User reported the chat input field disappearing when the chat
window was resized smaller — older entries pushed it past the
visible area. Standard ImGui chat-window pattern fixes it: scrollable
nested region for the chat tail, fixed footer for the
separator + input field below it.
IPanelRenderer extensions (Phase J Tier 3):
- BeginChild(string id, Vector2 size, bool border = false) — opens
a nested scrollable region. Size follows ImGui semantics:
0 = fill available, negative = fill available minus this much.
- EndChild() — closes the nested region.
- FrameHeightWithSpacing() — single-line widget height incl. frame
padding + item spacing. Lets panels compute footer reservations
without hardcoding pixel constants.
- SetScrollHereY(float ratio) — forces scroll within current region;
pass 1.0f to keep the latest line visible after new entries
arrive.
ImGuiPanelRenderer impls. ImGui.NET's BeginChild signature changed
across versions (third arg moved from `bool border` to
`ImGuiChildFlags`); we cast a numeric literal (0x01 = Border bit)
to sidestep the rename. FrameHeightWithSpacing maps to
ImGui.GetFrameHeightWithSpacing(); SetScrollHereY to ImGui.SetScrollHereY.
ChatPanel restructured:
- Reserves footer height = FrameHeightWithSpacing() + 6f (small pad
for the separator above the input).
- Wraps the chat tail in BeginChild("##chattail", (0, -footer))
so the inner region scrolls independently of the window.
- Tracks _lastRenderedCount across frames and calls SetScrollHereY(1f)
only when new entries appended — manual scroll-up isn't fought
against; new messages jump the view back down only when they
actually arrive.
- Header Separator removed (the BeginChild border is enough).
FakePanelRenderer extended with the four new methods + recording.
4 new tests in ChatPanelLayoutTests pin the layout invariants:
- Render order: Begin → BeginChild → ... → EndChild → Separator
→ InputTextSubmit → End.
- BeginChild size has X=0 + negative Y at least matching the
injected FrameHeightWithSpacingValue.
- SetScrollHereY fires when entries grow.
- SetScrollHereY does NOT fire when entries don't grow.
Solution total: 1067 green (243 Core.Net + 164 UI + 660 Core),
0 warnings.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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