Got the physics system applying gravity and drag correctly. (Mostly? Seems like it? Seems good.)

CMakeLists.txt

@@ -69,6 +69,8 @@ add_library(akgl SHARED
   src/heap.c
   src/json_helpers.c
   src/registry.c
+  src/renderer.c
+  src/physics.c
   src/sprite.c
   src/staticstring.c
   src/tilemap.c
@@ -142,6 +144,8 @@ install(FILES "include/akgl/controller.h" DESTINATION "include/akgl/")
 install(FILES "include/akgl/heap.h" DESTINATION "include/akgl/")
 install(FILES "include/akgl/iterator.h" DESTINATION "include/akgl/")
 install(FILES "include/akgl/json_helpers.h" DESTINATION "include/akgl/")
+install(FILES "include/akgl/renderer.h" DESTINATION "include/akgl/")
+install(FILES "include/akgl/physics.h" DESTINATION "include/akgl/")
 install(FILES "include/akgl/registry.h" DESTINATION "include/akgl/")
 install(FILES "include/akgl/sprite.h" DESTINATION "include/akgl/")
 install(FILES "include/akgl/staticstring.h" DESTINATION "include/akgl/")

include/akgl/SDL_GameControllerDB.h

@@ -1,7 +1,7 @@
 #ifndef _SDL_GAMECONTROLLERDB_H_
 #define _SDL_GAMECONTROLLERDB_H_
 
-// Taken from https://raw.githubusercontent.com/mdqinc/SDL_GameControllerDB/refs/heads/master/gamecontrollerdb.txt on Tue May 26 10:27:58 AM EDT 2026
+// Taken from https://raw.githubusercontent.com/mdqinc/SDL_GameControllerDB/refs/heads/master/gamecontrollerdb.txt on Tue May 26 04:12:10 PM EDT 2026
 
 #define AKGL_SDL_GAMECONTROLLER_DB_LEN         2228
 

include/akgl/actor.h

@@ -71,9 +71,31 @@ typedef struct akgl_Actor {
     void *actorData;
     bool visible;
     SDL_Time movetimer;
+    // Velocity. Combined effect of all forces acting on the actor resulting
+    // in energy along an axis.
     float32_t vx;
     float32_t vy;
     float32_t vz;
+    // Environmental velocity. These are the forces acting on the actor by the
+    // environment (such as gravity and atmospheric drag)
+    float32_t ex;
+    float32_t ey;
+    float32_t ez;
+    // Thrust. Energy originating only from the actor's own acceleration on a
+    // given axis, before the effects of gravity and drag.
+    float32_t tx;
+    float32_t ty;
+    float32_t tz;
+    // Acceleration. These are borrowed from the base character object.
+    // A given axis resets to 0 when the actor stops moving in a given axis.
+    float32_t ax;
+    float32_t ay;
+    float32_t az;
+    // Max speed. These are borrowed from the base character object.
+    float32_t sx;
+    float32_t sy;
+    float32_t sz;
+    // Position.
     float32_t x;
     float32_t y;
     float32_t z;
@@ -83,7 +105,7 @@ typedef struct akgl_Actor {
     akerr_ErrorContext AKERR_NOIGNORE *(*updatefunc)(struct akgl_Actor *obj);
     akerr_ErrorContext AKERR_NOIGNORE *(*renderfunc)(struct akgl_Actor *obj);
     akerr_ErrorContext AKERR_NOIGNORE *(*facefunc)(struct akgl_Actor *obj);
-    akerr_ErrorContext AKERR_NOIGNORE *(*movementlogicfunc)(struct akgl_Actor *obj, SDL_Time curtimems);
+    akerr_ErrorContext AKERR_NOIGNORE *(*movementlogicfunc)(struct akgl_Actor *obj, float32_t dt);
     akerr_ErrorContext AKERR_NOIGNORE *(*changeframefunc)(struct akgl_Actor *obj, akgl_Sprite *curSprite, SDL_Time curtimems);
     akerr_ErrorContext AKERR_NOIGNORE *(*addchild)(struct akgl_Actor *obj, struct akgl_Actor *child);
 } akgl_Actor;
@@ -92,7 +114,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_initialize(akgl_Actor *obj, char *
 akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_set_character(akgl_Actor *obj, char *basecharname);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_render(akgl_Actor *obj);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_update(akgl_Actor *obj);
-akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_logic_movement(akgl_Actor *obj, SDL_Time curtimems);
+akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_logic_movement(akgl_Actor *obj, float32_t dt);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_logic_changeframe(akgl_Actor *obj, akgl_Sprite *curSprite, SDL_Time curtimems);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_automatic_face(akgl_Actor *obj);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_actor_add_child(akgl_Actor *obj, akgl_Actor *child);

