Chams: per-colour alpha and a softer viewmodel additive base

- Colour picker gains an optional alpha bar (checkerboard preview, #RRGGBBAA
  readout); add_color_alpha is used for the chams colours. Chams colours are
  now r,g,b,a and chams_apply sets $alpha plus MATERIAL_VAR_TRANSLUCENT when
  alpha < 255. Config stores vis_a / inv_a / vm a.
- The additive viewmodel base is now a faint translucent tint (alpha/8)
  instead of an opaque fill, so additive/Fullbright stay see-through and the
  viewmodel no longer becomes a solid blob. Fullbright whitening reduced to
  25% so blue stays blue instead of turning lavender.

1 files changed, 16 insertions, 10 deletions

diff --git a/CONTEXT.md b/CONTEXT.md
index c75e36c..1bb0a6a 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -290,11 +290,16 @@ vocabulary / decisions.
   viewmodel entities (class contains `viewmodel` or model path `.../v_...`)
   are a fourth group.
 - Each relationship has independent **visible** and **through-wall** settings:
-  on/off, style, and colour. The viewmodel has on/off, style and colour only.
-  The through-wall pass uses `MATERIAL_VAR_IGNOREZ` (1 << 15) through
-  `IMaterial::SetMaterialVarFlag` (slot 29); colours use `$color`/`$color2`
-  (IMaterialVar slot 11, SetVecValue 3-float slot 11) and `ColorModulate`
-  (slot 28). Shared materials are restored after each draw.
+  on/off, style, colour and alpha. The viewmodel has on/off, style, colour and
+  alpha only. The through-wall pass uses `MATERIAL_VAR_IGNOREZ` (1 << 15)
+  through `IMaterial::SetMaterialVarFlag` (slot 29); colours use
+  `$color`/`$color2` (IMaterialVar slot 11, SetVecValue 3-float slot 11) and
+  `ColorModulate` (slot 28). Alpha uses `$alpha` (IMaterialVar slot 3,
+  SetFloatValue) and `MATERIAL_VAR_TRANSLUCENT` (1 << 21) when alpha < 255.
+  Shared materials are restored after each draw.
+- The GUI colour picker (`add_color_alpha`) has an alpha bar, checkerboard
+  preview and `#RRGGBBAA` readout; plain `add_color` keeps the old opaque
+  three-component behaviour. Chams colours are four ints (r, g, b, a).
 - Styles are built from `debug/debugtranslucentsinglecolor` (UnlitGeneric,
   `$color`) and material flags:
   0 Flat (solid + FLAT), 1 Wireframe (`debug/debugwireframe`), 2 Additive
@@ -310,12 +315,13 @@ vocabulary / decisions.
 - Viewmodels are collated by the engine as `RENDER_GROUP_VIEW_MODEL_OPAQUE`,
   so an additive forced material can wash out against a bright sky or wall
   (and the engine may not treat the draw as translucent). Additive styles on
-  the viewmodel therefore draw a dim opaque solid base first, then the
-  additive pass; the first-person model never disappears.
+  the viewmodel therefore draw a faint translucent base (alpha/8) first, then
+  the additive pass, so the model keeps a silhouette on bright backgrounds
+  without becoming an opaque blob.
 - Feature is off by default. Config sections: `[chams]` (active/bind),
-  `[chams_hostile|neutral|friendly]` (`vis`, `vis_mat`, `vis_r/g/b`, `inv`,
-  `inv_mat`, `inv_r/g/b`) and `[chams_vm]` (`on`, `mat`, `r/g/b`). The GUI has
-  a Hostile/Neutral/Friendly section each, plus Viewmodel.
+  `[chams_hostile|neutral|friendly]` (`vis`, `vis_mat`, `vis_r/g/b/a`, `inv`,
+  `inv_mat`, `inv_r/g/b/a`) and `[chams_vm]` (`on`, `mat`, `r/g/b/a`). The GUI
+  has a Hostile/Neutral/Friendly section each, plus Viewmodel.
 - This is a material override, not stencil outlines.
 
 ## Bones / ESP