Shadow artifacts with directional light and alpha quad

Troubleshooting graphics
#1

Hi all,

I’m getting very bad shadow artifacts when using a directional light, as you can see in this screenshot.

So I have a sphere with a quad intersecting it. The quad has an alpha texture applied to it and is rendered in the transparent queuebucket. I’ve tried everything I could think of; changing blendmodes, edge filtering techniques, lambda values, etc… I even tried a custom obj for the quad with more triangles, but nothing seems to have an effect.

Here’s the relevant code:

For the rings (quad):

Quad quad = new Quad((float)planet.getRadius() * scale, (float)planet.getRadius() * scale);
	spatial = new Geometry(planet.getName() + "Rings", quad);
	spatial.setLocalTranslation(-(float)planet.getRadius() * scale/2f, -(float)planet.getRadius() * scale/2f, 0);
	spatial.setShadowMode(ShadowMode.CastAndReceive);
	
	Material mat = new Material(assetManager, "Common/MatDefs/Light/Lighting.j3md");
	mat.setBoolean("UseMaterialColors",true);
	mat.setColor("Ambient", ColorRGBA.White);
	mat.setColor("Diffuse", ColorRGBA.White);
	mat.setTexture("DiffuseMap", assetManager.loadTexture("assets/Textures/" + planet.getName() + "RingsColor.png"));
	mat.setTexture("AlphaMap", assetManager.loadTexture("assets/Textures/" + planet.getName() + "RingsAlpha.png"));
	mat.getAdditionalRenderState().setFaceCullMode(FaceCullMode.Off);
	mat.getAdditionalRenderState().setBlendMode(BlendMode.PremultAlpha);
	spatial.setMaterial(mat);
	
	spatial.setQueueBucket(Bucket.Transparent);
	planetNode.attachChild(spatial);

For the shadow and light:

sunlight = new DirectionalLight();
	sunlight.setColor(ColorRGBA.White.mult(0.85f));
	Vector3d v = spaceship.getPos().subtract(planetMap.get("Sun").getPos()).norm();
	sunlight.setDirection(v.toFloat());
	rootNode.addLight(sunlight);

FilterPostProcessor fpp = new FilterPostProcessor(assetManager);

	final int SHADOWMAP_SIZE=2048;
	DirectionalLightShadowFilter sunshadow = new DirectionalLightShadowFilter(assetManager, SHADOWMAP_SIZE, 4);
	sunshadow.setLight(sunlight);
	sunshadow.setEdgeFilteringMode(EdgeFilteringMode.PCF8);
	fpp.addFilter(sunshadow);

and finally for the planet:

Geometry geo = planetGeo.clone();
	
	geo.setName(planet.getName());
	geo.setLocalTranslation(0, 0, 0);
	geo.scale((float)planet.getRadius());
	
	geo.setMaterial(planet.getMaterial());	
	geo.setShadowMode(ShadowMode.Cast);

I’d love to hear any ideas or solutions! The only thing that helped a tiny little bit was reducing the shadow map resolution to 512, but that didn’t exactly improve the quality and didn’t do anything to make the shadows soft…

#2

Try to use DirectionalLightShadowRenderer instead of ShadowFilter.

#3

It appears to me, that the shadow bias is too small. As far as I remember this value is handled through polygon offset values in the shadows’ .j3md material definition file, in the shadow techniques. I do not know if you can set the bias by calling a method, but this gives you a point to start investigating.

The outcome of the polygon offset may also be influenced by the view frustum’s near-far distance. As you’re working on a space game this could be an issue.

#4

Using DirectionalLightShadowRenderer does reduce the flickering. But now the shadows look like this, any idea what I should do? :confused:

@Apollo: what is the shadow bias? how can I modify that? As for the frustum, I dynamically scale the planets so that they always fall inside it, the near-far distances are 0.05 to 15000. If I increase the near distance to 10 the shadows do improve quite a bit! But that’s only with the ShadowFilter, there’s no change when using ShadowRenderer.

Edit: I changed the near and far distances tot 0.1 and 1500, which work for me (changed the dynamic scaling a bit and this should be no problem). Thanks! Then there only remains two smaller questions. First: the shadows still look a bit jagged, is there a way I can easily fix that?

And secondly, Is there a way to drop shadows of the rings onto the planet? So using the alpha values of the material applied to the ring-quad.

#5

For a basic introduction on shadow mapping and artifacts visit this tutorial: (it also covers the bias value)
http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-16-shadow-mapping/

There are more advanced methods to improve shadow quality but JME does not offer them yet.

Your far/near ratio should not exceed 50000 (if I remember correctly). You could adjust the bias by changing the polyoffset values in the .j3md files (or making your own j3md files, which is much cleaner).

#6

As for your first question, you could increase shadow map size. The second question is the one I cannot answer, since I never used JME’s shadow system, but maybe someone else knows how to do this?