I have made a rigid body for the player and have been trying to get the rigid body moving along with the player's controls.
What I mean is that whenever I press forward I want the rigid body to move forward in the direction the player is facing, same with back, left, right. So far I'm able to use apply force to move the rigid body in static directions.
My straight question is how do I move the player's rigid body in the direction the player is facing.
Other Details:
I don't really want to use kinematic bodies if not necessary mostly because their very fiddly at the moment
I'm using glfw3 for input
This is quite amazing that you would not see how to do that after you actually managed to apply forces in static directions to something you configured over bullet.
Come on, you HAVE the skill to figure it out.
Here, just a push in the direction (hehe), hem. Just take the vector of the facing direction (which could be determined by camera, 1st or 3rd view, or even something else...).
Congrats, this vector is your force by a k factor.
You should also modulate this force according to speed, you don't need to accelerate to infinite speed, just accelerate lots at first and then regulate force to tend to desired walk speed.
Then, the side directions are obtained by rotating the facing vector by 90 degrees around the standing axis (most surely the vertical). You can obtain that by simply swapping components and multiplying by -1 one of them. x,y,z becomes y,-x,z
To go backward, its just -x, -y, -z on the facing vector.
So your up key is not bound to 0,1,0 but to facing_dir actually. This facing dir can change with mouse or some other view controls, like numeric keys 2,6,8,4 for example. Or you could drop up,left,right,down for movement and use w,a,s,d like everybody else, and use direction keys to rotate facing direction. (+mouse)
It is much more difficult to obtain the facing vector from mouse movement or direction keys than finding out how to apply the force, so if you already have the facing vector I'm puzzled that you even have a problem.
Related
I am building an IOS game in Cocos2d - Chipmunk - Spritebuilder. I need to make a characters orbit around around a point, and I was having quite some difficulty in implementing orbits with real physics.
So far, I have tried two methods, one is creating a distance joint from the player to the planet, and then applying a 90 degree force on the player where an angle is created between the end of the distance joint and an imaginary line drawn at a 90 angle to it. He moves around crazily and this method is not working for me.
I then tried calculating 180 points on the circumference at a radius from the planet (which is the bounds of detecting and implementing its effects on the player) - and then in a scheduled update method [character.physicsbody applyForce:nextCircumferencePoint]; This does not work, as he does not follow the path exactly and is quite far from it. I am thinking that I need to also apply a gravitational force towards the planet which would cause him to circle it. Though I don't know how to calculate that force, apply it, or if it would even help.
A third method which would never work, but was used for testing was to set his position to the next circumference point. He does orbit, but any collision won't work (such as if a piece of space junk goes in his way.) He will simply be positioned right over any other object. This world great if you don't need collisions, are writing your own physics engine. This is not a polished way of doing things, so will avoid it.
Please correct anything I have already done and tell me how it would work, or shed light on other options and how to implement them.
Check out my answer here. It's for box2d, but you can do it with Chipmunk. If bodyA position will change, orbit will be same. You just need to change speed of body movement for your needs, just increase smoothness and slow down your update method.
I want to move the camera forward, which is equivalent to moving the world back towards camera. I'm using Glut and glTranslate would do the job, but my question is how should I use it?
Suppose initially I start with glLoadIdentity(), then I set up the look at point using gluLookAt, and then I did some translation/rotation to the model. In this case how should I use glTranslate to translate the object in the world so that they can move with respect to the camera instead of their own origin/coordinate?
I thought I could save the current matrix using glGet, load Identity matrix, then do the translation I wanted, and then multiply the previous matrix back using glMultmatrix. But this didn't work for me.
And also if I want to enable yaw/pitch using glrotate, how should I do? (Also in the sense to rotate the world to make it seems rotating camera)
Sorry for my poor wording or conceptual mistake if there is any. I'm quite new to opengl and graphic programming in general and I'm still trying to fully understand the opengl pipeline, especially the matrix part. Any detailed explanation to that will also be greatly appreciated!