include/akgl/physics.h

@@ -8,9 +8,9 @@
 
 typedef struct akgl_PhysicsBackend {
     akerr_ErrorContext AKERR_NOIGNORE *(*simulate)(struct akgl_PhysicsBackend *self, akgl_Iterator *opflags);
-    akerr_ErrorContext AKERR_NOIGNORE *(*gravity)(struct akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime);
+    akerr_ErrorContext AKERR_NOIGNORE *(*gravity)(struct akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt);
     akerr_ErrorContext AKERR_NOIGNORE *(*collide)(struct akgl_PhysicsBackend *self, akgl_Actor *a1, akgl_Actor *a2);
-    akerr_ErrorContext AKERR_NOIGNORE *(*move)(struct akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime);
+    akerr_ErrorContext AKERR_NOIGNORE *(*move)(struct akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt);
 
     double drag_x;
     double drag_y;
@@ -23,15 +23,15 @@ typedef struct akgl_PhysicsBackend {
     
 } akgl_PhysicsBackend;
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime);
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_collide(akgl_PhysicsBackend *self, akgl_Actor *a1, akgl_Actor *a2);
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_move(akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime);
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_move(akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_init_null(akgl_PhysicsBackend *self);
 
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime);
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_collide(akgl_PhysicsBackend *self, akgl_Actor *a1, akgl_Actor *a2);
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_move(akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime);
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_move(akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt);
 akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_init_sidescroller(akgl_PhysicsBackend *self);
 
 

src/actor.c

@@ -51,6 +51,10 @@ akerr_ErrorContext *akgl_actor_set_character(akgl_Actor *obj, char *basecharname
     obj->basechar = SDL_GetPointerProperty(AKGL_REGISTRY_CHARACTER, basecharname, NULL);
 
     FAIL_ZERO_RETURN(errctx, obj->basechar, AKERR_NULLPOINTER, "Character not found in the registry");
+    obj->ax = 0;
+    obj->ay = 0;
+    obj->sx = obj->basechar->sx;
+    obj->sy = obj->basechar->sy;
     SUCCEED_RETURN(errctx);
 }
 
@@ -113,20 +117,25 @@ akerr_ErrorContext *akgl_actor_logic_changeframe(akgl_Actor *obj, akgl_Sprite *c
     SUCCEED_RETURN(errctx);
 }
 
-// raises AKGL_ERR_LOGICINTERRUPT if we don't want the physics object to process us
+// raises AKGL_ERR_LOGICINTERRUPT if we don't want the physics simulator to process us
-akerr_ErrorContext *akgl_actor_logic_movement(akgl_Actor *obj, SDL_Time curtime)
+akerr_ErrorContext *akgl_actor_logic_movement(akgl_Actor *actor, float32_t dt)
 {
     PREPARE_ERROR(errctx);
-    FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "obj");
+    FAIL_ZERO_RETURN(errctx, actor, AKERR_NULLPOINTER, "actor");
-    FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "obj->basechar");
+    FAIL_ZERO_RETURN(errctx, actor, AKERR_NULLPOINTER, "actor->basechar");
-    if ( obj->vx > obj->basechar->sx ) {
+    actor->sx = actor->basechar->sx;
-	obj->vx = obj->basechar->sx;
+    actor->sy = actor->basechar->sy;
+    actor->sz = actor->basechar->sz;
+    if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_LEFT) ) {
+	actor->ax = -actor->basechar->ax;
+    } else if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_RIGHT) ) {
+	actor->ax = actor->basechar->ax;
     }
-    if ( obj->vy > obj->basechar->sy ) {
+    if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_UP) ) {
-	obj->vy = obj->basechar->sy;
+	actor->ay = -actor->basechar->ay;
+    } else if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_DOWN) ) {
+	actor->ay = actor->basechar->ay;
     }
-    // Effectively a NOOP, this is handled by the physics engine now
-    // These functions are still present in case the library user wants per-actor behavior
     SUCCEED_RETURN(errctx);
 }
 
