I'm trying to rotate an object towards a 3d point using OpenGL and glm. To find xRotation I am doing this:
xRotation=atan2(lookAtDiff.x,lookAtDiff.z)
Where xRotation is around the Y axis and lookAtDiff is a vec3 that is the difference between the object's position and what I am trying to make it face. This works flawlessly. So I decided to do yRotation (Rotation around X axis) in the same manner by doing this:
yRotation=atan2(lookAtDiff.y,lookAtDiff.x)
This gives me the wrong rotation. My question is why am I getting the wrong rotation from this and how can I fix it?
You have to use the diagonal:
yRotation = atan2(lookAtDiff.y, sqrt(lookAtDiff.x * lookAtDiff.x + lookAtDiff.z * lookAtDiff.z));
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I am making a camera in openGl and I am having troubles with first person camera. So I had a few versions of camera transformation and all of them had their own problems. So at first, I was doing transformations in this order: I would first translate the object in the positive direction when trying to move away from it and I would translate it in the negative direction when trying to move towards it. After this translation, I would perform rotations arround X and Y axis. Now, when I try to use this camera, I found out that when I have objects in my scene, lets say a few cubes, and when I rotate, everything is fine, but when after this rotation I try translation, all of the objects converge to me or better to say, towards the "player". So after I gave this some thought I realized that because I am doing translations first, in the next frame when I try to translate the player in the direction in which the camera is looking at that moment, what happens is, objects get translated first and then rotated so I get, as a result of this, movement of the objects towards or away from the player. Code for this is here (and dont mind camUp and camRight vectors, these are just y and x axis vectors and are not transformed at all):
m_ViewMatrix = inverse(glm::rotate(glm::mat4(1.0f), m_Rotation, camUp))* inverse(glm::rotate(glm::mat4(1.0f), m_TiltRotation, camRight)) * glm::translate(glm::mat4(1.0f), m_Position);
But option to rotate and then translate is not good because then I get editor sort of camera which is actually fine but that is not what I want.
So I thought about it some more and tried to make small transformations and then reset the parameters, acumulating all the transformations in this way:
m_ViewMatrix = inverse(glm::rotate(glm::mat4(1.0f), m_Rotation, camUp)) * glm::translate(glm::mat4(1.0f), m_Position)* inverse(glm::rotate(glm::mat4(1.0f), m_TiltRotation, camRight))*m_ViewMatrix;
m_Position = { 0.0f, 0.0f, 0.0f };
m_Rotation = 0.0f;
m_TiltRotation = 0.0f;
But now I have a problem with rotations arround z axis which I don't want. This problem was not there before. So now I have no idea what to do, I read some answers here but couldn't apply them I don't know why. So if anyone could help me in the context of the code I just copied here, that would be great.
I want my 2D sprite to rotate while always facing my cursor.
I am using glad, SDL2 & glm for the math.
the "original" way I tried was to calculate the angle between my Front and my desired LookAt vector of the object and put that angle in degrees into an glm::rotate matrix.
That did not work out for some strange reason.
The other way was to do it within a quat and apply the quat to my model matrix, which did not help either.
My object is rendered with its center at the origin (0,0,0) - so no translation needs to be done for the rotation.
I draw 2 triangles to make a rectangle on which I load my texture.
My model matrix looks like that in theory:
model = rotate * scale;
I then plug it into the shader (where Position is my vec3 Vertex)
position = projection * view * model * vec4(Position, 1.0f);
The first strange thing is, if I hardcode 90.0f as an angle into glm::rotate, my object is actually rotated about 120° clockwise.
If I plug in 80° it actually rotates about ~250° clockwise.
If I plug in 45° it's a perfect 45° clockwise rotation.
All rotations are around the z-axis, eg.:
model = glm::rotate(model, 90.0f, glm::vec3(0.0f,0.0f,1.0f);
If I use a quaternion to simulate an orientation, it gives me angles between 0,2&0,9 radians and my object seems only to rotate between 0.0° & 45° clockwise, no matter where I put my cursor.
If I calculate the angle btw. my two vectors (ObjectLookAt & MousePosition) and store them I get also quite correct angles, but the glm::rotate function does not work as I'd expected.
Finally if I simply code the angle as:
float angle = static_cast<float>(SDL_GetTicks()/1000);
Which starts by one it actually rotates even more weird.
I'd expect it to start to rate by 1° (as it starts with 1 second) and then rotate a full circle around the z axis until there are 360 seconds over.
However it rotates full 360° in about 6 second. so ever "1" that is added on the angle and plugged into glm::rotate as a degree represents 60°?
Is this now a flaw in my logic? Do I not rotate a sprite around the z-axis if it is drawn on a x-y plane?
I also tried the x & y axis just to be safe here, but that didn't work.
I am really stuck here, I (think I) get how it should work in theory, especially as it all happens in "2D", but I cannot get it work..
The first strange thing is, if I hardcode 90.0f as an angle into glm::rotate, my object is actually rotated about 120° clockwise. If I plug in 80° it actually rotates about ~250° clockwise. If I plug in 45° it's a perfect 45° clockwise rotation.
This is, because the function glm::rotate expects the angle in radians (since GLM version 0.9.6).
Adapt your code like this:
model = glm::rotate(model, glm::radians(angel_degrees), glm::vec3(0.0f,0.0f,1.0f);
see also:
glm rotate usage in Opengl
GLM::Rotate seems to cause wrong rotation?
GLM: function taking degrees as a parameter is deprecated (WHEN USING RADIANS)
So at the moment am working on a game for my coursework which is based around the idea of flying a rocket, I spent too much time thinking about the physics behind it that I completely ignored getting it to move properly.
