Home Forums General Discussion Havok 4 Reply To: Havok 4


I believe Kentaree’s point was that HL2 uses physics to drive gameplay and didnt mean to imply that the HL2 uses the same technology…[/quote:e7240f9c34]

It’s an interesting debate: gameplay vs. special effects. I’m not sure that HL2 has what you would definitely call gameplay physics. What they do have is a beautifully realised world utilising physics in a careful way to enhance the experience for the player. The majority of the puzzles were largely discrete (put heavy bricks on the see-saw, place floaty barrels in the net etc.) with very fixed outcomes (see-saw tips, net floats to surface). So the physics is there to give you a better experience of solving the puzzle (i.e. the puzzle is essentially solved when you realise you have to tip the see-saw). So I’d argue that this is actually physics special effects imparting a sense of analogue world mechanics on an essentially discrete puzzle. But I buy that fully – I still think HL2 is one of the finest examples of an immersive story-driven game.

There are clearly some genres where the physics is core to the game (sports titles, car racing games etc.), but usually in those cases the physical models employed are very specific to the game and not what we’d call a general purpose physics technology.

There’s nothing unusual in this. With graphics we don’t get too worried about the distinction between gameplay graphics and special effects graphics.

The definition of gameplay physics is somewhat vague. In practical terms you can often boil it down to 2 cases: a) what physics state needs to be synchronised in a network game b) what physics state needs to be serialised out in a save game. Both of these are different versions of the same thing: what stuff, under the control of the physics engine, has a direct and gameplay important impact on the game state.

So for example in the see-saw example of HL2, perhaps the only thing that needs to be saved is the state of the see-saw (or perhaps the current weight on the see-saw). So the current stack of blocks, their configuration, and the location of the remaining blocks are all irrelevant in that case of that puzzle. In another example, ragdolls are often seen as special effects only. They just make the death look better. But there are elements of the ragdoll sim that could be gameplay: what if the position of the ragdoll was important (e.g. you want to loot a dead character for their weapons) or if even the detailed dscription of the ragdoll state was required (e.g. if it were possible for an arm to block the closing of a door).

The vast majority of physics “gameplay” at the moment is in fact special effects physics, and game designers go to great length to keep physics out of the game state (because it’s hard to control, harder still to guarantee a particular difficulty path for the player). Analogue game logic is a nightmare. So designers ensure that ragdolls can never block doors (and do place invisible barriers to prevent this from happening).

Last case in point: take a FIFA soccer sim. Most would argue that the simulation of the motion of the ball is one of the canonical examples of gameplay physics. Well, yes, and no. The keen eyed player will spot the occasions when the ball is “warped” to the foot of the striker, just so he’s in the perfect position to make the score. The important gameplay state is that the striker’s foot is located sufficiently close to the ball, and if so the goal-attempt motion is played. So perhaps for a while the motion of the ball in the air was nice and parabolic, but ulimately the game took over to ensure a certain outcome. I’d argue that this is another case of special effects physics – use the physics when the ball is in flight and we’re not too worried about it, and take over control again when it really matters. So the physics is used to make the game seem real, but in fact the game logic is still lots of x’s and o’s in a 2D box.

That’s just the same as blowing a hole in a wall with tons of physics debris – the important fact is that the hole now exists (and presumably you can get through it), and the debris makes it feel real and that we’ve had a big impact on the world.

My point (and maybe there is no point really) is that the distinction between gameplay and special effects physics is not at all clear and is not simply a matter of hardware accelerated vs. software physics.