Is Pixel Perfect Collision Impossible? - CODING SECRETS 

Programmers - if you tell them something can't be done, even if you're the developer of the hardware.... They. Will. Find. A. Way.

It amazes me the ingenuity you guys had back in the day.

Working with limited hardware and space sure made things tricky and at times almost infuriating, but man, do we get some amazing dev diaries explaining their struggle and clever ways to get even further than what the machines were capable of.

Videos about techniques and how (and why) were they developed are the most interesting in my opinion.

This is one of those titles where the initial answer is easy (of course it can be done, it just takes resources you want for other things), but the workarounds are the interesting bit.

The amiga offered some interesting shortcuts. I always used three pass hit detection: Are two objects in the same region? If so, do their bounding boxes over lap? If so, do their pixels overlap? If so, collision detected. The main problem I found with collision detection is you spend way more time figuring out two things aren't colliding than you do are colliding. This is even true on the cpu level; the cpu will usually figure out two pixels are overlapping faster than finding out no pixels are overlapping. I figured if I just give the program plenty of easy opportunities to bail out of detecting collision between two objects that clearly aren't colliding most of the resources wasted on detection would be freed up

Wow, very clever use of the hardware there. Reminds me of an article "Contra Collision Detection" about clever use of hitboxes in Contra on NES, a system with only limited CPU power.

This channel always has the most fascinating videos.

this channel is so damn good. I'm not a programmer of any sort and these breakdown videos are so fascinating, emphasized by the hardware limitations of old times. so clever. I love it.

These videos of yours are just mesmerizing. Thank you so much for sharing all these insights! It makes me view many of these old games in a new light, and appreciate them even more

I love the logic of your coding. Thanks for sharing with us!

This is just a classic and concise coding secrets video. Your channel is such a joy

That was a great video, thank you! You made something that is very technical extremely easy to understand for a noob like me. That takes a lot of skill. This is my first video of yours that I watched. I am very glad I found your channel and can't wait to watch more!

Easily one of the most interesting series of videos I've ever found on RU-vid. Keep it up!

You have been such a blessing to the RU-vid space. Keep doing you man, we love your insight

your channel is amazing you deserve way more subscribers! I always get such nice insights from this channel. thank you so much in advance

Thank you. It's been a blast watching your videos.

I love these explanations. It's great to hear about the technical stuff in the background of games. Thanks so much for sharing!

thank you for the regular uploads ! :)

No wonder you got to work on so many great things. You come up with some really clever solutions!

These types of videos are always so interesting! It's so cool to see how the hardware dictated game design and was used to leverage what was given. Thanks!

Great, short easy-to-follow technical explanation from a gaming pioneer - thanks! - I LOVED Leander - The music, smoothness, tight control - superb classic! PS - Only just discovered your channel, will be subscribing!

Great work my guy! Just found your channel and its sick

Incredible, please don’t stop making these!

Just plowed through 5 videos.... This is a fascinating channel.

Thanks for the video Jon! I am very happy to see some Amiga related videos and indeed Leander is impressively colorful for a dual playfield game.I hope we will see more Amiga videos coming.

Shoutouts to that artist for making such beautiful art with only SEVEN colors.

So awesome, your channel is one of my favourites 😃

Loved this. Keep up the great videos!

I feel like you are a genius at this. I don't have any programming skills but your videos still amaze me.

feeling awestruck to see this up on youtube. Leander was one of my favourite amiga games of all time :)

This is not an empty compliment. This is not a blatant thank you. THANK. YOU. FOR. BEING. SO. DANG. CLEVER. This stuff is probably the single most intriguing thing I have ever found on the internet. Simply. AMAZING!

Thanks for the very interesting video and the brilliant Leander. I still play it every now and then.

I started programming in the 80s, and as soon as you said you'd found a way to solve the score collision problem, I guessed it had to involve chasing the raster :) That technique opened the door to so many clever hacks. Great video!

This was a brilliant and insightful video.

I found this just now, and I think it's a great showcase of how something can be done when optimized/developer for a specific hardware platform. Mostly thinking of PC vs console regarding this, but this was easy to understand and fascinating at the same time 😁 Thanks!

