Scene Graph Question

[jirzynek]

Hi!

Right now in my engine I've implemented 2 scene graphs. One takes care of game geometry (terrains, scenes, animation, particles) and second manages 2d objects (panels, menus, generaly everything what has something common with 2D and is on top of 3d layer).

What is the best way to handle priorities in SG? For example I have a skybox and I want to draw it first (before anything else) with Depth test disabled and all other geometry with Depth test enabled. What is the best way to do this? Another sortkey?

cheers
jirzynek

ps. sorry for my language mistakes...

[.oisyn]

Or you can alter the projection matrix so that you "allocate" the back portion of your z resolution for your skybox. Then it doesn't matter when you draw it. This also avoids overdraw when you do a z-pass of all your geometry first.

[Reedbeta]

In the engine I work on we have a system with several different sort keys. At the top there is a "primary key" that is set by the shader file and is one of an enumeration hard-coded into the engine. The engine binds render targets and sets a few other states based on the primary key as well. Within each primary key value we group by shader file, then by shader parameters (texture assignments etc). The list of things to render is regenerated each frame and kept sorted by this key system as things are inserted into the list, then we run through the list and draw everything.

In our case we have a special primary key values for the skybox which runs after the ones for all the opaque world geometry, but before the ones for transparent geometry. Like .oisyn suggest we use z-testing to ensure the skybox doesn't occlude the geometry (our sky is actually a screen-space quad, rather than a literal cube, and we set the vertices directly in clip space, which lets us put them exactly at the farthest possible z value).

Anyway, this kind of key system is a decent general paradigm for making sure things render in the right order.