Metrics/Debugger: replaced io.DebugDrawCmdCallback with chainable DebugAddDrawCmdHook() / DebugRemoveDrawCmdHook(). (#9459)

As suggested in review: a list of hooks instead of a single ImGuiIO field, so
several libraries can register. For every user callback command in
DebugNodeDrawList(), hooks are tried in registration order; the first one
returning true has fully displayed the command (TreeNode + contents, overlay
on hover in 'fg_draw_list'). If none handles it, the default
"Callback %p, user_data %p" bullet is shown.

- No change to the public API (imgui.h): the ImGuiIO field and its typedef are removed.
- imgui_internal.h: ImGuiDebugDrawCmdHookFn, ImGuiDebugDrawCmdHook,
  ImGuiContext::DebugDrawCmdHooks, DebugAddDrawCmdHook(), DebugRemoveDrawCmdHook(),
  and IMGUI_HAS_DEBUG_DRAWCMD_HOOKS for feature detection.
- No arbitrary text buffer or mesh/bbox parameters: hooks draw their own node
  and read DebugMetricsConfig / call DebugNodeDrawCmdShowMeshAndBoundingBox() as needed.

imgui.cpp

@@ -4590,6 +4590,28 @@ ImGuiID ImGui::AddContextHook(ImGuiContext* ctx, const ImGuiContextHook* hook)
     return g.HookIdNext;
 }
 
+// Metrics/Debugger: register a hook describing user draw callbacks (see ImGuiDebugDrawCmdHookFn).
+void ImGui::DebugAddDrawCmdHook(ImGuiDebugDrawCmdHookFn hook, void* user_data)
+{
+    ImGuiContext& g = *GImGui;
+    IM_ASSERT(hook != NULL);
+    ImGuiDebugDrawCmdHook entry;
+    entry.Callback = hook;
+    entry.UserData = user_data;
+    g.DebugDrawCmdHooks.push_back(entry);
+}
+
+void ImGui::DebugRemoveDrawCmdHook(ImGuiDebugDrawCmdHookFn hook, void* user_data)
+{
+    ImGuiContext& g = *GImGui;
+    for (int n = 0; n < g.DebugDrawCmdHooks.Size; n++)
+        if (g.DebugDrawCmdHooks[n].Callback == hook && g.DebugDrawCmdHooks[n].UserData == user_data)
+        {
+            g.DebugDrawCmdHooks.erase(g.DebugDrawCmdHooks.Data + n);
+            return;
+        }
+}
+
 // Deferred removal, avoiding issue with changing vector while iterating it
 void ImGui::RemoveContextHook(ImGuiContext* ctx, ImGuiID hook_id)
 {
@@ -17384,20 +17406,15 @@ void ImGui::DebugNodeDrawList(ImGuiWindow* window, ImGuiViewportP* viewport, con
     {
         if (pcmd->UserCallback)
         {
-            if (g.IO.DebugDrawCmdCallback)
-            {
-                char buf[300];
-                g.IO.DebugDrawCmdCallback(NULL, draw_list, pcmd, false, false, buf, IM_ARRAYSIZE(buf));
-                bool cb_node_open = TreeNode((void*)(pcmd - draw_list->CmdBuffer.begin()), "Callback: %s", buf);
-                if (IsItemHovered() && (cfg->ShowDrawCmdMesh || cfg->ShowDrawCmdBoundingBoxes) && fg_draw_list)
-                    g.IO.DebugDrawCmdCallback(fg_draw_list, draw_list, pcmd, cfg->ShowDrawCmdMesh, cfg->ShowDrawCmdBoundingBoxes, NULL, 0);
-                if (cb_node_open)
-                    TreePop();
-            }
-            else
-            {
+            bool handled = false;
+            for (ImGuiDebugDrawCmdHook& hook : g.DebugDrawCmdHooks)
+                if (hook.Callback(draw_list, pcmd, fg_draw_list, hook.UserData))
+                {
+                    handled = true;
+                    break;
+                }
+            if (!handled)
                 BulletText("Callback %p, user_data %p", pcmd->UserCallback, pcmd->UserCallbackData);
-            }
             continue;
         }
 

imgui.h

@@ -287,7 +287,6 @@ typedef int     (*ImGuiInputTextCallback)(ImGuiInputTextCallbackData* data);
 typedef void    (*ImGuiSizeCallback)(ImGuiSizeCallbackData* data);              // Callback function for ImGui::SetNextWindowSizeConstraints()
 typedef void*   (*ImGuiMemAllocFunc)(size_t sz, void* user_data);               // Function signature for ImGui::SetAllocatorFunctions()
 typedef void    (*ImGuiMemFreeFunc)(void* ptr, void* user_data);                // Function signature for ImGui::SetAllocatorFunctions()
-typedef void    (*ImGuiDebugDrawCmdCallbackFn)(ImDrawList* overlay_draw_list, const ImDrawList* draw_list, const ImDrawCmd* draw_cmd, bool show_mesh, bool show_aabb, char* out_text, int text_size); // Debug callback for custom draw commands
 
