I've got a camera set up, and I can move with WASD and rotate the view with the mouse. But now comes the problem: I want to add physics to the camera/player, so that it "interacts" with my other jBullet objects. How do I do that? I thought about creating a RigidBody for the camera and storing the position there, so that jBullet can apply its physics to the camera. Then, when I need to change something (the position), I could simply change it in the RigidBody. But I didn't find any methods for editing the position.
Can you push me in the right direction or maybe give me an example source code?
I was asking the same question myself a few days ago. My solution was as Sierox said. To create a RigidBody of BoxShape and add that to the DynaicsWorld. To move the camera arund, apply force to its rigidbody. I have damping set to .999 for linear and 1 for angular to stop the camera when no force is applied, i.e. the player stops pressing the button.
I also use body.setAngularFactor(0); so the box isn't tumbling all over the place. Also set the mass really low as not to interfere too much with other objects, but still be able to jump on then and run into them, and otherwise be affected by them.
Remember to convert your x,y, and z coordinates to cartesian a plane so you move in the direction of the camera. i.e.
protected void setCartesian(){//set xyz to a standard plane
yrotrad = (float) (yrot / 180 * Math.PI);
xrotrad = (float) (xrot / 180 * Math.PI);
float pd = (float) (Math.PI/180);
x = (float) (-Math.cos(xrot*pd)*Math.sin(yrot*pd));
z = (float) (-Math.cos(xrot*pd)*Math.cos(yrot*pd));
//y = (float) Math.sin(xrot*pd);
}//..
public void forward(){// move forward from position in direction of camera
setCartesian();
x += (Math.sin(yrotrad))*spd;
z -= (Math.cos(yrotrad))*spd;
//y -= (Math.sin(xrotrad))*spd;
body.applyForce(new Vector3f(x,0,z),getThrow());
}//..
public Vector3f getThrow(){// get relative position of the camera
float nx=x,ny=y,nz=z;
float xrotrad, yrotrad;
yrotrad = (float) (yrot / 180 * Math.PI);
xrotrad = (float) (xrot / 180 * Math.PI);
nx += (Math.sin(yrotrad))*2;
nz -= (Math.cos(yrotrad))*2;
ny -= (Math.sin(xrotrad))*2;
return new Vector3f(nx,ny,nz);
}//..
to jump just use body.setLinearVelocity(new Vector3f(0,jumpHt,0)); and set jumpHt to whatever velocity you wish.
I use getThrow to return a vector for other objects i may be "throwing" on screen or carrying. I hope I answered your question and didn't throw in too much non-essential information.I'll try and find the source that gave me this idea. I believe it was on the Bullet forums.
------- EDIT ------
Sorry to have left that part out
once you have the rigid body functioning properly you just have to get it's coordinates and apply that to your camera for example:
float mat[] = new float[16];
Transform t = new Transform();
t = body.getWorldTransform(t);
t.origin.get(mat);
x = mat[0];
y = mat[1];
z = mat[2];
gl.glRotatef(xrot, 1, 0, 0); //rotate our camera on teh x-axis (left and right)
gl.glRotatef(yrot, 0, 1, 0); //rotate our camera on the y-axis (up and down)
gl.glTranslatef(-x, -y, -z); //translate the screen to the position of our camera
In my case I'm using OpenGL for graphics. xrot and yrot represent the pitch and yaw of your camera. the code above gets the world transform in the form of a matrix and for the purposes of the camera you need only to pull the x,y, and z coordinates then apply the transform.
from here, to move the camera, you can set the linear velocity of the rigid body to move the camera or apply force.
Before you read this answer I would like to mention that I have a problem with the solution stated in my answer. You can follow my question about that problem so that you can have the solution too if you use this answer.
So. First, you need to create a new BoxShape:
CollisionShape cameraHolder = new BoxShape(SIZE OF CAMERAHOLDER);
And add it to your world so that it interacts with all the other objects. Now you need to change all the methods about camera movement (not rotation) so that the methods move your cameraHolder but not your camera. Then set the position of your Camera to the position of the cameraHolder.
Again, if you have a problem where you can't move properly, you can check my question and wait for an answer. You also can find a better way of doing this.
