Develop Reference

Shooting a bullet from the direction that a rectangle is facing

I have a Rectangle object that is placed on the screen and rendered using paintComponent.
I also have a rotation variable that determines the rotation of the object (using right and left keys to rotate) and repaints the object on the screen using Affine Transform.
In the keyPressed method, I have this which allows me to shoot bullets:
else if(key == KeyEvent.VK_SPACE) {
Bullet b = new Bullet(handler, player.x + 10, player.y - 10, ID.Bullet);
handler.addObject(b);
b.setDY(-3*Math.cos(player.rotation));
b.setDX(3*Math.sin(player.rotation));
}
If you see where I create a new bullet, in the second line, the second and third arguments in the new Bullet() are what determines where the bullets are created. Currently they just shoot from the same position on the rectangle regardless of the rotation.
I have failed at allowing the player to shoot a bullet from the direction they are facing, so if anyone has any suggestions that would be very helpful.

So basically you are trying to find the offset Vector from the player's position.
Let's assume, that you have the offset Vector, when you haven't rotated the object.
Then your task would be to rotate the given Vector by the rotation variable.
To do this we first need to look into geometry a bit. Let's think of a 2d-Vector as a triangle, that we can split into it's x and y components. We know, that the rotated Vector should have the same hypothenuse length as the original offset or in other terms the same magnitude.
This means that:
x₀² + y₀² = x₁² + y₁²
Since:
x² + y² = Vector-Magnitude
Your rotation variable keeps track of the inner angle of that "triangle vector" and hence we can describe the lengths as:
x = sin(rotation) * Vector Magnitude
y = cos(rotation) * Vector Magnitude
Now the only thing left to do is evalute those values. To do that, let us jump into the code, shall we?
float magnitude = offset.x*offset.x + offset.y*offset.y;
float x = Math.sin(rotation) * magnitude;
float y = Math.cos(rotation) * magnitude;
Bullet b = new Bullet(handler, player.x + x, player.y + y, ID.Bullet);
possible Errors and fixes
Make sure that you have the correct angle-format. The Java-Math class uses radiens for trigonometric methods.
There could be a constant rotation deviation, depending on what exactly you want your result to look like. This is a rather easy fix, as you just have to add this constant to the rotation variable. In unlikely instances you maybe also need to negate the rotation variable simply by using -rotation in the places I used rotation in my code.

If you know the rotation angle and the width of the rectangle then use this information to rotate the start position of the bullet too. For example to let the start position at the right side:
x = rectMiddleX + width/2 * cos(angle)
y = rectMiddleY + width/2 * sin(angle)
If angle is 0 it will start at the right side
else if(key == KeyEvent.VK_SPACE) {
Bullet b = new Bullet(handler, player.x + width/2 * cos(player.rotation), player.y - width/2 * sin(player.rotation), ID.Bullet);
//if player.x/y is in corner, add width/2 / height/2
handler.addObject(b);
b.setDY(-3*Math.cos(player.rotation));
b.setDX(3*Math.sin(player.rotation));
}

Android Java - postRotate not rotating around center?

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.

Libgdx first person camera controll

I just started playing arround with 3D in libgdx. I allready know how to draw basic Models and i tryed to play arround with the CameraController. Now i want to create a FirstPersonCamera or FirstPersonCameraController. I thought about extending PerspectiveCamera and adding a MyMovingObject target to it. The MyMovingObject would hold a x, y, z position, where y is a constant value, cause i can't move up/down at the moment. So my movement is basicly in 2D. The MyMovingObject would also store the left/right rotation, needed for its moving direction/ xSpeed, zSpeed. But the Player should also be able to look up and down, and this up/down rotation is not really needed for the MyMovingObject, as it only changes the view and no other properties. So i am not sure if i go the right way.
I want to be able to go forward, left, right, backward by using W,A,S,D and rotate left right by using the mouse. Also i want to look up and down by using the mouse, like in most First Person games.
Should i use another way, not creating my own camera by extending PerspectiveCamera?
Or is this approach good and i just have to store the up/down rotation in the MyMovingObject to, also if it is only needed for the view?
Or would it be better to controll the camera with W,A,S,D and mouse and update the MyMovingObjects position, depending on cameras position and rotation?
I hope you understand what I mean. It seems a bit complicated to explain it (at least for me).
EDIT: I am now using Vector3 direction, Vector3 position and Vector3 size for my NPCs and the player. I calculate the speed by doing: xSpeed = direction.x / (direction.x + direction.z) * speed; the same for zSpeed. By doing this i "filter" the y value out of it and i get only the percent of x and y. The only problem is, that when i look straight up x and z are 0. I could fix this by using an UpVecotr, which gets rotated when i do a "Pitch-rotation". But how do i rotate him? I need to rotate it arround the sideway Vector. Thanks
EDIT: The rotation and movement work now (see my answer), but i have really big problems with the limitation of the "Pitch-rotation". I am using: if (direction.y < 0.9 && angle > 1) doPitchRotation(); else if (direction.y > -0.9 && angle < 1) doPitchRotation(); so if i rotate down and i still look down at least at -0.9 y it just does not perform the rotation. But what really happens: I rotates to - 0.9 then it rotates arround the Y-Axis and at the other side it rotates up, even if i move my mous down. Can you explain why? Why does the Y-Axis flip when i turn arround by looking down?
EDIT: It works now. It seems like my upVector got some wrong values sometimes. For landbased cams you can also use crossproduct of Y-Axis and direction Vector. No need for upVector.