 // ImVec2: 2D vector used to store positions, sizes etc. [Compile-time configurable type]
 // - This is a frequently used type in the API. Consider using IM_VEC2_CLASS_EXTRA to create implicit cast from/to our preferred type.
@@ -2511,11 +2510,6 @@ struct ImGuiIO
     // Option to audit .ini data
     bool        ConfigDebugIniSettings;         // = false          // Save .ini data with extra comments (particularly helpful for Docking, but makes saving slower)
 
-    // Debug callback for custom draw commands (callbacks) in the Metrics/Debugger draw list viewer.
-    // When set, callback draw commands will show a tree node with descriptive text and mesh/bbox overlay on hover,
-    // instead of just "Callback %p, user_data %p". See ImGuiDebugDrawCmdCallbackFn typedef for parameters.
-    ImGuiDebugDrawCmdCallbackFn DebugDrawCmdCallback; // = NULL
-
     //------------------------------------------------------------------
     // Platform Identifiers
     // (the imgui_impl_xxxx backend files are setting those up for you)

imgui_internal.h

@@ -2195,6 +2195,19 @@ struct ImGuiIDStackTool
 typedef void (*ImGuiContextHookCallback)(ImGuiContext* ctx, ImGuiContextHook* hook);
 enum ImGuiContextHookType { ImGuiContextHookType_NewFramePre, ImGuiContextHookType_NewFramePost, ImGuiContextHookType_EndFramePre, ImGuiContextHookType_EndFramePost, ImGuiContextHookType_RenderPre, ImGuiContextHookType_RenderPost, ImGuiContextHookType_Shutdown, ImGuiContextHookType_PendingRemoval_ };
 
+// Metrics/Debugger: hooks describing user draw callbacks (ImDrawCmd::UserCallback) in DebugNodeDrawList().
+// Hooks are tried in registration order for every callback command; the first one returning true has fully
+// displayed the command (typically a TreeNode() and its contents, and an overlay on hover drawn in
+// 'fg_draw_list', which may be NULL). If none handles it, the default "Callback %p, user_data %p" is shown.
+#define IMGUI_HAS_DEBUG_DRAWCMD_HOOKS   // DebugAddDrawCmdHook() / DebugRemoveDrawCmdHook() are available
+typedef bool (*ImGuiDebugDrawCmdHookFn)(const ImDrawList* draw_list, const ImDrawCmd* draw_cmd, ImDrawList* fg_draw_list, void* user_data);
+
+struct ImGuiDebugDrawCmdHook
+{
+    ImGuiDebugDrawCmdHookFn     Callback;
+    void*                       UserData;
+};
+
 struct ImGuiContextHook
 {
     ImGuiID                     HookId;     // A unique ID assigned by AddContextHook()
@@ -2590,6 +2603,7 @@ struct ImGuiContext
     float                   DebugFlashStyleColorTime;
     ImVec4                  DebugFlashStyleColorBackup;
     ImGuiMetricsConfig      DebugMetricsConfig;
+    ImVector<ImGuiDebugDrawCmdHook> DebugDrawCmdHooks;           // Metrics/Debugger: user draw callback hooks (DebugAddDrawCmdHook)
     ImGuiDebugItemPathQuery DebugItemPathQuery;
     ImGuiIDStackTool        DebugIDStackTool;
     ImGuiDebugAllocInfo     DebugAllocInfo;
@@ -3818,6 +3832,8 @@ namespace ImGui
     IMGUI_API void          DebugNodeColumns(ImGuiOldColumns* columns);
     IMGUI_API void          DebugNodeDrawList(ImGuiWindow* window, ImGuiViewportP* viewport, const ImDrawList* draw_list, const char* label);
     IMGUI_API void          DebugNodeDrawCmdShowMeshAndBoundingBox(ImDrawList* out_draw_list, const ImDrawList* draw_list, const ImDrawCmd* draw_cmd, bool show_mesh, bool show_aabb);
+    IMGUI_API void          DebugAddDrawCmdHook(ImGuiDebugDrawCmdHookFn hook, void* user_data = NULL);
+    IMGUI_API void          DebugRemoveDrawCmdHook(ImGuiDebugDrawCmdHookFn hook, void* user_data = NULL);
     IMGUI_API void          DebugNodeFont(ImFont* font);
     IMGUI_API void          DebugNodeFontGlyphsForSrcMask(ImFont* font, ImFontBaked* baked, int src_mask);
     IMGUI_API void          DebugNodeFontGlyph(ImFont* font, const ImFontGlyph* glyph);