node editor: dragging!

src/gui/node_editor.h

@@ -119,7 +119,7 @@ public:
 
             Rect viewportRect = Rect(scrolling, canvas_size);
 
-            for (const auto &node : nodeList) {
+            for (auto &node : nodeList) {
                 bool visible = viewportRect.intersects(node.bbox);
                 if (visible) {
                     // TODO: this is garbage
@@ -128,6 +128,13 @@ public:
                     // -- Draw the node boxes
                     draw_list->ChannelsSetCurrent(0); // Switch to the background layer
 
+                    // draw an invisible button in the background, for dragging/hovering
+                    ImGui::SetCursorScreenPos(offset + node.bbox.pos);
+                    ImGui::InvisibleButton("node", node.bbox.size);
+
+                    if (ImGui::IsItemActive() && ImGui::IsMouseDragging(0))
+                        node.bbox.pos += ImGui::GetIO().MouseDelta;
+
                     ImVec2 upper_left = offset + node.bbox.pos;
                     ImVec2 lower_right = upper_left + node.bbox.size;