Hey thanks for sharing this link. I found it very useful.
Here's my code on rotating a land based camera and it seems to work without problems.
private int mouseX = 0;
private int mouseY = 0;
private float rotSpeed = 0.2f;
#Override
public boolean mouseMoved(int screenX, int screenY) {
int magX = Math.abs(mouseX - screenX);
int magY = Math.abs(mouseY - screenY);
if (mouseX > screenX) {
cam.rotate(Vector3.Y, 1 * magX * rotSpeed);
cam.update();
}
if (mouseX < screenX) {
cam.rotate(Vector3.Y, -1 * magX * rotSpeed);
cam.update();
}
if (mouseY < screenY) {
if (cam.direction.y > -0.965)
cam.rotate(cam.direction.cpy().crs(Vector3.Y), -1 * magY * rotSpeed);
cam.update();
}
if (mouseY > screenY) {
if (cam.direction.y < 0.965)
cam.rotate(cam.direction.cpy().crs(Vector3.Y), 1 * magY * rotSpeed);
cam.update();
}
mouseX = screenX;
mouseY = screenY;
return false;
}
This works for landbased cameras. If you want to make a flightcontroll camera, you have to do a pitch rotation arround the cam.direction.crs(cam.up). Instead of using the Vector3.cpy() i would store a Vector3 help, which gets those temporary values, because Vector3.cpy() creates a new Vector3 and this operation is performed every render loop.
For flightcontroll cameras you also need to add a roll rotation and do the yaw rotation arround the cam.up Vector.

This article is really helpful in my opinion. I have found a solution which should work, but i haven't tryed it yet. My MovingObjects all have a Vector3 position, Vector3 direction, Vector3 size and Vecotr3 upVector. The Player class extends this MovingObject class and adds Mouse and Keycontroll to the movement.
In the MovingObject class i have the moethods:
rotateYaw(float degrees): rotates the Vector3 direction arround the Y-Axis by the given degrees (libgdx has a rotate function for Vector3)--> Simple
rotatePitch(float degrees): rotates the Vector3 direction arround the: direction.cross(Vector3.Y), which is the rotated side Vector of your MovingObject, by the given degrees. Also a Pitch-Rotation has to rotate the upVector, so you rotate the upVector arround the same axis, by the given degrees. As soon as you understand this it is simple.
move(delta) moves your MovingObject in x,z direction by doing:
if (direction.y == 1) {
// You are looking straight up, no x,z direction, move in the opposite
// direction of upVector
xSpeed = upVector.x / (Math.abs(upVetor.x) + Math.abs(upVector.z)) * (-speed);
zSpeed = upVector.z / (Math.abs(upVetor.x) + Math.abs(upVector.z)) * (-speed);
position.add(xSpeed * delta, 0, ySpeed * delta);
} else if (direction.y == -1) {
// You are looking straight down, no x,z direction, move in the direction of
// upVector
xSpeed = upVector.x / (Math.abs(upVetor.x) + Math.abs(upVector.z)) * speed;
zSpeed = upVector.z / (Math.abs(upVetor.x) + Math.abs(upVector.z)) * speed;
position.add(xSpeed * delta, 0, ySpeed * delta);
} else {
// You are not looking straight up or down, so you have x,z direction. Use
// that.
xSpeed = direction.x / (Math.abs(direction.x) + Math.abs(direction.z)) * speed;
zSpeed = direction.z / (Math.abs(direction.x) + Math.abs(direction.z)) * speed;
position.add(xSpeed * delta, 0, ySpeed * delta);
}
I did not test this until now, but i think it should work. Note, that in the Pitch-rotation you should also limit it to straight up/ straight down. Do this by checking the signum of x and z. If they change while you are doing a Pitch-rotation you rotated over 90 degrees.
I am stil waiting for other answers and if i am wrong please correct me!
EDIT: I tested it. It works like this, but there are a few things to take care of:
direction.cross(upVector) changes the direction Vector. So store that data somewhere first! After using it reset the direction Vector.
The Pitch limitation has a problem: If you controll signum change, as i suggested the following happens: you look straight up, signum x and signum z are 0. You look down, signum changes and your action (limiting) starts. So take care that you also check, if it is not zero.
I stil don't know how to do the pitch limitation and i edit my question to explain my issue.
Think about normalizing your direction and upVector whenever you change something!
I think this should work pretty good. If you have any improvements let me know and i will update this here. If you have another solution please add an answer! Thanks

