So there were some concerns for the Bungie crew regarding the shields:
A) They had to be consistent with Halo 3 since Reach takes place only a couple months before it,
B) they had to be more transparent so that the character art wouldn't be hidden,
C) they had to be flexible enough to show different states in an obvious manner, and
D) they shouldn't add much art overhead - no custom geometry or texture coordinate UVs.
B) they had to be more transparent so that the character art wouldn't be hidden,
C) they had to be flexible enough to show different states in an obvious manner, and
D) they shouldn't add much art overhead - no custom geometry or texture coordinate UVs.
To solve D, the shield geometry is a shell extruded from the existing model and its texture coordinates - vertices pushed along the normal. This also means that the effect could be applied to any geometry such as those pesky generators in Firefight or the vehicles hit by some plasma overcharge. To assist with B, the depth buffer is sampled and the shield is faded as some function of the distance to the shell. In effect, the shield is more visible against an environment while it fades away when overlapping the shielded object. An edge fade control was also added to adjust how the edge begins to fade, effectively customizing the softness/hardness of the shell's highlight. Mixing these two controls allowed Bungie artists to create a number of different looking effects.
One clever use of the depth and edge fade controls was described, as Chris writes:
For example, feeding the depth fade value into a palettized plasma shader allowed us to give the appearance that electrical arcs were actually touching objects, without performing any additional computations.
The palette in this case is two dimensional – one dimension is indexed by the plasma to get the blue-white color transition,
And the other dimension is indexed by the depth fade, allowing the shape to change as it gets close to something – in this case the single ramp of the lightning bifurcates into two ramps.
The palette in this case is two dimensional – one dimension is indexed by the plasma to get the blue-white color transition,
And the other dimension is indexed by the depth fade, allowing the shape to change as it gets close to something – in this case the single ramp of the lightning bifurcates into two ramps.
Keeping the depth comparison in mind, the two controls could be manipulated to provide a glowing outline to objects passing through a shield portal or a King of the Hill boundary.