If you have problems or did not understand something about the answer, please state it as a comment.
Related
I am working on a 2D java game engine using AWT canvas as a basis. Part of this game engine is that it needs to have hitboxes with collision. Not just the built in rectangles (tried that system already) but I need my own Hitbox class because I need more functionality. So I made one, supports circular and 4-sided polygon shaped hitboxes. The way the hitbox class is setup is that it uses four coordinate points to serve as the 4 corner vertices that connect to form a rectangle. Lines are draw connecting the points and these are the lines that are used to detect intersections with other hitboxes. But I now have a problem: rotation.
There are two possibilities for a box hitbox, it can just be four coordinate points, or it can be 4 coordinate points attached to a gameobject. The difference is that the former is just 4 coordinates based on 0,0 as the ordin while the attached to gameobject stores offsets in the coordinates rather than raw location data, so (-100,-100) for example represents the location of the host gameobject but 100 pixels to the left, and 100 pixels up.
Online I found a formula for rotating points about the origin. Since Gameobject based hitboxes were centered around a particular point, I figured that would be the best option to try it on. This code runs each tick to update a player character's hitbox
//creates a rectangle hitbox around this gameobject
int width = getWidth();
int height = getHeight();
Coordinate[] verts = new Coordinate[4]; //corners of hitbox. topLeft, topRight, bottomLeft, bottomRight
verts[0] = new Coordinate(-width / 2, -height / 2);
verts[1] = new Coordinate(width / 2, -height / 2);
verts[2] = new Coordinate(-width / 2, height / 2);
verts[3] = new Coordinate(width / 2, height / 2);
//now go through each coordinate and adjust it for rotation
for(Coordinate c : verts){
if(!name.startsWith("Player"))return; //this is here so only the player character is tested
double theta = Math.toRadians(rotation);
c.x = (int)(c.x*Math.cos(theta)-c.y*Math.sin(theta));
c.y = (int)(c.x*Math.sin(theta)+c.y*Math.cos(theta));
}
getHitbox().vertices = verts;
I appologize for poor video quality but this is what the results of the above are: https://www.youtube.com/watch?v=dF5k-Yb4hvE
All related classes are found here: https://github.com/joey101937/2DTemplate/tree/master/src/Framework
edit: The desired effect is for the box outline to follow the character in a circle while maintaining aspect ratio as seen here: https://www.youtube.com/watch?v=HlvXQrfazhA . The current system uses the code above, the effect of which can be seen above in the previous video link. How should I modify the four 2D coordinates to maintain relative aspect ratio throughout a rotation about a point?
current rotation system is the following:
x = x*Cos(theta) - y *Sin(theta)
y = x*Sin(theta) + y *Cos(theta)
where theta is degree of rotation in raidians
You made classic mistake:
c.x = (int)(c.x*Math.cos(theta)-c.y*Math.sin(theta));
c.y = (int)(c.x*Math.sin(theta)+c.y*Math.cos(theta));
In the second line you use modified value of c.x. Just remember tempx = c.x
before calculations and use it.
tempx = c.x;
c.x = (int)(tempx*Math.cos(theta)-c.y*Math.sin(theta));
c.y = (int)(tempx*Math.sin(theta)+c.y*Math.cos(theta));
Another issue: rounding coordinates after each rotation causes distortions and shrinking after some rotations. It would be wise to store coordinates in floats and round them only for output, or remember starting values and apply rotation by accumulated angle to them.
Purpose
I'm implementing a polygon rotation with Java AWT.
I'm already able to draw polygons on the screen, and I'd like to apply a rotation matrix manually upon my polygons coordinates (rotation is done around the lookAt point of the user).
What I've already done
In order to rotate the world, the user first clicks on the screen and then drags the mouse around to perform the rotation.
Let's note the first click point as S, the following point from the drag event as L, and the center of the screen as C.
In order to calculate the rotation angle, when first clicking the screen, I keep a vector from C to S: C-S.
Then, when a drag event occurs, I calculate the vector from C to L: C-L.
I then calculate the angle in radians between C-S to C-L, and that's what I apply on my world.
This works well, and the polygon is indeed rotation around the lookAt point.
