Introduce the concept of "selection spans" instead of "rects"

[DHowett]

Right now, selections are stored as a set of points (start, end, pivot)
and converted into rectangles based on the contents of the screen buffer
every single render pass.

They are also painted fairly late in the rendering cycle.

This pull request makes a few changes to how selections happen.

Selections are now requested earlier in the rendering pass, during the
creation of the RenderInfo, and stored as a span<point_span>. To
make that span work, the selection data must be durably stored
somewhere.

Therefore, Terminal and conhost now take advantage of their new
generational selection data (#17676) to create and cache arrays of
point_spans covering their selections.

Unlike selection rects, linear (non-box) selections take only a single
entry in the span set. Also unlike selection rects, but like search
highlights, selection spans use buffer coordinates.

In the future, AtlasEngine can use the information sent in during
PrepareRenderInfo to influence text rendering decisions such as the
foreground and background color for a grapheme cluster or the gridlines.

Unfortunately, GDI is stuck with the old selection rendering
implementation and therefore, we still need to produce selection rects
with viewport coordinates and filter them down to the render engine's
dirty region. This is because GDI wants to invert all on-screen
pixels in the selection range after the final render to make sure
sixels, pixels, and lines are all displayed in the appropriate vintage
style.

As part of this change, I've migrated conhost's search highlight to not
read text directly out of the buffer but instead use the new
CopyRequest added by @tusharsnx in #16377.

Many of the tests for conhost behavior had a copy of conhost's code in
them, which sorta begs the question. I migrated them to use hardcoded
expected values to better catch regressions.

In Terminal, the "SelectAfterScroll" ControlCore tests weren't testing
anything they said they were, so I made them do so.

[DHowett]

Leonard said generation 0 would be OK. The first change to selection would set it to 1, and the default state is "no selection".

[carlos-zamora]

Nice work! Love how much simpler it is now 😊

[lhecker]

The only thing I had in mind were things that wouldn't even qualify as nits. 😅 LGTM. ✅

[DHowett]

@carlos-zamora I made your const changes and I'm letting the build spin. I'm surprised Audit mode didn't yell at me for it?

[DHowett]

Diff from before the rebase:

diff --git a/src/host/selectionInput.cpp b/src/host/selectionInput.cpp
index 426214465..d6190a113 100644
--- a/src/host/selectionInput.cpp
+++ b/src/host/selectionInput.cpp
@@ -675,14 +675,14 @@ bool Selection::_HandleColorSelection(const INPUT_KEY_INFO* const pInputKeyInfo)
         if (fShiftPressed)
         {
             // Search the selection and color *that*
-            auto req = TextBuffer::CopyRequest::FromConfig(textBuffer,
-                                                           til::point{ _d->srSelectionRect.left, _d->srSelectionRect.top },
-                                                           til::point{ _d->srSelectionRect.right, _d->srSelectionRect.bottom },
-                                                           true /* multi-line search doesn't make sense; concatenate all lines */,
-                                                           false /* we filtered out block search above */,
-                                                           true /* trim block selection */,
-                                                           true);
-            auto str = textBuffer.GetPlainText(req);
+            const auto req = TextBuffer::CopyRequest::FromConfig(textBuffer,
+                                                                 til::point{ _d->srSelectionRect.left, _d->srSelectionRect.top },
+                                                                 til::point{ _d->srSelectionRect.right, _d->srSelectionRect.bottom },
+                                                                 true /* multi-line search doesn't make sense; concatenate all lines */,
+                                                                 false /* we filtered out block search above */,
+                                                                 true /* trim block selection */,
+                                                                 true);
+            const auto str = textBuffer.GetPlainText(req);
             // Clear the selection and call the search / mark function.
             ClearSelection();
 
diff --git a/src/renderer/base/renderer.cpp b/src/renderer/base/renderer.cpp
index 4b4dcf2ce..33892087e 100644
--- a/src/renderer/base/renderer.cpp
+++ b/src/renderer/base/renderer.cpp
@@ -328,7 +328,7 @@ void Renderer::TriggerSelection()
 try
 {
     const auto spans = _pData->GetSelectionSpans();
-    if (spans.size() != _lastSelectionPaintSize || (spans.size() && _lastSelectionPaintSpan != til::point_span{ spans.front().start, spans.back().end }))
+    if (spans.size() != _lastSelectionPaintSize || (!spans.empty() && _lastSelectionPaintSpan != til::point_span{ spans.front().start, spans.back().end }))
     {
         std::vector<til::rect> newSelectionViewportRects;
 
