imgui drag reordering

gistfile1.cpp

void **editResources = gui->editResources;
float itemHeight = ImGui::GetTextLineHeightWithSpacing();
int displayStart = 0, displayEnd = gui->numEditResources;
int listItemHovered = -1;

ImGui::CalcListClipping(gui->numEditResources, itemHeight, &displayStart, &displayEnd);
ImGui::SetCursorPosY(ImGui::GetCursorPosY() + (displayStart * itemHeight));

ImVec4 dirtyColor(1.0f, 0.5f, 0.5f, 1.0f), normalColor(1.0f, 1.0f, 1.0f, 1.0f);

for (int i = displayStart; i < displayEnd; ++i)
{
    char buffer[128];
    const char *path = GetResourcePath(editResources[i]);
    snprintf(buffer, sizeof(buffer), !IsResourceDirty(editResources[i]) ? "%d. %s" : "%d. * %s", i + 1, path);
    ImGui::PushID(i);
    ImGui::PushStyleColor(ImGuiCol_Text, IsResourceDirty(gui->editResources[i]) ? dirtyColor : normalColor);

    if (ImGui::Selectable(buffer, gui->selected == i))
    {
        ResourceEditGuiSetSelected(gui, i);
    }

    ImGui::PopStyleColor();

    if (ImGui::IsItemHoveredRect())
    {
     	listItemHovered = i;
    }

    ImGui::PopID();
}

ImGui::SetCursorPosY(ImGui::GetCursorPosY() + ((gui->numEditResources - displayEnd) * itemHeight));
ImGui::EndChild();
ImGui::NextColumn();

if (0 <= listItemHovered)
{
    if (ImGui::IsMouseClicked(2))
    {
     	ResourceEditGuiMarkResourceForRemoval(gui, listItemHovered);
    }

    ImGui::SetTooltip(GetResourcePath(editResources[listItemHovered]));

    if (ImGui::IsMouseDragging() && gui->dragEditResourceCopy)
    {
     	// Reorder the list.                                                                                                                                                                                                                                                    
	void *dragging = gui->dragEditResourceCopy[gui->dragIndex];
	memmove(gui->editResources, gui->dragEditResourceCopy, SIZEOF_ARRAY(gui->editResources, gui->numEditResources));

	if (listItemHovered < gui->dragIndex)
	{
            int numMoving = gui->dragIndex - listItemHovered;
            void **src = gui->editResources + listItemHovered;
            void **dest = gui->editResources + listItemHovered + 1;
            memmove(dest, src, SIZEOF_ARRAY(gui->editResources, numMoving));
            gui->editResources[listItemHovered] = dragging;
        }
        else
        {
            int numMoving = listItemHovered - gui->dragIndex;
            void **src = gui->editResources + gui->dragIndex + 1;
            void **dest = gui->editResources + gui->dragIndex;
            memmove(dest, src, SIZEOF_ARRAY(gui->editResources, numMoving));
            gui->editResources[listItemHovered] = dragging;
        }

        // Terrible linear search to reset the selected item.                                                                                                                                                                                                                   
        for (int i = 0; i < gui->numEditResources; ++i)
        {
            if (gui->editResources[i] == gui->selectedAtDragStart)
            {
                ResourceEditGuiSetSelected(gui, i);
                break;
            }
        }
    }
    else if (leftPressed)
    {
        // Begin drag and drop logic.                                                                                                                                                                                                                                           
        gui->dragIndex = listItemHovered;
        gui->selectedAtDragStart = ResourceEditGuiGetSelectedResource(gui);
        gui->dragEditResourceCopy = PushArrayFront(&gui->guiMemory, void *, gui->numEditResources);
        memmove(gui->dragEditResourceCopy, gui->editResources, SIZEOF_ARRAY(gui->editResources, gui->numEditResources));
    }
}
else
{
    if (ImGui::IsMouseDragging() && gui->dragEditResourceCopy)
    {
        // Restore the original order if we're hovering off the list.                                                                                                                                                                                                            
        memmove(gui->editResources, gui->dragEditResourceCopy, SIZEOF_ARRAY(gui->editResources, gui->numEditResources));

        // Terrible linear search to reset the selected item.                                                                                                                                                                                                                   
        for (int i = 0; i < gui->numEditResources; ++i)
        {
            if (gui->editResources[i] == gui->selectedAtDragStart)
            {
                ResourceEditGuiSetSelected(gui, i);
                break;
            }
        }
    }
}

if (leftReleased && gui->dragEditResourceCopy)
{
    gui->dragIndex = -1;
    gui->selectedAtDragStart = NULL;
    gui->dragEditResourceCopy = NULL;
    PopArrayFront(&gui->guiMemory, void *, gui->numEditResources);
}