For example when I were to draw a cone with the top pointing to the sky, and I rotate it on the X axis it rotates properly however if I translate it on the Y axis it moves on the global Y axis instead on it's local coordinate system which would have the Y axis pointing out of the cone's top.
My question is does openGL have a local coordinate system or would I have to somehow make my own transformation matrices, and if so how would I go about doing that.
The way I am doing the transformation and rotation is as follows:
glPushMatrix();
glTranslatef(llmX, llmY + acceleration, llmZ);
glRotatef(rotX, 1.0f, 0.0f, 0.0f);
glRotatef(rotY, 0.0f, 0.0f, 1.0f);
drawRocket();
glPopMatrix();
Here is a picture better explaining what I mean hopefully offers a better explanation.
EDIT: I find it really weird that the rotations seem to work one after the other as in if I rotate it on the X axis once and then proceed to rotate it on the Z axis it rotates from the already rotated X axis instead of the world X axis.
Hoping somebody could help me with understanding this, really need to get it working for my project.
Thank you.
If you are using a translation matrix for moving up (i.e. moving in positive Y direction), no matter where you are in on the matrix stack or in the transformation process, you are going to move the vertices in the positive Y direction.
If you instead want it move in the rotated direction, I suggest translating along the Y axis first, and then rotate to your desired angle. Essentially, push the matrices in the opposite fashion.
I am currently struggling in finding a formula to rotate my OpenGL "Camera" (I tried do do it via a scene rotation, but have the same issue).
Basically my Camera is at a given position, looking a given point (all indicated to gluLookAt) and I would like to rotate the camera upwards for example, and still looking at the same point.
What should be the right process ?
What input data should I take to decide the amount of movement ? 2D mouse coordinates evolution or 3D unprojected mouse coordinates evolution ?
The trick is to see that a camera-rotation is the same as a scene rotation if you do it at the correct position. Move the camera into the point around which you want to rotate, then rotate the camera, then move back out by the same distance you moved in.
The amount by which you rotate depends on your application. Take G-Earth as an example: if you are close to the surface the rotation is (absolute) small, if you are far from the surface it is large.
If you're creating orbiting(oribitng around LookAt) camera for openGL I sugest you make it with these data:
LookAtPosition- 3D vector
CamUp - 3D unit vector
RelativeCamPosition - 3D unit vector
CamDistance - decimal number
LookAtPosition is a point on which you'll be looking. CamUp is vector that points up from camera, you can see it on this image. It's best to initialize camera at no rotation, so that CamUp = [0,1,0]. Note that it's unit vector so it's magnitude/size/length is always 1. RelativeCamPosition is again unit vector. You get it by taking LookAt to Camera
vector and dividing by it's magnitude, which you'll save in CamDistance. In intialized state it might look as this:
LookAtPosition = [0,0,0]
CamUp = [0,1,0]
RelativeCamPosition = [1,0,0]
CamDistance = 10
You can now get camera position by
CamPosition = LookAtPosition + RelativeCamPosition * CamDistance
But you need to rotate that camera arround right? Well there's a reason for unit vectors - they are easy to use in calculations. I believe you use angles for rotating so you need to use only sine and cosine. Rotate function might look like this:
Rotate(angleX, angleY){
RelativeCamPosition.x = sin(angleX)*cos(angleY);
RelativeCamPosition.z = cos(angleX)*cos(angleY);
RelativeCamPosition.y = sin(angleY);
}
where angleX and angleY are absolute (NOT RELATIVE) rotations in horizontal and vertical direction. You should always use absolute roations because there can be floating point errors while adding. Anyway I just made those calculations on scrap of paper so I hope they're allright.
Edit: I've just noticed that this will work just if your intiial state is like I wrote RelativeCamPosition = [1,0,0]. However it shouldn't be hard to edit them so it works for arbirtary initial state.
I am trying to make a very simple object rotate around a fixed point in 3dspace.
Basically my object is created from a single D3DXVECTOR3, which indicates the current position of the object, relative to a single constant point. Lets just say 0,0,0.
I already calculate my angle based on the current in game time of the day.
But how can i apply that angle to the position, so it will rotate?
:(?
Sorry im pretty new to Directx.
So are you trying to plot the sun or the moon?
If so then one assumes your celestial object is something like a sphere that has (0,0,0) as its center point.
Probably the easiest way to rotate it into position is to do something like the following
D3DXMATRIX matRot;
D3DXMATRIX matTrans;
D3DXMatrixRotationX( &matRot, angle );
D3DXMatrixTranslation( &matTrans, 0.0f, 0.0f, orbitRadius );
D3DXMATRIX matFinal = matTrans * matRot;
Then Set that matrix as your world matrix.
What it does is it creates a rotation matrix to rotate the object by "angle" around the XAxis (ie in the Y-Z plane); It then creates a matrix that pushes it out to the appropriate place at the 0 angle (orbitRadius may be better off as the 3rd parameter in the translation call, depending on where your zero point is). The final line multiplies these 2 matrices together. Matrix multiplications are non commutative (ie M1 * M2 != M2 * M1). What the above does is move the object orbitRadius units along the Z-axis and then it rotates that around the point (0, 0, 0). You can think of rotating an object that is held in your hand. If orbitRadius is the distance from your elbow to your hand then any rotation around your elbow (at 0,0,0) is going to form an arc through the air.
I hope that helps, but I would really recommend doing some serious reading up on Linear Algebra. The more you know the easier questions like this will be to solve yourself :)