Drag and drop: Added COL3F payload for color without alpha overwrite.…

… Exposed standard color payload types in imgui.h (#143)

imgui.cpp

@@ -9677,7 +9677,10 @@ bool ImGui::ColorButton(const char* desc_id, const ImVec4& col, ImGuiColorEditFl
 
     if (g.ActiveId == id && BeginDragDropSource()) // NB: The ActiveId test is merely an optional micro-optimization
     {
-        SetDragDropPayload(IMGUI_PAYLOAD_TYPE_COLOR_4F, &col, sizeof(col), ImGuiCond_Once);
+        if (flags & ImGuiColorEditFlags_NoAlpha)
+            SetDragDropPayload(IMGUI_PAYLOAD_TYPE_COLOR_3F, &col, sizeof(float) * 3, ImGuiCond_Once);
+        else
+            SetDragDropPayload(IMGUI_PAYLOAD_TYPE_COLOR_4F, &col, sizeof(float) * 4, ImGuiCond_Once);
         ColorButton(desc_id, col, flags);
         SameLine();
         TextUnformatted("Color");
@@ -9963,10 +9966,14 @@ bool ImGui::ColorEdit4(const char* label, float col[4], ImGuiColorEditFlags flag
 
     if (window->DC.LastItemRectHoveredRect && BeginDragDropTarget()) // NB: The LastItemRectHoveredRect test is merely an optional micro-optimization
     {
+        if (const ImGuiPayload* payload = AcceptDragDropPayload(IMGUI_PAYLOAD_TYPE_COLOR_3F))
+        {
+            memcpy((float*)col, payload->Data, sizeof(float) * 3);
+            value_changed = true;
+        }
         if (const ImGuiPayload* payload = AcceptDragDropPayload(IMGUI_PAYLOAD_TYPE_COLOR_4F))
         {
-            IM_ASSERT(payload->DataSize == sizeof(ImVec4));
-            memcpy((float*)col, payload->Data, sizeof(ImVec4));
+            memcpy((float*)col, payload->Data, sizeof(float) * components);
             value_changed = true;
         }
         EndDragDropTarget();

imgui.h

@@ -610,6 +610,10 @@ enum ImGuiDragDropFlags_
     ImGuiDragDropFlags_AcceptPeekOnly               = ImGuiDragDropFlags_AcceptBeforeDelivery | ImGuiDragDropFlags_AcceptNoDrawDefaultRect  // For peeking ahead and inspecting the payload before delivery.
 };
 
+// Standard Drag and Drop payload types. Types starting with '_' are defined by Dear ImGui.
+#define IMGUI_PAYLOAD_TYPE_COLOR_3F     "_COL3F"    // float[3]     // Standard type for colors, without alpha. User code may use this type. 
+#define IMGUI_PAYLOAD_TYPE_COLOR_4F     "_COL4F"    // float[4]     // Standard type for colors. User code may use this type.
+
 // User fill ImGuiIO.KeyMap[] array with indices into the ImGuiIO.KeysDown[512] array
 enum ImGuiKey_
 {

imgui_internal.h

@@ -169,8 +169,7 @@ inline void operator delete(void*, ImPlacementNewDummy, void*) {}
 // Types
 //-----------------------------------------------------------------------------
 
-// Drag and Drop payload types. String starting with '_' are managed by Dear ImGui.
-#define IMGUI_PAYLOAD_TYPE_COLOR_4F         "_COL4F"    // float[4]     // Standard type for colors. User code may use this type. Build a float[4] out of a float[3] if you don't have alpha.
+// Internal Drag and Drop payload types. String starting with '_' are reserved for Dear ImGui.
 #define IMGUI_PAYLOAD_TYPE_DOCKABLE         "_IMDOCK"   // ImGuiWindow* // [Internal] Docking/tabs
 
 enum ImGuiButtonFlags_