I'm working with OpenGL ES 2.0 and trying to build my object class with some methods to rotate/translate/scale them.
I just set up my object in 0,0,0 and move it afterwards to the desired position on the screen. Below are my methods to move it seperately. After that i run the buildObjectModelMatrix to pass all the matrices into one objectMatrix, so i can take the vertices and multiply them with my modelMatrix/objectMatrix and render it afterwards.
What i think is right, i have to multiply my matrices in this order:
[scale]x[rotation]x[translation]
->
[temp]x[translation]
->
[objectMatrix]
I've found some literature. Maybe i get it in a few Minutes, if i will, i will update it.
Beginning Android 3D
http://gamedev.stackexchange.com
setIdentityM(scaleMatrix, 0);
setIdentityM(translateMatrix, 0);
setIdentityM(rotateMatrix, 0);
public void translate(float x, float y, float z) {
translateM(translateMatrix, 0, x, y, z);
buildObjectModelMatrix();
}
public void rotate(float angle, float x, float y, float z) {
rotateM(rotateMatrix, 0, angle, x, y, z);
buildObjectModelMatrix();
}
public void scale(float x, float y,float z) {
scaleM(scaleMatrix, 0, x, y, z);
buildObjectModelMatrix();
}
private void buildObjectModelMatrix() {
multiplyMM(tempM, 0, scaleMatrix, 0, rotateMatrix, 0);
multiplyMM(objectMatrix, 0, tempM, 0, translateMatrix, 0);
}
SOLVED:
The Problem within the whole thing is, if you scale before you translate you get a difference in the distance you translate! the correct code for multiplying your matrices should be (correct me if i'm wrong)
private void buildObjectModelMatrix() {
multiplyMM(tempM, 0, translateMatrix, 0, rotateMatrix, 0);
multiplyMM(objectMatrix, 0, tempM, 0, scaleMatrix, 0);
}
with this you translate and rotate first. Afterwards you can scale the object.
Tested with multiple Objects... so i hope this helped :)
You know this is the most common issue with most people when beginning to deal with matrix operations. How matrix multiplication works is as if you were looking from the objects first person view getting some commands: For instance if you began at (0,0,0) facing toward positive X axis and up would be positive Y axis then translate (a,0,0) would mean "go forward", translate (0,0,a) would would mean "go left", rotate (a, 0, 1, 0) would mean "turn left"...
So if in your case you scaled by 3 units, rotated by 90 degrees and then translated by (2,0,0) what happens is you first enlarge yourself by scale of 3, then turn 90 degrees so you are now facing positive Z still being quite large. Then you go forward by 2 units measured in your own coordinate system which means you will actually go to (0,0,2*3). So you end up at (0,0,6) looking toward positive Z axis.
I believe this way is the best to be able to imagine what goes on when dealing with such operations. And might save your life when having a bug in matrix operation order.
You should know that although this kind of matrix operating is normal when beginning with a 3D scene you should try to move to a better system as soon as possible. What I mostly use is to have an object structure/class which contains 3 vectors: position, forward and up (this is much like using glLookAt but not totally the same). So when having these 3 vectors you can simply set a specific position or rotation using trigonometry or your matrix tools by multiplying the vectors with matrices instead of the matrices with matrices. Or you can work with them internally (first person) where for instance "go forward" would be done as position = position + position*forward*scale, turn left would be rotating a forward vector around the up vector. Anyway I hope can understand how to manipulate those 3 vectors to get a desired effect... So what you need to do to reconstruct the matrix from those 3 vector is need to generate another vector right which is a cross product of up and forward then the model matrix consists of:
right.x, right.y, right.z, .0
up.x, up.y, up.z, .0
forward.x, forward.y, forward.z, .0
position.x, position.y, position.z, 1.0
Just note the row-column order may change depending on what you are working with.
I hope this gives you some better understanding...
Related
I know this question has been asked many many times, but with all the knowledge out there I still can't get it to work for myself in the specific setting I now find myself in: Processing for Android.
The coordinate systems involved are (1) the real-world coordinate system as per Android's view: y is tangential to the ground and pointing north, z goes up into the sky, and x goes to your right, if you're standing on the ground and looking north; and (2) the device coordinate system as per Processing's view: x points to the right of the screen, y down, and z comes out of the screen.
