Mordeth Map07 (while under construction) Most nodesbuilders (warm, dmapedit) are able of creating this effect. It's a variation of known effects like invisible platforms and deep water, only now applied to the ceiling. In this case, the floor is brightly lit lava while the ceiling remains dark. Anthony Galica, moderator of Beyond Doom has taken this concept further with 'dynamic lighting', applying this effect to construction with different floor and ceiling heights, and even with 3D bridges.

SECTORS 1 : X/0, light level 100; 2 : ceiling/floor X/16, light level 100; 3 : ceiling/floor X+500/0, light level 255

LINEDEFS a : has missing upper textures.

Using this effect you can make sectors with different ceiling and floor light levels, or with different special attributes. First described by Justin Brown here (thanks for the pointer, Andrew!). Shadowcasting depends solely on sector 3 having a ceiling height way above the height of sector 2, with the bordering linedefs 'a' lacking upper textures.

Works perfectly with warm, dmapedit and BSP. The missing upper textures causes the engine to draw the ceiling texture at the same height with the same light level as the surrounding sector 2. Shadowcasting can be combined with other effects such as 'Deep Water' by creating another, entirely self-referencing sector within sector 3. These extra constructions however depend on the type of nodesbuilder you're using.

SECTORS 1 : ceiling/floor X/0 with light level 100; 2 : ceiling/floor X/16, light level 100; 3 : ceiling/floor X+500/0, light level 255; 4 : ceiling/floor X/0, light level 255

LINEDEFS a : has missing upper textures; b : both sides reference only to sector 4, no textures.

This is how to create 'normal' sectors within a Shadowcasting effect with BSP or Dmapedit. Note that this can also be used when working with Deep Water effects. In the example is shown how to have objects dangling from the (faked) ceiling within the shadowcast sector, like the one seen in the screenshot from Mordeth Map07. The extra sector '4' has a ceiling height from which you want the object to dangle from ('X', same as sector 2), with the same floor depth/texture as sector 3.

Both sides of linedefs 'b' reference back to sector 4. The blue dot represents the object. Depending on the nodesbuilder used it can be seen under different light levels. Warm fails to draw the object at the correct (faked) ceiling height.

SECTORS 1 : ceiling/floor X/Y with light level 100; 2 : ceiling/floor X/16, light level 100; 3 : ceiling/floor X+500/Y, light level 255; 4 : ceiling/floor X/Y-500, light level 100

LINEDEFS a : has missing upper textures; b : this linedefs has normal references, that is the front to sector 4 and the back to sector 3. Missing upper/lower textures; c : references on both sides back to sector 3.

This diagram shows how to make the same effect with Warm. Simple put, the effect is done here with another 'shadowcast' sector within the first one. While sector 3 is a normal sector with regards to its linedefs references, it is crossed by a linedef from sector 3, thus maintaining the first 'shadowcast' effect.

You can do a variation on this to create a shadowcasted floor, ie. bright ceiling but dark floor. This is done by "inverting" the process, by sinking the affected floor way deep and removing the lower textures. To prevent a player from falling in the hole another shadowcasted sector needs to be inserted in the first shadowcasted sector, with a heightened ceiling and missing upper textures, but with the correct (walking) floor height.