I know that this question already has good answers. But I had some issues with the selected answer. And I just want to help someone who is looking for the same solution.
I noticed some strange behaviour with the selected answer. I doesn't keep the Y exis as up. Which is of course very important on a fps. So this one is not perfect but I wanted to put this here.
// put into the create() method.
Gdx.input.setInputProcessor(new InputProcessor() {
private int dragX, dragY;
float rotateSpeed = 0.2f;
// dont' forget to override other methods.
#Override
public boolean mouseMoved(int screenX, int screenY) {
Vector3 direction = cam.direction.cpy();
// rotating on the y axis
float x = dragX -screenX;
// change this Vector3.y with cam.up if you have a dynamic up.
cam.rotate(Vector3.Y,x * rotateSpeed);
// rotating on the x and z axis is different
float y = (float) Math.sin( (double)(dragY -screenY)/180f);
if (Math.abs(cam.direction.y + y * (rotateSpeed*5.0f))< 0.9) {
cam.direction.y += y * (rotateSpeed*5.0f) ;
}
cam.update();
dragX = screenX;
dragY = screenY;
return true;
}
});
NOTE: Don't use any camera controllers.
NOTE2: This might come handy: Gdx.input.setCursorCatched(true);
EDIT: I just wanted to share the walking function I use to change position of the camera with wasd keys. When W key is down the forward is true. And when the key is up forward is false. Other directions have the same principle. To detect the key down and up, please use the InputProcessor in the above code.
This creates movement in the two dimensional space (X-Z axises). The direction of the camera will not change the direction of the movement as we are eliminating the Y axis. of the direction.
One must now even if camera is directed to the sky (at a non 90 degree angle with the ground), the length of the direction vector is not fixed to 1.0f. So there will not be any loss of movement speed.
To test this I rotated camera up and down (moved the mouse forward and backward) and the x and z values of the direction vector didn't change. So when the y axis of the direction vector is eliminated, we have a 2d direction vector which doesn't effected by the Y angle of the camera.
private void walking(float timeElapsed) {
float speed = movementSpeed;
if ((forward | back) & (right | left)) {
speed /= Math.sqrt(2);
}
System.out.println(speed);
if (forward) {
Vector3 v = cam.direction.cpy();
v.y = 0f;
v.x *= speed * timeElapsed;
v.z *= speed * timeElapsed;
cam.translate(v);
cam.update();
}
if (back) {
Vector3 v = cam.direction.cpy();
v.y = 0f;
v.x = -v.x;
v.z = -v.z;
v.x *= speed * timeElapsed;
v.z *= speed * timeElapsed;
cam.translate(v);
cam.update();
}
if (left) {
Vector3 v = cam.direction.cpy();
v.y = 0f;
v.rotate(Vector3.Y, 90);
v.x *= speed * timeElapsed;
v.z *= speed * timeElapsed;
cam.translate(v);
cam.update();
}
if (right) {
Vector3 v = cam.direction.cpy();
v.y = 0f;
v.rotate(Vector3.Y, -90);
v.x *= speed * timeElapsed;
v.z *= speed * timeElapsed;
cam.translate(v);
cam.update();
}
}

