Boulder Dash Forum

Episode 5 - cave 3 analysis

Once again the link:
https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 3 starts at 0:34.

What do we see?
At the left side, Rocky snaps down so the left boulder falls and frees the diamond, at the right side Rockford moves down and up again so that the right boulder falls and frees the diamond. Why does it work like this and only like this?

How does it work?
To understand this, we need a bit of theory again. This time, a boulder falls sideways from another boulder. I didn't discuss this piece of boulder physics yet, so here's a full overview of how a boulder behaves.

If the BD engine scans a boulder, it checks first what is directly below the boulder. There are three possibilities:
1. If below the boulder is empty space, then of course the boulder falls down by one unit and thereby converts into a "falling boulder". See also episode 3.
2. If below the scanned boulder is another boulder or a diamond or a brick wall, the engine checks next whether the scanned boulder can fall sideways.
2a. If there's empty space to the left and to the bottom-left side of the boulder, like this...
DDDDD
DSBDD
DSXDD
DDDDD
D=Dirt
B=Boulder
X=Boulder, diamond or brick wall
...then the boulder moves left by one unit and thereby converts into a "falling boulder".
2b. If this is not the case, the engine checks whether the boulder can fall to the right. That's just analogue.
3. If any other BD element is below the boulder, nothing happens.

So let's go back to cave 3. The interesting situation is basically the following one:
DDDDD
DDRDD
DBDBD
DBSBD
DDDDD
D=Dirt
R=Rockford
B=Boulder
S=empty space
Rockford wants a boulder to fall sideways. There are two possibilities to achieve this.

Possibility 1: Snap downwards
Let's do a frame-by-frame analysis again:

Frame 0 Picture see above
Let's see what the cave scanner does:
1. According to rule #1, Rockford is scanned first. He snaps down.
2. Next, the top-left boulder. Can it fall to the right? Yes! Rockford has just cleared the dirt to the boulder's right side, and there's also empty space to the bottom-right side of the boulder. So it moves right and becomes a "falling boulder".
3. Next, the top-right boulder. It can not fall to the left because the previous boulder just blocked the way. Nothing happens.
4./5. The two bottom boulders cannot do anything, either.
Frame 1
DDDDD
DDRDD
DSBBD
DBSBD
DDDDD
We can already stop here as it's clear what will happen - the boulder will fall down and that's it. So with this strategy, Rockford has made the top-left boulder fall down.

Possibility 2: Move down and up again
Frame 0
DDDDD
DDRDD
DBDBD
DBSBD
DDDDD
1. Rockford is scanned first. This time, we move down.
2. None of the boulders can fall yet, as Rockford blocks the way.

Frame 1
DDDDD
DDSDD
DBRBD
DBSBD
DDDDD
1. Now, the cave scanning order rule makes the top-left boulder be scanned first. Rockford still blocks it, so nothing happens.
2. Rockford's turn. We move up.
3. The top-right boulder's turn. What happens? As Rockford has just moved away, the boulder can now fall to the left!
4./5. The bottom boulders can't do anything again.

Frame 2
DDDDD
DDRDD
DBBSD
DBSBD
DDDDD
Once again, the boulder will fall and that's it. So this time, it was the top-right boulder that was falling! Let's summarize:

- If Rockford snaps down in frame 0, then the top-left boulder falls.
- If Rockford moves down and up again, then the right boulder falls.
And this explains everything about how this mini cave works!

I will not fail to mention that Arno has made a fantastic puzzle cave based on this idea:
https://www.youtube.com/watch?v=0Istmyw5nAs&t=1s
It may be hard to understand by just watching the solution, but the main idea is that you need the diamonds, boulders, light boulders and heavy boulders exactly where they are in the end. I remember that I solved this cave with pencil and paper after half an hour or so ;D

Episode 6 - cave 4 analysis

https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 4 starts at 0:46.

What do we see?
The solution shows the only way that Rockford can force the five-diamond-stack to fall in such a way that they come to lie in a row so the leftmost one can fall through the slime and free the exit. How does this work?

How does this work?
As this one is theoretically more complex than the previous caves, let's do some

Preliminary considerations
There are six diamonds in the cave, one of which has to fall through the slime and kill the bottom firefly to free the exit. So how to get a diamond onto the slime?
When I designed the cave, I just trial-and-errored around and I soon came to the conclusion that there's only one way to achieve this: the five pieces of dirt to the left of the 5-diamond stack must be cleared simultaneousely!
Three pieces of dirt can easily be cleared simultanousely with the explosion of the top firefly with the 6th diamond. So the other two pieces of dirt have to be cleared by Rockford - but how can Rocky clear two pieces of dirt simultanousely? That's where the cavescanning order comes into play again!

