TPT: Avoid stacking in INVS and FILT, and fix pressurised INVS graphics

src/simulation/Simulation.cpp

@@ -2988,6 +2988,7 @@ void Simulation::update_particles_i(int start, int inc)
     							create_part(i, x, y, PT_NBHL);
     							parts[i].temp = MAX_TEMP;
     							parts[i].tmp = pmap_count[y][x]-NPART;//strength of grav field
+    							if (parts[i].tmp>51200) parts[i].tmp = 51200;
     							pmap_count[y][x] = NPART;
     						}
     						else
@@ -4151,6 +4152,9 @@ void Simulation::update_particles()//doesn't update the particles themselves, bu
 					photons[y][x] = t|(i<<8);
 				else
 				{
+					// Particles are sometimes allowed to go inside INVS and FILT
+					// To make particles collide correctly when inside these elements, these elements must not overwrite an existing pmap entry from particles inside them
+					if (!pmap[y][x] || (t!=PT_INVIS && t!= PT_FILT))
 						pmap[y][x] = t|(i<<8);
 					pmap_count[y][x]++;
 				}

src/simulation/elements/INVIS.cpp

@@ -57,8 +57,7 @@ int Element_INVIS::graphics(GRAPHICS_FUNC_ARGS)
 		*colr = 15;
 		*colg = 0;
 		*colb = 150;
-		*pixel_mode &= PMODE;
-		*pixel_mode |= PMODE_BLEND;
+		*pixel_mode = PMODE_BLEND;
 	} 
 	return 0;
 }