Rewrite HwndTerminal to build on ControlInteractivity and -Core by DHowett · Pull Request #20812 · microsoft/terminal

Dustin L. Howett (DHowett) · 2026-10-16T20:01:45Z

This pull request replaces all of HwndTerminal, which used to be a thin layer on top of TerminalCore.lib, with a new implementation that relies on the Interactivity and Core layers in TerminalControl.lib.

We used to spend a lot of time reimplementing interactivity components for HwndTerminal or--if I'm being honest--letting it rot and never giving it the improvements the rest of the application got.

Among those improvements:

Automatic scrolling finally works (as of Move AutoScroll down into Interactivity with a render timer #20710)
Selection works the same way as it does in Terminal proper (starts on the half-cell, uses an exclusive range)
Consistent double- and triple-click behavior without having to reimplement word- and line-wise expansion
Scroll wheel behavior
Shift+Click to suppress VT mouse mode
Ctrl+Scroll zoom
Scrolling and focus handling move down into the Win32 message loop from WPF

This pull request seeks to get HwndTerminal back to where it was (plus the things we naturally get from switching over). In the future, we can more easily add:

title reporting (surprised we didn't have this)
clickable URLs
automatic copy-to-clipboard
right-click menu support
DTTERM window manipulation
shaders

Implementation Details

The WPF control is backed by a flat "C" API, which takes in a void* and does some stuff to it. We call that a PTERM. References to "Flat C" in this commit body describe the body of work below WPF.

X-macros are used to fill out the definintions of every C API and bridge it to a properly typed C++ member function. Ugh. No more crap where we split the implementation into half C export and half C++ member.

ControlCore and ControlInteractivity require something that looks like TerminalSettings. The WPF control only supports the most basic settings, in struct TerminalTheme, and so I've added a bridge WinRT type to adapt TerminalTheme to
IXxxSettings. Most of the values it returns are our "defaults", and some of them are overridden.

Core requires an ITerminalConnection, but the WPF API uses a pair of "write output" and "send input" callbacks. Flat C provides an ITerminalConnection that bridges those callbacks. It does not communicate connection state or anything
else. Resizing is probably going to be a problem.

Core requires a dispatcher queue to ensure that some operations happen on the UI thread. I have stubbed out an implementation of IDispatcherQueue that calls a couple function pointers with a context pointer; the WPF code hooks up to that
and bridges it into the WPF dispatcher. Yes, the Core's dispatcher queue is the WPF main UI thread. It has to be, otherwise we'll explode the first time we try to update the scroll bar. Prep work was done in #20713.

To make the above easier, I removed all use of DispatcherTimer (see #20711). Attempts to use it will almost certainly cause the WPF control to implode.

Core needed to be taught a couple tricks to start up targeting an HWND instead of a composition handle. See #20722 for more.

Refs #20710
Refs #20711
Refs #20713
Refs #20722

Required #20721
Refs #20745

Related to #6999

github-advanced-security

check-spelling found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

Dustin L. Howett (DHowett)

I recommend a...

git diff --color-moved=dimmed-zebra --color-moved-ws=ignore-all-space (git merge-base origin/dev/duhowett/win7-wpf-termcontrol-squash origin/main) origin/dev/duhowett/win7-wpf-termcontrol-squash

it'll show you what is copied (gray) and what has been rewritten (red, green)

I wonder if I should rename FlatC to HwndTerminal and really make a mess of the diff.

Dustin L. Howett (DHowett) · 2026-10-16T20:02:15Z

    <RootNamespace>Microsoft.Terminal.Wpf</RootNamespace>
    <AssemblyName>Microsoft.Terminal.Wpf</AssemblyName>
    <UseWpf>true</UseWpf>
+    <LangVersion>9.0</LangVersion>


yeah I used some fancy operators

Dustin L. Howett (DHowett) · 2026-10-16T20:03:10Z

+#undef GENERATOR_N
+#undef API_NAME
+
+__declspec(dllexport) HRESULT __stdcall CreateTerminal(HWND parentHwnd, TerminalDispatcherCallouts dispatcherCallouts, _Out_ void** hwnd, _Out_ PTERM* terminal);


THIS FILE IS NOT INTENDED FOR PUBLICATION AND IS AN IMPLEMENTATION DETAIL FOR NOW

The idea is that if we DO add a flat C API, we could generate it using these macros. This just makes my life easier.

