fatal error C1189: #error: Please '#define IMGUI_DEFINE_MATH_OPERATORS' _BEFORE_ including imgui.h!

[hoyeziyu]

May I ask how this problem should be solved?I have no other operations

[ivan-resetnikov]

Hey, I had to face this issue myself yesterday, I thought I may be of help, so I'm writing this.

I believe it is to do with an array of API changes on the ImGui's side - there are a couple of things that have to be changed for the library to work again.

---

• 1st error is fatal error C1189: #error: Please '#define IMGUI_DEFINE_MATH_OPERATORS' _BEFORE_ including imgui.h!:
  Just like that error says, you should check every line where ImGuizmo imports "imgui.h" (of which there aren't many) and make sure that IMGUI_DEFINE_MATH_OPERATORS is defined BEFORE the #include statement.

The end result should look like this:

...
#define IMGUI_DEFINE_MATH_OPERATORS
#include "imgui.h"
...

---

• 2nd error I had was at ln ~189 in GraphEditor.cpp

        ...
        if (options.mDisplayLinksAsCurves)
        {
            // curves
             drawList->AddBezierCurve(p1, p1 + ImVec2(50, 0) * factor, p2 + ImVec2(-50, 0) * factor, p2, 0xFF000000, options.mLineThickness * 1.5f * factor);
             drawList->AddBezierCurve(p1, p1 + ImVec2(50, 0) * factor, p2 + ImVec2(-50, 0) * factor, p2, col, options.mLineThickness * 1.5f * factor);
           ...

Here, ImGui deprecated their AddBezierCurve function in favor of AddBezierCubic

I do not claim this solution as a good one in any way - this was written by me when I was tired, it was late, I just wanted for things to work.

But the used, new ImGui function takes in one more argument (int num_segments), and if it is set to 0 the library will determine the needed number automatically, I assumed this was the intended behavior and set it to 0.

Like this:

// curves
drawList->AddBezierCubic(
    p1,
    p1 + ImVec2(50, 0) * factor,
    p2 + ImVec2(-50, 0) * factor,
    p2,
    0xFF000000,
    options.mLineThickness * 1.5f * factor,
    0 // no. of segments (0 = auto)
);

drawList->AddBezierCubic(
    p1,
    p1 + ImVec2(50, 0) * factor,
    p2 + ImVec2(-50, 0) * factor,
    p2,
    col,
    options.mLineThickness * 1.5f * factor,
    0
);

---

• 3rd error I had was at a lot of places, regarding another API change.

ImGui deprecated ImGui::CaptureMouseFromApp(); in favor of ImGui::GetIO().WantCaptureMouse (I suppose - to soften the context change, treat it as a request rather than a demand, give room for failure)

So to fix this one, you have to dig though every .cpp file of ImGuizmo and replace every line like this:

ImGui::CaptureMouseFromApp();

to this

ImGui::GetIO().WantCaptureMouse = true;

There are plenty of those, so I recommend (if you haven't already) to use global search.

---

I think that was everything, or at least, git diff says those were the changes I had done.

---

I believe most of these were addressed in the HEAD branch already, and this is not a good way to deal with this issue, but I wrote this because this is what I had to do to make the latest release (v1.83) of ImGuizmo work with the latest release (v1.91.9b) of ImGui as of today.

In hindsight, the release this regards, explicitly states to use ImGui version v1.83...

"Tag with dear imgui 1.83" - Release comment

---

Good luck!

[elmarsan]

@ivan-resetnikov thanks for sharing that!

[marcodiiga]

FWIW still happening with imgui v1.92.2b. Same sed fixes it