From reading your question, it sounds to me like what you're trying to do is simulate camera movement by translating every other object in the world about a fixed point (the camera)
While you're correct in saying that moving the camera actually moves everything else in the world about it, you seem to be going about it the wrong way. After all, look how much difficulty you're having just moving one box. Now imagine you have hundreds! Not much fun :)
Fortunately, there is a function that can help you, and you're already using it! gluLookAt (http://www.opengl.org/sdk/docs/man2/xhtml/gluLookAt.xml) is your guy. What it does under the hood is it creates a matrix (Not sure what a matrix is? Give this a read: http://solarianprogrammer.com/2013/05/22/opengl-101-matrices-projection-view-model/) that every other point in the world is multiplied by. This multiplication translates each point until its in its correct position relative to the camera. So you are correct in saying that moving the camera actually moves the whole world relative to the camera, this way we can do it all in one pass instead of having to calculate the new positions of each point manually.
So, you want to move the camera forward on the z axis? Just call gluLookAt, but pass in a value of eyez that is less than when you previously called gluLookAt. Here's an example:
gluLookAt(0,3,0,0,0,0,0,1,0);//This is out starting position, (0,3,0)
gluLookAt(0,2,0,0,0,0,0,1,0);//And this is out ending position. Notice that the eyez value has decreased by one
As for how to rotate, take a look at the second group of three parameters, the "center" parameters. Those determine what point is in the center of the camera, that is, what the camera is looking at. In the previous example, the center point was (0,0,0). You can rotate the camera by moving these points around. How you do it is a pretty complicated topic with a good bit of math thrown in, but the following links should help a bit:
http://ogldev.atspace.co.uk/www/tutorial15/tutorial15.html
http://www.fastgraph.com/makegames/3drotation/
http://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation
Don't get discouraged if it seems too hard, keep at it! Feel free to ask me if you need clarification on this answer.
I'm working on a Little Mobile Game with Cocos2D-X and Box2D.
The Point where I got stuck is the movement of a box2d-body (the main actor) and the according Sprite. Now I want to :
move this Body with a constant velocity along the x-axis, no matter if it's rolling (it's a circleshape) upwards or downwards
keep the body nearly sticking to the ground on which it's rolling
keep the Body and the according Sprite in the Center of the Screen.
What I tried :
in the update()- method I used body->SetLinearVelocity(b2Vec2(x,y)) to higher/lower values, if the Body was passing a constant value for his velocity
I used to set very high y-Values in body->SetLinearVelocity(b2Vec2(x,y))
First tried to use CCFollow with my playerSprite, which was also Scrolling along the y-axis, as i only need to scroll along the x-axis, so I decided to move the whole layer which is containing the ambience (platforms etc.) to the left of my Screen and my Player Body & Player sprite to the right of the Screen, adjusting the speed values to Keep the Player in the Center of the Screen.
Well...
...didn't work as i wanted it to, because each time i set the velocity manually (I also tried to use body->applyLinearImpulse(...) when the Body is moving upwards just as playing around with the value of velocityIterations in world->Step(...)) there's a small delay, which pushes the player Body more or less further of the Center of the Screen.
... didn't also work as I expected it to, because I needed to adjust the x-Values, when the Body was moving upwards to Keep it not getting slowed down, this made my Body even less sticky to the ground....
... CCFollow did a good Job, except that I didn't want to scroll along the y-axis also and it Forces the overgiven sprite to start in the Center of the Screen. Moving the whole Layer even brought no good results, I have tried a Long time to adjust values of the movement Speed of the layer and the Body to Keep it negating each other, that the player stays nearly in the Center of the Screen....
So my question is :
Does anyone of you have any Kind of new Approach for me to solve this cohesive bunch of Problems ?
Cheers,
Seb
To make it easy to control the body, the main figure to which the force is applied should be round. This should be done because of the processing mechanism of collisions. More details in this article: Why does the character get stuck?.
