I need to create a right angle with a triangular support, as seen in the example below (which I created in Blender). I know how to create the right angle, but I don't really know how to create the triangular support. The only way that I was able to think of would be to create a 2D polygon that would be the outer face of the object where the support is, then extrude it to the thickness of the support, and then extrude the rest to complete the object. This, however, seems clumsy and against the idea of CQ, where the code should be (kind of) similar to how a human would describe such object.
Is it possible to create the right angle first and then add the support? How?
Related
A recent question here made me think of SceneKit again, and I remembered a problem I never solved.
My app displays antenna designs using SK. Most antennas use metal rods and mesh reflectors so I used SCNCylinder for the rods, SCNPlane for the reflector and SCNFloor for the ground. The whole thing took a couple of hours, and I'm utterly noob at 3D.
But some antennas use wires bent into arcs or helixes, and I punted here and made crappy segmented objects using several cylinders end-to-end. It looks ass-tastic.
Ideally I would like a single object that renders the arc or helix with a cylindrical cross section. Basically SCNTorus, but with a start and end angle. This post talks about using a UIBezierPath in SK, but it uses extrude to produce a ribbon-like shape. Is there a way to do something similar but with a cylinder cross section (like a partial SCNTorus)?
I know I can make a custom shape by creating the vertexes (and normals and such) but I'm hoping I missed a simpler solution.
An arc you can do with SCNShape. Start with the technique from my other answer to get an extruded, ribbon-like arc. You'll want to make sure that the part where your path traces back on itself is offset by a distance the same as your extrusion depth, so you end up with a shape that's square in cross section.
To make it circular in cross section, use the chamferProfile property — give it a path that's a quarter circle, and set the chamfer radius equal to half the extrusion depth, and the four quarter-circle chamfers will meet, forming a circular cross section.
A helix is another story. SCNShape takes a planar path — one that varies in only two dimensions — and extrudes it to make a three-dimensional solid. A helix is a path that varies in three dimensions to start with. SceneKit doesn't have anything that describes a shape in such terms, so there's no super simple answer here.
The shader modifier solution #HalMueller alludes to is interesting, but problematic. It's simple to use a modifier at the geometry entry point to make a simple bend — say, offset every y coordinate by some amount, even by an amount that's a function of why. But that's a one-dimensional transform, so you can't use it to wrap a wire around on itself. (It also changes the cross section.) And on top of that, shader modifiers happen on the GPU at render time, so their effects are an illusion: the "real" geometry in SceneKit's model is still a cylinder, so features like hit testing apply to that and not to the transformed geometry.
The best solution to making something like a helix is probably custom geometry — generating your own vertex data (SCNGeometrySource). The math for finding the set of points on a helix is pretty simple if you follow that shape's definition. To wrap a cross section around it, follow the Frenet formulas to create a local coordinate frame at each point on the helix. Then make an index buffer (SCNGeometryElement) to stitch all those points into a surface with triangles or tristrips. (Okay, that's a lot of hand-waving around a deep topic, but a full tutorial is too big for an SO answer. This should be enough of a breadcrumb to get started, though...)
Here are some starting points that might help.
One approach would be to use more cylinders and make them shorter. That's the same idea behind the various segmentCount properties on the SCNGeometry primitives. Can we see a screenshot of the current linked cylinders version?
If you increase the heightSegmentCount, you could use the approach outlined here: scenekit, how to bend an object.
I just took a look at SCNShape. I was thinking you could use a shader modifier to warp the extruded shape into a circular cross section. But SCNShape doesn't seem to expose a segment count property, which I think you'd need to create enough extrusion segments for a good look. The chamferRadius and chamferProfile properties look interesting. I wonder if you could use those to create an extrusion that looks good.
I am dealing with storage of shapes. After a day spent to include the routines now I have some doubts.
The main trouble is recognize perfectly the new shape and know if already included or not.
