World: add world/sky material colour modulation

Port Amalgam's modulation approach: obtain IMaterialSystem from the already
loaded materialsystem.so (VMaterialSystem080) and walk materials with
FirstMaterial/NextMaterial/GetMaterial. ColorModulate the "World textures"
group (sky names excluded) and the "SkyBox textures"/sky-named group.

The walk runs only when the enabled groups or colours change, restores white
when disabled, and re-applies after level changes. Before touching materials,
GetNumMaterials() and the first material's name/group are sanity-checked so a
wrong vtable slot logs and aborts instead of walking garbage.

GUI: "World tint" card with world/sky toggles and RGB sliders; config section
[worldtint].

1 files changed, 20 insertions, 0 deletions

diff --git a/src/gui.cpp b/src/gui.cpp
index 3f1651d..9d27a09 100644
--- a/src/gui.cpp
+++ b/src/gui.cpp
@@ -375,6 +375,26 @@ static void build_cards() {
   add_card(2, &g_fullbright, "Fullbright",
            "Ignore world lighting so dark areas are visible.", true);
 
+  int tint = add_card(2, &g_world_tint, "World tint",
+                      "Multiply world and skybox material colour. "
+                      "Independent of Fullbright lighting.", true);
+  add_toggle(tint, "World brushes",
+             "Tint world textures (sky and water excluded from this part).",
+             &g_tint_world_on);
+  add_slider(tint, "World red", "Red channel of the world tint (0-255).", 0,
+             255, &g_tint_world_rgb[0]);
+  add_slider(tint, "World green", "Green channel of the world tint (0-255).", 0,
+             255, &g_tint_world_rgb[1]);
+  add_slider(tint, "World blue", "Blue channel of the world tint (0-255).", 0,
+             255, &g_tint_world_rgb[2]);
+  add_toggle(tint, "Skybox", "Tint the skybox textures.", &g_tint_sky_on);
+  add_slider(tint, "Sky red", "Red channel of the sky tint (0-255).", 0, 255,
+             &g_tint_sky_rgb[0]);
+  add_slider(tint, "Sky green", "Green channel of the sky tint (0-255).", 0,
+             255, &g_tint_sky_rgb[1]);
+  add_slider(tint, "Sky blue", "Blue channel of the sky tint (0-255).", 0, 255,
+             &g_tint_sky_rgb[2]);
+
   int spread = add_card(3, &g_spread, "Spread control",
                         "Choose a server shot seed that tightens the cone.",
                         true);