First off, I'm sorry if I confuse anyone because I don't know how to phrase this, exactly.
Anyway, What I want to do is rotate on 3 axis, but independent of eachother. If I have
glRotatef(getPitch(),1f,0,0);
glRotatef(getYaw(),0,1f,0);
glRotatef(getRoll(),0,0,1f);
Then, it rotates my object on the x axis just fine, but the other two axis rotate on the offset of the x rotation. How do I rotate these all independent of eachother? (On the same object)
Again, Sorry if I confused anyone.
You could push and pop the matrix onto and off the stack, so you could do:
glPushMatrix();
glRotatef( getPitch(), 1.0f, 0.0f ,0.0f );
glPopMatrix();
glPushMatrix();
glRotatef( getYaw(), 0.0f, 1.0f, 0.0f);
glPopMatrix();
glPushMatrix();
glRotatef( getRoll(), 0.0f, 0.0f, 1.0f);
glPopMatrix();
so basically, pushing the matrix, saves the transformation matrix in it's current state. You apply the transformations that you want on the object (in your case rotations around an axis), which updates the matrix. Popping it restores it to the original state before the rotation was applied. You can then apply each rotation independently of the other ones.
I'm trying to rotate a cube's vertexes with a rotation matrix but whenever I run the program the cube just disappears.
I'm using a rotation matrix that was given to us in a lecture that rotates the cube's x coordinates.
double moveCubeX = 0;
float xRotationMatrix[9] = {1, 0, 0,
0, cos(moveCubeX), sin(moveCubeX),
0, -sin(moveCubeX), cos(moveCubeX)
};
I'm adding to the moveCubeX variable with the 't' key on my keyboard
case 't':
moveCubeX += 5;
break;
And to do the matrix multiplication I'm using
glMultMatrixf();
However when I add this into my code when running it the cube has just disappeared. This is where I add in the glMultMatrixf() function.
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
gluLookAt(pan, 0, -g_fViewDistance,
pan, 0, -1,
0, 1, 0);
glRotatef(rotate_x, 1.0f, 0.0f, 0.0f); //Rotate the camera
glRotatef(rotate_y, 0.0f, 1.0f, 0.0f); //Rotate the camera
glMultMatrixf(xRotationMatrix);
I'm struggling to see where it is I have gone wrong.
OpenGL uses matrices of size 4x4. Therefore, your rotation matrix needs to be expanded to 4 rows and 4 columns, for a total of 16 elements:
float xRotationMatrix[16] = {1.0f, 0.0f, 0.0f, 0.0f,
0.0f, cos(moveCubeX), sin(moveCubeX), 0.0f,
0.0f, -sin(moveCubeX), cos(moveCubeX), 0.0f,
0.0f, 0.0f, 0.0f, 1.0f};
You will also need to be careful about the units for your angles. Since you add 5 to your angle every time the user presses a key, it looks like you're thinking in degrees. The standard cos() and sin() functions in C/C++ libraries expect the angle to be in radians.
In addition, it looks like your matrix is defined at a global level. If you do this, the elements will only be evaluated once at program startup. You will either have to make the matrix definition local to the display(), so that the matrix is re-evaluated each time you draw, or update the matrix every time the angle changes.
For the second option, you can update only the matrix elements that depend on the angle every time the angle changes. In the function that modifies moveCubeX, add:
xRotationMatrix[5] = cos(moveCubeX);
xRotationMatrix[6] = sin(moveCubeX);
xRotationMatrix[9] = -sin(moveCubeX);
xRotationMatrix[10] = cos(moveCubeX);
I have used glOrtho(500, 600, 600, 700, -100, 100) projection with this i want to use camera view settings with gluLookAt() method what should be the parameters for gluLookAt function on this projection..
glOrtho builds a matrix that forms the "lens" of your virtual camera. gluLookAt moves that virtual camera.
http://msdn.microsoft.com/en-us/library/windows/desktop/dd368663%28v=vs.85%29.aspx
eyeX/Y/Z are where the camera is.
centerX/Y/Z are the spot at which the camera is looking.
upX/Y/Z is which way up the camera is.
An example use might be:
gluLookAt
(
0.0f, 2.0f, -16.0f,
0.0f, 0.5f, 0.0f,
0.0f, 1.0f, 0.0f
);
This will put the camera 16 units backwards, raise it slightly, point slightly above 0, 0, 0, with the top of the screen pointing along Y+.
You could change the first value to move the camera.
Change the second to change which part of the scene it's pointed at.
Change the third to roll/bank the camera.
The important question, however, is what do you want to do with it?
I am following the OpenGL es rotation examples from google to rotate a simple square (not a cube) on my Android App, for example this code:
gl.glRotatef(xrot, 1.0f, 0.0f, 0.0f); //X
gl.glRotatef(yrot, 0.0f, 1.0f, 0.0f); //Y
gl.glRotatef(zrot, 0.0f, 0.0f, 1.0f); //Z
It works fine if you only rotate around one axis.
