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, 26 insertions, 9 deletions

diff --git a/src/studio.cpp b/src/studio.cpp
index bee6db5..07ebec3 100644
--- a/src/studio.cpp
+++ b/src/studio.cpp
@@ -248,6 +248,15 @@ void chams_color(void *mat, float r, float g, float b) {
   vfunc<ColorFn>(mat, 28)(mat, r, g, b);
 }
 
+void chams_alpha(void *mat, float a) {
+  using FindVarFn = void *(*)(void *, const char *, bool *, bool);
+  using SetFloatFn = void (*)(void *, float);
+  bool found = false;
+  void *var = vfunc<FindVarFn>(mat, 11)(mat, "$alpha", &found, false);
+  if (var)
+    vfunc<SetFloatFn>(var, 3)(var, a);
+}
+
 void chams_apply(void *mat, bool ignorez, int style, bool force_white,
                  const int *rgb, bool znearer) {
   using FlagFn = void (*)(void *, int, bool);
@@ -255,10 +264,12 @@ void chams_apply(void *mat, bool ignorez, int style, bool force_white,
   float g = force_white ? 1.0f : (float)rgb[1] / 255.0f;
   float b = force_white ? 1.0f : (float)rgb[2] / 255.0f;
   chams_color(mat, r, g, b);
+  chams_alpha(mat, (float)rgb[3] / 255.0f);
   // 0 Flat, 1 Wireframe, 2 Additive, 3 Solid, 4 White, 5 Fullbright
   // (additive white glow), 6 Glow outline (solid base; the wireframe overlay
   // is a second draw with ZNEARER so its contour is not hidden by the base).
   vfunc<FlagFn>(mat, 29)(mat, 1 << 15 /* IGNOREZ */, ignorez);
+  vfunc<FlagFn>(mat, 29)(mat, 1 << 21 /* TRANSLUCENT */, rgb[3] < 255);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 10 /* ZNEARER */, znearer);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 28 /* WIREFRAME */, style == 1);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 7 /* ADDITIVE */,
@@ -270,12 +281,14 @@ void chams_apply(void *mat, bool ignorez, int style, bool force_white,
 void chams_reset(void *mat) {
   using FlagFn = void (*)(void *, int, bool);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 15, false);
+  vfunc<FlagFn>(mat, 29)(mat, 1 << 21, false);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 10, false);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 28, false);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 7, false);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 12, false);
   vfunc<FlagFn>(mat, 29)(mat, 1 << 6, false);
   chams_color(mat, 1.0f, 1.0f, 1.0f);
+  chams_alpha(mat, 1.0f);
 }
 
 void hkdModelExecute(void *self, const void *state, const void *info,
@@ -306,20 +319,24 @@ void hkdModelExecute(void *self, const void *state, const void *info,
           // Fullbright is an additive, self-illuminated version of the
           // chosen colour: lift it toward white so it reads brighter than
           // the plain additive style.
-          int brgb[3];
+          int brgb[4];
           const int *use_rgb = rgb;
           if (style == 5) {
             for (int i = 0; i < 3; i++)
-              brgb[i] = rgb[i] + (255 - rgb[i]) / 2;
+              brgb[i] = rgb[i] + (255 - rgb[i]) / 4;
+            brgb[3] = rgb[3];
             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};
+          // some places. Lay down a faint translucent base so the first-person
+          // model keeps a silhouette on bright backgrounds without turning
+          // into an opaque blob; the additive pass still provides the glow.
+          if (is_vm && (style == 2 || style == 5) && rgb[3] > 0) {
+            int ba = rgb[3] / 8;
+            if (ba < 16)
+              ba = 16;
+            int drgb[4] = {rgb[0], rgb[1], rgb[2], ba};
             chams_apply(mat, ignorez, 3, false, drgb, false);
             g_force_override(self, mat, 0 /* OVERRIDE_NORMAL */);
             g_orig_model_exec(self, state, info, bone);
@@ -333,8 +350,8 @@ void hkdModelExecute(void *self, const void *state, const void *info,
             // the contour and bias it forward so the base cannot bury it.
             void *wire = g_style_mats[1];
             if (wire && wire != mat) {
-              int wrgb[3] = {(rgb[0] + 255) / 2, (rgb[1] + 255) / 2,
-                             (rgb[2] + 255) / 2};
+              int wrgb[4] = {(rgb[0] + 255) / 2, (rgb[1] + 255) / 2,
+                             (rgb[2] + 255) / 2, rgb[3]};
               chams_apply(wire, ignorez, 1, false, wrgb, true);
               g_force_override(self, wire, 0);
               g_orig_model_exec(self, state, info, bone);