Always enjoy these. Thanks for making them. on a side note, have you any plans on continuing those Genesis coding lesson videos further?

This is gold. You're like a wise elder bequeathing his knowledge to the next generations. Every video just gets better!

Me and a friend were very impressed by Leander back in the Amiga days, loved the gameplay and the graphics plus the nice intro!

It's incredible that you manage to find elegant solutions to a lot of the challenges you're faced with. I don't think I would have done the same.

Great video as always! Thanks for sharing some good knowledge with us! Take care

These videos make the perfect companion to my morning coffee, love it!

That you were an Amiga developer was enough to earn my subscription. :) Great content is a nice bonus

Love hearing these coding secrets. Thank you so much for sharing.

Another amazing insight into how games work.

Brilliant hardware solution! I love this kind of out of the box thinking. Fascinating stuff.

So you were the creator of Leander? WOW, I've spent my childhood playing and enjoying that game, nice to you see you here :)

Amiga fan here! Whilst I knew the Amiga was a special machine, and knew of its wonderful chipset, I never got into coding on it (Okay, a bit of AMOS, but not a lot). It’s videos like this that I absolutely love to see after all these years. More on Amiga projects please 😊

I sometimes wonder how people fit so much into their days? I assume as well as being a lead developer at Traveller’s Tales and a movie producer that you have a family and children you spend a lot of time with? And then you have enough free time to have a hobby making technical RU-vid videos and making director’s cuts of your old games. Anyway hats off to you man, I can barely get out of bed in the morning. Let alone work on that game I always planned to develop but never did. Love your channel keep up the great work!

love your channel!

I've spent so many hours playing this game, loved it, and the music.

What was the reason to rename it from Leander to Legend of Galahad?

this channel is a game programming goldmine 😍

I really love this channel!

Awesome video man.

Very clever use of hardware for the time. I always imagined pixel-perfect collision detection to be unnecessarily expensive, but I didn't know there was ever a hardware-level implementation of collision detection made until now. I'd have to say that collision boxes are still my preferred way of collision detection, as we have plenty of CPU time to handle the collision of even hundreds of on-screen entities on today's hardware. Often times, I have both a vertical and horizontal collision box for player-like entities so that vertical and horizontal collisions aren't confused when calculating where to move the player (for things like walls and floors).

I thought the level select crash handler was the best clever game design I'd seen, but this is better. Love your videos

Man, that takes me back! I remember saying to my brother, back when Leander came out on the Amiga, that games would never look better than this. Top game! Cheers for the memories.

I don't know a darn thing about coding, but I love your videos anyway. Keep up the good work!

Was the Megadrive version easier to write, or did it introduce new challenges?

Good Lord, this is insane! I'm so impressed!

A very clever and elegant solution! There is nothing more satisfying than figuring out how to accomplish a task such as this in such an efficient manner requiring very little overhead or wasted CPU cycles. Obviously though, it takes an intelligent individual to come up with these types of clever tricks otherwise (most likely) most games would have been utilizing the same workarounds.

Even thou I have no experience in coding and have no idea what you are talking about 50% of the time, I still find your videos fascinating.

You made one of my favorite games of all time? I salute you, sir!

Great video, great game and great computer!

This is my favorite youtube channel

Somewhat off-topic, but I just wanted to say that I think it's really awesome you included twin fire buttons support. Such a nice thing to have on an Amiga game.

Fascinating! Thanks.

Brilliant work

Beautiful!

Oh, that's a question/idea. Have you or are you planning on doing an episode with one or more of your former coworkers from Traveller's Tales?

Wow, very informative! This helps me a lot, as a beginner programmer

You have done Leander too?!?!? I accidentally subscribed to the channel of a legendary pioneer!

Hell yes, I love Leander so much Thanks, Jon!

So somebody was using it!

I totally dig the use of copper to flag the screen elements - mind blown!

Yunno, I think I enjoy learning about how older games on older systems were made because the same kind of ingenuity comes into play when I'm optimising my builds on Armored Core games. Well, not exactly the same, but clever tricks and work-arounds abound in both situations.

