I have an MFC appplication where the user have to move the mouse around a circle circonference with a dragging mouvement. I need to retrieve the number of degrees during this mouse drag "rotation" and I need to know if it's clockwise or counterclockwise.
At first, to determine the rotation direction, I was comparing x-coordinnate between the current mouse position and the mouse position where the user clicked to initiate the dragging. That works well until the user rotate over 180 degrees.
How can I handle the other half of the circle?
You'll need at least three ordered points to determine whether someone is moving clockwise or counterclockwise over time. With only two points, it isn't obvious whether (for instance) someone rotated 90 degrees or -270 degrees. So simply taking the cross product of the start and end won't work.
Try sampling the mouse during the dragging to get the additional information you need, and then taking incremental cross products between each pair of consecutive points. That will tell you what you want to know. However, you'll need to sample fast enough that no rotation of more than 180 degrees could have occurred; otherwise you'll wind up in an ambiguous situation again.
These might help you.
http://en.wikipedia.org/wiki/Atan2
http://www.phy.syr.edu/courses/java-suite/crosspro.html
And here is a simple example of recognizing gestures (it's in flash but the idea is the important bit)
http://www.bytearray.org/?p=91
Read about cross products. Computing a cross product between the X and Y vectors (differences from the start point) will always reliably give the rotation direction.
Related
Another tricky question. What you can see here is my physical pyramid built with 3 leds which form a triangle in 1 plane and another led in the mid center, about 18mm above the other 3. The 4th one makes the triangle to a pyramid. (You may can see it better if you look on the right triangle. This one is rotated about the horizontal achsis, and you can see a diode on a stick very well).
The second picture shows my running program. The left box shows the raw picture of the leds (photo with ir-filter). The picture in the center shows that my program found the points and is also able to tell which point is which, based on some conditions (like C is always where the both lines with maximal distance betweens diodes intersect; and the both longest lengths are always a and b). But dont care about this, i know the points are 100% correctly found.
Then on the right picture are some calculated values, like the height between C and c and so on. I would be able to calculate more, but i didnt bother to care for now, cause I am stuck.
I want to calculate the pyramids rotation and translation in the 3 dimensional space.
The yellow points are the leds after rotation arround an axis throught the center of the triangle in camera z- direction. So now i do not have to worry about this, when calculating the other 2. The Rotation arround the horizontal axis, and the rotation arround the vertical axis. I could easily calculate this with the lengths of the distance from the center of the triangle to the 4th diode (as you can see the 4th diode moves on the image plane with rotation), or the lengths of the both axes.
But my problem is the unknown depth.
It affects all lengths (a,b,c, and also the lengths from the center to the 4th diode if we call this d and e). I know the measurments of the real pyramid, with a tolerance of +-5% or so, but they get also affected by the zoom. So how do i deal with this?
I thought of an equation with a ratio between something with the lengths of the horizontal axis, the length of the vertical axis, the angles alpha, beta and gamma, and the lengths d and e.
Alpha, beta and gamma only get affected by rotation arround the axes (which i want to know. i want to know the rotation and the zoom), where a rotation arround one axis has the opposite effect than a rotation arround the other. So if you rotate arround both axes in the same angle, the ratio between the length of the axes is the same as before.
The zoom (real: how close it is to the camera; what i want to know in 1st place: multiplication factor 2x, 3x,0.5, 0,4322344,.....) does not affect the angles, but all the lengths: a,b,c,d,e,hc (vertical length of axis), hx (i have not calculated it yet, but it would be easy. the name hx can vary, i just thought of something random right now; it is the length of the horizontal axis) in the same way (i guess).
You see i have thought of many, but i think i am too dumb.
So, is there any math genius out there wo can give me the right equations, for either the rotation OR/AND the zoomfactor?
(i also thought about using Posit/Downhill- Simplex, and so on, but this would be the nicest, since i already know so much, like all Points, and so on and so on)
Please, please, i need your help really bad! I am writing this in C++ and with help of OpenCV if you need to know, but i think its more a mathematical problem.
Thanks in advance!
Ah, and Alpha seems to be always the same as Beta!
Edit: Had to delete the second picture
Have a look to Boost Geometry or here also
Have a look at SolvePnP() in OpenCV. Even if you don't use it directly, the documentation has citations for the methods used.
I am working on a simple mesh viewer implementation in C++ with basic functionality such as translation, rotation, scaling.
I'm stuck with with implementing the rotation of the object along z-axis using the mouse. What I want to implement is the following:
Click and drag the mouse vertically (almost vertical will do, as I use a simple threshold to filter slight deviations along the horizontal axis) to rotate the object along y-axis (this part is done).
Click and drag the mouse horizontally just as described above to rotate the object along x-axis (this part is done too).
For z-axis rotation, I want to detect a circular (or along an arc) mouse movement. I'm stuck with this part, and don't know how to implement this.