My problem
The problem occurs when the user finishes a rotation of PI, and then the polygon is rotating backward.
e.g. When the user starts rotating, the angle starts from 0.1.... 0.2... 1.. 2.. 3.. and in value ~3.1 (I assume PI), the values are starting to go down: 3... 2.. 1.. until 0, and vice versa.
This makes sense since the radians range is [0, PI].
I assume the base vector C-S lies on the right side of X axis, and when the rotation goes down below the X axis the polygon is rotating backwards.
However, I have no idea how to keep the polygon rotating in the same direction all the time (when the user performs a full rotation around the polygon).
Edit
Angle function is:
public final double angle(Vector2D v1)
{
double vDot = this.dot(v1) / ( this.length()*v1.length() );
if( vDot < -1.0) vDot = -1.0;
if( vDot > 1.0) vDot = 1.0;
return ((double) (Math.acos( vDot )));
}
This is a problem of the arcus cosine, acos(cos(x)) is a periodic hat function moving up and down in the range of 0 to pi.
In higher dimensions that can not be avoided, as there is no preferred frame of reference, so there is no way to say that phi should really be -phi. In 2 dimensions there is a prefered orientation of the plane so that one can say what is the first and what the second vector and define a unique angle in positive orientation. Rotate the situation so that the first vector comes to lay on the positive real half axis to get the angle and correct quadrant from the coordinates of the rotated second vector.
Easiest to reconstruct is the complex picture, to compute the angle from a=a.x+i*a.y to b=b.x+i*b.y rotate b back by multiplying with the conjugate of a to get an angle from the zero angle resp. the positive real axis,
arg((a.x-i*a.y)*(b.x+i*b.y))
=arg((a.x*b.x+a.y*b.y)+i*(a.x*b.y-a.y*b.x))
=atan2( a.x*b.y-a.y*b.x , a.x*b.x+a.y*b.y )
Note that screen coordinates use the opposite orientation to the cartesian/complex plane, thus change atan2(y,x) to atan2(-y,x) to get an angle in the usual direction.
public Point rotate(Point original, Point vertex, double angle){
Point translated = new Point(original.x - vertex.x, original.y - vertex.y);
int x = (int)Math.round(translated.x * Math.cos(angle) - translated.y * Math.sin(angle));
int y = (int)Math.round(translated.x * Math.sin(angle) + translated.y * Math.cos(angle));
return new Point(vertex.x+x,vertex.y+y);
}
This is a simple rotation method that you can use to rotate a point around a given vertex.
I believe this is more of a logic question than a java question, sorry.
My intent is rather straightforward, i want the ship to move and rotate with a matrix, with the bitmap ship1 being the center pivot of the rotation. The code works great except the pivot is off by a strange offset. (picture of conundrum linked at bottom)
The default value rotation at 0 works but all the other values seem to slide away from the center, with 180 being the furthest from the center.
centerX = playerValues[Matrix.MTRANS_X] + ship1.getWidth()/2;
centerY = playerValues[Matrix.MTRANS_Y] + ship1.getHeight()/2;
newRotation = ((float) Math.toDegrees(Math.atan2(fingery1 - centerY, fingerx1 - centerX)));
matrix.postRotate((newRotation - prevRotation), centerX, centerY);
prevRotation = newRotation;
if (fingerx1 > playerX) {
xspeed = 1;
} else
if (fingerx1 < playerX) {
xspeed = 0;
} else
if (fingery1 > playerY) {
yspeed = 1;
} else
if (fingery1 < playerY) {
yspeed = 0;
}
matrix.postTranslate(xspeed, yspeed);
matrix.getValues(playerValues);
I tried to draw how the relation of the bitmap looks at different angles. (the blue dot is where I intend to rotate the bitmap around, the arrow pointing right is the only correct one).
http://i.stack.imgur.com/2Yw76.png
Please let me know if you see any errors or any feedback helps! I just need a second pair of eyes on this because mine are going to explode soon.
Consider studying a good computer graphics text re matrix math. Foley and Van Dam is always a safe bet.
The matrix A is applied to point x with multiplication Ax. You have A = RT a rotation with translation post multiplied. The result is RTx which is R (T x) meaning the point is translated then rotated, when you probably meant the opposite.