Frame-by-frame analysis
It starts to get interesting the moment when the "smoke" from the first explosion is just about to vanish. We have the following situation:
Frame 0 - see video at 0:55
SSSD1T
SSSR2T
S***3T
S***4T
S***5T
S=empty space, D=Dirt, 12345=Diamonds, R=Rockford, *=Smoke
T=Titanium wall/ cave border
Apart from dirt, space and wall, the following elements are scanned in this order:
1. The topmost diamond. Nothing happens, as it cannot fall sideways yet.
2. Rockford. He moves upwards to clear the dirt.
3. The second diamond. Can it fall sideways? Let's check this in detail:
If a diamond wants to fall sideways from another diamond, there are two conditions, which we have already discussed in the previous episode:
a. To the left of the diamond, there has to be empty space. This is the case here, because Rockford has just moved away in step 2.!
b. To the bottom-left of the diamond, there also has to be empty space. And this is not the case here. There's still a piece of smoke there that will vanish only in step 4.!
So the diamond 2 can not fall sideways but stays where it is for now.
4. The top three pieces of smoke, one by one. So what happens if smoke is scanned? Well, smoke has, so to say, five phases before it vanishes, so it just goes into its next phase. In this case, we have smoke that is just about to vanish, i.e. phase 5, so all in all it just vanishes when the engine scans it.
5. The third diamond. This is similar to 3. - the diamond "sees" empty space to its left where the smoke has just disappeared, but the smoke to the bottom-left of the diamond is still there, so it cannot fall sideways, either.
6. The middle line of smoke vanishes.
7. Diamond 4 cannot fall sideways, same reasoning as above.
8. The bottom line of smoke vanishes.
9. Diamond 5 - nothing happens.

Frame 1
SSSR1T
SSSS2T
SSSS3T
SSSS4T
SSSS5T
1. This time, due to the cavescanning order, it's Rockford himself who is scanned first. This is important for the whole solution! Rockford has to move out of the way, in the video he moves up again - he could move left as well.
So this is worth another picture, a virtual one which exists "between the frames" and is thereby invisible for the player:

Between frame 1 and 2
SSSS1T
SSSS2T
SSSS3T
SSSS4T
SSSS5T
Voilà! We have magically reached the exact situation described above in the pre-considerations! All the dirt is gone - not exactly simultanousely, but the important thing is that now all the diamonds can start to fall simultanousely!
During the rest of the frame, diamonds 1,2,3 and 4 will all fall sideways, leading to the next "real" picture:

Frame 2
SSS1ST
SSS2ST
SSS3ST
SSS4ST
SSSS5T

As you see in the video, some frames later, all 5 diamonds lie side by side and the diamond 1 crushes the firefly and frees the exit so the cave is solved.

Dustin, you are doing a great job.
The more I read here on the forum, this also applies to dancing flies / thanks Arno /, I am increasingly realizing that I do not know Boulderdash completely.
Many caves are unsolvable to me because I don't know all these techniques.
That's why I am asking for more articles about BD physics as well as about all the game's tricks.
When I watch Boulderdash movies here, I think that really good players go through the caves.

Greetings to all BD fans.
Thanks

I second this. Great work and very interesting to read!

zsom, Arno, thx for the positive feedback!

Episode 7 - cave 5 analysis
https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 5 starts at 1:03.

What do we see?
1. Rockford takes the right butterfly out of its prison before the growing wall can block it off.
2. A few frames later, Rockford turns left, survives despite touching the fly for several frames and wins a small advantage over his chaser.
3. Rockford leads the butterfly to the bottom half through the left side, fooling another growing wall in the process.
4. Inside the small box with the boulders, Rockford takes the right path to lead a boulder down before another growing wall can block it off.
5. Step 4 also needs the exact right timing so that the boulder kills the butterfly. This, however, has little to do with our topic of cavescanning order, so I'll just mention it for sakes of completeness.

How does it work?

