Fix resize crash in OpenConsole with AtlasEngine (#13015)

`_api.cellCount` caches the `TextBuffer` size in AtlasEngine.
Calculating it based on the `_api.sizeInPixel` is incorrect as the
`TextBuffer` size doesn't necessarily have to be the size of the window.
This can occur when the window is resized, as the main thread is receiving its
`WM_SIZE` message and resizing the `TextBuffer` concurrently with the render
thread performing a render pass and AtlasEngine checking the `GetClientRect`.

In order to inform `AtlasEngine` about the initial buffer size, `Renderer`
was modified to also invoke `UpdateViewport()` on the first render cycle.

The only other user of `UpdateViewport()` is `VtEngine` which used to call
`InvalidateAll()` in these situations. In order to prevent the `InvalidateAll()`
call, `VtEngine::UpdateViewport()` was modified to suppress this.

## Validation Steps Performed
* Resizing wide characters doesn't crash the terminal anymore ✅
* The additional call to `UpdateViewport()` doesn't break VtEngine ✅

src/renderer/atlas/AtlasEngine.api.cpp

@@ -174,6 +174,9 @@ constexpr HRESULT vec2_narrow(U x, U y, AtlasEngine::vec2<T>& out) noexcept
 
 [[nodiscard]] HRESULT AtlasEngine::UpdateViewport(const SMALL_RECT srNewViewport) noexcept
 {
+    _api.cellCount.x = gsl::narrow_cast<u16>(srNewViewport.Right - srNewViewport.Left + 1);
+    _api.cellCount.y = gsl::narrow_cast<u16>(srNewViewport.Bottom - srNewViewport.Top + 1);
+    WI_SetFlag(_api.invalidations, ApiInvalidations::Size);
     return S_OK;
 }
 
@@ -396,7 +399,6 @@ void AtlasEngine::SetWarningCallback(std::function<void(HRESULT)> pfn) noexcept
     if (_api.sizeInPixel != newSize && newSize != u16x2{})
     {
         _api.sizeInPixel = newSize;
-        _api.cellCount = _api.sizeInPixel / _api.fontMetrics.cellSize;
         WI_SetFlag(_api.invalidations, ApiInvalidations::Size);
     }
 
@@ -536,7 +538,6 @@ void AtlasEngine::_updateFont(const wchar_t* faceName, const FontInfoDesired& fo
 
     if (previousCellSize != _api.fontMetrics.cellSize)
     {
-        _api.cellCount = _api.sizeInPixel / _api.fontMetrics.cellSize;
         WI_SetFlag(_api.invalidations, ApiInvalidations::Size);
     }
 }

src/renderer/base/renderer.cpp

@@ -390,12 +390,13 @@ bool Renderer::_CheckViewportAndScroll()
     const auto srOldViewport = _viewport.ToInclusive();
     const auto srNewViewport = _pData->GetViewport().ToInclusive();
 
-    if (srOldViewport == srNewViewport)
+    if (!_forceUpdateViewport && srOldViewport == srNewViewport)
     {
         return false;
     }
 
     _viewport = Viewport::FromInclusive(srNewViewport);
+    _forceUpdateViewport = false;
 
     COORD coordDelta;
     coordDelta.X = srOldViewport.Left - srNewViewport.Left;

src/renderer/base/renderer.hpp

@@ -123,6 +123,7 @@ namespace Microsoft::Console::Render
         std::vector<SMALL_RECT> _previousSelection;
         std::function<void()> _pfnRendererEnteredErrorState;
         bool _destructing = false;
+        bool _forceUpdateViewport = true;
 
 #ifdef UNIT_TESTING
         friend class ConptyOutputTests;

src/renderer/vt/state.cpp

@@ -246,18 +246,41 @@ CATCH_RETURN();
 [[nodiscard]] HRESULT VtEngine::UpdateViewport(const SMALL_RECT srNewViewport) noexcept
 {
     auto hr = S_OK;
-    const auto oldView = _lastViewport;
     const auto newView = Viewport::FromInclusive(srNewViewport);
+    const auto oldSize = _lastViewport.Dimensions();
+    const auto newSize = newView.Dimensions();
 
-    _lastViewport = newView;
-
-    if ((oldView.Height() != newView.Height()) || (oldView.Width() != newView.Width()))
+    if (oldSize != newSize)
     {
         // Don't emit a resize event if we've requested it be suppressed
         if (!_suppressResizeRepaint)
         {
-            hr = _ResizeWindow(newView.Width(), newView.Height());
+            hr = _ResizeWindow(newSize.X, newSize.Y);
         }
+
+        if (_resizeQuirk)
+        {
+            // GH#3490 - When the viewport width changed, don't do anything extra here.
+            // If the buffer had areas that were invalid due to the resize, then the
+            // buffer will have triggered it's own invalidations for what it knows is
+            // invalid. Previously, we'd invalidate everything if the width changed,
+            // because we couldn't be sure if lines were reflowed.
+            _invalidMap.resize(til::size{ newSize });
+        }
+        else
+        {
+            if (SUCCEEDED(hr))
+            {
+                _invalidMap.resize(til::size{ newSize }, true); // resize while filling in new space with repaint requests.
+
+                // Viewport is smaller now - just update it all.
+                if (oldSize.Y > newSize.Y || oldSize.X > newSize.X)
+                {
+                    hr = InvalidateAll();
+                }
+            }
+        }
+
         _resized = true;
     }
 
@@ -269,29 +292,7 @@ CATCH_RETURN();
     // If we only clear the flag when the new viewport is different, this can
     //      lead to the first _actual_ resize being suppressed.
     _suppressResizeRepaint = false;
-
-    if (_resizeQuirk)
-    {
-        // GH#3490 - When the viewport width changed, don't do anything extra here.
-        // If the buffer had areas that were invalid due to the resize, then the
-        // buffer will have triggered it's own invalidations for what it knows is
-        // invalid. Previously, we'd invalidate everything if the width changed,
-        // because we couldn't be sure if lines were reflowed.
-        _invalidMap.resize(til::size{ newView.Dimensions() });
-    }
-    else
-    {
-        if (SUCCEEDED(hr))
-        {
-            _invalidMap.resize(til::size{ newView.Dimensions() }, true); // resize while filling in new space with repaint requests.
-
-            // Viewport is smaller now - just update it all.
-            if (oldView.Height() > newView.Height() || oldView.Width() > newView.Width())
-            {
-                hr = InvalidateAll();
-            }
-        }
-    }
+    _lastViewport = newView;
 
     return hr;
 }