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Drag and Drop: Added a mechanism to allow widgets with no identifiers (such as Text/Image) to be used with BeginDragDropSource() given the explicit ImGuiDragDropFlags_SourceAllowNullID flag.

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This commit is contained in:
omar 2017-10-29 23:10:44 +01:00
parent acf78da742
commit 0e775807b4
3 changed files with 46 additions and 2 deletions
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46
imgui.cpp
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@ -1860,6 +1860,16 @@ ImGuiID ImGuiWindow::GetIDNoKeepAlive(const char* str, const char* str_end)
return ImHash(str, str_end ? (int)(str_end - str) : 0, seed);
}
// This is particularly dodgy and used in extremely rare situation.
ImGuiID ImGuiWindow::GetIDFromRectangle(const ImRect& r_abs)
{
ImGuiID seed = IDStack.back();
const int r_rel[4] = { (int)(r_abs.Min.x - Pos.x), (int)(r_abs.Min.y - Pos.y), (int)(r_abs.Max.x - Pos.x), (int)(r_abs.Max.y - Pos.y) };
ImGuiID id = ImHash(&r_rel, sizeof(r_rel), seed);
ImGui::KeepAliveID(id);
return id;
}
//-----------------------------------------------------------------------------
// Internal API exposed in imgui_internal.h
//-----------------------------------------------------------------------------
@ -10606,16 +10616,48 @@ bool ImGui::BeginDragDropSource(ImGuiDragDropFlags flags, int mouse_button)
ImGuiWindow* window = g.CurrentWindow;
if (g.IO.MouseDown[mouse_button] == false)
return false;
if (g.ActiveId != window->DC.LastItemId)
ImGuiID id = window->DC.LastItemId;
if (id == 0)
{
// If you want to use BeginDragDropSource() on an item with no unique identifier for interaction, such as Text() or Image(), you need to:
// A) Read the explanation below, B) Use the ImGuiDragDropFlags_SourceAllowNullID flag, C) Swallow your programmer pride.
if (!(flags & ImGuiDragDropFlags_SourceAllowNullID))
{
IM_ASSERT(0);
return false;
}
// Magic fallback (=somehow reprehensible) to handle items with no assigned ID, e.g. Text(), Image().
// We build a throwaway ID based on current ID stack + relative AABB of items in window.
// THE IDENTIFIER WON'T SURVIVE ANY REPOSITIONING OF THE WIDGET, so if your widget moves your dragging operation will be canceled.
// If you want fail-proof dragging,
// We don't need to maintain/call ClearActiveID() as releasing the button will early out this function and trigger !ActiveIdIsAlive.
bool is_hovered = window->DC.LastItemRectHoveredRect;
if (!is_hovered && (g.ActiveId == 0 || g.ActiveIdWindow != window))
return false;
id = window->DC.LastItemId = window->GetIDFromRectangle(window->DC.LastItemRect);
if (is_hovered)
SetHoveredID(id);
if (is_hovered && g.IO.MouseClicked[mouse_button])
{
SetActiveID(id, window);
FocusWindow(window);
}
if (g.ActiveId == id) // Allow the underlying widget to display/return hovered during the mouse release frame, else we would get a flicker.
g.ActiveIdAllowOverlap = is_hovered;
}
if (g.ActiveId != id)
return false;
if (IsMouseDragging(mouse_button))
{
if (!g.DragDropActive)
{
IM_ASSERT(id != 0);
ImGuiPayload& payload = g.DragDropPayload;
payload.Clear();
payload.SourceId = g.ActiveId;
payload.SourceId = id;
payload.SourceParentId = window->IDStack.back();
g.DragDropActive = true;
g.DragDropSourceFlags = flags;

1
imgui.h
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@ -599,6 +599,7 @@ enum ImGuiDragDropFlags_
// BeginDragDropSource() flags
ImGuiDragDropFlags_SourceNoAutoTooltip = 1 << 0,
ImGuiDragDropFlags_SourceNoDisableHover = 1 << 1, // By default, when dragging we clear data so that IsItemHovered() will return true, to avoid subsequent user code submitting tooltips.
ImGuiDragDropFlags_SourceAllowNullID = 1 << 2, // Allow items such as Text(), Image() that have no unique identifier to be used as drag source, by manufacturing a temporary identifier based on their window-relative position. This is extremely unusual within the dear imgui ecosystem and so we made it explicit.
// BeginDragDropTarget() flags
ImGuiDragDropFlags_AcceptBeforeDelivery = 1 << 10, // AcceptDragDropPayload() returns true even before the mouse button is released. You can then call IsDelivery() to test if the payload needs to be delivered.
ImGuiDragDropFlags_AcceptNoDrawDefaultRect = 1 << 11, // Do not draw the default highlight rectangle when hovering over target.

1
imgui_internal.h
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@ -754,6 +754,7 @@ public:
ImGuiID GetID(const char* str, const char* str_end = NULL);
ImGuiID GetID(const void* ptr);
ImGuiID GetIDNoKeepAlive(const char* str, const char* str_end = NULL);
ImGuiID GetIDFromRectangle(const ImRect& r_abs);
ImRect Rect() const { return ImRect(Pos.x, Pos.y, Pos.x+Size.x, Pos.y+Size.y); }
float CalcFontSize() const { return GImGui->FontBaseSize * FontWindowScale; }