Conhost window is not refreshed after software scroll

[alabuzhev]

Windows Terminal version

1.18.1462.0

Windows build number

10.0.19045.3324

Other Software

No response

Steps to reproduce

1. Compile the code:

#include <iostream>
#include <stdexcept>
#include <string>

#include <windows.h>

void scroll(bool page, bool up)
{
	const auto out = GetStdHandle(STD_OUTPUT_HANDLE);
	CONSOLE_SCREEN_BUFFER_INFO csbi;
	if (!GetConsoleScreenBufferInfo(out, &csbi))
		throw std::runtime_error("GetConsoleScreenBufferInfo");

	if (up && !csbi.srWindow.Top)
		return;

	if (!up && csbi.srWindow.Bottom == csbi.dwSize.Y - 1)
		return;

	auto lines = page?
		csbi.srWindow.Bottom - csbi.srWindow.Top + 1:
		1;

	if (up)
		lines = -lines;

	csbi.srWindow.Top += lines;
	csbi.srWindow.Bottom += lines;

	if (csbi.srWindow.Top < 0)
	{
		csbi.srWindow.Bottom -= csbi.srWindow.Top;
		csbi.srWindow.Top = 0;
	}

	if (csbi.srWindow.Bottom >= csbi.dwSize.Y)
	{
		csbi.srWindow.Top -= (csbi.srWindow.Bottom - (csbi.dwSize.Y - 1));
		csbi.srWindow.Bottom = csbi.dwSize.Y - 1;
	}

	if (!SetConsoleWindowInfo(out, true, &csbi.srWindow))
		throw std::runtime_error("SetConsoleWindowInfo");
}

void run()
{
	const auto width = 80, height = 25;
	const auto screens = 5;
	const auto out = GetStdHandle(STD_OUTPUT_HANDLE);
	const SMALL_RECT Window{ 0, 0, width - 1, height - 1 };
	SetConsoleWindowInfo(out, true, &Window);
	SetConsoleScreenBufferSize(out, { width, height * screens });

	for (size_t i = 0; i != height * screens - 1; ++i)
	{
		const auto data = L"Line " + std::to_wstring(i) + L"\n";
		DWORD n;
		WriteConsole(out, data.data(), static_cast<DWORD>(data.size()), &n, {});
	}

	const auto in = GetStdHandle(STD_INPUT_HANDLE);
	for (;;)
	{
		INPUT_RECORD r;
		DWORD n;
		if (!ReadConsoleInput(in, &r, 1, &n))
			break;

		if (r.EventType != KEY_EVENT || !r.Event.KeyEvent.bKeyDown)
			continue;

		switch (const auto key = r.Event.KeyEvent.wVirtualKeyCode)
		{
		case VK_UP:
		case VK_DOWN:
		case VK_NEXT:
		case VK_PRIOR:
			scroll(key == VK_NEXT || key == VK_PRIOR, key == VK_UP || key == VK_PRIOR);
		}
	}
}

int main()
{
	try
	{
		run();
	}
	catch(const std::exception& e)
	{
		std::cerr << e.what();
	}
}

2. Run it with the latest published OpenConsole, e.g. from WT 1.18.1462.
3. Press Up and Down a few times.
4. Press PgUp and PgDn a few times.

Expected Behavior

The viewport moves up or down, line by line or page by page.

Actual Behavior

Pressing Up or Down works as expected.
Pressing PgUp or PgDown doesn't.

When PgUp/PgDown are pressed, the scrollbar on the right moves appropriately, indicating that the viewport has moved, but the window is not refreshed and shows the very same content.

The issue occurs only if the number of lines to scroll is >= window height.

The original issue is described here:
FarGroup/FarManager#727
According to the comments, the default conhost in Windows 11 is also affected to some extent.

[zadjii-msft]

• This isn't SetConsoleWindowInfo doesn't scroll visible region in Terminal #10191, because that's conpty specific.
• Kinda the inverse of [Product-Conhost] Scrollbar issue using SetConsoleWindowInfo() #6659. In that one the contents update but the scrollbar doesn't. This is the opposite
• It's not conhost: SetConsoleWindowInfo broken when used in alternate screen buffer #13741 - that's alt-buffer specific
• @lhecker believes this is probably the same root cause as OpenConsole: Duplicate output lines when connecting to Ubuntu via SSH #15769 - he'll bisect it

[lhecker]

FYI #15769 will be closed by #15935, but that's just because I'm effectively working around this bug. The timing of you filing this issue is great, because it just made me realize that the cause for #15769 is not SSH's handling of SIGWINCH directly, but rather SetConsoleWindowInfo itself.

[lhecker]

This regression was caused by 81b7e54. Reverting it has no or negligible impact on performance at this point, likely due to the overall vastly better performance of conhost nowadays.