The goal is simply to draw a cube on the screen and have it rotate on device rotation such that it seems that it is stable in actual space. That is: I want a map between the two coordinate systems so that I can draw in terms of the real-world coordinates instead of the screen coordinates.
In the code I'm using the Ketai sensor library, and subscribe to the onRotationVectorEvent(float x, float y, float z) event. Also, I have a simple quaternion class lying around that I got from https://github.com/kynd/PQuaternion. So far I have the following code, in which I have two different ways of trying to map, that coincide, but nevertheless don't work as I want them to:
import ketai.sensors.*;
KetaiSensor sensor;
PVector rotationAngle = new PVector(0, 0, 0);
Quaternion rot = new Quaternion();
void setup() {
fullScreen(P3D);
sensor = new KetaiSensor(this);
sensor.start();
}
void draw() {
background(#333333);
translate(width/2, height/2);
lights();
// method 1: draw lines for real-world axes in terms of processing's coordinates
PVector rot_x_axis = rot.mult(new PVector(400, 0, 0));
PVector rot_y_axis = rot.mult(new PVector(0, 0, -400));
PVector rot_z_axis = rot.mult(new PVector(0, 400, 4));
stroke(#ffffff);
strokeWeight(8); line(0, 0, 0, rot_x_axis.x, rot_x_axis.y, rot_x_axis.z);
strokeWeight(5); line(0, 0, 0, rot_y_axis.x, rot_y_axis.y, rot_y_axis.z);
strokeWeight(2); line(0, 0, 0, rot_z_axis.x, rot_z_axis.y, rot_z_axis.z);
// method 2: first rotate appropriately
fill(#f4f7d2);
rotate(asin(rotationAngle.mag()) * 2, rotationAngle.x, rotationAngle.y, rotationAngle.z);
box(200, 200, 200);
}
void onRotationVectorEvent(float x, float y, float z) {
rotationAngle = new PVector(x, y, z);
// I believe these two do the same thing.
rot.set(x, y, z, cos(asin(rotationAngle.mag())));
//rot.setAngleAxis(asin(rotationAngle.mag())*2, rotationAngle);
}
The above works well enough that the real-world axis lines coincide with the cube drawn, and both rotate in an interesting way. But still, there seems to be some "gimbal stuff" going on, in the sense that, when I rotate my device up and down standing one way, the cube also rotates up and down, but standing another way, the cube rotates sideways --- as if I'm applying the rotations in the wrong order. However, I'm trying to avoid gimbal madness by working with quaternions this way --- how does it still apply?
I've solved it now, just by a simple "click to test next configuration" UI, to test all possible 6 * 8 configurations of rotate(asin(rotationAngle.mag()) * 2, <SIGN> * rotationAngle.<DIM>, <SIGN> * rotationAngle.<DIM>, <SIGN> * rotationAngle.<DIM>); -- the solution to which seemed to be 0, -1, 2, i.e.:
rotate(asin(rotationAngle.mag()) * 2, rotationAngle.x, -rotationAngle.y, rotationAngle.z);
I am trying to create a 2D game. Because I am using OpenGL ES I have to plot everything in 3D, but I just fix the z coordinate, which is fine. Now what I want to do is calculate the angle between two vectors (C = player center, P = point just above player, T = touch point) CP and CT so that I can make the player face that direction. I know how to get the angle between 2 vectors, but my problem is getting all the points to exist on the same plane (by translating the T).
I know that T exists on a plane where (0,0) is upper left and UP is actually DOWN (visually). I also know that C and P's UP is actually UP and that any their X and Y is on a completely 3 dimensional different plane to T. I need to get either C and P onto T's plane (which I have tried below) or get T onto C and P's plane. Can anyone help me? I am using the standard OpenGL projection model and I am 0,0,-4 zoomed out of the frustrum (I am looking directly at (0,0,0)). My 2D objects all sit on the plane (0,0,1);
private float getRotation(float touch_x, float touch_y)
{
//center_x = this.getWidth() / 2;
//center_y = this.getHeight() / 2;
float cx, cy, tx, ty, ux, uy;
cx = (player.x * _renderer.centerx);
cy = (player.y * -_renderer.centery);
ux = cx;
uy = cy+1.0f;
tx = (touch_x - _renderer.centerx);
ty = (touch_y - _renderer.centery);
Log.d(TAG, "center x: "+cx+"y:"+cy);
Log.d(TAG, "up x: "+ux+"y:"+uy);
Log.d(TAG, "touched x: "+tx+"y:"+ty);
float P12 = length(cx,cy,tx,ty);
float P13 = length(cx,cy,ux,uy);
float P23 = length(tx,ty,ux,uy);
return (float)Math.toDegrees(Math.acos((P12*P12 + P13*P13 - P23*P23)/2.0 * P12 * P13));
}
Basically I want to know if there is a way I can translate (tx, ty, -4) to (x, y, 1) using the standard view frustum.
