ImGui 自定义控件框架，有简单的事件处理机制，当然比起不 im 的 gui，略显简陋：

 1 // InvisibleButton() 测试代码
 2 void display_panel()
 3 {
 4     static ImVec2 location;
 5     static ImVec2 size;
 6 
 7     static ImVec2 mousePos;
 8     static ImVec2 localMousePos;
 9     static ImVec2 delta;
10 
11 
12     ImGui::DragFloat2(u8"位置", (float*) &location);
13     ImGui::DragFloat2(u8"大小", (float*) &size);
14     ImGui::DragFloat2(u8"鼠标", (float*) &mousePos);
15     ImGui::DragFloat2(u8"本地鼠标", (float*) &localMousePos);
16     ImGui::DragFloat2("delta", (float*) &delta);
17 
18     static int click     = 0;
19     static int down      = 0;
20     static int up        = 0;
21     static bool hovering = false;
22 
23     ImGui::Text("click: %d  down: %d  up: %d  hover: %d", click, down, up, hovering);
24 
25     ImGui::InvisibleButton("Panel##", ImVec2(100.0f, 100.0f));
26     location            = ImGui::GetItemRectMin();
27     size                = ImGui::GetItemRectSize();
28     const ImVec2 minPos = ImGui::GetItemRectMin();
29     const ImVec2 maxPos = ImGui::GetItemRectMax();
30     mousePos            = ImGui::GetMousePos();
31     localMousePos       = mousePos - minPos;
32 
33     if (ImGui::IsItemActive()) {
34         if (ImGui::IsMouseDragging(ImGuiMouseButton_Left)) {
35             // delta = ImGui::GetIO().MouseDelta; // 即时拖动向量
36             delta = ImGui::GetMouseDragDelta(ImGuiMouseButton_Left); // 累计拖动
37             // ImGui::ResetMouseDragDelta(ImGuiMouseButton_Left);
38         }
39 
40         // 鼠标按下
41         if (ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
42             ++click;
43         }
44 
45         // 鼠标连发点击
46         if (ImGui::IsMouseDown(ImGuiMouseButton_Left)) {
47             ++down;
48         }
49     }
50     else if (ImGui::IsItemDeactivated()) {
51         // 鼠标弹起
52         if (ImGui::IsMouseReleased(ImGuiMouseButton_Left)) {
53             ++up;
54         }
55     }
56     else {
57         // 鼠标是否在控件范围内
58         hovering = ImGui::IsMouseHoveringRect(minPos, maxPos);
59         if (ImGui::IsMouseHoveringRect(minPos, maxPos)) {
60         }
61     }
62 
63     ImDrawList* draw_list = ImGui::GetWindowDrawList();
64     ImGui::PushClipRect(minPos, maxPos, true);
65     draw_list->AddRectFilled(minPos, maxPos, IM_COL32(0, 127, 255, 255));
66     // draw_list->AddImageRounded((ImTextureID) fboArcball.color_buffer().id(), p0, p1, ImVec2(0.0f, 0.0f), ImVec2(1.0f, 1.0f), 0xFFFFFFFF, 1.0f);
67     ImGui::PopClipRect();
68 }