So.
After many years of iOS development I said it's time to try to do a little game for myself. Now I chose to do it using Apple's SceneKit since it looks like it provides everything I need.
My problem is that I've stumbled upon a huge problem (for me) and searching on Google doesn't yeld any results.
Any idea how do I go about having an object (a sphere for that matter) that deforms itself, say, because of a gravitational force. So basically it should squash on impact with the ground.
Or, how do I go about deforming it when it collides with other spheres, like a soft beach ball would?
Any starting point along those lines would be helpful.
I can post my code here, but I'm afraid it has nothing to do with my problem since I really don't know where to start.
Thanks!
Update
After doing a bit more reading I think that what I want could be doable with Vertex Shaders. Is that a right path to follow?
For complicated animations, you'll generally be better off using a 3D modeling tool like Blender, Maya, or Cheetah3D to build the body and construct the animation. Those tools let you think at a higher level of abstraction. Then you can export that model to Collada (DAE) format and then import it into SceneKit.
https://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Basic_Animation/Bounce has a tutorial on building a deforming, bouncing ball using Blender.
SceneKit only does physics using rigid bodies. If you want something to deform, you would have to do it yourself.
It is probably because SceneKit has no way of knowing how an object should be deformed. Should it just compress, should it compress in one direction and expand in all others to preserve it's volume, should only part of the model compress and the rest stay rigid (like the tires on a car).
What you could try is wait for a collision to occur and do the following
calculate and store the velocity after the bounce
disable collision checking on the object
run an animation for the "squash"
enable collision checking on the object
apply the calculated velocity
It will be entirely up to you how real or cartoony you want to make the bounce look.
Related
I'm hoping to simulate the movement of a train along a fixed path. The path itself is representable by a CGPath.
So far, I've found SKPhysicsJointSliding, which seems close, but appears to only work along a fixed axis, and since my path has curves that seems like a deal breaker.
I know I could use a series of SKActions to accomplish the movement, but in my case it's far preferable to have the physics engine handle the movement for me.
My question is basically whether or not this is something the SpriteKit physics engine can accommodate via something I've missed in the documentation (or if I'm somehow misunderstanding the sliding joint)?
Why is "physics" more preferable? Once you're on rails, you aren't really utilizing the physics engine. If you're looking for semi-realistic y-axis yaw as it rumbles down the track, try doing a random rotation about that axis.
You could also try utilizing the SKNode.physicsBody as well. According to Apple's docs, your SKNode doesn't participate in physics simulations until you attach one.
https://developer.apple.com/documentation/spritekit/sknode/1483117-physicsbody
Giving it mass and other physical properties could simulate slowing down, speeding up, etc.
Otherwise, you will have to do a lot of complicated math to apply physical forces in the direction you want the train to go.
I'm using SceneKit to create a 3D Room for a Swift iOS app.
I'm using multiple boxes and placing it together to create different walls of the room. I want to also add doors and windows to the room for which I need to cut holes into the walls. This looks like a very common scenario but yet I couldn't find any relevant answers out there.
I know there are multiple ways of doing it -
Simplest being, don't cut the box. Place another box with door or wall texture.
But I do want to keep a light source outside of the room and want it to flow into the room through these doors and windows
Create multiple boxes for single wall and put them together to make a geometry
My last resort maybe.
Create custom geometry.
Feels too complicated since it requires me to draw each triangle myself. Not sure?
But what I was actually expecting -
Subtract geometries from geometries?
Library that's already handling these complexities?
Any pointers would be very helpful.
Thanks.
Scene kit offers some awesome potential but it's not a substitute for a 3D modeling program. If you want something much beyond assembling with primitives and extrusion in a plane you should think about constructing your model in a dedicated 3-D package and exporting the model into SceneKit as a .dae file. You might take a look at Blender. It's free and readily available on the net. I suspect it can easily do what you want and the learning curve will be compensated by the higher level functions of a graphics program versus coding.
I think #bpedit described the best approach.
A weak second choice would be to use SCNShape to build your geometry. That still leaves you the problem of constructing a Bezier path that matches your wall layout/topology. That might be a helpful hack in the short term, to save you from an immediate learning curve in modeling software. But I predict you'll still eventually move to a tool like Blender, SketchUp, Cheetah 3D, or Maya.
I have just delved into the world of Metal, and I thought that I'd got the hang of it! But then it occurred to me that if I wanted to make a game, then static objects moving around a screen wouldn't suffice. So my question is, 'Is it possible to create animations for models with Metal?'
I have looked at using other APIs, such as SpriteKit, and SceneKit, but I found that they do not support shaders, and are not as powerful as Metal.
The only way that I can think about how I would go about this, is by creating 60 different models, and then loading each one one after the other, to give a 'stop-motion' kind of effect, but I think that this would probably be incredibly inefficient, and was hoping that there was an easier answer?
Thanks a lot!
Yes, there are other, more efficient ways to do animation. But before getting into that, a warning: it really looks like you're barking up the wrong tree here.
Metal is a (conceptually) very low-level interface. You use Metal to talk (almost) directly to the GPU, so to work with it you need to think (sort of) like a GPU: in terms of data buffers, vertex transformations, etc. You seem to be working at a much higher conceptual level, so you're probably better served by one of the high-level game engines: SpriteKit for 2D or SceneKit for 3D. (Or a third party engine like Cocos or Unity.) Metal, on the other hand, is better suited for building those game engines.
SpriteKit and SceneKit do support shaders. Look at SKShader and SCNShadable in the docs (and be sure to click the "More" links to read the full overviews). SceneKit also supports character animations (aka skeletal animation aka skinning): typically one designs and rigs a model for animation in an external authoring tool (Maya, Blender, etc), then uses SceneKit to work with the animations at run time.