This pull request replaces all of HwndTerminal, which used to be a thin layer on top of TerminalCore.lib, with a new implementation that relies on the Interactivity and Core layers in TerminalControl.lib. We used to spend a lot of time reimplementing interactivity components for HwndTerminal or--if I'm being honest--letting it rot and never giving it the improvements the rest of the application got. Among those improvements: - Automatic scrolling finally works (as of #20710) - Selection works the same way as it does in Terminal proper (starts on the half-cell, uses an exclusive range) - Consistent double- and triple-click behavior without having to reimplement word- and line-wise expansion - Scroll wheel behavior - Shift+Click to suppress VT mouse mode - Ctrl+Scroll zoom This pull request seeks to get HwndTerminal back to where it was (plus the things we naturally get from switching over). In the future, we can more easily add: - title reporting (surprised we didn't have this) - clickable URLs - automatic copy-to-clipboard - right-click menu support - DTTERM window manipulation - shaders Implementation Details ---------------------- The WPF control is backed by a flat "C" API, which takes in a `void*` and does some stuff to it. We call that a `PTERM`. References to "Flat C" in this commit body describe the body of work below WPF. X-macros are used to fill out the definintions of every C API and bridge it to a properly typed C++ member function. Ugh. No more crap where we split the implementation into half C export and half C++ member. ControlCore and ControlInteractivity require something that looks like TerminalSettings. The WPF control only supports the most basic settings, in `struct TerminalTheme`, and so I've added a bridge WinRT type to adapt TerminalTheme to IXxxSettings. Most of the values it returns are our "defaults", and some of them are overridden. Core requires an `ITerminalConnection`, but the WPF API uses a pair of "write output" and "send input" callbacks. Flat C provides an ITerminalConnection that bridges those callbacks. It does not communicate connection state or anything else. Resizing is probably going to be a problem. Core requires a dispatcher queue to ensure that some operations happen on the UI thread. I have stubbed out an implementation of `IDispatcherQueue` that calls a couple function pointers with a context pointer; the WPF code hooks up to that and bridges it into the WPF dispatcher. Yes, the Core's dispatcher queue _is_ the WPF main UI thread. It has to be, otherwise we'll explode the first time we try to update the scroll bar. Prep work was done in #20713. To make the above easier, I removed all use of DispatcherTimer (see #20711). Attempts to use it will almost certainly cause the WPF control to implode. Core needed to be taught a couple tricks to start up targeting an HWND instead of a composition handle. See #20722 for more. Refs #20710 Refs #20711 Refs #20713 Refs #20722 Related to #6999

Dustin L. Howett (DHowett) · 2026-10-19T22:59:27Z

/cc Javier (@javierdlg) it is finally here

Leonard Hecker (lhecker)

Typing literally lags by up to 5s while in the diff view.

GitHub, this is the most awful experience imaginable and it's been going even further downhill for years.

If you were to make a graph of website performance, it would be a vertical line through the floor. That takes some special talent.

Leonard Hecker (lhecker) · 2026-10-20T11:26:49Z

+        auto scrollbarSize = GetSystemMetrics(SM_CXVSCROLL);
+        scrollbarSize = gsl::narrow_cast<decltype(scrollbarSize)>(scrollbarSize * (dpi / 96));


Eh?

And also: scrollbarSize * (dpi / 96) = integer scale only.

Leonard Hecker (lhecker) · 2026-10-20T11:28:25Z

+  TerminalTriggerResize
+  TerminalTriggerResizeWithDimension


SCHOCKSCHWERENOT! AN UNSORTED LIST!

Leonard Hecker (lhecker) · 2026-10-20T11:30:19Z

+typedef void(__stdcall* PSCROLLCB)(int, int, int);
+typedef void(__stdcall* PWRITECB)(const wchar_t*);


Weird names with no param names?

BTW C# does not support strings with lengths huh? (For PWRITECB.)

Leonard Hecker (lhecker) · 2026-10-20T11:31:03Z

+    bool(__stdcall* pDispatcherTryEnqueueWork)(void*, int, void*);
+    bool(__stdcall* pDispatcherHasThreadAccess)(void*);


Why p prefix? If anything, it should be fn or pfn, right?

Leonard Hecker (lhecker) · 2026-10-20T11:31:55Z

+} TerminalDispatcherCallouts;
+
+#define TERMINAL_API_TABLE(XX)                                                                                 \
+    XX(SendOutput, LPCWSTR, data)                                                                              \


I cannot discern an order of these functions, but I think it could be sorted.

Leonard Hecker (lhecker) · 2026-10-20T11:58:25Z

+                0, // Mouse
+                MouseButtonStateFromWParam(wParam),
+                uMsg,
+                std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count(),


We use std::chrono::microseconds throughout ControlCore for timings? What the heck, that completely went by me!

And why system_clock? It should be steady_clock I'm pretty sure. And we should pass std::chrono::steady_clock::time_point or we migrate over to double and seconds, which would be good for the next 2000 years.