Additionally it appears you are concatenating incremental changes repeatedly. Floating point errors will accumulate, visible as worsening distortions. Instead maintain orientation parameters x, y, theta for each ship. These are controlled by the UI. Set the matrix from these in each rendering. The transform will be rotation about the point (w/2, h/2) followed by translation to (x, y). But the matrix to effect this is the translation post multiplied by the rotation! Also you must reset the matrix for each ship.
Im developing simple game. I have cca. 50 rectangles arranged in 10 columns and 5 rows. It wasn't problem to put them somehow to fit the whole screen. But when I rotate the canvas, let's say about 7° angle, the old coordinates does't fit in the new position of the coordinates. In constructor I already create and define the position of that rectangles, in onDraw method I'm drawing this rectangles (of course there are aready rotated) bud I need some method that colliding with the current rectangle. I tried to use something like this (i did rotation around the center point of the screen)
int newx = (int) ((x * Math.cos(ROTATE_ANGLE) - (y * Math.sin(ROTATE_ANGLE))) + width / 2);
int newy = (int) ((y * Math.cos(ROTATE_ANGLE) + (x * Math.sin(ROTATE_ANGLE))) + height / 2);
but it doesn't works (becuase it gives me absolute wrong new coordinates). x and y are coordinates of the touch that I'm trying to calculate new position in manner of rotation. ROTATE_ANGLE is the angle of rotation the screen.
Does anybody know how to solve this problem, I already go thorough many articles, wiki, wolframalpha categories but not luck. Maybe I just need some link to understand problem more.
Thank you
You use a rotation matrix.
Matrix mat = new Matrix(); //mat is identity
mat.postRotate(ROTATE_ANGLE); //mat is a rotation matrix of ROTATE_ANGLE degrees
float point[] = {10.0, 20.0}; //create a new float array representing the point (10, 20)
mat.mapPoints(point); //rotate the point by the requested amount
Ok, find the solution.
First it is important to convert from angle to radian
Then I personly need to negate that radian value.
That's all, this solution is correct
i'm fairly new to libgdx and java but am learning everything I can! I'm working on an orthogonal 2d tiled game. Basically, i've got my character walking around and the camera following him. I am trying to set it up so the camera stops when the character is near the edge of the map so no black space is seen. The camera should stop at the edge and the player should continue moving.
This is my code for moving the camera. It's a bit messy now as i've been trying everything. The map is 30x30.
if (mainPlayer.getPosition().x >= 15 && mainPlayer.getPosition().x <= 30) {
camera.position.x = mainPlayer.getPosition().x;
}
camera.position.y = mainPlayer.getPosition().y;
camera.update();
camera.apply(gl);
This is inside my render method. I've only messed with the x part, so ignore the y for now.
EDIT I think I need to reword that. I know how to make it stop..It works using my code, but I can't figure out how to determine where to stop it. I'm using 15 in my code above which is half the map..which of course doesn't work.
EDIT I think I need to reword that. I know how to make it stop..It
works using my code, but I can't figure out how to determine where to
stop it. I'm using 15 in my code above which is half the map..which of
course doesn't work.
The minimum x would need to be:
map.position.x + camera.viewportWidth/2;
And the maximum x would need to be:
map.position.x+mapwidth-camera.viewportWidth/2;
Assuming the map position is in (0,0) you can just ignore the map.position.x part.
You need to fix the bounds of the Camera rectangle to inside the world rectangle. A function such as below would help:
public void fixBounds() {
float scaledViewportWidthHalfExtent = viewportWidth * zoom * 0.5f;
float scaledViewportHeightHalfExtent = viewportHeight * zoom * 0.5f;
// Horizontal
if (position.x < scaledViewportWidthHalfExtent)
position.x = scaledViewportWidthHalfExtent;
else if (position.x > xmax - scaledViewportWidthHalfExtent)
position.x = xmax - scaledViewportWidthHalfExtent;
// Vertical
if (position.y < scaledViewportHeightHalfExtent)
position.y = scaledViewportHeightHalfExtent;
else if (position.y > ymax - scaledViewportHeightHalfExtent)
position.y = ymax - scaledViewportHeightHalfExtent;
}