I want to implement zoom in\out of my plaine object.
Now i try scaling :
Matrix.translateM(mModelMatrix, 0, mFocalPoint.x, mFocalPoint.y, 0f);
Matrix.scaleM(mModelMatrix, 0, mCurrentScaleFactor, mCurrentScaleFactor, 1f);
Matrix.translateM(mModelMatrix, 0, -mFocalPoint.x, -mFocalPoint.y, 0f);
In first zoom i have success result, but on the next zoom i have a problem - looks like a focal point calculated based on old matrix.
Here i calculated a focal point
float glX = detector.getFocusX() * mScaleCoefX - mGLSceneWidth/2;
float glY = mGLSceneHeight - detector.getFocusY() * mScaleCoefY - mGLSceneHeight/2;
mFocalPoint = new PointF(glX, glY);
Also i save my model matrix after each zoom and restore before each draw.
So i have a question. Why my zoom doesn't work if i save matrix after each zoom and start scaling on new matrix?
Also - maybe i should recalculate my mFocalPoint?
Each time you use a Matrix, be sure to initialize it with the identity matrix before you use Translate, Scale or Rotate. I don't see that in your code. The calculated Matrix should then be multiplied to the projection matrix either before or in the Vertex shader.
Related
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...
I am trying to translate a set of points in one coordinate system to another coordinate system for my Android OpenGL project.
Assume matrix is a float array of 16 elements.
Assume points is a reference to an array of float arrays each with 4 elements. (points = new float[8][4])
I set the matrix to an identity matrix, I then translate it and multiply by the rotation of the gameobject. I then try to translate each of the 8 vertices into the new matrices coordinates system, but none of the points are changing.
Matrix.setIdentityM(matrix, 0);
Matrix.translateM(matrix, 0, go.getPosition().getX(), go.getPosition().getY(), go.getPosition().getZ());
Matrix.multiplyMM(matrix, 0, matrix, 0, go.getRotationArray(), 0);
//Matrix.rotateM(matrix, 0, 30f, 1.5f, -5f, 0f); testing debug purpose
for(int i=0;i<8;i++)
{
Matrix.multiplyMV(points[i], 0, matrix, 0, points[i], 0);
}
I am basically trying to do what Android's 2D canvas and Matrix 'mapPoints' does.
When you have a vector, your last element of the 4 long vector must be 1 and not 0! So non of the translation data was being multiplied correctly. (Well it was being done correctly, just not how I wanted it.) So when android.opengl.Matrix asks for a vector of four long and the first three elements represent your x,y,z, make sure the fourth element is set to 1!
I have a java code for SVG drawing. It processes transforms including rotate, and does this very well, as far as I can see in numerous test pictures compared against their rendering in Chrome. Next what I need is to get actual object location, which is in many images declared via transforms. So I decided just to read X and Y from Matrix used for drawing. Unfortunately I get incorrect values for rotate transform, that is they do not correspond to real object location in the image.
The stripped down code looks like this:
Matrix matrix = new Matrix();
float cx = 1000; // suppose this is an object X coordinate
float cy = 300; // this is its Y coordinate
float angle = -90; // rotate counterclockwise, got from "rotate(-90, 1000, 300)"
// shift to -X,-Y, so object is in the center
matrix.postTranslate(-cx, -cy);
// rotate actually
matrix.postRotate(angle);
// shift back
matrix.postTranslate(cx, cy);
// debug goes here
float[] values = new float[9];
matrix.getValues(values);
Log.v("HELLO", values[Matrix.MTRANS_X] + " " + values[Matrix.MTRANS_Y]);
The log outputs the values 700 and 1300 respectively. I'd expect 0 and 0, because I see the object rotated inplace in my image (that is there is no any movement), and postTranslate calls should compensate each other. Of course, I see how these values are formed from 1000 and 300, but don't understand why. Once again, I point out that the matrix with these strange values is used for actual object drawing, and it looks correct. Could someone explain what happens here? Am I missing something? So far I have only one solution of my problem: just do not try to obtain position from rotate, do it only for explicit matrix and translate transforms. But this approach lacks generality, and anyway I thought matrix should have reasonable values (including offsets) for any transformation type.
The answer is that the matrix is an operator for space transformation, and should not be used for direct extraction of object position. Instead, one should get initial object coordinates, as specified in x and y attributes of an SVG tag, and apply the matrix on them:
float[] src = new float[2];
src[0] = cx;
src[1] = cy;
matrix.mapPoints(src);
After this we get proper location values in x and y variables.
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.
How do you calculate the direction that your camera is pointing towards in Android? Azimuth works only if the device is vertical. How do you account for the pitch and roll?
If R is the rotation matrix, I want to find something like:
getRotationMatrix(R, I, grav, mag);
float[] rotated = R {0, 0, -1} ; //not sure how to do matrix multiplication
float direction = Math.atan(rotated[0]/rotated[1]);
I would lookup the Accelerometer API. Also, check out this article, it might help: http://www.anddev.org/convert_android_accelerometer_values_and_get_tilt_from_accel-t6595.html