LibGDX - Orthogonal Camera won't stop at edge of map

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;
}

Isometric Tile Selection

I'm not all that good with Maths, so i was hoping some of you guys could help?
I'm trying to make a function to convert mouse coordiantes into a particular tile in an isometric view.
It won't let me post images for a stupid reason, so ill just link the image:
Link
All of the algorithms i have seen so far work with the X & Y axes going diagonal, my game is currently set up like this, and i would like to keep it so.
Is there an algorithm so that if the mouse was at the red dot, it would return the coordinates of the tile that it is sitting on? (6,2)
Thanks in advance!

There is a good start : http://www.java-gaming.org/index.php?topic=23656.0
Enjoy :)
EDIT
Full-trusted "DrDobb's" website, full article on this : http://www.drdobbs.com/parallel/designing-isometric-game-environments/184410055

<0;4>
x <0;3> <1;4>
<0;2> <1;3> <2;4>
<0;1> <1;2> <2;3> <3;4>
<0;0> <1;1> <2;2> <3;3> <4;4>
<1;0> <2;1> <3;2> <4;3>
<2;0> <3;1> <4;2>
y <3;0> <4;1>
<4;0>
I rendered the tiles like above.
the sollution is VERY simple!
first thing:
my Tile width and height are both = 32 this means that in isometric view, the width = 32 and height = 16! Mapheight in this case is 5 (max. Y value)
y_iso & x_iso == 0 when y_mouse=MapHeight/tilewidth/2 and x_mouse = 0
when x_mouse +=1, y_iso -=1
so first of all I calculate the "per-pixel transformation"
TileY = ((y_mouse*2)-((MapHeight*tilewidth)/2)+x_mouse/2;
TileX = x_mouse-TileY;
to find the tile coordinates I just devide both by tilewidth
TileY = TileY/32; TileX = TileX/32;
DONE!! never had any problems!

It's quite easy actually once you get your head wrapped around it. All you do is find out where your mouse is relative to the map and then reverse to how you are drawing the tiles.
I draw my map in the double "for" loop like this:
For x coord: x * (TileWidth / 2) - (y * (TileWidth / 2))
For y coord: x * (TileHeight / 2) + (y * (TileHeight / 2))
So my x goes from top left to bottom right and my y goes from top right to bottom left. Mind though, like for the first tile the world coord will be 0,0 but the top pixel starts at x=0 + (tilewidth / 2) so we have to compensate for that when we are looking to find which tile the mouse is over. (or we could do that for the whole world itself by giving it a offset).
Now first we have to find the mouse position in relation to the world since you probably want a moving camera. My camera's centre starts as 0,0 so i have to compensate the mouse by half the screen width like so:
mouseWorldPosX = mouse.x + cam.x - (screen.width / 2)
mouseWorldPosY = mouse.y + cam.y - (screen.height / 2)
This is all we need to calculate the mouse position back to tile position.
For X:
tileX = (mouseWorldPosX + (2 * mouseWorldPosY) - (tileWidth / 2)) / tileWidth
As you can see we divide the whole thing by the tilewidth since we multiplied it in the draw method. The (tileWidth / 2) is just there to compensate for the offset i mentioned earlier.
For Y:
tileY = (mouseWorldPosX - (2 * mouseWorldPosY) - (tileHeight / 2) / -tileWidth
It's practically the same but the other way around. We subtract the Y world position since the Y axis runs the other way around. This time we compensate the offset for the height of the tile and we divide the whole thing by negative tilewidth, again since it runs the other way.
I hope this helps below is a working example of a method i looked up, it returns a vector with the tile coordinates:
public Vector2 MouseTilePosition(Camera cam, GraphicsDevice device)
{
float mPosX = newMouseState.X + (cam.Position.X - (device.Viewport.Width / 2));
float mPosY = newMouseState.Y + (cam.Position.Y - (device.Viewport.Height / 2));
float posx = (mPosX + (2 * mPosY) - (Map.TileWidth / 2)) / Map.TileWidth;
float posy = (mPosX - (2 * mPosY) - (Map.TileHeight / 2)) / -Map.TileWidth;
return new Vector2((int)posx, (int)posy);
}