Fixing ScatterSky

For a while now, people have been asking to add the ScatterSky z-offset hack into the engine to fix their ScatterSky issues. It's never been added. I can't speak for previous committees but for myself I know I don't want to add a hack into the engine. I'd prefer a proper solution.


This illustrates the problem: ScatterSky is just an umbrella, and if you fly high enough, you can see its edges. This is bad. The z-offset hack simply changes the height the sky is rendered at, if I understand it correctly, dropping it down so the edges sit beneath your horizon again. The change touches this line:

Point3F camPos2 = state->getCameraPosition();
   MatrixF xfm(true);
   xfm.setPosition(camPos2);//-Point3F( 0, 0, 200000.0f));

Interestingly, there are also constants for the earth's radius and atmosphere thickness, as well as the viewer height, which is a fixed constant 1m. It's used to pass additional parameters into the shader:

Point3F camPos( 0, 0, smViewerHeight );
   Point4F miscParams( camPos.z, camPos.z * camPos.z, mScale, mScale / mRayleighScaleDepth );

   ...

   mShaderConsts->setSafe( mMiscSC, miscParams );
   mShaderConsts->setSafe( mCamPosSC, camPos );

What I'd feel best about is having the ScatterSky capable of rendering a full sphere. This would not only fix this issue, but also be useful for people making games without a terrain (think of floating Marble Blast levels, for example). Of course, there should be an option to not render the full dome if you don't want to (performance?).

If that's not feasible, I think we should review the use of the constant 1m height, and the use of camPos2. The z-offset hack touches that line of code, so let's see if we can fix it without making a 'hack'.

If worst comes to worst and no other solutions eventuate, let's add the hack into the main repo, and there will be much weeping and gnashing of teeth, mostly by me.

EDIT: Screenshots (and more) thanks to Azaezel.


You can clearly see the mesh which is generated, and only covers a small portion of a sphere. It looks like it's just a warped grid, too, though it might make a UVsphere if it were extended all the way around. It appears this geometry is constructed here-ish, though that's different to what's generated in mSkyPoints, purpose unclear.