UIDragDrop.h file

Drag and drop.

ui.DragSource(asset);                                           // any small trivially-copyable value
ui.DragSource(asset, { .Preview = [=](UI& ui) { ui.Image(ThumbOf(asset)); ui.Label(NameOf(asset)); } });
ui.DropTarget<AssetID>([=](const AssetID& dropped) { Assign(dropped); });
ui.DropTarget<AssetID>([=](const AssetID& dropped, const DropEvent& at) { ... });
ui.DropTarget<AssetID>(onDrop, { .OnOver  = [=](const AssetID& a, const DropEvent& at) { Preview(a, at); },
                                 .OnLeave = [=] { EndPreview(); } });

Declared inside the element, like any other reaction. Targets are typed: an element is only a target while a value of its type is being dragged.

A press that moves past a small threshold starts the drag.
The target under the pointer gets the :drop style state.
Releasing over a target delivers the value. Releasing elsewhere, Escape, or the pointer leaving the window cancels.
OnOver hears every move of a matching drag over the target; OnLeave, the drag leaving it or being cancelled over it. A drop is the drop handler's, with no OnLeave.
A drag suppresses the click on the pressed element.
The cursor shows whether the element under it would accept the drop.
Preview is shown beside the pointer. List, tree, table, and tile rows provide their own.

Rows of a list, tree, or table are reordered by giving the view an OnMove:

ui.Tree(source, { .OnMove = [=](std::span<const ItemID> items, ItemID onto, GGDropPlace place) { ... } });

The view only reports the move; the owner of the data performs it.

Namespaces

namespace GGUI

Classes

struct GGUI::DropEvent: A drag over, or dropped on, a target.
struct GGUI::DragSourceProps: Properties of ui.DragSource.
template<typename T> class GGUI::DropOverFn: A drop target's hover callback: [=](const T& value, const DropEvent& at) { ... }.
template<typename T> struct GGUI::DropTargetProps: Properties of ui.DropTarget for values of type T.
struct GGUI::DragBridge: Lets a host route a drag between documents (windows). Called from the source document while it handles input.
struct GGUI::ItemMove: Rows a view reports moved (its OnMove).
class GGUI::ItemMoveFn: Row-move callback: [=](std::span<const ItemID> items, ItemID onto, GGDropPlace place) { ... }.