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Polytonic / Glitter

Dead Simple OpenGL
http://polytonic.github.io/Glitter/
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Troubleshooting steps / Failed to Create OpenGL Context #12

Closed ghost closed 9 years ago

ghost commented 9 years ago

This may be out of scope for this project, but would it be possible to include some troubleshooting steps for those of us who get Failed to Create OpenGL Context instead of a GL window? I'm on an Intel HD4000 chipset right now but I should be able to get some kind of window.

ghost commented 9 years ago

More information in my case. It seems like I get to if (!_glfwIsValidContext(&ctxconfig)) in GLFW and whatever checks are done inside _glfwIsValidContext(&ctxconfig) are failing so I get NULL instead of a context.

For the tutorial itself, maybe some wording about debugging and seeing where the context is failing is appropriate? In my case I've just been single stepping the code in Visual Studio.

ghost commented 9 years ago

Found it. In glfwIsValidContext, two OpenGL contexts are checked against each other and if the version doesn't match, we get NULL.

I'm on Windows 10 on a Lenovo X1 Carbon (3443CTO) ctxconfig = 0x003ef8a8 {api=196609 major=4 minor=1 ...} //the context we're checking window->context = {api=196609 major=4 minor=0 ...} //result of _glfwPlatformGetCurrentContext

Further than that, I don't really understand - maybe someone else can provide more insight.

FWIW, making _glfwIsValidContext return GL_TRUE gets me a grey window, but I have no idea if it's usable / working.

Polytonic commented 9 years ago

Can you try generating an OpenGL 3.3 context instead?

glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);

I don't have an HD 4000 anymore, but I can ask around and try to have someone else reproduce this.

ghost commented 9 years ago 
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);

works, and so does

glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);

Maybe something in the README about dropping the OpenGL version down if you have trouble? Or is there a way to make the "Failed" message spit out the system's supported OpenGL version?

Polytonic commented 9 years ago

@voltagex according to Wikipedia, the Intel HD 4000 only supports OpenGL 4.0 under Windows. Looks like that's what your error messages were saying as well. You'll want:

glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);

I tested this on an HD 4000 in OSX, where 4.1 is available. Should have caught this, sorry about that!

ghost commented 9 years ago

Edit: Similar problems under Linux.

Polytonic commented 9 years ago

This chart says it only runs 3.3 under Linux.

Looks like it's time to roll back to an older GL version or maybe insert more error messages ...

ghost commented 9 years ago

Depends what you expect from your target audience. If this is intended for classrooms where all the machines would have the same version supported, maybe hardcoding 4.0 is OK.

Should I open another issue for something like "Minimum OpenGL requirements"?

Polytonic commented 9 years ago

Fundamentally, GL 3 and GL 4 are pretty similar. They're both within the scope of "Modern OpenGL" though there are a few nice things about 4 that aren't available in 3. 4.0 and 4.1 is miniscule differences, so it's probably safe to drop to 4.0. It'll still create a forward compatible context when possible.

I'm more concerned about users who are on older graphics cards that aren't GL 4 compatible. They are out there, but evidently a lot more are still floating around than I realized, considering this is the second issue raised about this so far.

ghost commented 9 years ago

Setting an error callback could be helpful: http://www.glfw.org/docs/latest/quick.html#quick_capture_error - but in this case, the error message produced is useless. I wonder if that's worth a bug report to GLFW...

Polytonic commented 9 years ago

I want to avoid callbacks as much as possible. This project is used by a significant number of "non-programmers" (art majors, etc. who just want OpenGL to "work"). Ideally the main code should be as short and simple as possible, and should be easy to read without having to go "oh, this is called when an error happens? But why?!"

ghost commented 9 years ago

Fair enough. Thanks for helping me get started.

Polytonic commented 9 years ago

@voltagex sure thing!

I set it to OpenGL 4.0, so you should be able to pull latest and pick up that change.