I have tried some other things now. In my touch event I am trying to do this:
float[] coords = new float[4];
GLU.gluUnProject(touch_x, touch_y, -4.0f, renderer.model, 0, renderer.project, 0, renderer.view, 0, coords, 0);
Which is throwing an exception I am setting up the model, projection and view in the OnSurfaceChanged of the Renderer object:
GL11 gl11 = (GL11)gl;
model = new float[16];
project = new float[16];
int[] view = new int[4];
gl11.glGetFloatv(GL10.GL_MODELVIEW, model, 0);
gl11.glGetFloatv(GL10.GL_PROJECTION, project, 0);
gl11.glGetIntegerv(GL11.GL_VIEWPORT, view, 0);
I have several textbooks on openGL and after dusting one off I found that the term for what I want to do is called picking. Once I knew what I was asking, I found a lot of good web sites and references:
http://www.lighthouse3d.com/opengl/picking/
OpenGL ES (iPhone) Touch Picking
Coordinate Picking with OpenGL ES 2.0
Android OpenGL 3D picking
converting 2D mouse coordinates to 3D space in OpenGL ES
Coordinate Picking with OpenGL ES 2.0
Ray-picking in OpenGL ES 2.0
Android: GLES20: Called unimplemented OpenGL ES API
...
The list is almost innumerable. There are 700 ways to do this, and none of them worked for me. Ultimately I have decided to go back to basics and do a thorough OpenGL|ES learning stint, to which effect I have bought the book here: http://www.amazon.com/Graphics-Programming-Android-Programmer-ebook/dp/B0070D83W2/ref=sr_1_2?s=digital-text&ie=UTF8&qid=1362250733&sr=1-2&keywords=opengl+es+2.0+android
One thing I have already learnt is that I was most definitely using the wrong type of projection. I should not use full 3D for a 2D game. In order to do picking in a full 3D environment I would have to cast a ray from the screen point onto the surface of the 3D plane where the game was taking place. In addition to being a horrendous waste of resources (raycasting per click), there were other tell-tales. I would render my player with a circle encompassing her, and as I moved her, the circle would go off center of the player. This is due to the full 3D environment rendered on a 2D plane. It just will not produce a professional result. I need to use an orthographic projection.
I think you're trying to do too much all at once. I can understand each sentence of your question separately; but strung all together, it's very confusing.
For the exceptions, you probably need to pass identity matrices instead of zero matrices to get a basic 1-to-1 projection.
Then I'd suggest that you scale the y dimension by -1 so all the UPs and DOWNs match at least.
I hope this helps, because I'm not 100% sure what you're trying to do. Particularly, " translate (tx, ty, -4) to (x, y, 1) using the standard view frustum" doesn't make sense to me. You can translate with a translation matrix. You can clip to a view frustum, or project an object from the frustum to a plane (usually the view plane). But if all your Zs are constant, you can just discard them right? So, assuming x=tx and y=ty, then tz += 5?
I want to program a racinggame for Android. My Problem is, that if I rotate the car and want to translate the position it doesn't translate into the new direction of the car , but always in the X axis of the world.
Here is my wrong code.. thank you
gl.glTranslatef(car.position.x, car.position.y, car.position.z);
gl.glRotatef(car.currentAngle, 0, 1, 0);
Opengl uses matrices to create images.
In Matrices, multiplication do not have an associative property. Therefore when you rotate an object and then translate it, the object will end up in a different position as opposed if you did not translate it first.
A solution to transforming and translating an object would be to animate and translate. That way you can translate anywhere you want without worrying about object rotation's associative property.