@@ -268,10 +277,12 @@ akerr_ErrorContext *akgl_actor_add_child(akgl_Actor *obj, akgl_Actor *child)
 akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_left_on(akgl_Actor *obj, SDL_Event *event)
 {
     PREPARE_ERROR(errctx);
-    FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
+    FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "actor");
-    FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
+    FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "event");
+    FAIL_ZERO_RETURN(errctx, obj->basechar, AKERR_NULLPOINTER, "actor->basechar");
     //SDL_Log("event %d (button %d / key %d) moves actor left", event->type, event->gbutton.which, event->key.key);
     AKGL_BITMASK_DEL(obj->state, (AKGL_ACTOR_STATE_FACE_ALL | AKGL_ACTOR_STATE_MOVING_ALL));
+    obj->ax = -(obj->basechar->ax);
     AKGL_BITMASK_ADD(obj->state, (AKGL_ACTOR_STATE_MOVING_LEFT | AKGL_ACTOR_STATE_FACE_LEFT));
     //SDL_Log("new target actor state: %b", obj->state);
     SUCCEED_RETURN(errctx);
@@ -283,6 +294,9 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_left_off(akgl_Actor *obj, SDL
     FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
     FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
     //SDL_Log("event %d (button %d / key %d) stops moving actor left", event->type, event->gbutton.which, event->key.key);
+    obj->ax = 0;
+    obj->ex = 0;
+    obj->tx = 0;
     obj->vx = 0;
     AKGL_BITMASK_DEL(obj->state, AKGL_ACTOR_STATE_MOVING_LEFT);
     //SDL_Log("new target actor state: %b", obj->state);
@@ -294,7 +308,9 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_right_on(akgl_Actor *obj, SDL
     PREPARE_ERROR(errctx);
     FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
     FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
+    FAIL_ZERO_RETURN(errctx, obj->basechar, AKERR_NULLPOINTER, "actor->basechar");
     //SDL_Log("event %d (button %d / key %d) moves actor right", event->type, event->gbutton.which, event->key.key);
+    obj->ax = obj->basechar->ax;
     AKGL_BITMASK_DEL(obj->state, (AKGL_ACTOR_STATE_FACE_ALL | AKGL_ACTOR_STATE_MOVING_ALL));
     AKGL_BITMASK_ADD(obj->state, (AKGL_ACTOR_STATE_MOVING_RIGHT | AKGL_ACTOR_STATE_FACE_RIGHT));
     //SDL_Log("new target actor state: %b", obj->state);
@@ -307,6 +323,9 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_right_off(akgl_Actor *obj, SD
     FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
     FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
     //SDL_Log("event %d (button %d / key %d) stops moving actor right", event->type, event->gbutton.which, event->key.key);
+    obj->ax = 0;
+    obj->ex = 0;
+    obj->tx = 0;
     obj->vx = 0;
     AKGL_BITMASK_DEL(obj->state, AKGL_ACTOR_STATE_MOVING_RIGHT);
     //SDL_Log("new target actor state: %b", obj->state);
@@ -319,6 +338,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_up_on(akgl_Actor *obj, SDL_Ev
     FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
     FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
     //SDL_Log("event %d (button %d / key %d) moves actor up", event->type, event->gbutton.which, event->key.key);	
+    obj->ay = -(obj->basechar->ay);
     AKGL_BITMASK_DEL(obj->state, (AKGL_ACTOR_STATE_FACE_ALL | AKGL_ACTOR_STATE_MOVING_ALL));
     AKGL_BITMASK_ADD(obj->state, (AKGL_ACTOR_STATE_FACE_UP | AKGL_ACTOR_STATE_MOVING_UP));
     //SDL_Log("new target actor state: %b", obj->state);
@@ -331,6 +351,9 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_up_off(akgl_Actor *obj, SDL_E
     FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
     FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
     //SDL_Log("event %d (button %d / key %d) stops moving actor up", event->type, event->gbutton.which, event->key.key);
+    obj->ay = 0;
+    obj->ey = 0;
+    obj->ty = 0;
     obj->vy = 0;
     AKGL_BITMASK_DEL(obj->state, AKGL_ACTOR_STATE_MOVING_UP);
     //SDL_Log("new target actor state: %b", obj->state);
@@ -343,6 +366,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_down_on(akgl_Actor *obj, SDL_
     FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
     FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
     //SDL_Log("event %d (button %d / key %d) moves actor down", event->type, event->gbutton.which, event->key.key);
+    obj->ay = obj->basechar->ay;
     AKGL_BITMASK_DEL(obj->state, (AKGL_ACTOR_STATE_FACE_ALL | AKGL_ACTOR_STATE_MOVING_ALL));
     AKGL_BITMASK_ADD(obj->state, (AKGL_ACTOR_STATE_MOVING_DOWN | AKGL_ACTOR_STATE_FACE_DOWN));
     //SDL_Log("new target actor state: %b", obj->state);
@@ -355,6 +379,9 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_Actor_cmhf_down_off(akgl_Actor *obj, SDL
     FAIL_ZERO_RETURN(errctx, obj, AKERR_NULLPOINTER, "NULL actor");
     FAIL_ZERO_RETURN(errctx, event, AKERR_NULLPOINTER, "NULL event");
     //SDL_Log("event %d (button %d / key %d) stops moving actor down", event->type, event->gbutton.which, event->key.key);
+    obj->ty = 0;
+    obj->ey = 0;
+    obj->ay = 0;
     obj->vy = 0;
     AKGL_BITMASK_DEL(obj->state, AKGL_ACTOR_STATE_MOVING_DOWN);
     //SDL_Log("new target actor state: %b", obj->state);

