Fix gravity sometimes persisting a frame after ctrl+z / clearing sim, f…

…ixes #571

src/simulation/Gravity.cpp

@@ -31,13 +31,16 @@ void Gravity::bilinear_interpolation(float *src, float *dst, int sw, int sh, int
 		}
 }
 
+bool ignoreNextResult = false;
 void Gravity::Clear()
 {
 	std::fill(gravy, gravy+((XRES/CELL)*(YRES/CELL)), 0.0f);
 	std::fill(gravx, gravx+((XRES/CELL)*(YRES/CELL)), 0.0f);
 	std::fill(gravp, gravp+((XRES/CELL)*(YRES/CELL)), 0.0f);
 	std::fill(gravmap, gravmap+((XRES/CELL)*(YRES/CELL)), 0.0f);
 	std::fill(gravmask, gravmask+((XRES/CELL)*(YRES/CELL)), 0xFFFFFFFF);
+
+	ignoreNextResult = true;
 }
 
 void Gravity::gravity_init()
@@ -90,7 +93,7 @@ void Gravity::gravity_update_async()
 				//Switch the full size gravmaps, we don't really need the two above any more
 				float *tmpf;
 
-				if(th_gravchanged)
+				if (th_gravchanged && !ignoreNextResult)
 				{
 				#if !defined(GRAVFFT) && defined(GRAV_DIFF)
 					memcpy(gravy, th_gravy, (XRES/CELL)*(YRES/CELL)*sizeof(float));
@@ -110,6 +113,7 @@ void Gravity::gravity_update_async()
 					th_gravp = tmpf;
 				#endif
 				}
+				ignoreNextResult = false;
 
 				tmpf = gravmap;
 				gravmap = th_gravmap;

src/simulation/Simulation.cpp

@@ -517,6 +517,7 @@ void Simulation::Restore(const Snapshot & snap)
 	std::copy(snap.WirelessData.begin(), snap.WirelessData.end(), &wireless[0][0]);
 	if (grav->ngrav_enable)
 	{
+		grav->Clear();
 		std::copy(snap.GravVelocityX.begin(), snap.GravVelocityX.end(), gravx);
 		std::copy(snap.GravVelocityY.begin(), snap.GravVelocityY.end(), gravy);
 		std::copy(snap.GravValue.begin(), snap.GravValue.end(), gravp);