Develop Reference

How to optimize 3D AABB Rotate (Java)

recently I have been implementing 3D AABB's into my game engine, to accomplish rotations I use a simple method of rotating all 8 calculated corners around the center of the box using my Vector3f.rotate() method. But as you may notice below it is very inefficient. If you want to sort though the whole class here is the github (https://github.com/EquilibriumGames/Flounder-Engine/blob/master/src/flounder/physics/AABB.java) otherwise here is the snipit I need help with, I beleve there could be simpler methods out there but I want to know what you think. Thank you!
// Creates the 8 AABB corners and rotates them.
Vector3f FLL = new Vector3f(destination.minExtents.x, destination.minExtents.y, destination.minExtents.z);
Vector3f.rotate(FLL, rotation, FLL);
Vector3f FLR = new Vector3f(destination.maxExtents.x, destination.minExtents.y, destination.minExtents.z);
Vector3f.rotate(FLR, rotation, FLR);
Vector3f FUL = new Vector3f(destination.minExtents.x, destination.maxExtents.y, destination.minExtents.z);
Vector3f.rotate(FUL, rotation, FUL);
Vector3f FUR = new Vector3f(destination.maxExtents.x, destination.maxExtents.y, destination.minExtents.z);
Vector3f.rotate(FUR, rotation, FUR);
Vector3f BUR = new Vector3f(destination.maxExtents.x, destination.maxExtents.y, destination.maxExtents.z);
Vector3f.rotate(BUR, rotation, BUR);
Vector3f BUL = new Vector3f(destination.minExtents.x, destination.maxExtents.y, destination.maxExtents.z);
Vector3f.rotate(BUL, rotation, BUL);
Vector3f BLR = new Vector3f(destination.maxExtents.x, destination.minExtents.y, destination.maxExtents.z);
Vector3f.rotate(BLR, rotation, BLR);
Vector3f BLL = new Vector3f(destination.minExtents.x, destination.minExtents.y, destination.maxExtents.z);
Vector3f.rotate(BLL, rotation, BLL);
destination.minExtents = Maths.min(FLL, Maths.min(FLR, Maths.min(FUL, Maths.min(FUR, Maths.min(BUR, Maths.min(BUL, Maths.min(BLR, BLL)))))));
destination.maxExtents = Maths.max(FLL, Maths.max(FLR, Maths.max(FUL, Maths.max(FUR, Maths.max(BUR, Maths.max(BUL, Maths.max(BLR, BLL)))))));

libgdx Fixed point after camera.rotateAround

Good night friends.
I'm having trouble drawing a fixed point on the screen when the screen is rotated. I used the method "rotateAround" from the position of the player.
It seems to me. I have to rotate this fixed point also from the position of the player. I use this stretch learned here in stackoverflow.
public void rotate(Vector3 position, Vector3 centerPoint){
this.cosTemp = MathUtils.cosDeg(this.anguloAtual);
this.senTemp = MathUtils.sinDeg(this.anguloAtual);
this.xTemp = centerPoint.x + ((position.x - centerPoint.x) * this.cosTemp) - ((position.y - centerPoint.y) * this.senTemp);
this.yTemp = centerPoint.y + ((position.y - centerPoint.y) * this.cosTemp) + ((position.x - centerPoint.x) * this.senTemp);
position.set(this.xTemp, this.yTemp, 0);
}
In the drawing that the player on the screen. I used the position of the player, then called "camera.project" then the method "rotate". The fixed point appears, however it is not exactly fixed.
I used the example of a fixed point slightly ahead of the player.
public void meDesenhar(SpriteBatch spriteBatch) {
spriteBatch.begin();
this.spritePlayer.setPosition(this.positionPlayer.x - (this.spritePlayer.getWidth() / 2),
this.positionPlayer.y - this.spritePlayer.getHeight() / 2);
this.spritePlayer.draw(spriteBatch);
spriteBatch.end();
originPosition.set(positionPlayer, 0);
fixedPosition.set(positionPlayer.x, positionPlayer.y + 10, 0);
cameraTemp.project(fixedPosition);
cameraTemp.project(originPosition);
cameraManagerTemp.rotate(fixedPosition, originPosition);
Debugagem.drawPointInScreen(Color.BLUE, fixedPosition);
}
My questions:
1 - I am doing something wrong, or just it is a result of rounding? I realized when debugging. The position of the player changed a little every rotation after the "camera.project". Example position (540, 320) turned (539.99, 320.013)
2 - I tried using and enjoying the SpriteBatch the draw method to perform the rotation however, could not make the rotation from the player. I would arrive at the same result.
3 - Can I use two cameras? Each camera would be a layer. A camera at the map and the player would be. The other for fixed point. It's viable? I could not find any example that works with more than one camera at the same time. Anyone know any examples please. I'm not talking about huds or cameras to stage.
Video follows.
https://www.youtube.com/watch?v=1Vg8haN5ULE
Thank you.

