I'm trying to figure out how to draw an stretchy/elastic line between two points in openGL/Cocos2d on iPhone. Something like this
Where the "band" get's thinner as the line gets longer. iOS uses the same technique I'm aiming for in the Mail.app, pull to refresh.
First of all, is there a name for this kind of thing?
My first thought was to plot a point on the radius of the starting and ending circles based on the angle between to the two, and draw a quadratic bezier curve using the distance/2 as a control point. But I'm not a maths whizz so I'm struggling to figure out how to place the control point which will adjust the thickness of the path.
But a bigger problem is that I need to fill the shape with a colour, and that doesn't seem to be possible with OpenGL bezier curves as far as I can tell since curves don't seem to form part of a shape that can be filled.
So I looked at using a spline created using a point array, but that opens up a whole new world of mathematical pain as I'd have to figure out where all the points along the edge of the path are.
So before I go down that rabbit hole, I'm wondering wether there's something simpler that I'm overlooking, or if anyone can point me towards the most effective technique.
I'm not sure about a "common" technique that people use, other than calculating it mathematically, but this project, SlimeyRefresh, is a good example of how to accomplish this.
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Using threesJs. I'm trying to move an object along a bezier curve (idealy beziercurve3).
My purpose is to move a little point by mouse and then after use this point to cut this curve in two,
or start an other curve3 attached to this point.
From what I search before I suppose I should use something like clamp_to_curve function.
I saw that Line3 got closestPointTPoint Is it a good idea to do the same with a bezier curve?
Maybe getPoint and getPointAt from curve can help but I don't know how to use them. After searching for a while I fill a little bite lost.
What is the best way to start this ?
Recently I found an amazing APP called Photo Lab,and I'm curious about one effect called Paper Rose.In the pictures below，one is the original picture，the other is the effected picture.My question is what kind of algorithm can do this effect,and it would be better if you can show me some code or demo.Thanks in advance!
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I am afraid that this is not just an algorithm, but a complex piece of software.
The most difficult part is to model the shape of the rose. The petals are probably a meshed surface. It is not so difficult to give them a curved shape, but the hard issue is to group them in such a way that they do not intersect.
It is not quite impossible that this can be achieved by first putting them in a flat geometry where you can master intersections, then to wrap it around an axis with a king of polar transform. But I don't really believe in that. I rather think that they have a collision-avoiding geometric modeller.
The next steps, which are more classical, are to texture-map the pictures onto the petals and to perform the realistic rendering of the whole scene.
But there's another option, which I'll call the "poor man's rendering".
You can start from a real picture of a paper rose, where the petals have an empty black, thick frame. Then on the picture, you detect (either in some automated way or just by hand) points that correspond to a regular grid on the flattened paper.
As the petals are not wholly visible, the hidden parts must be clipped out from the mesh, possibly by using a polygonal fence.
Now you can take any picture, fit it over the undistorted mesh, clip out the hidden areas and warp to the distorted position. Then by compositing tricks, you will give it a natural shaded appearance on the rose.
Note: the process is eased by drawing a complet grid inside the frame. Anyway, you will need to somehow erase it before doing the compositing, in order to retrieve just the shading information.
I would tend to believe that the second approach was used here, as I see a few mapping anomalies along some edges, which would not arise on a fully synthetic scene.
In any case, hard work.
How can I determine whether a point is above an irregular mesh/surface in PCL?
I have one cloud of points that I would like to convert to a surface/mesh (not sure which terminology I should use.) Think of it as an irregular ground plane. For example:
This just shows that the surface can be sort of random, even have holes in it where data wasn't available.
Now, I have another point cloud, and I'd like to be able to filter out all the points that are below this surface.
The way I've been converting my points to a surface was by following the Fast triangulation of unordered point clouds tutorial.
If I can do this without converting the points to a surface, that would be great too. I'm new at this so I can easily imagine I'm going about this all wrong.
When I tried using straight point clouds, sparsity became a big issue. For example, in the image below, I generated a dense surface of points, and to filter the other cloud, used used getPointsInBox() (as suggested here) to search beneath the points. But as you can see, it fails with sparsity (the blue points circled in black.)
If I could create a more-or-less continuous mesh grid of points from my original points, the getPointsInBox() method would work quite well, but I also haven't been able to figure out how to do that.
I have a SKShapeNode curve that i need to detect collision with. The problem is i can't find solution to collide only with line, it seems all the options (including detection of nodeAtPoint) treat my curve as a rectangle, or polygon thing, but not as a curved line. Is there any way to make physics body for a curved line that doesn't connect to it self?
Was not able to find the right answer I came up to solution to use same line with reversed points so I have a loop that works well with physics.
I am in the process of developing a very simple physics engine. The only non-static objects in it will be circles and the only collision detection I will be performing is between circles and line pieces.
For the purpose I am utilizing the principals described in Advanced Character Physics. That is, I do integration by using a simple Verlet integrator. I perform collision detection and response simply by calculating the distance between the circles and the line pieces and in case that the distance is less than the cirles radius I project the circle out of the line piece.
This works very well and the result is a practically perfect moving circle. The current state of the engine can be seen here: http://jsfiddle.net/8K4Wj/. This however, also shows the one major problem I am facing: The circle does not rotate at all.
As far as I can figure out there is three different collision cases that will have to be dealt with seperately:
When the circle is colliding with a line vertex and is not rolling along the line.
When the circle has just hit or rolled of a line. Then the exact point of impact will have to be calculated (how?) and the circle is rotated according to the distance between the impact position and the projected position.
When the circle is rolling along a line. Then is it simply rotated according to the distance traveled since last frame.
Here is the closest I have got to solving the problem: http://jsfiddle.net/vYjzt/. But as the demo shows it doesn't handle the edge cases probably.
I have searched for a solution online but I can not find any material that deals with the given problem specifically (as I said the physics engine is relatively simple and I do not want to bother with complex physic simulation concepts).
What looks wrong in your demo is that you're not considering angular moment and energy when determining the motion.
For the easy case, when the wheel is dropping to the floor in your demo, it stops spinning while in free fall. Angular momentum should keep it going.
A more complicated situation is when the wheel finally lands on the floor, it moves with the same horizontal velocity it had before hitting floor. This would be correct if it wasn't rolling but since it is rolling, some of the kinetic energy will have to go into the spinning motion, and this should slow it down. As a more clear example of this, consider the opposite case where the wheel is spinning quickly but has no linear momentum. When this wheel is set on the floor, it should take off and the spinning should slow. Also, for example, as the wheel rolls down a hill, it accelerates more slowly because the energy needs to go into both linear and circular motion.
It's not too hard to do, but to show a rolling object in a way that looks intuitively correct, I think you'll need to consider the kinetic energy and angular momentum associated with rolling. By "not too hard", I mean that all of your equations will essentially but twice as long, with one term for linear motion and another for angular. I won't recite all of the equations, it's basically just the chapter in rotational motion from any physics text.
(Nice demo, btw!)