Models w/ translucency not rendered from the inside

[Tormentor667]

Just playing around with some stuff and noticed that models with an Tranclucency value aren't rendered from the inside, just from the outside - where as normal rendered models (like cubes or globes) are rendered from the inside and outside both.

*EDIT*
Added an example to demonstrate the problem:
https://www.dropbox.com/s/tk0tqbihc381j ... e.zip?dl=0

1 is rendered normal, step "into" the moon model and you will see the textures from the inside.
2 is rendered translucent with full alpha, step into the inside of the model and it will "disappear" (no textures drawn from the inside)
3 is rendered additive with full alpha, you can already see the problem.

It is clear to me why this has been solved the way it has been, but some option that forces rendering the inside of a model even when it is translucent would help a lot to do the skybox effect people have been suggested in the other thread

[dpJudas]

This is because the model translucency support was never really properly finished. It makes the model "translucent" by turning on backface culling, which only works for simple models.

A better way to do it would be to render the model twice. First with color output disabled that fills the zbuffer. Then draw it again with color enabled. That will make the second pass not draw faces that are occluded by the model itself.

Relying on two-sided materials is bad in general. This is because it has to render all faces no matter what, effectively making it twice as expensive for the GPU to draw the model. It is much better to make your faces always point in the right direction.

[Tormentor667]

Thanks for the explanation, so all I need is actually a model for "planet.md3" that has its faces inversed? (no idea how to do it btw)

[Major Cooke]

I would like to know how to do inverted modelling as well.

[dpJudas]

Normally you do this in the modelling tool (Blender, 3ds max, Maya), which differs. It sounds like you don't have the original source, but only the exported planet.md3. I don't know if there's any tool out there that can edit a md3 file directly.

[Tormentor667]

It sounds like you don't have the original source, but only the exported planet.md3.

Exactly that. So what about an option for the MODELDEF instead that forces to render the inside?

[Rachael]

If you are adept at creating models, you can create a large cube, and then put your source model inside the cube and set it to be a negative intersection (in other words, a cut-out). You can then use a raw polygon editor and remove the extra 6 outside faces this created.

[Tormentor667]

If this is not a bug, can it be turned into a feature request - actually an additional flag in the MODELDEF to force rendering of the inside?

[Major Cooke]

I'll just make one for you Tormentor. Worst case scenario, it's 6 planes because god knows how the texture placement is going to work... so six actors in total, if it doesn't go according to plan. In fact I think that actually might be easier than trying to stitch together 6 whole images to perfection via photoshop...

[AFADoomer]

@Major Cooke -

You can specify textures per surface/group in MODELDEF - so as long as each plane is a separate group, you can just set the texture for each one as appropriate (using the SurfaceSkin property). Or you can compile the model with the relative paths to the skybox textures and they'll work fine in-game.

As a thought (and I haven't tested this at all...), could a 3D floor set to render inside and to use the sidedef's lower or upper texture for the sides be used for this instead of a model?
(EDIT: No, you can't, unless someone knows of a way to change the alpha of a 3d floor in game).

[Major Cooke]

Please do show me then. I'm having a hard time figuring out how that's done.

[AFADoomer]

Check out the model that Talon1024 put together for WolfenDoom here. It is just a plain cube, but each face is grouped as a separate surface - top, bottom, east, west, north, south. Additionally, the textures on the model were set in whatever editor was used, pointing them to "textures/skyboxes/plainssun/_____.png" (where _____ is the appropriate texture for that side of the skybox).

The MODELDEF entry for this actor is relatively simple:

Code: Select all

Model PlainsSun3D
{
	Path "models"
	Model 0 "plainssun3D.md3"
	Scale 1.0 1.0 1.2
	USEACTORPITCH
	USEACTORROLL
	FrameIndex MDLA A 0 0
}

If we wanted to specify the skin via MODELDEF instead of using the compiled-in texture paths, we'd use the SurfaceSkin property:

Code: Select all

SurfaceSkin model-index surface-index skin-file

To get the surface-index number, we need to know the order of the surfaces within the model file. The easiest way to see this is to import the model into your editor or model viewer and look at the order that the groups are listed in. In the case of the plainssun3d model, surface indexes 0 to 5 correspond to west, south, east, top, bottom, and north, in that order.

Defining the various face's textures in MODELDEF would then look something like this:

Code: Select all

Model PlainsSun3D
{
	Path "models"
	Model 0 "plainssun3D.md3"
	Scale 1.0 1.0 1.2
	USEACTORPITCH
	USEACTORROLL

	Path "textures/skyboxes/plainssun"
	SurfaceSkin 0 0 "abra_w.jpg"
	SurfaceSkin 0 1 "abra_s.jpg"
	SurfaceSkin 0 2 "abra_e.jpg"
	SurfaceSkin 0 3 "abra_t.jpg"
	SurfaceSkin 0 4 "abra_b.jpg"
	SurfaceSkin 0 5 "abra_n.jpg"

	FrameIndex MDLA A 0 0
}

This also allows you to use the same model again with different textures without having to bloat your mod and add additional copies of model files.