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ComradeSlice

OpenGL OpenGL Camera

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This is my first post (which is sad because I've been a member for years) Hello, world!

 

I've got to say, I'm eager to learn from what is probably a very obvious mistake I'm making. This is my code for a free-flying camera. I don't have any movement code yet, so the camera just rotates around the origin. As I move the camera, it's almost as if the axis is slowly drifting, until I'm no longer rotating on the right axes!

glm::float_t scale = -500.0;
m_LookLR += (glm::float_t)analogEvent.x / scale;
m_LookUD += (glm::float_t)analogEvent.y / scale;

m_LookUD = glm::clamp<glm::float_t>(m_LookUD, -glm::half_pi<glm::float_t>(), glm::half_pi<glm::float_t>());

const glm::quat rotLR(0, glm::sin(m_LookLR / 2.0), 0, glm::cos(m_LookLR / 2.0));
const glm::quat rotUD(0, 0, glm::sin(m_LookUD / 2.0), glm::cos(m_LookUD / 2.0));
oglContext->rotViewMatrix = glm::mat4_cast(rotLR * rotUD);

From here, "rotViewMatrix" is multiplied against the translation view matrix and the projection matrix. Model matrix is multiplied in the shader.

 

I've seen other posts where some people use Euler Angles and others use Quaternions. I'm completely open to suggestion. Ease of use doesn't really bother me, but if one is a couple of floats and the other takes 2K of memory I'd go with the smaller footprint.

 

Regards,

ComradeSlice

 

EDIT: editor won't let me add spacing before/after the code block. Sorry for scrunched up post...

Edited by ComradeSlice

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I'm not sure what you mean by the axis drifting, but there is something that looks off in your code.

looking at the quaternion reference form glm, it looks like you are getting the parameter order wrong in the quat constructor. It expects w first, you are passing it in last.

 

Also, usually the forward vector for the camera goes along the z axis. For your up down rotation, it looks like you are rotating around the z axis. This will result in the camera rolling instead of pitching. Try switching the rotUP to rotate around the x axis.

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I'm not sure what you mean by the axis drifting, but there is something that looks off in your code.

looking at the quaternion reference form glm, it looks like you are getting the parameter order wrong in the quat constructor. It expects w first, you are passing it in last.

 

Also, usually the forward vector for the camera goes along the z axis. For your up down rotation, it looks like you are rotating around the z axis. This will result in the camera rolling instead of pitching. Try switching the rotUP to rotate around the x axis.

 

Now that makes a lot more sense. I changed the camera code accordingly:

const glm::quat rotLR(glm::cos(m_LookLR / 2.0), 0, glm::sin(m_LookLR / 2.0), 0);
const glm::quat rotUD(glm::cos(m_LookUD / 2.0), glm::sin(m_LookUD / 2.0), 0, 0);

I was still having issues with the camera rolling after this, but then I remembered reading about order of operations in glm. I changed the order that both quaternions were being multiplied:

//oglContext->rotViewMatrix = glm::mat4_cast(rotLR*rotUD);
oglContext->rotViewMatrix = glm::mat4_cast(rotUD*rotLR);

Voilà! It works perfectly now. Thank you!

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I was a little surprised to see that you take issue with OpenGL because of legacy support and the API in general. I was reading what you wrote in a thread with someone asking for beginner's advice. Do you think OpenGL is too old to really take full advantage of the graphics resources today's hardware has to offer? I'm sticking with OGL for cross-platform support, but if there were significant potential performance gains from using DX11, I would make a Windows wrapper to support both.

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OpenGL is still a good option. I just recommended DirectX because of an experience I had learning OpenGL. I had been using OpenGL for a few years now. I then learned DirectX11 and by using DirectX I learned that the way I have been using OpenGL was outdated. A few examples of features are constant buffers, samplers, and seperate shader objects. DirectX forced me to use these features since it didn't allow me to do them the old way. OpenGL let me stay in the past, that is all I was saying there.

 

I don't think OpenGL is bad, what you learn using OpenGL will carry over to DirectX, you just need to learn a few API differences.

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All you had to do was create a forward compatible context, HappyCoder.

Some pros and cons:

DX:

* object-oriented

* locked-in (windows, xbox, ...)

* has wonderful tools to help you find problems

* microsoft has reference tools that forces implementations to conform

 

GL:

* C API, with a zillion bindings (meaning you can use absolutely any language you so desire, eg. Python, Java)

* multi-platform

* has had really bad tools and support for a long long time, but that's probably changing now with vogl(?) and co.

* hasn't had reference implementations, but that may change (there's a reference shader compiler now at least)

* has a baggage train from dinosaur era (which you can disable with forward-compatibility)

 

With that said, I still prefer OpenGL. Modern OpenGL has no significant problems. I don't know which is better for beginners. I'm just going to assume DirectX, but that's only if beginners actually use debugging tools.....

Edited by Kaptein

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All you had to do was create a forward compatible context, HappyCoder.
Some pros and cons:
DX:
* object-oriented
* locked-in (windows, xbox, ...)
* has wonderful tools to help you find problems
* microsoft has reference tools that forces implementations to conform
 
GL:
* C API, with a zillion bindings (meaning you can use absolutely any language you so desire, eg. Python, Java)
* multi-platform
* has had really bad tools and support for a long long time, but that's probably changing now with vogl(?) and co.
* hasn't had reference implementations, but that may change (there's a reference shader compiler now at least)
* has a baggage train from dinosaur era (which you can disable with forward-compatibility)
 
With that said, I still prefer OpenGL. Modern OpenGL has no significant problems. I don't know which is better for beginners. I'm just going to assume DirectX, but that's only if beginners actually use debugging tools.....


I have starting doing OpenGL dev only about 6+ months ago and so far it has been OK. Compared to DirectX OpenGL seems easier.

I believe the biggest problem that I face as a new Dev with OpenGL is the huge change OpenGL had a few years ago with modernization (OpenGL 3+)

That left a huge gap between all of the information out there regarding "old" OpenGL and new; in many ways it looks like a whole new language compared to the old stuff.

Once you get the hang of it everything starts getting easier; it seems to me due to OpenGL being the true cross-platform low level graphics API that DirectX's days are numbered.

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I have starting doing OpenGL dev only about 6+ months ago and so far it has been OK. Compared to DirectX OpenGL seems easier.

I believe the biggest problem that I face as a new Dev with OpenGL is the huge change OpenGL had a few years ago with modernization (OpenGL 3+)

That left a huge gap between all of the information out there regarding "old" OpenGL and new; in many ways it looks like a whole new language compared to the old stuff.

Once you get the hang of it everything starts getting easier; it seems to me due to OpenGL being the true cross-platform low level graphics API that DirectX's days are numbered.

 

 

I think I'm almost at the point where I can say I've got the hang of it. It used to drive me crazy how most of the material out there is for legacy OpenGL. I was only able to pave my way in modern OpenGL after finding a very small number of wonderful modern tutorials. I completely agree that OpenGL 3+ looks like a completely different API, it being Object Oriented vs the ugly State Machine in earlier standards.

 

I appreciate all the opinions. I now feel justified in using OpenGL on Windows, and not just using it lazily to make a half-ass port. HappyCoder, thanks for help with the camera.

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