Pre-considerations: Passing a growing wall
Analyzing cave 1, we have already seen a way to "fool" a growing wall. Here, the situation is a bit different, as Rockford stands directly beside a growing wall several times and then moves away. Let's compare two situations - the G-Wall my be to the left or right side of Rockford.
1. G-Wall to Rockford's right side
Some ASC II art again
Frame 0
DDDDD
DDRGD
DDDDD
Cave scanning order:
1. Rockford is scanned and moves away, let's say up - it doesn't matter.
2. The G-Wall is scanned immediately after Rockford. It "sees" that R has just moved out of the way and grows left.
Frame 1
DDRDD
DDGGD
DDDDD
So the path that Rockford cleared is immediately filled by the G-Wall. Thus, there's no way that Rockford could lead any flies or boulders past the G-Wall this way!
2. G-Wall to Rockford's left side
Frame 0
DDDDD
DGRDD
DDDDD
1. This time, the G-Wall is first. It can not grow because R is in its way.
2. Now Rocky. Let's say we move down.
Frame 1
DDDDD
DGSDD
DDRDD
Ahhh! There's a space gap that the G-Wall hasn't filled yet! That's what we wanted, because now it is possible for a fly or boulder to get past the G-Wall. There are two possibilities:

Possibility I: A fly touches Rockford from his right or bottom side and fills the gap that Rockford cleared before the G-Wall does. This would then happen between frame 0 and 1.
Possibility II: A fly or boulder follows Rockford from above with a one-space gap in-between. Then it will be scanned before the G-Wall between frames 1 and 2 and still get past it.

So what can we conclude w.r.t. the cave solution?
1. We've seen that it's necessary that Rockford has the G-Wall on his left side if he wants anything to get past. You can see in the video that this is the case all three times Rockford uses this trick.
2. Pssibility I is used at the beginning when RF lets the butterfly out of its cage.
Possibility II is used when Rockford leads the fly to the bottom half and again when Rockford leads the boulder past the G-Wall to crush the fly in the end.
BTW, if you read again/ remember episode 1 of this thread, you shouldn't be too surprised anymore how Rockford can survive touching the butterfly for so many frames! Short repetition - if Rockford touches a fly from
left or above, he'll be scanned before the fly and thereby still get the chance to escape! That's also the reason why a right turn at the beginning of the cave would be lethal - Rockford would then touch the fly from its right side, the fly would be scanned first and kill our hero!

Next episode - next cave!

Episode 8 - cave 6 analysis
https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 6 starts at 1:24.

What do we see?
Interesting for our topic is the process of leading the butterflies past the G-Wall down to the bottom half. The rest - getting the maximum diamond amount out of the butterflies - is a technical thing rather than a cavescanning order issue.

How does it work?
First of all, let's note that one again, the growing wall is to Rockford's left side again - this is, as we have seen in the previous episode, a necessary condition to make the whole thing work!
Actually we see a variation of "Possibility II" of the previous episode.

Possibility II: A fly or boulder follows Rockford from above with a one-space gap in-between. Then it will be scanned before the G-Wall between frames 1 and 2 and still get past it.

Here, the butterflies follow Rockford from the top-left side. Let's focus on what happens when one butterfly approaches Rockford - it's the exact same method for all 4 flies anyway. First of all, Rockford lets the butterfly approach until it isdirectly at his top-left side, so the action starts here:
Frame 0
SSSBSSSS
ggggRSSS
SSSSSSSS
S=empty space, g=growing wall, B=Butterfly, R=Rockford
Cave-scanning order:
1. Apart from uninteresting empty space, the butterfly is scanned first.
--> First, the butterfly checks whether there's a reason to explode. There isn't, as Rockford is still far enough.
--> Second, the butterfly wants to move right, so it does.
--> Now the fly touches Rockford and there would be a reason to explode, but after making a movement, the flies' turn is over!
2. The growing walls are scanned one by one - they can't grow.
3. Now Rockford. Of course, it's time to move now, as the butterfly would otherwise kill him next frame, so we move right.
Now there would be space for the growing wall to grow, but its turn for this frame is already over! So that's the next picture:
Frame 1
SSSSBSSS
ggggSRSS
SSSSSSSS
1. The butterfly is first again. It has just moved right, so it would like to move down as its first priority, and indeed this is possible!
2. What about the growing wall? Well, it would love to grow, but it is blocked by the butterfly now! Bad luck - try again next frame! ;D
3. Now Rockford. He has to move again, because the butterfly is again too close, so we move right.
Frame 2
SSSSSSSS
ggggBSRS
SSSSSSSS
1. Now, it's the growing wall first because the butterfly has moved into a position "behind" the wall in terms of the cavescanning order. The wall still can't grow! Still the butterfly in the way!
2. The butterfly is next. As it has just moved down, it would like to move left now, but here's the G-Wall's revenge - this time it blocks the fly So the flies' second priority is to move down again, and so it does.
3. Rockford's turn. As the butterfly has moved out of the danger zone, he could immediately move left again, but in the video he stops for one frame, so let's do the same here.
Frame 3
SSSSSSSS
ggggSSRS
SSSSBSSS
1. Finally good news for the G-wall - it can finally grow and does so immediately!
2. Rockford's turn. He moves left and prevents the wall from growing further. This is important because only this way there will be enough space to lead all 4 butterflies to the bottom half!
3. The butterfly has passed the growing wall and moves left now.
Frame 4
SSSSSSSS
gggggRSS
SSSBSSSS
There we have it! The butterfly is where we wanted it, the wall has grown by one unit and Rockford waits for the next bfly to come along...

