Chams: keep additive viewmodel visible on bright backgrounds

Viewmodels are collated as RENDER_GROUP_VIEW_MODEL_OPAQUE, so an additive
forced material can vanish against a bright sky/wall (additive adds nothing to
an already-bright surface). Draw a dim opaque solid base before the additive
viewmodel pass so the first-person model always has a visible silhouette; the
additive layer still provides the glow.

2 files changed, 17 insertions, 0 deletions

diff --git a/CONTEXT.md b/CONTEXT.md
index ad9ce2d..c75e36c 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -307,6 +307,11 @@ vocabulary / decisions.
   VGUI additive material was invisible on NPCs.
 - Style materials are preloaded from `outer_draw` (throttled) and cached; the
   render hook never calls FindMaterial itself. A missing style uses solid.
+- 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.
 - 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
diff --git a/src/studio.cpp b/src/studio.cpp
index 4941142..bee6db5 100644
--- a/src/studio.cpp
+++ b/src/studio.cpp
@@ -313,6 +313,18 @@ void hkdModelExecute(void *self, const void *state, const void *info,
               brgb[i] = rgb[i] + (255 - rgb[i]) / 2;
             use_rgb = brgb;
           }
+          // Additive blending vanishes against bright backgrounds (sky,
+          // white walls, strong fog), which made the viewmodel disappear in
+          // some places. Lay down a dim opaque base first so the first-person
+          // model always has a visible silhouette; the additive pass still
+          // adds the glow on top.
+          if (is_vm && (style == 2 || style == 5)) {
+            int drgb[3] = {rgb[0] / 2, rgb[1] / 2, rgb[2] / 2};
+            chams_apply(mat, ignorez, 3, false, drgb, false);
+            g_force_override(self, mat, 0 /* OVERRIDE_NORMAL */);
+            g_orig_model_exec(self, state, info, bone);
+            chams_reset(mat);
+          }
           chams_apply(mat, ignorez, style, white, use_rgb, false);
           g_force_override(self, mat, 0 /* OVERRIDE_NORMAL */);
           g_orig_model_exec(self, state, info, bone);