Better player mesh collision

game_patch/CMakeLists.txt

@@ -226,6 +226,7 @@ set(SRCS
     object/monitor.cpp
     object/particle.cpp
     object/obj_light.cpp
+    object/mesh_collision.cpp
     object/alpine_mesh.cpp
     object/alpine_corona.cpp
     object/alpine_corona.h

game_patch/object/mesh_collision.cpp

@@ -0,0 +1,79 @@
+#include <algorithm>
+#include <patch_common/CallHook.h>
+#include <patch_common/FunHook.h>
+#include <patch_common/CodeInjection.h>
+#include <patch_common/AsmWriter.h>
+#include <xlog/xlog.h>
+#include "../rf/vmesh.h"
+#include "../rf/physics.h"
+#include "../rf/object.h"
+
+// Mesh collision in the RF engine uses per-triangle intersection tests (vmesh_collide)
+// rather than BSP-based solid collision (GSolid::collide). This makes it fundamentally
+// less robust: triangle soup has gaps at edges/seams, no concept of a closed solid
+// volume, and limited multi-hit resolution. These patches improve mesh collision
+// reliability to reduce "falling through" and "getting stuck" on mesh surfaces.
+
+// Small margin added to the collision sphere radius when testing physics collision
+// against mesh triangles. This closes gaps at triangle edges/seams by making the
+// effective collision volume slightly larger, preventing the sphere from slipping
+// between adjacent triangles. The margin is small enough to not noticeably affect
+// gameplay feel.
+static constexpr float mesh_radius_margin = 0.02f;
+
+// Small amount subtracted from hit_time after mesh collision detection. This ensures
+// the object stops slightly before the mesh surface, providing clearance that prevents
+// the object from getting embedded in the mesh on the next frame. This reduces the
+// oscillation/"stuck" behavior that occurs when conflicting normals from adjacent
+// triangles push the player back and forth.
+static constexpr float mesh_hit_time_safety = 0.005f;
+
+// Hook vmesh_collide (0x005031F0) at its call sites in the physics collision paths.
+// This inflates the collision radius for the duration of the mesh test only, making
+// the swept sphere slightly larger and closing edge gaps between mesh triangles.
+//
+// Call sites:
+//   0x00499BD2 - collide_spheres_mesh: ground contact and stick-to-ground tests
+//   0x0049B332 - collide_object_object_mesh: object-pair mesh collision
+//
+// Other vmesh_collide callers (weapon raycasts, line-of-sight, glare occlusion)
+// are intentionally not hooked as they need precise triangle-level accuracy.
+CallHook<bool(rf::VMesh*, rf::VMeshCollisionInput*, rf::VMeshCollisionOutput*, bool)>
+mesh_physics_collide_radius_hook{
+    {
+        0x00499BD2, // in collide_spheres_mesh
+        0x0049B332, // in collide_object_object_mesh
+    },
+    [](rf::VMesh* vmesh, rf::VMeshCollisionInput* in, rf::VMeshCollisionOutput* out, bool clear) {
+        float original_radius = in->radius;
+        in->radius += mesh_radius_margin;
+        bool result = mesh_physics_collide_radius_hook.call_target(vmesh, in, out, clear);
+        in->radius = original_radius;
+        return result;
+    },
+};
+
+// Hook collide_object_object_mesh (0x0049AFE0) to apply a safety margin to the
+// collision hit_time. When a mesh collision is detected, the object is stopped at
+// (hit_time - margin) instead of exactly at hit_time. This small clearance prevents
+// the object from being positioned right on the mesh surface where floating-point
+// imprecision and conflicting triangle normals can cause it to get stuck or embedded.
+FunHook<bool(rf::Object*, rf::Object*)> collide_object_object_mesh_hook{
+    0x0049AFE0,
+    [](rf::Object* sphere_obj, rf::Object* mesh_obj) {
+        bool result = collide_object_object_mesh_hook.call_target(sphere_obj, mesh_obj);
+        if (result) {
+            float& hit_time = sphere_obj->p_data.collide_out.hit_time;
+            if (hit_time > mesh_hit_time_safety) {
+                hit_time -= mesh_hit_time_safety;
+            }
+        }
+        return result;
+    },
+};
+
+void mesh_collision_apply_patches()
+{
+    mesh_physics_collide_radius_hook.install();
+    collide_object_object_mesh_hook.install();
+}

game_patch/object/object.cpp

@@ -524,4 +524,5 @@ void object_do_patch()
     mover_do_patch();
     particle_do_patch();
     obj_light_apply_patch();
+    mesh_collision_apply_patches();
 }

game_patch/object/object_private.h

@@ -13,3 +13,4 @@ void entity_do_patch();
 void item_do_patch();
 void particle_do_patch();
 void obj_light_apply_patch();
+void mesh_collision_apply_patches();