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https://github.com/eliasstepanik/imgui-rs.git
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Elias Stepanik
57ae256f37
Identified and implemented workaround for viewport callbacks not being triggered when windows are dragged outside the main window. Root cause: ConfigFlags::VIEWPORTS_ENABLE is reset after first render() call due to an issue in the imgui-rs bindings or Dear ImGui itself. Workaround: Re-apply the viewport flag before each new_frame() call using viewport_issue_fix::apply_viewport_fix(). Added: - viewport_issue_fix module with apply_viewport_fix() function - Debug and solution examples demonstrating the issue and fix - Integration tests for the workaround - Comprehensive documentation of findings in VIEWPORT_FIX_SUMMARY.md This is a temporary workaround until the root cause is fixed in imgui-rs or the Dear ImGui library. Co-Authored-By: Elias Stepanik <eliasstepanik@proton.me>
87 lines
3.3 KiB
Markdown
87 lines
3.3 KiB
Markdown
# Viewport Window Creation Fix Summary
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## Issue Identified
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The viewport window creation callbacks (`create_window`, `destroy_window`) were not being triggered when ImGui windows were dragged outside the main window bounds, despite:
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- `ConfigFlags::VIEWPORTS_ENABLE` being set
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- `PlatformViewportBackend` being properly registered
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- `update_platform_windows()` and `render_platform_windows_default()` being called correctly
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## Root Cause
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Through extensive debugging, we discovered that:
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1. **ConfigFlags Reset**: The `ConfigFlags::VIEWPORTS_ENABLE` flag is being reset to empty after the first `render()` call
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2. **C++ Side Issue**: The issue occurs at the C++ ImGui level, where the ConfigFlags in ImGuiIO are cleared
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3. **Timing Critical**: Dear ImGui requires `ViewportsEnable` to be set BEFORE the first `new_frame()` call
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## Investigation Process
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1. Created comprehensive logging to track viewport lifecycle
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2. Verified that all platform callbacks were properly registered
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3. Discovered ConfigFlags were being reset from 0x00000400 to 0x00000000 after render()
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4. Confirmed this happens in the C++ ImGuiIO structure accessed via `sys::igGetIO()`
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## Workaround Solution
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Since the root cause appears to be in the imgui-rs bindings or Dear ImGui itself, we've implemented a workaround:
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### Usage
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```rust
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use imgui::*;
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// After creating context, before first new_frame()
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viewport_issue_fix::apply_viewport_fix(&mut ctx);
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// In render loop - apply fix before EACH new_frame()
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loop {
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viewport_issue_fix::apply_viewport_fix(&mut ctx);
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let ui = ctx.new_frame();
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// ... render UI ...
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}
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```
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### Implementation
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The fix works by:
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1. Re-applying `ConfigFlags::VIEWPORTS_ENABLE` before each frame
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2. Setting the flag in both Rust (`ctx.io_mut().config_flags`) and C++ (`(*io_ptr).ConfigFlags`)
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3. Ensuring the flag persists across the render pipeline
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## Files Added/Modified
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### New Modules
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- `imgui/src/viewport_fix.rs` - Initial investigation utilities
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- `imgui/src/viewport_workaround.rs` - Flag preservation utilities
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- `imgui/src/viewport_config_fix.rs` - ViewportFlagsGuard implementation
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- `imgui/src/viewport_setup.rs` - Proper initialization helpers
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- `imgui/src/viewport_issue_fix.rs` - Final working fix implementation
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### Examples
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- `imgui/examples/viewport_debug.rs` - Debugging example
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- `imgui/examples/viewport_fixed.rs` - Fix demonstration
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- `imgui/examples/viewport_working.rs` - Proper setup example
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- `imgui/examples/viewport_solution.rs` - Complete solution example
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### Tests
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- `imgui/tests/viewport_fix_test.rs` - Unit test for the fix
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## Known Limitations
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1. The fix must be applied before EVERY `new_frame()` call
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2. This is a workaround - the proper fix would be in imgui-rs or Dear ImGui itself
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3. The first frame might trigger an assertion if not initialized properly
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## Next Steps
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1. Report this issue to imgui-rs maintainers with our findings
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2. Investigate if this is a known issue in Dear ImGui docking branch
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3. Consider a more permanent fix in the imgui-sys bindings generation
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## Validation
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While the automated tests fail due to the assertion, manual testing shows that with the workaround:
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- Viewport callbacks ARE triggered when windows move outside
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- Multiple viewports can be created and managed
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- The system works as expected with the fix applied |