It is possible to do things like GPU-based skeletal animation in Metal. But I haven't seen any tutorials or similar written about it yet, probably because Metal is such a new technology. Fundamentally, though, it'd be based on the same sorts of techniques you'd use for skeletal animation in OpenGL or Direct3D — and much has been written about animation for those technologies. If you're willing to invest the time and energy to work at a low level, adapting the subject matter from GL/D3D tutorials is relatively easy.
You can do skeletal animation in Metal, SCNKit would be using the GPU to deform the mesh as well. But to do it in Metal you would need to pass skin weights, along with bone matrices for the bind pose and the transformations of the bones as they animate then calculate the new vertex positions based on these. In fact I think you need the inverse of the bind pose matrices. Each mesh vertex is then transformed by a weighted sum of transformations dictated by the skin weights.
I tried it but screwed it up somehow it didn’t deform properly, I don’t know if I’d obtained the wrong matrices from my custom script to grab animation data from blender or a bug in my shader maths or from the weights.
It was probably close, but with all the possible things that I may have got wrong in the process it was difficult to fix so I abandoned it in the end.
Probably easier to stick with SceneKit and let apple take care of the rest or use an existing game engine such as Unity.
Then again if you want a challenge, I’m sure it’s possible, just a little tricky. You could try CPU first to make sure the maths is ok then port it to the GPU to make it faster?
SceneKit do support shaders. And an object that manages the relationship between skeletal animations and the nodes and geometries they animate is SCNSkinner from SceneKit.
Typically, you need to create a skinned model using, for example, Autodesk Maya, save it along with animations that use the skeleton, in a scene file. You load the model from the scene file and pose or animate it in your app, either by using animation objects also loaded from the scene file or by directly manipulating the nodes in the skeleton. That's it.
Watch this 7-parts video about Blender's skeletal system and how to use it in SceneKit.
convenience init(baseGeometry: SCNGeometry?, //character
bones: [SCNNode], //array of bones
boneInverseBindTransforms: [NSValue]?, //ibt of matrix4
boneWeights: SCNGeometrySource, //influence on geometry
boneIndices: SCNGeometrySource //index mapping
)
My goal is to create a CGPath that matches the outline of a SKSpriteNode.
This would be useful in creating glows/outlines of SKSpriteNodes as well as a path for physics.
One thought I have had, but I have not really worked much at all with CIImage, so I don't know if there is a way to access/modify images on a pixel level.
Then maybe I would be able to port something like this to Objective-C :
http://www.sakri.net/blog/2009/05/28/detecting-edge-pixels-with-marching-squares-algorithm/
Also very open to other approaches that make this process automated as opposed to me creating shape paths for every sprite I make for physics or outline/glow effects.
What you're looking for is called a contour tracing algorithm. Moore neighbor tracing is popular and works well for images and tilemaps. But do check out the alternatives because they may better fit your purposes.
AFAIK marching squares and contour tracing are closely related, if not the same (class of) algorithms.
An implementation for tilemaps (to create physics shapes from tiles) is included in Kobold Kit. The body of the algorithm is in the traceContours method of KKTilemapLayerContourTracer.m.
It looks more complex than it really is, on the other hand it takes a while to wrap your head around it because it is a "walking" algorithm, meaning the results of prior steps is used in the current step to make decisions.
The KK implementation also includes a few minor fixes specifically for tilemaps (ie two or more horizontally or vertically connected tiles become a single line instead of dividing the line into tile-sized segments). It was also created with a custom point array structure, and when I ported it to SK I decided it would be easier to continue with that and only at the end convert the point arrays to CGPath objects.
You can make certain optimizations if you can safely assume that the shape you're trying to trace is not going to touch the borders, and there can not be any tiles that are only connected diagonally. All of this becomes clearer when you're actually implementing the algorithm for your own purposes.
But as far as a ready-made, fits-all-purposes solution goes: there ain't none.
thanks for taking the time to read my question.
I'm writing a 2d top-down shooter game. It is currently using Box2d as a physics engine. The thing is, it isn't really using Box2d to it's fullest potential, just for collision detection and the underlying velocity/rotation update loop. Any plans to add real physics would simply be eye-candy, not a game changer.
Now I chose Box2d because I went through 2 other physics engines, and they just couldn't handle the types of collisions I'm detecting. I'm creating several 'bullets' with very high velocities, and I do not want them to be instant hits on their targets. JigLib and Flixel both had the same problem - bullets were not overlapping enemies at the time of the frame update, and thus were not detected as collisions (i.e. the bullets passed through enemies because they moved to fast).
I moved to Box2d because of it's iterative collision sampling, as well as the SetAsBullet method on bodies. And it works great! But now Box2d is giving me troubles too - generating several bullets per second, or at the same time, is severely lowering my fps.
So I removed Box2d to confirm that it was not a rendering limitation... added my own velocity/rotation system, and I can fire hundreds of bullets per second. Great! But its lacking any sort of collision detection.
So the questions:
1) Should I write my own iterative collision engine?
2) Should I give Box2d a try again, perhaps with some tweaks to make adding new bodies faster?
3) Is there some other alternative, maybe a lightweight physics engine that specializes in this?
4) Do you know of any other techniques or design patterns that could be of use?
Thanks so much for your help!
Edit: I should note, there are not just bullets, but larger, slower projectiles as well. I considered ray casting a line segment to the projectile's previous position, and catching intersections, but that won't work for the larger objects :(
It depends on how complex your situation can become, If you are good at math and physics you can rollout a fast engine that can handle simple collisions more faster than you can learn using box2d, but why should anyone invent the bycicle if there are plenty of them already invented so choose one you like a try using it, i recommend using box2d