src/physics.c

@@ -1,3 +1,4 @@
+#include <math.h>
 #include <akstdlib.h>
 #include <akgl/physics.h>
 #include <akgl/actor.h>
@@ -6,7 +7,7 @@
 #include <akgl/heap.h>
 #include <akgl/registry.h>
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime)
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt)
 {
     PREPARE_ERROR(e);
     FAIL_ZERO_RETURN(e, self, AKERR_NULLPOINTER, "self");
@@ -20,7 +21,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_collide(akgl_PhysicsBackend
     SUCCEED_RETURN(e);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_move(struct akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime)
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_null_move(struct akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt)
 {
     PREPARE_ERROR(e);
     FAIL_ZERO_RETURN(e, self, AKERR_NULLPOINTER, "self");
@@ -41,25 +42,19 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_init_null(akgl_PhysicsBackend *s
 }
 
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime)
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_gravity(akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt)
 {
     PREPARE_ERROR(e);
     FAIL_ZERO_RETURN(e, self, AKERR_NULLPOINTER, "self");
-    // Do nothing
+    FAIL_ZERO_RETURN(e, actor, AKERR_NULLPOINTER, "actor");
-    // Calculate the drop of all relevant actors which is a function of their mass and the
+    
-    // world's gravity
+    // Assume the X origin is - (screen left)
+    actor->ex -= (self->gravity_x * dt);
+    // Assume Y origin is + (down screen)
+    actor->ey += (self->gravity_y * dt);
+    // Assume Z origin is - (behind the camera)
+    actor->ez -= (self->gravity_z * dt);
 
-    //Gravity is applied in units per second. So we apply
-    // (unit / milliseconds per second) * (milliseconds since last update)
-    actor->vx += ((self->gravity_x / AKGL_TIME_ONESEC_NS) * (curtime - self->gravity_time));
-    actor->vy += ((self->gravity_y / AKGL_TIME_ONESEC_NS) * (curtime - self->gravity_time));
-    actor->vz += ((self->gravity_z / AKGL_TIME_ONESEC_NS) * (curtime - self->gravity_time));
-
-    // Apply atmospheric drag
-    actor->vx -= actor->vx * self->drag_x * (curtime - self->gravity_time);
-    actor->vy -= actor->vy * self->drag_x * (curtime - self->gravity_time);
-    actor->vz -= actor->vz * self->drag_x * (curtime - self->gravity_time);
-    // Need a euler function
     SUCCEED_RETURN(e);
 }
 
@@ -71,42 +66,14 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_collide(akgl_PhysicsBackend *
     SUCCEED_RETURN(e);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_move(struct akgl_PhysicsBackend *self, akgl_Actor *actor, SDL_Time curtime)
+akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_ss_move(struct akgl_PhysicsBackend *self, akgl_Actor *actor, float32_t dt)
 {
     PREPARE_ERROR(e);
     FAIL_ZERO_RETURN(e, self, AKERR_NULLPOINTER, "self");
     FAIL_ZERO_RETURN(e, actor, AKERR_NULLPOINTER, "actor");
-
+    actor->x += actor->vx * dt;
-    if ( actor->parent != NULL ) {
+    actor->y += actor->vy * dt;
-	// Children don't move independently of their parents, they just have an offset
+    actor->z += actor->vz * dt;    
-	SUCCEED_RETURN(e);
-    } else if ( actor->basechar == NULL ) {
-	SUCCEED_RETURN(e);
-    } else { 
-	if ( (curtime - actor->movetimer) >= actor->basechar->speedtime ) {
-	    actor->movetimer = curtime;
-	    ATTEMPT {
-		CATCH(e, actor->movementlogicfunc(actor,curtime));
-	    } CLEANUP {
-	    } PROCESS(e) {
-	    } HANDLE(e, AKGL_ERR_LOGICINTERRUPT) {
-		// The actor told us NOT to process them, they handled their own update
-		SUCCEED_RETURN(e);
-	    } FINISH(e, true);
-	    if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_LEFT) ) {
-		actor->x += -actor->vx;
-	    }
-	    if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_RIGHT) ) {
-		actor->x += actor->vx;
-	    }
-	    if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_UP) ) {
-		actor->y += -actor->vy;
-	    }
-	    if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_DOWN) ) {
-		actor->y += actor->vy;
-	    }
-	}
-    }
     SUCCEED_RETURN(e);
 }
 
