to do it in vertex shader or something like this?

I hope you can help me, that i can get on with my current work ;)

You do it on the CPU side - sort your meshes by distance, then issue the draw commands for those meshes in that order

Thank you!

Ok can you give me a little code snippet how i compute the distance to the camera?
Do i have to use the worldMatrix for each object?

like this:

D3DXVECTOR vObjPos = (D3DXVECTOR) *m_World.41;
D3DXVECTOR3 vDistance = vObjPos - camera.vEye;
float fDistance = length(vObjPos);


Isn´t this to inefficient for 100 leaves on a tree or 100 grass tufts?

EDIT: How can i do that with the LPD3DXMESH class?

like this:

D3DXVECTOR vObjPos = (D3DXVECTOR) *m_World.41;
D3DXVECTOR3 vDistance = vObjPos - camera.vEye;
float fDistance = length(vObjPos);


Isn´t this to inefficient for 100 leaves on a tree or 100 grass tufts?

What's inefficient about it? How long does it take on your hardware?

Computing the lengthSquared might be slightly cheaper as it'll avoid a divide, and you can sort by that just the same

ill take std::sort for it(i think its a quick sort) and I think an i7 can handle this ;)
Thank you very much!

Now i have a tree. His leaves need alpha blending. But how can i sort LPD3DXMESH?

Hello
I'm currently experimenting an algorithm to sort objects per distance very fastly, here's a description :

The main structure of the sorting object is an hash table ;for instance, let's say the depth range (in view space) is [0,1000], and there are 1000 entries in the hash table : the first entry covers [0,1] depth range, the second covers [1,2] depth range and so on. So when just storing objects , we already presort them in subsets . Each entry of the hash table contains a subset of objects that now must be sorted. I use then std::qsort() on each table entry. (I cut into chunks the entries and put a worker thread on each chunk)

Results : I sort 1.000.000 int objects in 8 ms (average)
CPU : Phenom 4 Cores
RAM : 3 GB
OS : Vista 32 bit
config for this result : 1024 entries in the table, 4 threads (one on each core) (the computation time seems more stable with 8 threads) ; depth range : [0,1000]

(It needed 100 ms for a 'single entry hash table' with one thread ; ie pure std::qsort() sort)

My plan is to sort transparent faces ( I ignore the intersection case and the "A over B ; B over C ; C over A" overlap case )
Today, my transparent faces all use united color so I will build a (pre sized at cooking) unique buffer containing all these faces, so I'd need only one draw call for transparency

But that's just a personal experiment, I think it can work mostly because there's quite few transparent primitives and because they all use the same layout/technique.

I can post/send my code for this if you're interested or just curious

For what it worthes

Nico