To see the effects of the non-associative multiplication on your object, try this: rotate and translate your object about 8 times, rotating and translating 8 times each respectively. You will notice that your object will disappear. As opposed to "rotate in a circle while changing position".
Ok I have the solution. All I have to do is to translate my Car towards the new directional vector who gets changed by the new angle of my car :)
if (accel < 0)
position.add((float) Math.sin(current * Math.PI/180)/5, 0, (float) Math.cos(currentangle * Math.PI/180)/5);
if (accel > 0)
position.sub((float) Math.sin(current * Math.PI/180)/5, 0, (float) Math.cos(currentangle * Math.PI/180)/5);
and in the rendering class
gl.glTranslatef(car.position.x, car.position.y, car.position.z);
gl.glRotatef(car.currentAngle, 0, 1, 0);
Using Android opengl I need to move an object from point A to point B and rotate it around its local Z axis in the same time. I have been reading tutorials for the past 3 days, everybody gives you bits of informations and hints, but nobody is capable of explaining this from top to bottom for beginners.
I know how to only translate the object from point A to point B.
I also know how to rotate the object in point A around its local axis (translate it to origin, rotate it, translate it back)
I DON'T know how to rotate and translate in the same time.
I've tried to translate to origin, rotate, translate back, then translate to point B. It doesn't work, and I think I know why (the rotation is messing the object axis, so the translation to point B is incorrect)
A(-x1, y1 , -z1)
B(-x1 + deltaX, y1 + deltaY, -z1 + deltaZ)
_gl.glTranslatef(x1, -y1 , z1);
_gl.glRotatef(degrees, x1, -y1 , z1);
_gl.glTranslatef(-x1, y1 , -z1);
_gl.glTranslatef(deltaX, deltaY, deltaZ);
I need to take into consideration the way the rotation is chaning the axes. Some say I can do that with quaterninons, or with rotation matrixes, etc.
But I don't have enough opengl knowledge to use apis to resolve this.
Can someone explain this to me? With somecode also?
Thank you in advance.
If you have the following code:
glTranslate(x, y, z);
glRotatef(angle, 0, 0, 1);
drawObject();
The object will first be rotated around it's local z-axis and then translated with (x, y, z). The transform call that is closest to the draw call is the one that happens first.
From your code it seems like you actually don't want to rotate the object around it's own origin but some other point, in this case you should do the following:
glTranslate(x, y, z); //Transform 4
glTranslate(origin.x, origin.y, origin.z); //Transfrom 3
glRotatef(angle, 0, 0, 1); // Transform 2
glTranslate(-origin.x, -origin.y, -origin.z); // Transform 1
drawObject();
How do I get the current translate position from a Canvas? I am trying to draw stuff where my coordinates are a mix of relative (to each other) and absolute (to canvas).
Lets say I want to do
canvas.translate(x1, y1);
canvas.drawSomething(0, 0); // will show up at (x1, y1), all good
// now i want to draw a point at x2,y2
canvas.translate(x2, y2);
canvas.drawSomething(0, 0); // will show up at (x1+x2, y1+y2)
// i could do
canvas.drawSomething(-x1, -y1);
// but i don't always know those coords
This works but is dirty:
private static Point getCurrentTranslate(Canvas canvas) {
float [] pos = new float [2];
canvas.getMatrix().mapPoints(pos);
return new Point((int)pos[0], (int)pos[1]);
}
...
Point p = getCurrentTranslate(canvas);
canvas.drawSomething(-p.x, -p.y);
The canvas has a getMatrix method, it has a setTranslate but no getTranslate. I don't want to use canvas.save() and canvas.restore() because the way I'm drawing things it's a little tricky (and probably messy ...)
Is there a cleaner way to get these current coordinates?
You need to reset the transformation matrix first. I'm not an android developer, looking at the android canvas docs, there is no reset matrix, but there is a setMatrix(android.graphics.Matrix). It says if the given matrix is null it will set the current matrix to the identity matrix, which is what you want. So I think you can reset your position (and scale and skew) with:
canvas.setMatrix(null);
It would also be possible to get the current translation through getMatrix. There is a mapVectors() method you could use for matrices to see where the point [0,0] would be mapped to, this would be your translation. But in your case I think resetting the matrix is best.