Interactive exercise!
As we've learned quite a lot about the growing walls in this and the previous episode, perhaps you want to have a look at the next cave in the video and figure out for yourself why Rockford has to take the little detour at the beginning!? Solution in the next episode!

Double thumb up - this motivates me to write...
Episode 9 - Cave 7 analysis
https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 7 starts at 1:54.
BTW, from this cave on I started to name the caves - this one is called "Stalker"

What do we see?
Rockford is chased by a bidirectional growing wall. In order to get both diamonds at the very right, it's necessary to block the g-wall off! After taking a small detour at the beginning, Rockford manages to gain a 1-space gap between himself and the g-wall. This is enough to block the wall off with the upper-left diamond.

How does it work?/ Solution to the exercise
Let's first summarize what we have discussed in the previous 2 episodes:
1. If Rockford has a g-wall at his right side, the wall will be scanned after Rockford, which means that it'll immediately fill the gap as soon as Rockford moves. The same goes if the wall is at Rockford's bottom side.
2. If Rockford has a g-wall at his left - or top side, however, the wall is scanned before Rockford, so it can not immediately fill the gap if Rockford moves. So in this case, it's possible to get a 1-space gap between Rockford and the wall.

In this cave, Rockford needs such a 1-space gap or the wall will always follow him. At the start, however, the wall is at Rocky's right side, which means the gap can not immediately be won. That's the reason for the whole detour!

It gets interesting when Rockford approaches the upper-left diamond with the g-wall close on his heels. Let's start our frame-by-frame analysis the moment when Rockford is at the diamond's bottom-right side and the g-wall is above Rockford:

Frame 0
#GDD
DRDD
DDDD
DDDD
#=Diamond
G=growing wall
R=Rocky
D=Dirt
Unimportant pieces of growing wall or titanium wall are replaced by dirt.

That's a simplified version - the g-wall has already grown much bigger of course, but what is important is that Rockford has only a g-wall at his
top side, while there's only dirt at his right and bottom side. That's what had to be achieved by taking the detour at the beginning!
Now let's analyse the cavescanning order:
1. The diamond is first, but it can't fall.
2. The g-wall next. Rockford blocks it, so nothing happens.
3. Rockford moves left.

Frame 1
#GDD
RSDD
DDDD
DDDD
S=empty space
Here we see it - the gap between Rockford and the wall!
What happens now?
1. The diamond still cannot fall.
2. The g-wall can now grow down.
3. Rockford moves down.

Frame 2
#GDD
SGDD
RDDD
DDDD
The gap is still there- looks good! Now comes the decisive moment:
1. The diamond is first and now it can fall down!
2. The upper g-wall grows left, where the diamond has just cleared the way.
3. The lower g-wall can not grow left because the diamond was quicker and already blocks the way!
4. Rockford moves down again.

Frame 3
GGDD
#GDD
SDDD
RDDD
Here we can stop, as it's clearly visible that the g-wall got blocked off by the diamond! The rest of the cave is rather trivial now!

If you have managed to figure this out by yourself, then you're on the best way to become a true cavescanning-order-expert!

BTW, this weekend Arno has uploaded 10 more cavescanning order caves - thx Arno! Here they are:
https://www.youtube.com/watch?v=mIrh1jqXzNQ

In the next episode, we will see a compilation of everything we've learned about safely touching fireflies!

These caves from the movie 'Cave Scanning Order 31-40' are impossible to pass, but it's nice to see how the masters of this game do it.

Funnily, some of the caves I couldn't solve in practice myself! For example, the very first one where I required only 19d because I wasn't sure whether all 20 are possible myself, or the one where Rockford is in the 2x2 cage with the butterfly - this one I solved in theory with a frame-by-frame analysis, but I couldn't do these rhythmic movements in practice even at lower speed...

Episode 10 - cave 8 analysis
https://www.youtube.com/watch?v=l1k1UkszZTw&t=4s
Cave 8 starts at 2:11.
Cave name: "Pursuit"!

