Unexpected behavior when dragging windows to screen's edge

[Luc16]

Version/Branch of Dear ImGui:

Version 1.91.6, Branch: docking

Back-ends:

imgui_impl_glfw.cpp + imgui_impl_opengl3.cpp

Compiler, OS:

Linux + GCC 11.4

Full config/build information:

Dear ImGui 1.91.6 WIP (19151)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=201103
define: __linux__
define: __GNUC__=11
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: imgui_impl_glfw
io.BackendRendererName: imgui_impl_opengl3
io.ConfigFlags: 0x00000483
 NavEnableKeyboard
 NavEnableGamepad
 DockingEnable
 ViewportsEnable
io.ConfigViewportsNoDecoration
io.ConfigNavCaptureKeyboard
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00001C0E
 HasMouseCursors
 HasSetMousePos
 PlatformHasViewports
 HasMouseHoveredViewport
 RendererHasVtxOffset
 RendererHasViewports
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 1280.00,720.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 8.00,8.00
style.WindowBorderSize: 1.00
style.FramePadding: 4.00,3.00
style.FrameRounding: 0.00
style.FrameBorderSize: 0.00
style.ItemSpacing: 8.00,4.00
style.ItemInnerSpacing: 4.00,4.00

Details:

When a window is dragged to an edge of the screen, the position is still updated as if the window was partially outside the screen, but the rendering is clipped. This causes the mouse to be offset when interacting with widgets.

Screenshots/Video:

tela_bug_imgui.mp4

Minimal, Complete and Verifiable Example code:

ImGui::Begin("Image Window");

ImVec2 p = ImGui::GetWindowPos();
ImGui::Text("window pos %.1f %.1f", p.x, p.y);
ImVec2 s = ImGui::GetWindowSize();
ImGui::Text("window size %.1f %.1f", s.x, s.y);

if (ImGui::Button("hover")) {}

ImGui::End();

[GamingMinds-DanielC]

Are you doing something special to restrict the window to remain on the screen, maybe by altering the draw data? Normal behavior should be that the window isn't restricted, and ImGui seems to think that it isn't when processing the inputs.

[ocornut]

This is the main issue we always have with multi-viewports under Linux, e.g. #2117
Our current code always expect our desired size/pos to be successfully applied, which should be fixed.

[BlueMoonHunt]

I am encountering same issue on Linux [fedora 41]. + being unable to control new window after moving them out of the main sometimes.