Leonard Hecker (lhecker) · 2026-10-20T12:02:37Z

+                0,
+                term_window_class,
+                nullptr,
+                WS_CHILD | WS_CLIPCHILDREN | WS_CLIPSIBLINGS | WS_VISIBLE,


Why all these flags? We're a swap chain so we aren't subject to GDI in the first place, aren't we?

Leonard Hecker (lhecker) · 2026-10-20T12:03:49Z

+        wil::assign_to_opt_param(dimensions, til::size{
+                                                 static_cast<til::CoordType>(width / fontSizeInPx.Width),
+                                                 static_cast<til::CoordType>(height / fontSizeInPx.Height),
+                                             });


Odd indentation.

Leonard Hecker (lhecker) · 2026-10-20T12:09:02Z

+        auto concatenated = std::accumulate(std::begin(strings), std::end(strings), std::wstring{}, [](auto&& l, auto&& r) {
+            return l + r;
+        });


That's an odd way to copy a hstring into a wstring. :D
It's also not needed, because make_cotaskmem_string_nothrow takes a hstring.c_str() anyway.

Leonard Hecker (lhecker) · 2026-10-20T12:10:30Z

+    bool _initialized{ false };
+    bool _focused{ false };


Unfortunate struct order?

Dustin L. Howett (DHowett) added this pull request to stack #20813 October 16, 2026 20:01

github-advanced-security Bot found potential problems Oct 16, 2026

View reviewed changes

This comment has been minimized.

Sign in to view

Dustin L. Howett (DHowett) commented Oct 16, 2026

View reviewed changes

Dustin L. Howett (DHowett) force-pushed the dev/duhowett/win7-wpf-termcontrol-squash branch 3 times, most recently from dcf463d to 4f3012e Compare October 16, 2026 20:29

This comment has been minimized.

Sign in to view

Dustin L. Howett (DHowett) force-pushed the dev/duhowett/win7-wpf-termcontrol-squash branch from 4f3012e to 8f9cd1e Compare October 16, 2026 20:34

Dustin L. Howett (DHowett) removed this pull request from stack #20813 October 19, 2026 15:25

Base automatically changed from dev/duhowett/scoped-no-resources to main October 19, 2026 16:32

Dustin L. Howett (DHowett) force-pushed the dev/duhowett/win7-wpf-termcontrol-squash branch from 8f9cd1e to 0591c34 Compare October 19, 2026 16:34

github-advanced-security Bot found potential problems Oct 19, 2026

View reviewed changes

This comment has been minimized.

Sign in to view

Dustin L. Howett (DHowett) changed the title ~~WIP: Replace HwndTerminal with HwndTerminal v2 (harder better faster stronger)~~ Rewrite HwndTerminal to build on ControlInteractivity and -Core Oct 19, 2026

Dustin L. Howett (DHowett) added 8 commits October 19, 2026 17:05

ControlCore: Add some support methods for HWND boot

5ef9462

Replace HwndTerminal with FlatC

4ef8a79

FlatC: add a11y and TSF

d77e9b2

spelling

a652288

Revert some of the spelling fixes which broke the code in other ways

df7d5ce

spell: use the real types

cde7432

Slightly better namespacing to fix spell issues

a4cbab2

Dustin L. Howett (DHowett) force-pushed the dev/duhowett/win7-wpf-termcontrol-squash branch from 3bdc1e8 to 86b388c Compare October 19, 2026 22:05

Ah, well

29e424f

Leonard Hecker (lhecker) reviewed Oct 20, 2026

View reviewed changes

		auto scrollbarSize = GetSystemMetrics(SM_CXVSCROLL);
		scrollbarSize = gsl::narrow_cast<decltype(scrollbarSize)>(scrollbarSize * (dpi / 96));

		typedef void(__stdcall* PSCROLLCB)(int, int, int);
		typedef void(__stdcall* PWRITECB)(const wchar_t*);

		bool(__stdcall* pDispatcherTryEnqueueWork)(void, int, void);
		bool(__stdcall* pDispatcherHasThreadAccess)(void*);

Conversation

Dustin L. Howett (DHowett) commented Oct 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Implementation Details

Uh oh!

github-advanced-security AI left a comment

Choose a reason for hiding this comment

Uh oh!

This comment has been minimized.

Dustin L. Howett (DHowett) left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

This comment has been minimized.

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

This comment has been minimized.

Dustin L. Howett (DHowett) commented Oct 19, 2026

Uh oh!

Leonard Hecker (lhecker) left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Dustin L. Howett (DHowett) commented Oct 16, 2026 •

edited

Loading

Leonard Hecker (lhecker) left a comment •

edited

Loading