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, 248 insertions, 0 deletions

diff --git a/src/world.cpp b/src/world.cpp
new file mode 100644
index 0000000..eeffb99
--- /dev/null
+++ b/src/world.cpp
@@ -0,0 +1,248 @@
+// world.cpp — world/sky material colour modulation.
+//
+// Same mechanism Amalgam uses for its "World modulation": walk every material
+// in the material system and call IMaterial::ColorModulate on the ones whose
+// texture group is the world (or the skybox). This multiplies the material's
+// albedo; it does not touch lightmaps, so it is cheap and does not recompile
+// shaders.
+//
+// HL2's materialsystem.so registers "VMaterialSystem080" (the SDK 2013 name
+// for the modern layout) and exports CreateInterface, so the interface is
+// obtained exactly like VClient017/VGUI_Surface030 elsewhere in this cheat.
+//
+// Vtable slots are taken from the 2013 SDK headers:
+//   IMaterialSystem: FirstMaterial=73 NextMaterial=74 InvalidMaterial=75
+//                    GetMaterial=76 GetNumMaterials=77
+//   IMaterial:       GetName=0 GetTextureGroupName=1 ColorModulate=28
+
+#include "hl2h.h"
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <dlfcn.h>
+
+namespace {
+
+constexpr int MATSYS_FirstMaterial = 73;
+constexpr int MATSYS_NextMaterial = 74;
+constexpr int MATSYS_InvalidMaterial = 75;
+constexpr int MATSYS_GetMaterial = 76;
+constexpr int MATSYS_GetNumMaterials = 77;
+
+constexpr int MAT_GetName = 0;
+constexpr int MAT_GetTextureGroupName = 1;
+constexpr int MAT_ColorModulate = 28;
+
+constexpr const char *GROUP_WORLD = "World textures";
+constexpr const char *GROUP_SKYBOX = "SkyBox textures";
+
+void *g_matsys = nullptr;
+bool g_matsys_tried = false;
+bool g_matsys_failed = false;
+bool g_matsys_logged = false;
+
+// Last state handed to the material system. Colour changes are applied when
+// this differs from the desired state, so the all-material walk runs only on
+// toggles/colour edits/level changes, never every frame.
+struct Tint {
+  bool valid;
+  int world_r, world_g, world_b;
+  int sky_r, sky_g, sky_b;
+};
+Tint g_applied{false, 255, 255, 255, 255, 255, 255};
+
+struct MatCalls {
+  using FirstFn = unsigned short (*)(void *);
+  using NextFn = unsigned short (*)(void *, unsigned short);
+  using InvalidFn = unsigned short (*)(void *);
+  using GetFn = void *(*)(void *, unsigned short);
+  using CountFn = int (*)(void *);
+  using NameFn = const char *(*)(void *);
+  using GroupFn = const char *(*)(void *);
+  using ModulateFn = void (*)(void *, float, float, float);
+};
+
+// Reject obviously bogus strings returned by a mis-mapped vtable slot instead
+// of walking thousands of materials with garbage pointers.
+bool plausible_name(const char *s) {
+  if (!s || !*s)
+    return false;
+  size_t n = strnlen(s, 512);
+  if (n == 0 || n >= 512)
+    return false;
+  for (size_t i = 0; i < n; i++) {
+    unsigned char c = (unsigned char)s[i];
+    if (c < 0x20 || c == 0x7f)
+      return false;
+  }
+  return true;
+}
+
+std::string find_loaded_module(const char *needle) {
+  FILE *maps = fopen("/proc/self/maps", "r");
+  if (!maps)
+    return {};
+  char line[1024];
+  std::string found;
+  while (fgets(line, sizeof(line), maps)) {
+    char *p = strchr(line, '/');
+    if (!p)
+      continue;
+    size_t pl = strlen(p);
+    while (pl && (p[pl - 1] == '\n' || p[pl - 1] == '\r'))
+      p[--pl] = 0;
+    if (!strstr(p, needle) || !strstr(p, ".so"))
+      continue;
+    found = p;
+    if (!strstr(p, "(deleted)"))
+      break;
+  }
+  fclose(maps);
+  return found;
+}
+
+void *material_system() {
+  if (g_matsys_tried)
+    return g_matsys;
+  g_matsys_tried = true;
+
+  std::string path = find_loaded_module("materialsystem");
+  void *h = nullptr;
+  if (!path.empty())
+    h = dlopen(path.c_str(), RTLD_NOLOAD | RTLD_LAZY | RTLD_GLOBAL);
+  // The engine always dlopens the module by name; NOLOAD only attaches to the
+  // already-mapped copy, so we never spawn a second material system.
+  if (!h)
+    h = dlopen("materialsystem.so", RTLD_NOLOAD | RTLD_LAZY | RTLD_GLOBAL);
+  if (!h) {
+    g_matsys_failed = true;
+    logf("tint: materialsystem.so not loaded");
+    return nullptr;
+  }
+  auto cf = (CreateInterfaceFn)dlsym(h, "CreateInterface");
+  if (!cf) {
+    g_matsys_failed = true;
+    logf("tint: materialsystem CreateInterface missing");
+    return nullptr;
+  }
+  static const char *names[] = {"VMaterialSystem080", "VMaterialSystem082",
+                                "VMaterialSystem081", nullptr};
+  for (const char **n = names; *n; n++) {
+    int ret = 0;
+    void *ms = cf(*n, &ret);
+    if (!ms)
+      continue;
+    g_matsys = ms;
+    logf("tint: %s = %p via %s", *n, ms,
+         path.empty() ? "materialsystem.so" : path.c_str());
+    return ms;
+  }
+  g_matsys_failed = true;
+  logf("tint: material system interface not exposed");
+  return nullptr;
+}
+
+// Push one colour pair over all materials. Groups that are off get white so a
+// previously tinted world is restored.
