Props: forward DrawModel's modelOrigin argument

DrawModel takes (this, results, info, boneToWorld, flexWeights,
flexDelayedWeights, const Vector &modelOrigin, flags). The hook dropped
modelOrigin, so flags landed in its slot and the real flags were read from
caller stack garbage. studiorender.so 0x83ad0 reads 0x20(%ebp) as the
modelOrigin pointer and 0x24(%ebp) as the flags; passing both restores the
engine's normal draw.

This is the cause of the intermittent (~50%) checkerboard/error-material
props: the draw was being issued with a garbage flag word.

1 files changed, 16 insertions, 3 deletions

diff --git a/src/studio.cpp b/src/studio.cpp
index 485b4fb..2d6c826 100644
--- a/src/studio.cpp
+++ b/src/studio.cpp
@@ -25,8 +25,12 @@ namespace {
 using SetColorFn = void (*)(void *, const float *);
 using SetAlphaFn = void (*)(void *, float);
 using DrawStaticFn = void (*)(void *, void *, void *, int);
+// DrawModel takes (this, results, info, boneToWorld, flexWeights,
+// flexDelayedWeights, modelOrigin, flags). The modelOrigin argument is a
+// `const Vector &`, so it arrives as a pointer; omitting it shifts flags into
+// modelOrigin and leaves flags as caller stack garbage.
 using DrawModelFn = void (*)(void *, void *, void *, void *, void *, void *,
-                             int);
+                             const void *, int);
 using DrawArrayFn = void (*)(void *, void *, int, void *, int, int);
 
 SetColorFn g_orig_set_color = nullptr;
@@ -107,16 +111,25 @@ void hook_set_alpha(void *self, float alpha) {
 
 
 void hook_draw_model(void *self, void *results, void *info, void *bone,
-                     void *flex, void *flex_delayed, int flags) {
+                     void *flex, void *flex_delayed, const void *model_origin,
+                     int flags) {
   const char *model = info_model_name(info);
   bool prop = prop_tint_on() && is_prop_model(model);
+  static int prop_logs = 0;
+  if (prop && prop_logs < 12) {
+    prop_logs++;
+    void *client = info ? *(void **)((uintptr_t)info + 24) : nullptr;
+    logf("studio: prop draw model=\"%s\" client=%p origin=%p flags=%d",
+         model ? model : "?", client, model_origin, flags);
+  }
   if (prop) {
     float c[4];
     prop_color(c);
     g_orig_set_color(self, c);
     g_prop_depth++;
   }
-  g_orig_draw_model(self, results, info, bone, flex, flex_delayed, flags);
+  g_orig_draw_model(self, results, info, bone, flex, flex_delayed,
+                    model_origin, flags);
   if (prop)
     g_prop_depth--;
 }