But if you rotate around one axis, and after that, you rotate around another axis, the rotation is not fair. I mean that the rotation is done around the axes of base (global) coordinate system and not the square's own coordinate system.
EDIT with code for Shahbaz
public void onDrawFrame(GL10 gl) {
//Limpiamos pantalla y Depth Buffer
gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
gl.glLoadIdentity();
//Dibujado
gl.glTranslatef(0.0f, 0.0f, z); //Move z units into the screen
gl.glScalef(0.8f, 0.8f, 0.8f); //Escalamos para que quepa en la pantalla
//Rotamos sobre los ejes.
gl.glRotatef(xrot, 1.0f, 0.0f, 0.0f); //X
gl.glRotatef(yrot, 0.0f, 1.0f, 0.0f); //Y
gl.glRotatef(zrot, 0.0f, 0.0f, 1.0f); //Z
//Dibujamos el cuadrado
square.draw(gl);
//Factores de rotación.
xrot += xspeed;
yrot += yspeed;
}
Draw of the square:
public void draw(GL10 gl) {
gl.glFrontFace(GL10.GL_CCW);
//gl.glEnable(GL10.GL_BLEND);
//Bind our only previously generated texture in this case
gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);
//Point to our vertex buffer
gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);
//Enable vertex buffer
gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
//Draw the vertices as triangle strip
gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);
//Disable the client state before leaving
gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
//gl.glDisable(GL10.GL_BLEND);
}
VERTEX BUFFER VALUES:
private FloatBuffer vertexBuffer;
private float vertices[] =
{
-1.0f, -1.0f, 0.0f, //Bottom Left
1.0f, -1.0f, 0.0f, //Bottom Right
-1.0f, 1.0f, 0.0f, //Top Left
1.0f, 1.0f, 0.0f //Top Right
};
.
.
.
public Square(int resourceId) {
ByteBuffer byteBuf = ByteBuffer.allocateDirect(vertices.length * 4);
byteBuf.order(ByteOrder.nativeOrder());
vertexBuffer = byteBuf.asFloatBuffer();
vertexBuffer.put(vertices);
vertexBuffer.position(0);
.
.
.
First thing you should know is that in OpenGL, transformation matrices are multiplied from right. What does it mean? It means that the last transformation you write gets applied to the object first.
So let's look at your code:
gl.glScalef(0.8f, 0.8f, 0.8f);
gl.glTranslatef(0.0f, 0.0f, -z);
gl.glRotatef(xrot, 1.0f, 0.0f, 0.0f); //X
gl.glRotatef(yrot, 0.0f, 1.0f, 0.0f); //Y
gl.glRotatef(zrot, 0.0f, 0.0f, 1.0f); //Z
gl.glTranslatef(0.0f, 0.0f, z);
square.draw(gl);
This means that, first, the object is moved to (0.0f, 0.0f, z). Then it is rotated around Z, then around Y, then around X, then moved by (0.0f, 0.0f, -z) and finally scaled.
You got the scaling right. You put it first, so it gets applied last. You also got
gl.glTranslatef(0.0f, 0.0f, -z);
in the right place, because you first want to rotate the object then move it. Note that, when you rotate an object, it ALWAYS rotates around the base coordinate, that is (0, 0, 0). If you want to rotate the object around its own axes, the object itself should be in (0, 0, 0).
So, right before you write
square.draw(gl);
you should have the rotations. The way your code is right now, you move the object far (by writing
gl.glTranslatef(0.0f, 0.0f, z);
before square.draw(gl);) and THEN rotate which messes things up. Removing that line gets you much closer to what you need. So, your code will look like this:
gl.glScalef(0.8f, 0.8f, 0.8f);
gl.glTranslatef(0.0f, 0.0f, -z);
gl.glRotatef(xrot, 1.0f, 0.0f, 0.0f); //X
gl.glRotatef(yrot, 0.0f, 1.0f, 0.0f); //Y
gl.glRotatef(zrot, 0.0f, 0.0f, 1.0f); //Z
square.draw(gl);
Now the square should rotate in place.
Note: After you run this, you will see that the rotation of the square would be rather awkward. For example, if you rotate around z by 90 degrees, then rotating around x would look like rotating around y because of the previous rotation. For now, this may be ok for you, but if you want to it to look really good, you should do it like this:
Imagine, you are not rotating the object, but rotating a camera around the object, looking at the object. By changing xrot, yrot and zrot, you are moving the camera on a sphere around the object. Then, once finding out the location of the camera, you could either do the math and get the correct parameters to call glRotatef and glTranslatef or, use gluLookAt.
