Unisolid hitboxes for objects (#2647)

CollisionObject now contains a unisolid property. If it's true, only bottom constraints to the top of the bounding box would be applied to objects, colliding with that object.

The property is also settable from sprite file actions with the name unisolid. Default is false.

Fixes #2644.

src/collision/collision_object.cpp

@@ -27,6 +27,7 @@ CollisionObject::CollisionObject(CollisionGroup group, CollisionListener& listen
   m_group(group),
   m_movement(0.0f, 0.0f),
   m_dest(),
+  m_unisolid(false),
   m_objects_hit_bottom(),
   m_ground_movement_manager(nullptr)
 {

src/collision/collision_object.hpp

@@ -63,6 +63,9 @@ class CollisionObject
 
   void clear_bottom_collision_list();
 
+  bool is_unisolid() const { return m_unisolid; }
+  void set_unisolid(bool unisolid) { m_unisolid = unisolid; }
+
   /** returns the bounding box of the Object */
   const Rectf& get_bbox() const
   {
@@ -155,6 +158,12 @@ class CollisionObject
       during collision detection */
   Rectf m_dest;
 
+  /** Determines whether the object is unisolid.
+
+      Only bottom constraints to the top of the bounding box would be applied for objects,
+      colliding with unisolid objects. */
+  bool m_unisolid;
+
   /** Objects that were touching the top of this object at the last frame,
       if this object was static or moving static. */
   std::unordered_set<CollisionObject*> m_objects_hit_bottom;

src/collision/collision_system.cpp

@@ -98,6 +98,11 @@ CollisionSystem::draw(DrawingContext& context)
     }
     const Rectf& rect = object->get_bbox();
     context.color().draw_filled_rect(rect, color, LAYER_FOREGROUND1 + 10);
+
+    // If unisolid, draw a line on top of the rectangle.
+    if (object->is_unisolid())
+      context.color().draw_line(rect.p1(), Vector(rect.get_right(), rect.get_top()),
+                                Color::YELLOW, LAYER_FOREGROUND1 + 11);
   }
 }
 
@@ -131,22 +136,25 @@ collision::Constraints check_collisions(const Vector& obj_movement, const Rectf&
 
   bool shiftout = false;
 
-  if (fabsf(obj_movement.y) > fabsf(obj_movement.x)) {
-    if (ileft < SHIFT_DELTA) {
-      constraints.constrain_right(grown_other_obj_rect.get_left());
-      shiftout = true;
-    } else if (iright < SHIFT_DELTA) {
-      constraints.constrain_left(grown_other_obj_rect.get_right());
-      shiftout = true;
-    }
-  } else {
-    // Shiftout bottom/top.
-    if (itop < SHIFT_DELTA) {
-      constraints.constrain_bottom(grown_other_obj_rect.get_top());
-      shiftout = true;
-    } else if (ibottom < SHIFT_DELTA) {
-      constraints.constrain_top(grown_other_obj_rect.get_bottom());
-      shiftout = true;
+  if (!other_object || !other_object->is_unisolid())
+  {
+    if (fabsf(obj_movement.y) > fabsf(obj_movement.x)) {
+      if (ileft < SHIFT_DELTA) {
+        constraints.constrain_right(grown_other_obj_rect.get_left());
+        shiftout = true;
+      } else if (iright < SHIFT_DELTA) {
+        constraints.constrain_left(grown_other_obj_rect.get_right());
+        shiftout = true;
+      }
+    } else {
+      // Shiftout bottom/top.
+      if (itop < SHIFT_DELTA) {
+        constraints.constrain_bottom(grown_other_obj_rect.get_top());
+        shiftout = true;
+      } else if (ibottom < SHIFT_DELTA) {
+        constraints.constrain_top(grown_other_obj_rect.get_bottom());
+        shiftout = true;
+      }
     }
   }
 
@@ -158,6 +166,18 @@ collision::Constraints check_collisions(const Vector& obj_movement, const Rectf&
         return constraints;
     }
 
+    if (other_object && other_object->is_unisolid())
+    {
+      // Constrain only on fall on top of the unisolid object.
+      if (moving_obj_rect.get_bottom() - obj_movement.y <= grown_other_obj_rect.get_top())
+      {
+        constraints.constrain_bottom(grown_other_obj_rect.get_top());
+        constraints.hit.bottom = true;
+      }
+
+      return constraints;
+    }
+
     const float vert_penetration = std::min(itop, ibottom);
     const float horiz_penetration = std::min(ileft, iright);
 

src/object/conveyor_belt.cpp

@@ -117,6 +117,8 @@ ConveyorBelt::draw(DrawingContext &context)
 void
 ConveyorBelt::update_hitbox()
 {
+  MovingSprite::update_hitbox();
+
   m_col.m_bbox.set_size(m_sprite->get_current_hitbox_width() * static_cast<float>(m_length),
                         m_sprite->get_current_hitbox_height());
 }

src/object/moving_sprite.cpp

@@ -127,6 +127,7 @@ void
 MovingSprite::update_hitbox()
 {
   m_col.set_size(m_sprite->get_current_hitbox_width(), m_sprite->get_current_hitbox_height());
+  m_col.set_unisolid(m_sprite->is_current_hitbox_unisolid());
 }
 
 void

src/sprite/sprite.cpp

@@ -192,6 +192,12 @@ Sprite::get_height() const
   return static_cast<int>(m_action->surfaces[m_frameidx]->get_height());
 }
 
+bool
+Sprite::is_current_hitbox_unisolid() const
+{
+  return m_action->hitbox_unisolid;
+}
+
 float
 Sprite::get_current_hitbox_x_offset() const
 {

src/sprite/sprite.hpp

@@ -89,6 +89,8 @@ class Sprite final
   int get_width() const;
   int get_height() const;
 
+  /** Return the "unisolid" property for the current action's hitbox. */
+  bool is_current_hitbox_unisolid() const;
   /** return x-offset of current action's hitbox, relative to start of image */
   float get_current_hitbox_x_offset() const;
   /** return y-offset of current action's hitbox, relative to start of image */

src/sprite/sprite_data.cpp

@@ -35,6 +35,7 @@ SpriteData::Action::Action() :
   y_offset(0),
   hitbox_w(0),
   hitbox_h(0),
+  hitbox_unisolid(false),
   fps(10),
   loops(-1),
   loop_frame(1),
@@ -127,6 +128,7 @@ SpriteData::parse_action(const ReaderMapping& mapping)
         throw std::runtime_error("hitbox should specify 2/4 coordinates");
     }
   }
+  mapping.get("unisolid", action->hitbox_unisolid);
   mapping.get("fps", action->fps);
   if (mapping.get("loops", action->loops))
   {

src/sprite/sprite_data.hpp

@@ -62,6 +62,9 @@ class SpriteData final
     /** Hitbox height */
     float hitbox_h;
 
+    /** Whether the hitbox is unisolid */
+    bool hitbox_unisolid;
+
     /** Frames per second */
     float fps;