I wrote something, and it works. I select all the shapes with same area and same number of vertex, and than I perform an Heuristic comparison. But, so just to be sure, I would ask you, if you know some direct algorithms, such matrix, spectrum, G theorm that gave two set of point can understand if the two sets are the same shape?
Before somebody screams about gis, the shapes can contain negatives shapes, better known with the name of holes. That are not to analyze in own coordinate system but in owner shape coord sys, where is the hole inside the other shape and his orientation. As far as I know, can gis nest shapes in other shapes and recognize them as whole shape.
Second place, what is the best way to store shape? I was thinking to store as array but I find it uncomfortable.
I am able to draw shapes using the UIBezierPath object. Now I want to identify different shapes drawn using this eg. Rectangle , Square , Triangle , Circle etc. Then next thing I want to do is that user should be able to select a particular shape and should be able to move the whole shape to different location on the screen. The actual requirement is even more complex , but If I could make this much then I can work out on the rest.
Any suggestion or links or points on how do I start with this is welcome . I am thinking of writing a separate view to handle every shape but not getting how do I do that..
Thank You all in advance !!
I recommend David Gelphman’s Programming with Quartz.
In his chapter “Drawing with Paths” he has a section on “Path Construction Primitives” which provides a crossroads:
If you use CGContextAddLineToPoint your user could make straight lines defined by known Cartesian points. You would use basic math to deduce the geometric shapes defined by those points.
If you use CGContextAddCurveToPoint your user could make curved lines defined by known points, and I’m pretty sure that those lines would run through the points, so you could still use basic math to determine at least an approximation of the types of shapes formed.
But if you use CGContextAddQuadCurveToPoint, the points define a framework outside of the drawn curve. You’d need more advanced math to determine the shapes formed by curves along tangents.
Gelphman also discusses “Path Utility Functions,” like getting a bounding box and checking whether a given point is inside the path.
As for moving the completed paths, I think you would use CGContextTranslateCTM.
I am interested in using the CGContextEOFillPath feature provided by apple. I am guessing with the way the EOFill works, it probably has a way to take the filled in areas and calculate an area.
So my question is does anyone know of a way to use CGContextEOFillPath and find the area of the filled in sections.
If this isn't something that is easily done, maybe some pointers to a better way of doing this would be helpful. Though I need to use the EO style graphing.
Thanks.
What do you mean "Calculate the area"?
As in calculate the surface area of a complex shape?
It depends on your shapes.
Are they all polygons?
What about circles?
There are well known formulas for calculating the area of a polygon. (Wikipedia has it) Part of that calculation involves using an ABS() function because shapes drawn "counterclockwise" have the opposite sign as those drawn "clockwise". If you're looking to simulate the EO behavior, you can simply ignore the sign change, because, for you, it's desirable.
If you have more complicated shapes that involve curves, then you need to break the problem down into multiple parts - one part to solve for polygons - one to solve for circles - one to solve for other shapes, etc.
i want to make fruit ninja blade. i am using cocos2d and the MotionStreak is really ugly for this. Any other approach or better settings for MotionStreak? maybe particle system? any free great tools similar to ParticleDesigner?
I have my own implementation with OpenGL triangle strips mapped with texture. The blade is very smooth if the distances between adjacent points are small enough. I use linear interpolation to insert more points between two points which the distance is greater than a predefined constant. I'm thinking of use order 2 interpolation but the implementation is more difficult and the performance may reduces.
Source code is available here https://github.com/hiepnd/CCBlade
i don't know how much effort it will take but the thing is you can create and change shape of filter and just apply a white to gray gradient as it's texture, it'll give a very good looking results. i myself am working with cocos2d-x (it's just a c++ port of cocos2d) and it has samples for dynamic filters (it's just like you create and manipulate a mesh and all the things are done automaticaly), it uses CCActionGrid class but i just didn't used this class yet if you couln't solve your problem using that ask me to search deeper.
http://pixlatedstudios.com/2012/02/fruit-ninja-like-blade-effect/
Worth Checking out!!!! based on hiepnd CCBlade tutorial.