I want to pass a method function as the ImGuiInputResizeCallback

[RicardoDazzling]

Version/Branch of Dear ImGui:

Version 1.90.4, Branch: master

Back-ends:

imgui_impl_glfw.cpp + imgui_impl_opengl3.cpp

Compiler, OS:

Windows 10

Full config/build information:

Dear ImGui 1.90.5 WIP (19043)

sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20 define: __cplusplus=199711 define: _WIN32 define: _WIN64 define: _MSC_VER=1939 define: _MSVC_LANG=201402

io.BackendPlatformName: imgui_impl_glfw io.BackendRendererName: imgui_impl_opengl3 io.ConfigFlags: 0x00000003 NavEnableKeyboard NavEnableGamepad io.ConfigInputTextCursorBlink io.ConfigWindowsResizeFromEdges io.ConfigMemoryCompactTimer = 60.0 io.BackendFlags: 0x00000006 HasMouseCursors HasSetMousePos

io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64 io.DisplaySize: 1280.00,720.00 io.DisplayFramebufferScale: 1.00,1.00

style.WindowPadding: 8.00,8.00 style.WindowBorderSize: 1.00 style.FramePadding: 4.00,3.00 style.FrameRounding: 0.00 style.FrameBorderSize: 0.00 style.ItemSpacing: 8.00,4.00 style.ItemInnerSpacing: 4.00,4.00

Details:

My Issue/Question:

Hello!

My problem is that I want to use a input that don't have a max size, such is used in the demo file. But I see that in the demo file is used a static method, but I want to create a class with a object (str) that was updated when the resize callback was called, it object is defined inside the class, but when I try to create the Input, it don't accept the class method, only static methods. Its a example that my code:

class ResizableInputTextMultiline {
private:
    ImVector<char>* str;
public:
    ResizableInputTextMultiline(ImVector<char>* str);
    bool Draw(const char* label, const ImVec2& size = ImVec2(0, 0), ImGuiInputTextFlags flags = 0);
    int ResizeCallback(ImGuiInputTextCallbackData* data);
};

bool ResizableInputTextMultiline::Draw(const char* label, const ImVec2& size, ImGuiInputTextFlags flags)
{
    IM_ASSERT((flags & ImGuiInputTextFlags_CallbackResize) == 0);
    return ImGui::InputTextMultiline(label, this->str->begin(), (size_t)this->str->size(), size, flags | ImGuiInputTextFlags_CallbackResize, this->ResizeCallback, (void*)this->str); //Error (active)  E0300   a pointer to a bound function may only be used to call the function
}

Can I solve this and give the class method as a resize callback argument?

Screenshots/Video:

No response

Minimal, Complete and Verifiable Example code:

// Here's some code anyone can copy and paste to reproduce your issue
ImGui::Begin("Example Bug");
MoreCodeToExplainMyIssue();
ImGui::End();

[cfillion]

data->UserData is the string in your snippet, so if you don't need to access other members of your object the above is fine. Just make ResizeCallback static or non-member. Otherwise:

ImGui::InputTextMultiline(label, str->begin(), str->size(), size, flags | ImGuiInputTextFlags_CallbackResize, [](ImGuiInputTextCallbackData *data) {
  return static_cast<ResizableInputTextMultiline *>(data->UserData)->ResizeCallback(data);
}, this);

Also have a look at misc/cpp/imgui_stdlib.h to not re-invent the wheel.

[RicardoDazzling]

The error from IDE solved, but I'm not understand at all. With your code, it will call the ResizeCallback from my object or I'll need to made it static before?

[GamingMinds-DanielC]

It is a normal member (non-static) in that short code snippet. The call passes the object's this-pointer as user data to the function and gives it a lambda (available since C++ 11) as a wrapper. That lambda then takes the user data, casts it back into the object pointer and calls the method on the object.