Text widget: Use rounded line height to make render output more stable when scrolling vertically

Source/Core/Elements/ElementFormControlTextArea.cpp

@@ -124,7 +124,7 @@ void ElementFormControlTextArea::SetCompositionRange(int range_start, int range_
 bool ElementFormControlTextArea::GetIntrinsicDimensions(Vector2f& dimensions, float& /*ratio*/)
 {
 	dimensions.x = (float)(GetNumColumns() * ElementUtilities::GetStringWidth(this, "m"));
-	dimensions.y = (float)GetNumRows() * GetLineHeight();
+	dimensions.y = (float)GetNumRows() * Math::Round(GetLineHeight());
 
 	return true;
 }

Source/Core/Elements/WidgetTextInput.cpp

@@ -556,10 +556,10 @@ void WidgetTextInput::ProcessEvent(Event& event)
 		case Input::KI_END:     selection_changed = MoveCursorHorizontal(ctrl ? CursorMovement::End : CursorMovement::EndLine, shift, out_of_bounds); break;
 
 		case Input::KI_NUMPAD9: if (numlock) break; //-fallthrough
-		case Input::KI_PRIOR:   selection_changed = MoveCursorVertical(-int(internal_dimensions.y / parent->GetLineHeight()) + 1, shift, out_of_bounds); break;
+		case Input::KI_PRIOR:   selection_changed = MoveCursorVertical(-int(internal_dimensions.y / GetLineHeight()) + 1, shift, out_of_bounds); break;
 
 		case Input::KI_NUMPAD3: if (numlock) break; //-fallthrough
-		case Input::KI_NEXT:    selection_changed = MoveCursorVertical(int(internal_dimensions.y / parent->GetLineHeight()) - 1, shift, out_of_bounds); break;
+		case Input::KI_NEXT:    selection_changed = MoveCursorVertical(int(internal_dimensions.y / GetLineHeight()) - 1, shift, out_of_bounds); break;
 
 		case Input::KI_BACK:
 		{
@@ -1056,8 +1056,7 @@ void WidgetTextInput::SetCursorFromRelativeIndices(int cursor_line_index, int cu
 
 int WidgetTextInput::CalculateLineIndex(float position) const
 {
-	float line_height = parent->GetLineHeight();
-	int line_index = int(position / line_height);
+	int line_index = int(position / GetLineHeight());
 	return Math::Clamp(line_index, 0, (int)(lines.size() - 1));
 }
 
@@ -1239,7 +1238,7 @@ Vector2f WidgetTextInput::FormatText(float height_constraint)
 	selected_text_element->ClearLines();
 
 	// Determine the line-height of the text element.
-	const float line_height = parent->GetLineHeight();
+	const float line_height = GetLineHeight();
 
 	const float half_leading = 0.5f * (line_height - (font_metrics.ascent + font_metrics.descent));
 	const float top_to_baseline = font_metrics.ascent + half_leading;
@@ -1415,7 +1414,7 @@ Vector2f WidgetTextInput::FormatText(float height_constraint)
 void WidgetTextInput::GenerateCursor()
 {
 	cursor_size.x = Math::Round(ElementUtilities::GetDensityIndependentPixelRatio(text_element));
-	cursor_size.y = text_element->GetLineHeight() + 2.0f;
+	cursor_size.y = GetLineHeight() + 2.0f;
 
 	Colourb color = parent->GetComputedValues().color();
 
@@ -1450,7 +1449,7 @@ void WidgetTextInput::UpdateCursorPosition(bool update_ideal_cursor_position)
 
 	cursor_position = {
 		(float)string_width_pre_cursor + alignment_offset,
-		-1.f + (float)cursor_line_index * text_element->GetLineHeight(),
+		-1.f + (float)cursor_line_index * GetLineHeight(),
 	};
 
 	const bool word_wrap = parent->GetComputedValues().white_space() == Style::WhiteSpace::Prewrap;
@@ -1584,6 +1583,11 @@ void WidgetTextInput::SetKeyboardActive(bool active)
 	}
 }
 
+float WidgetTextInput::GetLineHeight() const
+{
+	return Math::Round(parent->GetLineHeight());
+}
+
 float WidgetTextInput::GetAvailableWidth() const
 {
 	return parent->GetClientWidth() - parent->GetBox().GetFrameSize(BoxArea::Padding).x;

Source/Core/Elements/WidgetTextInput.h

@@ -234,6 +234,8 @@ private:
 	/// Returns the offset that aligns the contents of the line according to the 'text-align' property.
 	float GetAlignmentSpecificTextOffset(const Line& line) const;
 
+	/// Returns the used line height.
+	float GetLineHeight() const;
 	/// Returns the width available for the text contents without overflowing, that is, the content area subtracted by any scrollbar.
 	float GetAvailableWidth() const;
 	/// Returns the height available for the text contents without overflowing, that is, the content area subtracted by any scrollbar.