For the above two, i just use atan2() to determine the angle of movement. But how do I detect circular movements?
The only way to deal with this is to have a delay between the user starting to make the motion and the object rotating:
When user clicks and begins to move the mouse you need to determine if its going to become a straight line movement, or a circular one. This will require a certain amount of data to be collected before that judgement can be made.
The most extreme case would be requiring the user to make one complete circle first, then the rotation begins (in reality you could do much better than this). Just how small you are able to cut this period down to will depend on a) how precise you dictate your users actions must be, and b) how good you are with pattern recognition algorithms.
To get you started heres an outline of an extremely poor algorithm:
On user click store the x and y coordinates.
Every 1/10 of a second store the new coordinates and process_for_pattern.
in process_for_pattern you're looking for:
A period where the x coordinates and the y coordinates regularly both increase, both decrease, or one increases and one decreases. Over time if this pattern changes such that either the x or the y begins to reverse whilst the other continues as it was, then at that moment you can be fairly sure you've got a circle.
This algorithm would require the user to draw a quarter circle before it was detected, and it does not account for size, direction, or largely irregular movements.
If you really want to continue with this method you can get a much better algorithm, but you might want to reconsider your control method.
Perhaps, you should define a screen region (e.g. at window boundaries), which, when was clicked, will initiate arc movement - or use some other modifier, a button or whatever.
Then at a mouse click you capture the coordinates and center of rotation (mesh axis) in 2D screen space. This gets you a vector (mesh center, button down pos)
On every mouse move you calculate a new vector (mesh center, mouse pos) and the angle between the two vectors is the angle of rotation.
I don't think it works like that...
You could convert mouse wheel rotation to z-axis, or use quaternion camera orientation, which is able to rotate along every axis almost intuitively...
The opposite is true for quarternion camera: if one tries to rotate the mesh along a straight line, the mesh appears to rotate slightly around some other weird axis -- and to compensate that, one intuitively tries to follow some slightly curved trajectory.
It's not exactly what you want, but should come close enough.
Choose a circular region within which your movements numbered 1 and 2 work as described (in the picture this would be some region that is smaller than the red circle. However, when the user clicks outside the circular region, you save the initial click position (shown in green). This defines a point which has a certain angle relative to the x-axis of your screen (you can find this easily with some trig), and it also defines the radius of the circle on which the user is working (in red). The release of the mouse adds a second point (blue). You then find the angle this point has relative to the center of the screen and the x-axis (just like before). You then project that angle onto your circle with the radius determined by the first click. The dark red arc defines the amount of rotation of the model.
This should be enough to get you started.
That will not be a good input method, I think. Because you will always need some travel distance to discriminate between a line and a curve, which means some input delay. Here is an alternative:
Only vertical mouse having their line crossing the center of the screen are considered vertical. Same for horizontal. In other cases it's considered a rotation, and to calculate its amplitude, calculate the angle between the last mouse location and the current location relatively to the center of the screen.
Alternatively you could use the center of the selected mesh if your application works like that.
You can't detect the "circular, along an arc" mouse movement with anywhere near the precision needed for 3d model viewing. What you want is something like this: http://thetechartist.com/?p=80
You nominate an axis (x, y, or z) using either keyboard shortcuts or on-screen axis indicators that you can grab with the mouse.
This will be much more precise than trying to detect an "arc" gesture. Any "arc" recognition would necessarily involve a delay while you accumulate enough mouse samples to decide whether an arc gesture has begun or not. Gesture recognition like this is non-trivial (I've done some gesture work with the Wii-mote). Similarly, even your simple "vertical" and "horizontal" mouse movement detection will require a delay for the same reason. Any "simple threshold to filter slight deviations" will make it feel dampened and weird.
For 3d viewing you want 1:1 mouse responsiveness, and that means just explicitly nominating an axis with a shortcut key or UI etc. For x-axis rotation, just restrict it to mouse x, y-axis to mouse y if you like. For z you could similarly restrict to x or y mouse input, or just take the total 2d mouse distance travelled. It depends what feels nicest to you.
As an alternative, you could try coding up support for a 3D mouse like the 3dConnexion SpaceExplorer.
Using Cocos2d and Box2d I have made a rope of revolute joint segments with a body attached to the lowest segment (weldJoint) which I move using a mouse joint. The rope is hanging downward. How can I set conditions to tell when the attached body has covered double the distance it is swiped (mouseJoint) in the opposite direction. For example, if I swipe the body (attached to the rope) 45 degrees to the left I should know (maybe by some message or something) when it swings back 45 degrees to the right. Please help.
Perhaps I'm oversimplifying, but have you tried adding a sensor (Section 6.3 of Box2dManual) when you release it? If your physics are pretty simple, you should be able to get away with adding it at the same Y as the release point and making it's X flipped about the joint location.
