[Verse-dev] Bug in enough library

[Jiří Hnídek]

Hi,
I found bug in enough library e_storage_object.c (physics stuff):

you use this equation:

x(t) = x(0) + speed*t + acceleration*t*t + drag

it is of course wrong. Correct equation seems so:

x(t) = x(0) + speed*t + 0.5*acceleration*t*t + drag

You can find patch in attachment.

btw: it is interesting that drag isn't supported in enough. What is 
definition of drag in this case? ... I guess, that no physicist would 
add drag to this equation ;-), because this equation is about kinematics 
not dynamics :-).

Best regards,

Jiri

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Index: e_storage_object.c
===================================================================
RCS file: /cvsroot/verse/quelsolaar/e_storage_object.c,v
retrieving revision 1.7
diff -u -p -r1.7 e_storage_object.c
--- e_storage_object.c	13 Jun 2005 11:13:48 -0000	1.7
+++ e_storage_object.c	25 Jul 2005 09:00:29 -0000
@@ -298,9 +298,9 @@ void e_nso_get_pos_time(ESObjectNode *no
 	t = &((ESObjectNode *)node)->trans;
 	dt = e_get_delta_time(time_s, time_f);
 	/* FIXME: These equations seem to miss a 0.5 factor in the last term. /emil */
-	pos[0] = t->pos[0] + t->pos_speed[0] * dt + t->pos_accelerate[0] * dt * dt;
-	pos[1] = t->pos[1] + t->pos_speed[1] * dt + t->pos_accelerate[1] * dt * dt;
-	pos[2] = t->pos[2] + t->pos_speed[2] * dt + t->pos_accelerate[2] * dt * dt;
+	pos[0] = t->pos[0] + t->pos_speed[0] * dt + t->pos_accelerate[0] * dt * dt / 2;
+	pos[1] = t->pos[1] + t->pos_speed[1] * dt + t->pos_accelerate[1] * dt * dt / 2;
+	pos[2] = t->pos[2] + t->pos_speed[2] * dt + t->pos_accelerate[2] * dt * dt / 2;
 }
 
 void e_nso_get_rot_time(ESObjectNode *node, VNQuat64 *rot, uint32 time_s, uint32 time_f)
@@ -311,10 +311,10 @@ void e_nso_get_rot_time(ESObjectNode *no
 	/* FIXME: This code is very certainly incorrect -- you can't interpolate quaternions like this, can you? */
 	t = &((ESObjectNode *)node)->trans;
 	dt = e_get_delta_time(time_s, time_f);
-	rot->x = t->rot.x + t->rot_speed.x * dt + t->rot_accelerate.x * dt * dt;
-	rot->y = t->rot.y + t->rot_speed.y * dt + t->rot_accelerate.y * dt * dt;
-	rot->z = t->rot.z + t->rot_speed.y * dt + t->rot_accelerate.y * dt * dt;
-	rot->w = t->rot.w + t->rot_speed.w * dt + t->rot_accelerate.w * dt * dt;
+	rot->x = t->rot.x + t->rot_speed.x * dt + t->rot_accelerate.x * dt * dt / 2;
+	rot->y = t->rot.y + t->rot_speed.y * dt + t->rot_accelerate.y * dt * dt / 2;
+	rot->z = t->rot.z + t->rot_speed.y * dt + t->rot_accelerate.y * dt * dt / 2;
+	rot->w = t->rot.w + t->rot_speed.w * dt + t->rot_accelerate.w * dt * dt / 2;
 }
 
 void e_nso_get_scale(ESObjectNode *node, double *scale)