@@ -338,7 +338,7 @@ try
             _lastSelectionPaintSpan = til::point_span{ spans.front().start, spans.back().end };
 
             const auto& buffer = _pData->GetTextBuffer();
-            auto bufferWidth = buffer.GetSize().Width();
+            const auto bufferWidth = buffer.GetSize().Width();
             const til::rect vp{ _viewport.ToExclusive() };
             for (auto&& sp : spans)
             {
diff --git a/src/renderer/uia/UiaRenderer.cpp b/src/renderer/uia/UiaRenderer.cpp
index 8e5bfb824..155ea792a 100644
--- a/src/renderer/uia/UiaRenderer.cpp
+++ b/src/renderer/uia/UiaRenderer.cpp
@@ -20,7 +20,6 @@ UiaEngine::UiaEngine(IUiaEventDispatcher* dispatcher) :
     _textBufferChanged{ false },
     _cursorChanged{ false },
     _isEnabled{ true },
-    _prevSelection{},
     _prevCursorRegion{},
     RenderEngineBase()
 {
@@ -110,34 +109,13 @@ CATCH_RETURN();
 // - rectangles - One or more rectangles describing character positions on the grid
 // Return Value:
 // - S_OK
-[[nodiscard]] HRESULT UiaEngine::InvalidateSelection(std::span<const til::rect> rectangles) noexcept
-try
+[[nodiscard]] HRESULT UiaEngine::InvalidateSelection(std::span<const til::rect> /*rectangles*/) noexcept
 {
-    // early exit: different number of rows
-    if (_prevSelection.size() != rectangles.size())
-    {
-        _selectionChanged = true;
-        _prevSelection.assign(rectangles.begin(), rectangles.end());
-        return S_OK;
-    }
-
-    _selectionChanged = false; // assume they're the same
-
-    auto i = rectangles.begin();
-    auto j = _prevSelection.begin();
-    // safe to iterate j until i is exhausted because we checked their sizes
-    for (; i != rectangles.end(); ++i, ++j)
-    {
-        if (*i != *j)
-        {
-            _selectionChanged = true;
-            _prevSelection.assign(rectangles.begin(), rectangles.end());
-            break;
-        }
-    }
+    // INVARIANT: Renderer checks the incoming selection spans and only calls InvalidateSelection
+    // if they have actually changed.
+    _selectionChanged = true;
     return S_OK;
 }
-CATCH_LOG_RETURN_HR(E_FAIL);
 
 // Routine Description:
 // - Scrolls the existing dirty region (if it exists) and
diff --git a/src/renderer/uia/UiaRenderer.hpp b/src/renderer/uia/UiaRenderer.hpp
index 8bdeb15f4..c6038751f 100644
--- a/src/renderer/uia/UiaRenderer.hpp
+++ b/src/renderer/uia/UiaRenderer.hpp
@@ -74,7 +74,6 @@ namespace Microsoft::Console::Render
 
         Microsoft::Console::Types::IUiaEventDispatcher* _dispatcher;
 
-        std::vector<til::rect> _prevSelection;
         til::rect _prevCursorRegion;
     };
 }

[DHowett]

I bet the changes to SetViewportPosition have broken the scroll test. Let me re-figure that one.

[DHowett]

Latest push:

commit 492fb1b3744d3615cee7b04403617c49695d562a
Author: Dustin L. Howett <[email protected]>
Date:   Thu Aug 15 12:12:15 2024 -0500

    fixup! terminal: port TerminalSelection to GetSelectionSpans

diff --git a/src/cascadia/UnitTests_TerminalCore/SelectionTest.cpp b/src/cascadia/UnitTests_TerminalCore/SelectionTest.cpp
index 5b21b3e41..11f01c752 100644
--- a/src/cascadia/UnitTests_TerminalCore/SelectionTest.cpp
+++ b/src/cascadia/UnitTests_TerminalCore/SelectionTest.cpp
@@ -259,8 +259,8 @@ namespace TerminalCoreUnitTests
         {
             Terminal term{ Terminal::TestDummyMarker{} };
             DummyRenderer renderer{ &term };
-            til::CoordType scrollbackLines = 5;
-            term.Create({ 100, 100 }, scrollbackLines, renderer);
+            til::CoordType scrollbackLines = 100;
+            term.Create({ 120, 30 }, scrollbackLines, renderer);
 
             const til::CoordType contentScrollLines = 15;
             // Simulate a content-initiated scroll down by 15 lines