I'm fairly new to directx so this may sound really basic.
I have started working on a first person game where you can walk through rooms, the language i am coding in is c++ and I'm using directx to help me create my game.
So far i have all the rooms drawn with doors etc but im a bit stuck how to make a first person camera and allow the user move forwards, backwards and side to side using the arrow keys on a keyboard.
The simpler the better as i am a beginner.
Could anyone help me out with this or point me in the right direction?
Thanks in advance
There's a lot of tutorials in web covering this topic, so Google will certainly help you.
As for the basics: You will want to store your position and camera rotation. Assuming Z is your up-axis, you should use the arrows to change only the X and Y.
Let's also say, that you will store your camera orientation is stored as a composition of rotations along Z-axis (movement direction) and X axis (looking up-down).
Simple class:
class Player
{
protected:
float3 Position; // Z-up
float2 CameraRotation; // X for turning, Y for up-down
public:
void MoveForward()
{
Position.X += -cosf(CameraRotation.X) * PLAYER_SPEED;
Position.Y += -sinf(CameraRotation.X) * PLAYER_SPEED;
}
// when using any other arrow, just add a multiply of PI/2 to the camera rotation
// PI for backwards, +PI/2 for left strafe and -PI/2 for right strafe.
// If you don't want to use mouse, use left and right arrow to modify camera rotation
// and MoveForward and Backward will look the same, having different signs.
};
The '-' signs in front of sinf and cosf functions are there because you will probably want this kind of behavior, feel free to change them.
As for camera, you will have to implement mouse delta between frames. In every frame compare the mouse position with the previous one. Then multiply it by turning and looking speed and set directly to camera value.
Hope this helped.
I am more of an OpenGL guy so I cannot help you with the technical side, what I can do is give you a direction.
In general, a 3D camera has:
Translation - where the camera is (x, y, z)
Rotation - angle of the camera around each axis
What you want do is related to the translation part only:
Monitor the user input, and capture when he presses one of the arrow keys.
When an arrow key is down, you want to start changing the camera translation. If the user presses the up key, you would add a constant value to the corresponding camera translation component (x) each iteration of your main game loop until he releases the key. If he presses the down key, you would want to subtract that value instead of adding it.
When he releases the key, your code needs to stop adding that value to the camera translation.
Let's assume that your game runs at 60Hz, and you add, say, 1/60 units to the camera translation each iteration for each direction the user wants to go. If the user held up the up arrow key for 2 seconds, the camera would have moved forward 2 units.
This is the "theory" in general, now I can only point you to web pages I found that may be useful for solving the technical side of your problem:
DirectX camera movement - I'm guessing this article has a lot more than you need, but it looked pretty good and I think that you should read it anyway... But you can just skip to the View Transformation part.
Input handling - nothing much to say, regular Win32 input handling. If you are not familiar with win32 input handling I think that you should take an hour or two to learn that first.
Alright that's it, hope I helped
I've been using OpenGL with SFML 1.6 for some time now, and it has been a blast! With one exception: I can't seem to implement a camera class correctly. You see, I am trying to create a C++ class called "Camera". Here are my functions:
Camera::Strafe(float fSpeed)
checks whether the WASD keys are pressed, and if so, move the camera at "fSpeed" in their respective directions.
Camera::MouseMove(int currentX, int currentY)
should provide a first-person mouse look, taking in the current mouse coordinates and rotating the camera accordingly. My Strafe() implementation works fine, but I can't seem to get MouseMove() right.
I already know from reading other resources on OpenGL mouse look implementations that I must center the mouse after every frame, and I have that part down. But that's about it. I can't seem to get how to actually rotate the camera on the spot from the mouse coordinates. Probably need to use some trig, I bet.
I've done something similar to this (it was a 3rd person camera). If I remember what I did correctly, I took the change in mouse position and used that to calculate two angles (I did that with some trig, I believe). One angle gave me horizontal rotation, the other gave me vertical rotation. Pitch, Yaw and Roll specifically, although I can't remember which refers to which direction. There is also one you have to do before the other, or else things will rotate funny. I'm pretty sure it was pitch first, then yaw or roll.
Hopefully it should be obvious what the change in mouse position did. It allowed mouse senesitivity. If I moved the mouse fast, I would have a larger change, and so I would rotate "faster."
EDIT: Ok, I looked at my code and it's a very simple calculation.
This was done with C#, so bear with me for syntax:
_angles.X += MathHelper.ToDegrees(changeInX / 100);
_angles.Y += MathHelper.ToDegrees(changeInY / 100);
my angles were stored in a 2 dimensional vector (since I only rotated on two axes). You'll see I took my changeInX and changeInY values and simply divided them by 100 to get some arbitrary radian value, then converted that number to degrees. Adjust the 100 for sensitivity. Keep in mind, no solid-math was done here to figure this out. I just did some trial-and-error until I got something that worked well.