+bool apply_tint(int world_r, int world_g, int world_b, int sky_r, int sky_g,
+                int sky_b) {
+  void *ms = material_system();
+  if (!ms)
+    return false;
+
+  auto invalid = vfunc<MatCalls::InvalidFn>(ms, MATSYS_InvalidMaterial);
+  auto first = vfunc<MatCalls::FirstFn>(ms, MATSYS_FirstMaterial);
+  auto next = vfunc<MatCalls::NextFn>(ms, MATSYS_NextMaterial);
+  auto get = vfunc<MatCalls::GetFn>(ms, MATSYS_GetMaterial);
+  auto count = vfunc<MatCalls::CountFn>(ms, MATSYS_GetNumMaterials);
+
+  int total = count(ms);
+  if (total <= 0 || total > 200000) {
+    logf("tint: GetNumMaterials() = %d (unexpected; disabled)", total);
+    g_matsys_failed = true;
+    toastf(TOAST_ERROR, "World tint: material system layout mismatch");
+    return false;
+  }
+
+  float wr = world_r / 255.0f, wg = world_g / 255.0f, wb = world_b / 255.0f;
+  float sr = sky_r / 255.0f, sg = sky_g / 255.0f, sb = sky_b / 255.0f;
+
+  unsigned short inv = invalid(ms);
+  int seen = 0, world_hits = 0, sky_hits = 0;
+  for (unsigned short h = first(ms); h != inv; h = next(ms, h)) {
+    if (++seen > total + 16) {
+      logf("tint: material walk runaway (%d > %d); stopped", seen, total);
+      break;
+    }
+    void *mat = get(ms, h);
+    if (!mat)
+      continue;
+    auto name_fn = vfunc<MatCalls::NameFn>(mat, MAT_GetName);
+    auto group_fn = vfunc<MatCalls::GroupFn>(mat, MAT_GetTextureGroupName);
+    auto mod_fn = vfunc<MatCalls::ModulateFn>(mat, MAT_ColorModulate);
+    const char *name = name_fn(mat);
+    const char *group = group_fn(mat);
+    if (!plausible_name(name) || !plausible_name(group))
+      continue;
+    // The first material's name also validates the IMaterial vtable mapping
+    // before we poke any colour state.
+    if (!g_matsys_logged) {
+      g_matsys_logged = true;
+      logf("tint: first material \"%s\" group \"%s\"", name, group);
+    }
+    bool is_world = strncmp(group, GROUP_WORLD, strlen(GROUP_WORLD)) == 0;
+    bool is_sky = strncmp(group, GROUP_SKYBOX, strlen(GROUP_SKYBOX)) == 0 ||
+                  strstr(name, "sky") != nullptr;
+    if (is_world && !strstr(name, "sky")) {
+      mod_fn(mat, wr, wg, wb);
+      world_hits++;
+    } else if (is_sky) {
+      mod_fn(mat, sr, sg, sb);
+      sky_hits++;
+    }
+  }
+  logf("tint: applied world=%d(%d,%d,%d) sky=%d(%d,%d,%d) of %d materials",
+       world_hits, world_r, world_g, world_b, sky_hits, sky_r, sky_g, sky_b,
+       total);
+  return true;
+}
+
+} // namespace
+
+void world_tint_invalidate() { g_applied.valid = false; }
+
+void world_tint_update() {
+  bool on = feature_active(FEAT_WORLD_TINT);
+  bool world_on = on && g_tint_world_on;
+  bool sky_on = on && g_tint_sky_on;
+
+  int wr = world_on ? g_tint_world_rgb[0] : 255;
+  int wg = world_on ? g_tint_world_rgb[1] : 255;
+  int wb = world_on ? g_tint_world_rgb[2] : 255;
+  int sr = sky_on ? g_tint_sky_rgb[0] : 255;
+  int sg = sky_on ? g_tint_sky_rgb[1] : 255;
+  int sb = sky_on ? g_tint_sky_rgb[2] : 255;
+
+  bool white = wr == 255 && wg == 255 && wb == 255 && sr == 255 &&
+               sg == 255 && sb == 255;
+  if (g_applied.valid && g_applied.world_r == wr && g_applied.world_g == wg &&
+      g_applied.world_b == wb && g_applied.sky_r == sr &&
+      g_applied.sky_g == sg && g_applied.sky_b == sb)
+    return;
+  // Nothing was ever tinted and nothing is requested: no need to walk the
+  // material list just to write white over white.
+  if (!g_applied.valid && white) {
+    g_applied = {true, wr, wg, wb, sr, sg, sb};
+    return;
+  }
+  if (g_matsys_failed && !world_on && !sky_on) {
+    g_applied = {true, wr, wg, wb, sr, sg, sb};
+    return;
+  }
+  if (!apply_tint(wr, wg, wb, sr, sg, sb)) {
+    if (g_matsys_failed)
+      g_applied = {true, wr, wg, wb, sr, sg, sb};
+    return;
+  }
+  g_applied = {true, wr, wg, wb, sr, sg, sb};
+}