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Scrollbar: stabilize visibility of ScrollbarX when detecting a feedback loop. (#8488, #3285, #4539)

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ocornut 2025-03-12 14:15:51 +01:00
parent 6e30c42101
commit d9dad2f4a1
3 changed files with 28 additions and 3 deletions
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14
imgui.cpp
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@ -7456,9 +7456,23 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
ImVec2 needed_size_from_last_frame = window_just_created ? ImVec2(0, 0) : window->ContentSize + window->WindowPadding * 2.0f;
float size_x_for_scrollbars = use_current_size_for_scrollbar_x ? avail_size_from_current_frame.x : avail_size_from_last_frame.x;
float size_y_for_scrollbars = use_current_size_for_scrollbar_y ? avail_size_from_current_frame.y : avail_size_from_last_frame.y;
bool scrollbar_x_prev = window->ScrollbarX;
//bool scrollbar_y_from_last_frame = window->ScrollbarY; // FIXME: May want to use that in the ScrollbarX expression? How many pros vs cons?
window->ScrollbarY = (flags & ImGuiWindowFlags_AlwaysVerticalScrollbar) || ((needed_size_from_last_frame.y > size_y_for_scrollbars) && !(flags & ImGuiWindowFlags_NoScrollbar));
window->ScrollbarX = (flags & ImGuiWindowFlags_AlwaysHorizontalScrollbar) || ((needed_size_from_last_frame.x > size_x_for_scrollbars - (window->ScrollbarY ? style.ScrollbarSize : 0.0f)) && !(flags & ImGuiWindowFlags_NoScrollbar) && (flags & ImGuiWindowFlags_HorizontalScrollbar));
// Track when ScrollbarX visibility keeps toggling, which is a sign of a feedback loop, and stabilize by enforcing visibility (#3285, #8488)
// (Feedback loops of this sort can manifest in various situations, but combining horizontal + vertical scrollbar + using a clipper with varying width items is one frequent cause.
// The better solution is to, either (1) enforce visibility by using ImGuiWindowFlags_AlwaysHorizontalScrollbar or (2) declare stable contents width with SetNextWindowContentSize(), if you can compute it)
window->ScrollbarXStabilizeToggledHistory <<= 1;
window->ScrollbarXStabilizeToggledHistory |= (scrollbar_x_prev != window->ScrollbarX) ? 0x01 : 0x00;
const bool scrollbar_x_stabilize = (window->ScrollbarXStabilizeToggledHistory != 0) && ImCountSetBits(window->ScrollbarXStabilizeToggledHistory) >= 4; // 4 == half of bits in our U8 history.
if (scrollbar_x_stabilize)
window->ScrollbarX = true;
//if (scrollbar_x_stabilize && !window->ScrollbarXStabilizeEnabled)
// IMGUI_DEBUG_LOG("[scroll] Stabilize ScrollbarX for Window '%s'\n", window->Name);
window->ScrollbarXStabilizeEnabled = scrollbar_x_stabilize;
if (window->ScrollbarX && !window->ScrollbarY)
window->ScrollbarY = (needed_size_from_last_frame.y > size_y_for_scrollbars - style.ScrollbarSize) && !(flags & ImGuiWindowFlags_NoScrollbar);
window->ScrollbarSizes = ImVec2(window->ScrollbarY ? style.ScrollbarSize : 0.0f, window->ScrollbarX ? style.ScrollbarSize : 0.0f);