Transparent windows in a secondary viewport

[fsfuzhu]

Version/Branch of Dear ImGui:

docking

Back-ends:

imgui_impl_dx11.cpp

Compiler, OS:

Windows11 + MSVC2022

Full config/build information:

No response

Details:

• Issue: When dragging an IMGUI window outside of the main application window, the transparency style that is applied within the main window is no longer effective. This causes the window to lose its transparency and revert to an opaque style.
• Reproduction Steps:
  1. Apply a transparency style to the IMGUI window.
  2. Drag the IMGUI window outside of the main application window.
  3. Observe that the transparency style is lost.
• Expected Behavior: The IMGUI window should retain its transparency style even when dragged outside the main application window.
• Actual Behavior: The IMGUI window loses its transparency style and becomes opaque when dragged outside the main application window.
• Attempted Solutions: I have tried updating to the latest version and double-checked the transparency settings, but the issue persists.

Screenshots/Video:

https://github.com/user-attachments/assets/13af910a-6a3b-4f04-ae6d-3d801047a32e

Minimal, Complete and Verifiable Example code:

No response

[GamingMinds-DanielC]

That is not something that can be solved in a general way. Inside of your main viewport you can basically render however you want, but when dragged into a new viewport, a new platform window gets created. Your ImGui window will still be transparent, but it will be transparently rendered on top of whatever is in the back buffer of your platform window (cleared to red in your case). Same as with you main viewport which happens to have a solid background color as well.

You might be able to achieve some transparency on your own if you create transparent platform windows, you can override ImGui::GetPlatformIO().Platform_CreateWindow with your own version for that.

[fsfuzhu]

That is not something that can be solved in a general way. Inside of your main viewport you can basically render however you want, but when dragged into a new viewport, a new platform window gets created. Your ImGui window will still be transparent, but it will be transparently rendered on top of whatever is in the back buffer of your platform window (cleared to red in your case). Same as with you main viewport which happens to have a solid background color as well.

You might be able to achieve some transparency on your own if you create transparent platform windows, you can override ImGui::GetPlatformIO().Platform_CreateWindow with your own version for that.

Sure, thx bro. And could u give me a example for invoking this function? idk how to invoke this, sry

[GamingMinds-DanielC]

It's not a function you invoke yourself, it is a hook for a function that gets called by the library when needed. You just need to replace it with your own version right after initializing the ImGui context. Since you are using DX11, I'm guessing you are using Win32 as a backend as well, so after your call to ImGui_ImplWin32_Init. You have sources for the backends, take a look at ImGui_ImplWin32_CreateWindow (that one is the default for that platform hook) as a reference and build your own based on that.