For processing collisions with the present contour of the body you can use the additional fixtures and sensors with an id or using category and mask bits. For of constant velocity is often better to use SetLinearVelocity, because even when using impulse velocity gets lost at sharp uphill or when jumping. If you want to use the implulse to change the position of the body, then you need to use the code for the type of this:
b2Vec2 vel = m_pB2Body->GetLinearVelocity();
float desiredVel = mMoveSpeed.x; //set there your speed x value
float velChange = desiredVel - vel.x;
float impulse = m_pB2Body->GetMass() * velChange;
m_pB2Body->ApplyLinearImpulse( b2Vec2(impulse, mMoveSpeed.y), m_pB2Body->GetWorldCenter());
This will allow maintain a constant speed most of the time. Do not forget that these functions must be called every time in your game loop. You can combine these forces, depending on the situation. For example, if the at the beginning you need to make a small acceleration, it is possible to use ApplyForce to the body, and when a desired speed is to use ApplyLinearImpulse or SetLinearVelocity. How correctly to use it is described here: Moving at constant speed
If you use world with the normal gravity(b2Vec2(0, -9.81)), then it should not be a problem.
I answer for this question here: Cocos2D-x - Issues when with using CCFollow. I use this code, it may be useful to you:
CCPoint position = ccpClamp(playerPosition, mLeftBounds, mRightBounds);
CCPoint diff = ccpSub(mWorldScrollBound, mGameNode->convertToWorldSpace(position));
CCPoint newGameNodePosition = ccpAdd(mGameNode->getPosition(), mGameNode->getParent()->convertToNodeSpace(diff));
mGameNode->setPosition(newGameNodePosition);
P.S. If you are new to box2d, it is advisable to read all the articles iforce2d(tuts), they are among the best in the network, as well as his Box2D Editor - RUBE. At one time they really helped me.
I do not know if this is possible but I have an idea:
Keep the circle at a fixed position and move the background relatively. For example, during the course of the game, if the circle has a velocity of 5 towards left then keep circle fixed and move screen with velocity 5 towards right. If circle has 5 velocity towards left and screen has 3 velocity towards right, then keep circle fixed and move screen with 8 velocity towards left and so on. This should allow you to fix the circle at the center of the screen.
Another method would be to translate the entire screen along with the ball. Make everything on the screen an object that can have a velocity. And the x-component of the velocity of the ball (circle) should be the velocity of all other objects. This way, whenever the circle moves, all the other objects will try and keep up with it.
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.
So, I have a Triangle->AABB collision algorithm and I have it returning the triangle that the AABB collided with. I was hoping with the 3 vectors of the triangle and the direction/magnitude of the movement would let me determine a deflected vector so that when you run against the wall at an angle you move slower, depending on the angle of collision, but along side the wall. This would remove the sticky collision problem with only moving when there is not a collision. Any suggestions or references would be greatly appreciated! Thanks.
First, I would convert magnitude/direction to a vector (it's much more convenient).
Then (c++):
float towards=dot(velocity,norm); // velocity component into triangle
if(towards<0) // is moving into triangle
velocity-=towards*norm; // remove component
Then it can't move into the triangle. towards<0 might need to be reversed depending on your normal. It's also nice to have a spring force pushing it out.
Remove the component of the velocity along the normal of the triangle.
The idea is that you can represent the movement as the part that's moving "into" the triangle and the remainder (which will be in perpendicular directions). If you then just move with the remainder, you will no longer be getting any closer to the triangle by the movement (or further, but you shouldn't be detecting a collision in that case).
In pseudo-code:
// v := velocity vector of moving object
// p[3] := points that make up the triangle
triangle_normal = cross(p[2]-p[0], p[1]-p[0])
problematic_v = project(v, onto=triangle_normal)
safe_movement = v - problematic_movement
Note that this intentionally doesn't preserve the magnitude of the movement vector, as doing so would make you slide along a wall very quickly when running straight at it.
For more details and some nice pictures, see Pool Hall Lessons: Fast, Accurate Collision Detection Between Circles or Spheres at Gamasutra. You're not using spheres, but you are essentially doing a perfectly plastic (since you don't bounce) collision.