Method CalcListClipping

KBotExt/imgui/imgui.cpp:2692–2733

Legacy helper to calculate coarse clipping of large list of evenly sized items. This legacy API is not ideal because it assumes we will return a single contiguous rectangle. Prefer using ImGuiListClipper which can returns non-contiguous ranges.

// This legacy API is not ideal because it assumes we will return a single contiguous rectangle.
// Prefer using ImGuiListClipper which can returns non-contiguous ranges.
void ImGui::CalcListClipping(int items_count, float items_height, int* out_items_display_start, int* out_items_display_end)
{
	ImGuiContext& g = *GImGui;
	ImGuiWindow* window = g.CurrentWindow;
	if (g.LogEnabled)
	{
		// If logging is active, do not perform any clipping
		*out_items_display_start = 0;
		*out_items_display_end = items_count;
		return;
	}
	if (GetSkipItemForListClipping())
	{
		*out_items_display_start = *out_items_display_end = 0;
		return;
	}

	// We create the union of the ClipRect and the scoring rect which at worst should be 1 page away from ClipRect
	// We don't include g.NavId's rectangle in there (unless g.NavJustMovedToId is set) because the rectangle enlargement can get costly.
	ImRect rect = window->ClipRect;
	if (g.NavMoveScoringItems)
		rect.Add(g.NavScoringNoClipRect);
	if (g.NavJustMovedToId && window->NavLastIds[0] == g.NavJustMovedToId)
		rect.Add(WindowRectRelToAbs(window, window->NavRectRel[0])); // Could store and use NavJustMovedToRectRel

	const ImVec2 pos = window->DC.CursorPos;
	int start = (int)((rect.Min.y - pos.y) / items_height);
	int end = (int)((rect.Max.y - pos.y) / items_height);

	// When performing a navigation request, ensure we have one item extra in the direction we are moving to
	// FIXME: Verify this works with tabbing
	const bool is_nav_request = (g.NavMoveScoringItems && g.NavWindow && g.NavWindow->RootWindowForNav == window->RootWindowForNav);
	if (is_nav_request && g.NavMoveClipDir == ImGuiDir_Up)
		start--;
	if (is_nav_request && g.NavMoveClipDir == ImGuiDir_Down)
		end++;

	start = ImClamp(start, 0, items_count);
	end = ImClamp(end + 1, start, items_count);
	*out_items_display_start = start;
	*out_items_display_end = end;
}
#endif

static void ImGuiListClipper_SortAndFuseRanges(ImVector<ImGuiListClipperRange>& ranges, int offset = 0)