[cimgui 1.53.1] Add raw bindings to drag/drop API

Unfortunately, it seems necessary to pull a new dependency, libc, to be able
to use size_t.

Is there any alternative?

imgui-sys/Cargo.toml

@@ -13,6 +13,7 @@ build = "build.rs"
 travis-ci = { repository = "Gekkio/imgui-rs" }
 
 [dependencies]
+libc = "0.2"
 bitflags = "1.0"
 glium = { version = "0.21", default-features = false, optional = true }
 gfx = { version = "0.17", optional = true }

imgui-sys/src/lib.rs

@@ -3,6 +3,8 @@
 #[macro_use]
 extern crate bitflags;
 
+extern crate libc;
+
 #[cfg(feature = "gfx")]
 #[macro_use]
 extern crate gfx;
@@ -380,6 +382,46 @@ bitflags!(
     }
 );
 
+bitflags!(
+    /// Flags for igBeginDragDropSource(), igAcceptDragDropPayload()
+    #[repr(C)]
+    pub struct ImGuiDragDropFlags: c_int {
+        // BeginDragDropSource() flags
+        /// By default, a successful call to igBeginDragDropSource opens a
+        /// tooltip so you can display a preview or description of the source
+        /// contents. This flag disable this behavior.
+        const SourceNoPreviewTooltip   = 1 << 0;
+        /// By default, when dragging we clear data so that igIsItemHovered()
+        /// will return true, to avoid subsequent user code submitting tooltips.
+        /// This flag disable this behavior so you can still call
+        /// igIsItemHovered() on the source item.
+        const SourceNoDisableHover     = 1 << 1;
+        /// Disable the behavior that allows to open tree nodes and collapsing
+        /// header by holding over them while dragging a source item.
+        const SourceNoHoldToOpenOthers = 1 << 2;
+        /// Allow items such as igText(), igImage() 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.
+        const SourceAllowNullID        = 1 << 3;
+        /// External source (from outside of imgui), won't attempt to read
+        /// current item/window info. Will always return true. Only one Extern
+        /// source can be active simultaneously.
+        const SourceExtern             = 1 << 4;
+        // AcceptDragDropPayload() flags
+        /// igAcceptDragDropPayload() will returns true even before the mouse
+        /// button is released. You can then call igIsDelivery() to test if the
+        /// payload needs to be delivered.
+        const AcceptBeforeDelivery     = 1 << 10;
+        /// Do not draw the default highlight rectangle when hovering over target.
+        const AcceptNoDrawDefaultRect  = 1 << 11;
+        /// For peeking ahead and inspecting the payload before delivery.
+        const AcceptPeekOnly           = ImGuiDragDropFlags::AcceptBeforeDelivery.bits
+            | ImGuiDragDropFlags::AcceptNoDrawDefaultRect.bits;
+    }
+);
+
 bitflags!(
     /// Flags for indictating which corner of a rectangle should be rounded
     #[repr(C)]
@@ -672,6 +714,28 @@ pub struct ImGuiTextFilter {
     pub count_grep: c_int,
 }
 
+/// Data payload for Drag and Drop operations
+#[repr(C)]
+pub struct ImGuiPayload {
+    /// Data (copied and owned by dear imgui)
+    pub data: *const c_void,
+    /// Data size
+    pub data_size: c_int,
+
+    /// Source item id
+    source_id: ImGuiID,
+    /// Source parent id (if available)
+    source_parent_id: ImGuiID,
+    /// Data timestamp
+    data_frame_count: c_int,
+    /// Data type tag (short user-supplied string)
+    data_type: [c_char; 8 + 1],
+    /// Set when AcceptDragDropPayload() was called and mouse has been hovering the target item (nb: handle overlapping drag targets)
+    preview: bool,
+    /// Set when AcceptDragDropPayload() was called and mouse button is released over the target item.
+    delivery: bool,
+}
+
 #[repr(C)]
 pub struct ImGuiTextBuffer {
     pub buf: ImVector<c_char>,
@@ -1687,6 +1751,24 @@ extern "C" {
     pub fn igLogText(fmt: *const c_char, ...);
 }
 
+// DragDrop
+extern "C" {
+    /// Call when current ID is active.
+    ///
+    /// When this returns true you need to:
+    ///
+    /// 1. call [`igSetDragDropPayload`] exactly once,
+    /// 2. you may render the payload visual/description,
+    /// 3. pcall [`igEndDragDropSource`]
+    pub fn igBeginDragDropSource(flags: ImGuiDragDropFlags, mouse_button: c_int) -> bool;
+    /// Use 'cond' to choose to submit payload on drag start or every frame
+    pub fn igSetDragDropPayload(type_: *const c_char, data: *const c_void, size: libc::size_t, cond: ImGuiCond) -> bool;
+    pub fn igEndDragDropSource();
+    pub fn igBeginDragDropTarget() -> bool;
+    pub fn igAcceptDragDropPayload(type_: *const c_char, flags: ImGuiDragDropFlags) -> *const ImGuiPayload;
+    pub fn igEndDragDropTarget();
+}
+
 // Clipping
 extern "C" {
     pub fn igPushClipRect(