This requires some understanding of math and 3d imagination. So if you don't get it right the first day, don't get frustrated.
Edit: This is the idea of how to rotate along rotated object coordinates;
First, let's say you do the rotation around z. Therefore you have
gl.glRotatef(zrot, 0.0f, 0.0f, 1.0f); //Z
Now, the global Y unit vector is obviously (0, 1, 0), but the object has rotated and thus its Y unit vector has also rotated. This vector is given by:
[cos(zrot) -sin(zrot) 0] [0] [-sin(zrot)]
[sin(zrot) cos(zrot) 0] x [1] = [ cos(zrot)]
[0 0 1] [0] [ 0 ]
Therefore, your rotation around y, should be like this:
gl.glRotatef(yrot, -sin(zrot), cos(zrot), 0.0f); //Y-object
You can try this so far (disable rotation around x) and see that it looks like the way you want it (I did it, and it worked).
Now for x, it gets very complicated. Why? Because, the X unit vector is not only first rotated around the z vector, but after it is rotated around the (-sin(zrot), cos(zrot), 0) vector.
So now the X unit vector in the object's cooridnate is
[cos(zrot) -sin(zrot) 0] [1] [cos(zrot)]
Rot_around_new_y * [sin(zrot) cos(zrot) 0] x [0] = Rot_around_new_y * [sin(zrot)]
[0 0 1] [0] [0 ]
Let's call this vector (u_x, u_y, u_z). Then your final rotation (the one around X), would be like this:
gl.glRotatef(xrot, u_x, u_y, u_z); //X-object
So! How to find the matrix Rot_around_new_y? See here about rotation around arbitrary axis. Go to section 6.2, the first matrix, get the 3*3 sub matrix rotation (that is ignore the rightmost column which is related to translation) and put (-sin(zrot), cos(zrot), 0) as the (u, v, w) axis and theta as yrot.
I won't do the math here because it requires a lot of effort and eventually I'm going to make a mistake somewhere around there anyway. However, if you are very careful and ready to double check them a couple of times, you could write it down and do the matrix multiplications.
Additional note: one way to calculate Rot_around_new_y could also be using Quaternions. A quaternion is defined as a 4d vector [xs, ys, zs, c], which corresponds to rotation around [x, y, z] by an angle whose sin is s and whose cos is c.
This [x, y, z] is our "new Y", i.e. [-sin(zrot), cos(zrot), 0]. The angle is yrot. The quaternion for rotation around Y is thus given as:
q_Y = [-sin(zrot)*sin(yrot), cos(zrot)*sin(yrot), 0, cos(yrot)]
Finally, if you have a quaternion [a, b, c, d], the corresponding rotation matrix is given as:
[1 - 2b^2 - 2c^2 2ab + 2cd 2ac - 2bd ]
[ 2ab - 2cd 1 - 2a^2 - 2c^2 2bc - 2ad ]
[ 2ac - 2bd 2bc + 2ad 1 - 2a^2 - 2b^2]
I know next-to-nothing about openGL, but I imagine translating to 0, rotating and then translating back should work...
gl.glTranslatef(-x, -y, -z);
gl.glRotatef(xrot, 1.0f, 0.0f, 0.0f); //X
gl.glRotatef(yrot, 0.0f, 1.0f, 0.0f); //Y
gl.glRotatef(zrot, 0.0f, 0.0f, 1.0f); //Z
gl.glTranslatef(x, y, z);
I think you need quaternions to do what you want to do. Using rotations about the coordinate axes works some of the time, but ultimately suffers from "gimbal lock". This happens when the rotation you want passes close by a coordinate axis and creates an unwanted gyration as the rotation required around the axis approaches 180 degrees.
A quaternion is a mathematical object that represents a rotation about an arbitrary axis defined as a 3D vector. To use it in openGL you generate a matrix from the quaternion and multiply it by your modelview matrix. This will transform your world coordinates so that the square is rotated.
You can get more info here http://content.gpwiki.org/index.php/OpenGL:Tutorials:Using_Quaternions_to_represent_rotation
I have a Quaternion C++ class I could send you if it helps.
Try adding
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
before the render code for a single cube that's being rotated, and then
glPopMatrix();
after the rendering is done. It will give you an extra view matrix to work with without affecting your primary modelview matrix.
Essentially what this does is create a new modelview camera, render, then destroy it.
I'm using opentk, nevertheless it's the same.
First move the object half all it's dimensions size, then rotate and move back:
model = Matrix4.CreateTranslation(new Vector3(-width/2, -height / 2, -depth / 2)) *
Matrix4.CreateRotationX(rotationX) *
Matrix4.CreateRotationY(rotationY) *
Matrix4.CreateRotationZ(rotationZ) *
Matrix4.CreateTranslation(new Vector3(width / 2, height / 2, depth / 2));