What do we see?
Phase 1: With the firefly close on his heels, Rockford escapes to the upper-left corner.
Phase 2: He then manages to switch positions with the fly in a narrow 2x2 square.
Phase 3: Having gained some advantage over his chaser, Rockford runs all the way back, collects diamonds as quickly as possible and escapes into the outbox passing even more fireflies.

How does it work?
Well, phases 1 and 3 can't surprise us too much anymore. In phase 1, Rockford always touches the fly from above or left, which means he is scanned first and escapes before the fly can explode. Of course, it's understandable that Rockford has no time for the diamonds lying aside! In phase 3, Rockford again touches the fly from left, and the final is a multi-firefly version of what we discussed in episode 1, experiment 2!

Phase 2 might be the most interesting one, so let's make another frame-by-frame analysis. Perhaps you want to figure it out by yourself before reading on

Frame 0
TTTTT
TRFSS
TSSTT
TTTTT
T=Titanium wall/cave border, R=Rocky, F=Ffly, S=Space as usual.
We start the moment Rockford has reached the upper-left cave corner. It all comes down to the duel Rockford vs. the fly!
Cavescanning order:
1. Luckily, Rockford is first. He must move, of course, and the only way to do so is down.
2. Now the fly. It "sees" Rockford at diagonal distance, so it doesn't explode but moves down as well.

Frame 1
TTTTT
TSSSS
TRFTT
TTTTT
1. Rocky is first again. He has no choice but to move up to survive.
2. The fly again sees Rockford at diagonal distance and doesn't explode. It doesn't move either, as fireflies can't make right turns immediately, so it waits.

Frame 2
TTTTT
TRSSS
TSFTT
TTTTT
1. Rockford is first again. Finally, for the first time in the cave, the fly doesn't touch him! So what to do? Move right? Move down? No. Both would make the fly explode immediately, so Rockford has to wait for one frame.
2. Now the fly makes its right turn, which is left from our perspective.

Frame 3
TTTTT
TRSSS
TFSTT
TTTTT
1. Rockford is first again. The firefly touches him again, which forces him to move right.
2. The fly waits before making another right turn.

Frame 4
TTTTT
TSRSS
TFSTT
TTTTT
Voilà! Rockford now easily escapes to the right and has managed to switch positions with the fly. Also, he gained some advantage over the fly so he can now collect the diamonds on the way!

In the next episode, we'll see a new guest in this thread - the good old amoeba! Let's see what cavescanning-order tricks Rockford can do with his slimy friend!
Or perhaps the time has come to first summarize some rules about "dos and don'ts" in the presence of fireflies? Well, let's see...

Gentlemen and Ladies

I have a problem
Help
There is a beginning of the cave:

WWWWW
WDDBW
WDDDW
WDRDW
WDDDW
WFDDDW
WWWWW

W - wall
D - dirt
B - boulder
F - firefly
R - Rockforf

How to solve

zsom wrote:How to solve

Releasing the firefly by snapping the dirt from its right side works, and this seems the easiest method to me.

Yes, that's how I'd release the fly, too.
But, perhaps the trickier thing is to blast the wall after releasing the fly!
Blasting walls with fflies is usually a lot easier if the wall is at the left side.
I even just rebuilt and played this to find a good strategy. I see two main possibilities:

Possibility 1 - easier but 50/50 luck dependant
- Move right, down, down and snap left to release the fly.
- Then immediately move up, free the boulder and let is fall down as quickly as possible.
- Why is this 50/50? Well, the ffly has four possible directions in which it can face.
1. If it faces right or down the moment you snap it free, then it will follow you with only a 1-space gap in-between, and in this case you won't be quick enough to crush the fly.
2. If the fly faces up when freed, it will follow you with a 2-space gap, and that's just enough to crush it the way I described.
3. If it faces left, then there's even a 3-space gap and the fly will also get crushed.
As there's no possibility to "see" in which direction the fly faces, you might just have to try it out with different timings, as the ffly changes its direction every frame. After some tries, this solution should work.

Possibility 2: harder but no "luck" needed
Clear all the dirt you can before releasing the fly. Then you'll get a situation similar to this one:
WWWWW
WFSBW
WSSDW
WSSSW
WSSSW
WRSsSW
WWWWW with S=space.
With the right timing, it's now possible to drop the boulder in a waqy that it kills the ffly at the spot I marked with a small "s".
I needed quite some tries for this

Dustin, Arno.
thank you
After many unsuccessful attempts ... we finally succeeded.
Very professional explanation of how to play in this position.
Greeting