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I'm attempting to write a bouncing ball game using flame in flutter. To detect collisions the onCollision and onCollisionStart methods are provided. What I had hoped is that onCollisionStart would give a precise location when two objects first hit each other. However, instead it gives a list of positions indicating where the two objects overlap after the first game-tick when this happens (i.e. onCollisionStart is called at the same time as onCollision, but is not called a second time if the same two objects are still colliding on the next tick).
This is illustrated in the attached picture. The collision points are marked with red dots. If the ball were moving downwards, then the ball would have hit the top of the rectangle and so should bounce upwards. However, if the ball were moving horizontally, then its first point of contact would have been the top left corner of the box, and the ball would bounce upwards and to the left.
If I want to work out correct angle that the ball should fly off, then I would need to do some clever calculations to work out the point that the ball first started hitting the other object (those calculations would depend on the precise shape of the other object). Is there some way to work out the point at which the two objects first started colliding? Thanks
What you usually need for this is the normal of the collision, but unfortunately we don't have that for the collision detection system yet.
We do have it in the raytracing system though, so what you could do is send out a ray and see how it will bounce and then just bounce the ball in the same way.
If you don't want to use raytracing I suggest that you calculate the direction of the ball, which you might already have, but if you don't you can just store the last position and subtract it from the current position.
After that you need to find the normals of the edges where the intersection points are.
Let's say the ball direction vector is v, and the two normal vectors are n1 and n2.
Calculate the dot product (this is build in to the vector_math library) of the ball direction vector and each of the normal vectors:
dot1 = v.dot(n1)
dot2 = v.dot(n2)
Compare the results of the dot products:
If dot1 > 0, n1 is facing the ball.
If dot2 > 0, n2 is facing the ball.
After that you can use v.reflect(nx) to get the direction where your ball should be going (where nx is the normal facing the ball).
Hopefully we'll have this built-in to Flame soon!
My main character moves by touching and holding him and then moving your finger left or right to move the character. To do this I just simply update the node's x position (walks left and right on a flat surface) in touchesMoved() with the x position of the touch location, and apply an animation depending on the direction he's moving.
I want to kind of take this to the next level and accomplish the same effect, but using physics, so that when I'm done moving him and release my finger, he may slide a little bit in the direction he was moving given the speed I was moving him at, if that makes sense. Does anyone know how I can accomplish this effect?
Would I have to do as I'm currently doing and update the position as it moves, but also apply a force/impulse at the same time? Kind of confused on how to approach this
Moving the physics body via force, impulse, or velocity will automatically update the player position.
So you will have to play around with the correct way to accomplish your goal. But based on this, what I would suggest is replace your .position code with .physicsBody!.velocity code in your touchesMoved. Then, on your touchesEnded, you can apply a bit of an impulse to give the player that little bit of an "on ice" effect to keep them going a tad.
You will need to experiment with how much velocity you want to get the character to move at the correct speed, and then you will need to play with the impulse figures as well to get it just right.
This could get a bit tricky though, in touchesMoved... because at some point you will want to reset the velocity to 0 (so they stop moving when your finger stops).
To do that, you will need to to use the .previousLocation from your touch object, and compare the distance of X moved. if the distance X moved is >0 (or some deadzone threshold) then apply the velocity; if the deltaX is 0, then set the velocity to 0.
This may actually be more complicated than just using .position to move the character, then having the character slide a bit with physics on touchesEnded.
You will have to play with it to get it right.
I'm using the first person controller for my characters movement. On a left arrow keypress, I'd like the character to instantly rotate 90 degrees and keep moving forward. Currently, when I hit the arrow key, the character makes the sharp 90 degree turn, but the forward momentum the character previously had takes a second to wear off so the character ends up sliding in the direction he was previously moving a short bit.
The closest example I can think of to visually explain what I'm trying to do is how the character turns sharp in Temple Run. How my game is currently working, if I had the character on a ledge make a sharp left turn, he'd likely keep the original momentum and slide off the edge right after he turns.
Since my character is running on the x/z axis, I'm wondering if there would just be some way to maybe swap the directional velocity/momentum? The speed the character had on the x axis would instantly be switched to the z when it turns and the other would be set to zero. I'm obviously open to any solution that accomplishes what I'm looking for.
I dug into the CharacterMotor class in the first person controller, but have yet to find what part I can tweak to accomplish this.
I'd greatly appreciate any help.
Thank you.
You can try to stop the velocity of the Rigidbody before turning.
this.rigidbody.velocity = Vector3.zero;
this.rigidbody.angularVelocity = Vector3.zero;
If you want the object to continue like it did, you can try playing around with it by saving the current velocity in a variable, setting it to 0, rotate it and then putting back the old velocity (still forward).
If it works with global vectors (so from the point of view of the world, not the object), then you can try negativing the velocity, actually causing it to go 'backwards'. I can't test it for now but either way I think you need to set the velocity to zero first before turning the character.
I am making a paper toss kind of game in Unity3d. I am implementing wind effect using constant force. I wanted to know how to make object fall in line with the target ie, if the object gets over the target, it should go in or fall in line with the target, not go behind or in front of the target. At present when I swipe applying a constant force, for different angles of swipe the distance moved by the object differs. Help would be much appreciated.
In FixedUpdate, use Physics.Raycast to check to see if the object is over the target. If so, set the x and z values of rigidbody.velocity to be zero (assuming y is the up/down axis in your game world) and disable the ConstantForce component (i.e. gameObject.GetComponent<ConstantForce>().enabled = false). Note that this won't be most realistic of movements, as it will seem like the object suddenly moves straight down when it goes over the target -- but it sounds like that's what you want.
I have two balls in my game. Both are affected as is by gravity (i.e. if I tilt the device right the balls roll to the right etc...).
What I want is that the second ball will be rolled in the opposite direction. (So if I tilt the device right the ball will roll to the left !)
Since gravity affects my bodies direction I cannot find a way to make the second ball roll in reverse.
What is the efficient and correct way of doing this ?
Thanks
Just use body->applyForce. Use GetLinearVelocity of bodyA and apply the opposite of it to bodyB + (gravity * -1)... (or something like that)
OR
create two worlds one with gravity set to b2Vec2(0.0f, -12.0f); and the other to b2Vec2(0.0f, 12.0f); then just do opposites in your accelerometer method to change each worlds gravity
If you are only going to ever have just two balls, option one would most likely be best.