Custom rendering order with no need for a z buffer

[Munger]

The application I'm working on is composed of layers going back into the screen. Imagine an old parallax scrolling game for example. Each layer can have little 2D tiles over it though, so at the moment I'm suffering from z-fighting. I could offset the tiles slightly above the layer they are on, but that won't completely solve the problem entirely and since I know the order I want to draw everything in, I'd like to call the render method of each scene node individually.

I tried a straight-forward approach and it just rendered the background color. Then I looked through the Irrlicht source and realized I hadn't added the camera to my custom rendering loop. So I copied that in (along with anything else that seemed relevant), but I still just get the background color.

So how would I go about specifying the render order of my objects? I'd really prefer not to use actual z-differences to get the effect, and it seems like a simple thing to ask. I know in straight OpenGL or DirectX it would be really straight-forward.

My original loop (ripped pretty much straight from the examples) was:

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driver->beginScene(true, true, video::SColor(255,128,0,0));
smgr->drawAll();
env->drawAll();
driver->endScene();

The current (non-working) version is:

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driver->beginScene(true, true, video::SColor(255,128,0,0));
if ( driver )
{
	core::matrix4 identity;
	driver->setTransform ( video::ETS_PROJECTION, identity );
	driver->setTransform ( video::ETS_VIEW, identity );
	driver->setTransform ( video::ETS_WORLD, identity );
	driver->setTransform ( video::ETS_TEXTURE_0, identity );
	driver->setTransform ( video::ETS_TEXTURE_1, identity );
	driver->setTransform ( video::ETS_TEXTURE_2, identity );
	driver->setTransform ( video::ETS_TEXTURE_3, identity );
}
smgr->getActiveCamera()->OnRegisterSceneNode();
smgr->getActiveCamera()->render();
controller->GetTarget()->GetSection()->Render();
env->drawAll();
driver->endScene();

I also notice in the source code that regular scene nodes are sorted according to material before rendering.

[fmx]

I'm sure there's better ways of achieving what you want, but to render nodes manually, just set their visibility to false and render them in whatever order you want at a later time:

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node1->setVisibility(false);
node2->setVisibility(false);

...

node2->render();
node1->render();

I can't remember the exact syntax, but something like that

[Munger]

That makes a lot of sense. I'll give it try.

[Munger]

It's not working like that. I suspect it's because the 'CurrentRendertime' of the SceneManager is no longer what it needs to be for the mesh's 'render' method to work. It's going to be caught in this section of CMeshSceneNode.cpp:

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video::IMaterialRenderer* rnd = driver->getMaterialRenderer(material.MaterialType);
bool transparent = (rnd && rnd->isTransparent());

// only render transparent buffer if this is the transparent render pass
// and solid only in solid pass
if (transparent == isTransparentPass) 
{
	driver->setMaterial(material);
	driver->drawMeshBuffer(mb);
}

It'll skip over the 'drawMeshBufferCall'. I'll try recreating the important parts of the render method and call driver->drawMeshBuffer(mb) myself.

[Munger]

Now I'm getting somewhere. The geometry is there, but it's black. I'll keep at it

Here's the code I'm using (you'll notice it's quite similar to the render method of CMeshSceneNode):

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void GTRenderable::RenderToDevice(IVideoDriver *driver, IMeshSceneNode *node)
{
	IMesh* mesh = node->getMesh();
	driver->setTransform(video::ETS_WORLD, node->getAbsoluteTransformation());
	for (unsigned int i=0; i<mesh->getMeshBufferCount(); ++i)
	{
		scene::IMeshBuffer* mb = mesh->getMeshBuffer(i);
		if (mb)
		{
			const video::SMaterial& material = mb->getMaterial();
			driver->setMaterial(material);
			driver->drawMeshBuffer(mb);
		}
	}
}

[Munger]

OK. I'm back in business the problem with the last code chunk was with the material. I was ignoring the read-only material flag - incorrectly. They updated (and functional) line is:

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const video::SMaterial& material = node->isReadOnlyMaterials() ? mb->getMaterial() : node->getMaterial(i);

Thanks fmx for getting me going in a better direction.

[Munger]

And one last thing for anyone else trying to do the same thing, you'll need to call updateAbsolutePosition() on the node manually since that gets called as part of the rendering process normally.

[fmx]

good to hear you got it working

[Mikhail9]

After a lot of time digging in the forum trying to figure out why my shadows quit working when my mini-map was on the screen, I discovered they worked when I set the map node as invisible in order to completely prevent the first render pass from drawing it. Apparently, it's presence close to the camera fools the stencil buffer shadow system into thinking no shadows need to be drawn.

Then I discovered my manual node->render() call after drawAll() wasn't actually doing anything. After much digging through the Irrlicht source code, I discovered your post about calling node->updateAbsolutePosition() and it fixed the problem. That function normally gets called as part of OnAnimate() in the drawAll() call. Why it needs called again when nothing has changed is somewhat of mystery to me.

Anyway, thanks for following up by posting your solution. I wouldn't have thought to try that, at least not for many more hours.