@@ -151,6 +118,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_simulate(akgl_PhysicsBackend *se
 	.layerid = 0
     };
     SDL_Time curtime = SDL_GetTicksNS();
+    float32_t dt = (float32_t)(curtime - self->gravity_time) / (float32_t)AKGL_TIME_ONESEC_NS;
     akgl_Actor *actor = NULL;
 
     FAIL_ZERO_RETURN(e, self, AKERR_NULLPOINTER, "self");
@@ -160,27 +128,79 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_physics_simulate(akgl_PhysicsBackend *se
 	opflags = &defflags;
     }
     
+    
     for ( int i = 0; i < AKGL_MAX_HEAP_ACTOR; i++ ) {
 	actor = &HEAP_ACTOR[i];
 	if ( actor->refcount == 0 ) {
 	    continue;
 	}
+	if ( actor->parent != NULL ) {
+	    // Children don't move independently of their parents, they just have an offset
+	    actor->x = actor->parent->x + actor->vx;
+	    actor->y = actor->parent->y + actor->vy;
+	    actor->z = actor->parent->z + actor->vz;
+	    continue;
+	} else if ( actor->basechar == NULL ) {
+	    continue;
+	}
 	if ( AKGL_BITMASK_HAS(opflags->flags, AKGL_ITERATOR_OP_LAYERMASK) ) {
 	    if ( actor->layer != opflags->layerid ) {
 		continue;
 	    }
 	}
+	
+	// thrust is a function of acceleration on a given axis
 	if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_LEFT) ||
 	    AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_RIGHT) ) {
-	    actor->vx += actor->basechar->ax;
+	    actor->tx += actor->ax * dt;
 	}
 	if ( AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_UP) ||
 	    AKGL_BITMASK_HAS(actor->state, AKGL_ACTOR_STATE_MOVING_DOWN) ) {
-	    actor->vy += actor->basechar->ay;
+	    actor->ty += actor->ay * dt;
 	}
-	PASS(e, self->gravity(self, actor, curtime));
+
-	PASS(e, self->move(self, actor, curtime)); 
+	// velocity equals thrust unless thrust exceeds max speed
-	self->gravity_time = curtime;
+	if ( fabsf(actor->tx) > fabsf(actor->sx) ) {
+	    if ( actor->tx < 0 ) {
+		actor->tx = -actor->sx;		
+	    } else {
+		actor->tx = actor->sx;
+	    }
+	}
+	if ( fabsf(actor->ty) > fabsf(actor->sy) ) {
+	    if ( actor->ty < 0 ) {
+		actor->ty = -actor->sy;
+	    } else {
+		actor->ty = actor->sy;
+	    }
+	}
+	if ( fabsf(actor->tz) > fabsf(actor->sz) ) {
+	    if ( actor->tz < 0 ) {
+		actor->tz = -actor->sz;
+	    } else {
+		actor->tz = actor->sz;
+	    }
+	}
+	ATTEMPT {
+	    CATCH(e, actor->movementlogicfunc(actor, dt));
+	    PASS(e, self->gravity(self, actor, dt));
+
+	    // Counteract velocity with atmospheric drag
+	    actor->ex -= actor->ex * self->drag_x * dt;
+	    actor->ey -= actor->ey * self->drag_y * dt;
+	    actor->ez -= actor->ez * self->drag_z * dt;
+
+	    actor->vx = actor->ex + actor->tx;
+	    actor->vy = actor->ey + actor->ty;
+	    actor->vz = actor->ez + actor->tz;
+
+	    PASS(e, self->move(self, actor, dt)); 
+	} CLEANUP {
+	} PROCESS(e) {
+	} HANDLE(e, AKGL_ERR_LOGICINTERRUPT) {
+	    // noop
+	} FINISH(e, true);
     }
+    self->gravity_time = curtime; 
     SUCCEED_RETURN(e);
 }