Thank you, for amazing and interesting videos!

Man, that was fascinating. I genuinely wish I knew more about programming...

This approach reminded me of how I kept thinking about today's tech "But surely, there must be a way to use stencil buffers or something like it for collision detection!". Unfortunately, I don't have a lot of time to spare for game dev experiments and my limited research efforts have resulted in "Nope, not possible [possibly as in 'not feasible']" so far.

I really love the programming secrets series you have going. A question, would it be possible to pull off the same kind of parallax effect on the Amiga as you guys did on the Mega Drive version? Perhaps not in Leander since there was really no playfield left for the background, but could you use the copper and a background playfield to create the same parallax effect seen in The Legend of Galahad and the Sonic games?

Thanks for this video 😁👍 i love your content

I love these videos

Many thanks for this fascinating explanation Jon! Leander was an absolutely beautiful game back in the day, and it still holds up incredibly well today - a fantastic achievement given the modest hardware of the time. I’m curious as to whether there are any changes you would make to the game today? Perhaps there features you would have liked to have implemented, but simply ran out of time, or memory? I really appreciate watching your videos, but those featuring Amiga titles are the most enjoyable, as it is the machine I grew up with. Thanks again, keep up the great work!

I'm way more in favor of multi-rectangle (or poly's) collisions, though. Makes a lot more sense for gameplay. To start with, you only want your blade to act as a weapon, not the character's ponytail. Then, games that favor the player by enlarging their hit boxes & shrinking the enemy's, are more fun to play. Then different box IDs are useful to mark spots from which bullets are shot, items are held, etc. Having multiple boxes isn't even much time-consuming, as a pre-test using the largest bounding box already eliminates most of the objects.

So elegant!

Woah. I think we take modern collision for granted. Thanks for yet another intriguing look into a veteran programmer's masterpieces!

Leander had larger sprites than most games at the time, was really impressed with it. Makes sense since you were able to optimize it better.

Great video.

Hey Jon, great explanation! Is there a possibility you make a video series commenting the Sonic 3D Blast source code? It will be very interesting for all your programmers subscribers :)

but does that mean that if another's objetc box toucher your box but doesn't overlap your pixels WHILE another object overlaps one of your pixel the collision detection returns that you're hitting both objetcts ?

Legendary! very inspiring!

Damn, that is clever!!! My hat is off to you.

Sometimes these secrets amaze me so much that I think you were born to code video games

Leander was my favourite game, still have it! Thanks Jon :O)

Those thoughts. amazing

I wish you made a new Amiga game.

Huh. I know about that feature on a lot of older systems, but I personally never really understood what it gets you that's worth bothering with. Interesting solution, certainly. Probably my lack of appreciation for it stems from learning to code on PC which lacks any such feature, (and since we're talking pentium 2/3 era stuff checking bounding boxes for a few dozen objects is kinda trivial). Also for the retro hardware I work with... SNES has no hardware collision support. And the Atari 800XL... Well it does, but it does collisions based on which background/sprite palette pair is involved... Probably still has some utility I guess. Pixel perfect collision isn't always desirable of course, so it does require caution. Part of what rendered E.T. on the 2600 so broken was the pixel perfect collision between the player sprite and the pits in the game, which had an effect which was counter-intuitive. Then again that kind of orthogonal top-down perspective actually calls for ignoring collisions with the ground and walls for most of the sprite; Only the base of the sprite should collide with ground based obstacles. (yet the whole sprite should collide with enemies). Collision detection is such an overlooked topic...

Nice

after having programmed many games, distance is the best collision detection. Because it is circular. It's perfect and fast. The problem with boxes is you can't rotate them well and they are unprecise compared to the entity. For my fighting game and space ship shooter I used dist (circles), because even for something long straight like a laser I just place distance tests along the line. the advantage over line colision is that it works 100% the time. With line colision detection I had the problem of lines going through other lines sometimes. I guess rounding errors. Anyway, the other advantage of distance colision over other colisions is, that you have different colision zones for different effects. Pretty cool video. Amiga coders are the best. Also best artists and music.