allow Node/Ref to accept drag&drop

common/dir_item.hh

@@ -10,10 +10,11 @@ namespace nf7 {
 class DirItem : public File::Interface {
  public:
   enum Flag : uint8_t {
-    kNone    = 0,
-    kTree    = 1 << 0,
-    kMenu    = 1 << 1,
-    kTooltip = 1 << 2,
+    kNone           = 0,
+    kTree           = 1 << 0,
+    kMenu           = 1 << 1,
+    kTooltip        = 1 << 2,
+    kDragDropTarget = 1 << 3,
   };
   using Flags = uint8_t;
 
@@ -28,6 +29,7 @@ class DirItem : public File::Interface {
   virtual void UpdateTree() noexcept { }
   virtual void UpdateMenu() noexcept { }
   virtual void UpdateTooltip() noexcept { }
+  virtual void UpdateDragDropTarget() noexcept { }
 
   Flags flags() const noexcept { return flags_; }
 

common/gui_dnd.hh

@@ -0,0 +1,69 @@
+#pragma once
+
+#include <cstring>
+#include <optional>
+#include <string>
+#include <string_view>
+
+#include <imgui.h>
+
+#include "nf7.hh"
+
+
+namespace nf7::gui::dnd {
+
+// data entity is char[] of file path
+constexpr const char* kFilePath = "nf7::File::Path";
+
+
+template <typename T>
+bool Send(const char* type, const T&) noexcept;
+
+template <>
+inline bool Send<std::string>(const char* type, const std::string& v) noexcept {
+  return ImGui::SetDragDropPayload(type, v.data(), v.size());
+}
+template <>
+inline bool Send<std::string_view>(const char* type, const std::string_view& v) noexcept {
+  return ImGui::SetDragDropPayload(type, v.data(), v.size());
+}
+template <>
+inline bool Send<File::Path>(const char* type, const File::Path& p) noexcept {
+  return Send(type, p.Stringify());
+}
+
+
+template <typename T>
+T To(const ImGuiPayload&) noexcept;
+
+template <>
+inline std::string To<std::string>(const ImGuiPayload& pay) noexcept {
+  std::string ret;
+  ret.resize(static_cast<size_t>(pay.DataSize));
+  std::memcpy(ret.data(), pay.Data, ret.size());
+  return ret;
+}
+template <>
+inline File::Path To<File::Path>(const ImGuiPayload& pay) noexcept {
+  return File::Path::Parse(To<std::string>(pay));
+}
+
+
+template <typename T>
+std::optional<T> Accept(const char* type, ImGuiDragDropFlags flags = 0) noexcept {
+  if (auto pay = ImGui::AcceptDragDropPayload(type, flags)) {
+    return To<T>(*pay);
+  }
+  return std::nullopt;
+}
+template <typename T>
+const ImGuiPayload* Peek(const char* type, auto& v, ImGuiDragDropFlags flags = 0) noexcept {
+  flags |= ImGuiDragDropFlags_AcceptBeforeDelivery;
+  if (auto pay = ImGui::AcceptDragDropPayload(type, flags)) {
+    if (pay->IsDelivery()) v = To<T>(*pay);
+    return pay;
+  }
+  return nullptr;
+}
+
+}  // namespace nf7::gui::dnd

common/gui_file.hh

@@ -7,6 +7,8 @@
 
 #include "nf7.hh"
 
+#include "common/gui_dnd.hh"
+
 
 namespace nf7::gui {
 
@@ -128,4 +130,18 @@ struct FileCreatePopup final {
   std::string type_filter_;
 };
 
-}  // namespace nf7
+
+inline bool InputFilePath(const char* id, std::string* path) noexcept {
+  bool ret = ImGui::InputText(id, path, ImGuiInputTextFlags_EnterReturnsTrue);
+
+  if (ImGui::BeginDragDropTarget()) {
+    if (auto str = gui::dnd::Accept<std::string>(gui::dnd::kFilePath)) {
+      *path = *str;
+      ret   = true;
+    }
+    ImGui::EndDragDropTarget();
+  }
+  return ret;
+}
+
+}  // namespace nf7::gui