It can be result of rounding because its moving a pixel.
You can calculate rotation from the player but its not necessary.
Of course you can use multiple cameras in your game and you should also in this case.
Its few screenshot from my old projects that i used multiple cameras
As you can see you can even use different type of cameras like ortho and perspective both 2D and 3D.
Just create new camera like first one and change projection matrix
camrotate = new OrthographicCamera(540, 960);
//...
camfixed = new OrthographicCamera(540, 960);
//...
And in render method
batch.setProjectionMatrix(camrotate.combined);
batch.begin();
//draw in camrotate now
//...
//...
batch.end();
batch.setProjectionMatrix(camfixed.combined);
batch.begin();
//draw fixed elements now
//...
//...
batch.end();
//add one more camera if you need
Edit:
Change projection matrix outside of batch.begin()/end() otherwise the current batch will flushed.

Why doesn't gluUnProject() seem to behave?

I am trying to find the coordinates of my mouse on a flat 3D surface. After googling a bit on that, I found out that you use gluUnProject for doing so. So, I implemented that. Here is my code (when taking away the parts that are not interesting):
public class Input {
private FloatBuffer modelView = BufferUtils.createFloatBuffer(16);
private FloatBuffer projection = BufferUtils.createFloatBuffer(16);
private IntBuffer viewport = BufferUtils.createIntBuffer(16);
private FloatBuffer location = BufferUtils.createFloatBuffer(3);
private FloatBuffer winZ = BufferUtils.createFloatBuffer(1);
public float[] getMapCoords(int x, int y)
{
modelView.clear().rewind();
projection.clear().rewind();
viewport.clear().rewind();
location.clear().rewind();
winZ.clear().rewind();
glGetFloat(GL_MODELVIEW_MATRIX, modelView);
glGetFloat(GL_PROJECTION_MATRIX, projection);
glGetInteger(GL_VIEWPORT, viewport);
float winX = (float)x;
float winY = (float)viewport.get(3) - (float)y;
glReadPixels(x, (int)winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, winZ);
gluUnProject(winX, winY, winZ.get(0), modelView, projection, viewport, location);
return new float[] {location.get(0), location.get(1), location.get(2)};
}
}
When I call this function, passing in the X and Y coordinates of the mouse, I get some numbers that increase by 100 for every pixel I move with my mouse (it should be around 1). After doing some prints from various variables, I found out that the winZ buffer contains the value 1.0. My gluPerspective is set up in such a way that its near clipping point it at 0.1 and its far point at 10000, which would explain why the number is increasing that rapidly. Yet I don't know how to force openGl to use my flat plane instead for finding this distance.
So now I am wondering; if this is the correct/best/easiest method for finding the mouse coordinates on a surface in the 3D world, what could I be doing wrong? If it is not, what is a better way of doing it?

Yes, this is the correct method to use. You are probably just calling it at the point where the matrices do not contain "good values" (might be caused by glPush/PopMatrix() functions in your code).
To confirm you are getting good coordinates, draw a single GL_POINT at the coordinates you get, after you get them (disable depth test and increase point size to, say, 10 pixels). If the point is moving under your mouse, then the calculated coords are correct but the matrices are not.

Getting object coordinates from camera

I've implemented a camera in Java using a position vector and three direction vectors so I can use gluLookAt(); moving around in `ghost mode' works fine enough, but I want to add collision detection. I can't seem to figure out how to transform my position vector to coordinates in which OpenGL draws my objects.
A rough sketch of my drawing loop is this:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
camera.setView();
drawer.drawTheScene();
I'm at a loss of how to proceed; looking at the ModelView matrix between calls and my position vector, I haven't found any kind of correlation.

