Add native winapi OpenGL2 example

[learn-more]

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Mashed together DirectX9 + glfw opengl2 into a new example that runs on Winapi + OpenGL2 Built on Visual studio 2017, win10, docking branch.

Platform windows work:

Project downgraded to use the same platform toolset as the rest.

[learn-more]

@ocornut is there something you want me to change on this, or add? I tried to modify no other code, but the change in imgui_impl_win32.cpp was required to get this working.

[learn-more]

Rebased on the new docking branch, corrected paths in the .bat and project files for the new backends layout.

[ocornut]

Sorry for the late answer.... I'm digging through the many PR attempting this and every one of them has issue. But this solution here seems particularly simple and elegant, can you explain why/how this is much simpler than #6086 ?

Would it make sense to add a ImGui_ImplWin32_InitForOpenGL(void* hwnd); function? Would this work with the imgui_impl_opengl3.cpp example?

[learn-more]

I don't see this being simpler than #6086, but this did have platform windows working.

The reason why there was not a lot of new coded added, was because the opengl2 backend did already bring everything that was needed, and the win32 platform was almost compatible. (It just needed a modification so it owns the DC.)

[learn-more]

@ocornut do you want me to fix the merge conflict here, or are you going to move forward with another PR?

[ocornut]

Hello,

Your PR seems simpler as it requires much less involvement from imgui_impl_win32, which is better.

The question is will it work with the opengl3 backend? If you can spare some work to confirm that it works with opengl3 backend I would be interested in that.

I don't think it will conflict much so probably easy to fix conflicts.

May I suggest to change:

IMGUI_IMPL_API bool ImGui_ImplWin32_Init(void* hwnd, bool platformHasOwnDC = false);

to

IMGUI_IMPL_API bool ImGui_ImplWin32_Init(void* hwnd);
IMGUI_IMPL_API bool ImGui_ImplWin32_InitForOpenGL(void* hwnd);

[learn-more]

@ocornut I have changed the code to use ImGui_ImplWin32_InitForOpenGL in the header. Also added the same example, ported for OpenGL3 (just changed all 2 to 3 in the code seems to work fine).

[ocornut]

Apologies in previous messages I referred to #6086 which is not viewports-compliant. I actually meant to compare your PR to #5170

[ocornut]

While experimenting I noticed that the example worked even when calling ImGui_ImplWin32_Init() instead of ImGui_ImplWin32_InitForOpenGL().

Can you clarify why you said CS_OWNDC is needed?

Things works well here and although this is putting a little more responsibility on user app, I think the complexity trade-off is well worth it and this may be the best solution to this problem.

[learn-more]

Khronos specifies it: https://www.khronos.org/opengl/wiki/Creating_an_OpenGL_Context_(WGL)#The_Window_Itself

This StackOverflow post goes into some detail: https://stackoverflow.com/a/48670747/4928207

In OpenGL you need a context, which is attached with a DC. This means that the DC must exist while the context exists. Thus, you do need CS_OWNDC style for the window where OpenGL draws. Call ReleaseDC after you have deleted the context.

[ocornut]

I went through this and merged, was a little bit tedious as had to split this but it's now done.

• a566ecc your commit but only the parts applicable to master.
• 9308cfd my amends but only the parts applicable to master.
• 4f692ba merge
• 4bc51c6 remaining parts of your commit applicable to multi-viewports
• f498f08 remaining parts of my amends

Closing... 🥁 🥁 🥁 🥁 🥁 #3218 yours, was initially for GL2 and docking only #5170 was missing example app (incl main viewport creation) + lots of GL specific code in win32 backend #6086 no multi-viewport support (hence simpler but incomplete), GL2. #2772 GL3 specific code in win32 + hardcoded the whole thing for GL only #2600 not a PR per-se but had lots of discussions. #2359 no multi-viewport support, GL2. #2022 no multi-viewport support, GL3. #1553 no multi-viewport support, GL3.

Your solution won, but I'm assuming we may need to revisit something and I honestly worry this "low-level" example may attract issues so I am explicitly NOT recommending people using it, best to stick to SDL or GLFW for OpenGL. We'll see.

Thanks a lot!

[wrightwriter]

Anything specific you need to do on core context creation to get this working? I'm getting black viewport windows, and i'm 1:1 following the example code. I assume something must be wrong with my core context creation. No OpenGL errors.

Here's the code if anyone has an idea 🤷‍♂️ https://gist.github.com/wrightwriter/4666c989eadba9b8932bf632b01b00f1