Finally figured it out by reviewing http://fly.cc.fer.hr/~unreal/theredbook/chapter03.html again. To get from eye space (camera) to object space, you have to multiply that vector with the inverse of the ModelView matrix, or in code:
Vector4f vpos = new Vector4f(0, 0, 0, 1);
// (0,0,0,1) because it's relative to the cam
float mv[]=new float[16];
ByteBuffer temp = ByteBuffer.allocateDirect(64);
temp.order(ByteOrder.nativeOrder());
GL11.glGetFloat(GL11.GL_MODELVIEW_MATRIX, (FloatBuffer)temp.asFloatBuffer());
temp.asFloatBuffer().get(mv);
Matrix4f m4 = new Matrix4f();
m4.load((FloatBuffer)temp.asFloatBuffer());
m4.invert();
vpos = Matrix4f.transform(m4, vpos, vpos);

Rotation matrix for direction vector

I've been playing with some algorithms on the internet for a while and I can't seem to get them to work, so I'm tossing the question out here;
I am attempting to render a velocity vector line from a point. Drawing the line isn't difficult: just insert a line with length velocity.length into the graph. This puts the line centered at the point in the y-axis direction. We need to get this now in the proper rotation and translation.
The translational vector is not difficult to calculate: it is half the velocity vector. The rotational matrix, however, is being exceedingly elusive to me. Given a directional vector <x, y, z>, what's the matrix I need?
Edit 1: Look; if you don't understand the question, you probably won't be able to give me an answer.
Here is what I currently have:
Vector3f translation = new Vector3f();
translation.scale(1f/2f, body.velocity);
Vector3f vec_z = (Vector3f) body.velocity.clone();
vec_z.normalize();
Vector3f vec_y; // reference vector, will correct later
if (vec_z.x == 0 && vec_z.z == 0) {
vec_y = new Vector3f(-vec_z.y, 0f, 0f); // could be optimized
} else {
vec_y = new Vector3f(0f, 1f, 0f);
}
Vector3f vec_x = new Vector3f();
vec_x.cross(vec_y, vec_z);
vec_z.normalize();
vec_y.cross(vec_x, vec_z);
vec_y.normalize();
vec_y.negate();
Matrix3f rotation = new Matrix3f(
vec_z.z, vec_z.x, vec_z.y,
vec_x.z, vec_x.x, vec_x.y,
vec_y.z, vec_y.x, vec_y.y
);
arrowTransform3D.set(rotation, translation, 1f);
based off of this article. And yes, I've tried the standard rotation matrix (vec_x.x, vec_y.x, etc) and it didn't work. I've been rotating the columns and rows to see if there's any effect.
Edit 2:
Apologies about the rude wording of my comments.
So it looks like there were a combination of two errors; one of which House MD pointed out (really bad naming of variables: vec_z was actually vec_y, and so on), and the other was that I needed to invert the matrix before passing it off to the rendering engine (transposing was close!). So the modified code is:
Vector3f vec_y = (Vector3f) body.velocity.clone();
vec_y.normalize();
Vector3f vec_x; // reference vector, will correct later
if (vec_y.x == 0 && vec_y.z == 0) {
vec_x = new Vector3f(-vec_y.y, 0f, 0f); // could be optimized
} else {
vec_x = new Vector3f(0f, 1f, 0f);
}
Vector3f vec_z = new Vector3f();
vec_z.cross(vec_x, vec_y);
vec_z.normalize();
vec_x.cross(vec_z, vec_y);
vec_x.normalize();
vec_x.negate();
Matrix3f rotation = new Matrix3f(
vec_x.x, vec_x.y, vec_x.z,
vec_y.x, vec_y.y, vec_y.z,
vec_z.x, vec_z.y, vec_z.z
);
rotation.invert();

This should do you

Dupe.
The question there involves getting a rotation to a certain axis, whereas I'm concerned with getting a rotation matrix.
Gee, I wonder if you could turn convert one to the other?
BTW, your current solution of picking an arbitrary y axis and then reorthogonalising should work fine; it looks bugged though, or at least badly written. 'z_vec' is not a good variable-name for the y-axis. What's with the 'z,x,y' ordering, anyway?
If it still doesn't work, try making random changes until it does - transpose the matrix, negate vectors until you have an even number of sign errors, that kind of thing.
Also your tone of voice comes across as sort-of rude, given that you're asking strangers to spend their time helping you.