Follow-up of 32dc4709a4 -> A more general fix

src/slic3r/GUI/GLCanvas3D.cpp

@@ -2264,12 +2264,7 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
         return;
 
     if (m_gizmos.on_char(evt))
-    {
-        // FIXME: Without the following call to render(), the gimgui dialogs are not shown the first time the user tries to open them using the keyboard shortcuts
-        //        (it looks like as if 2 render calls are needed before they show up)
-        render();
         return;
-    }
 
 //#ifdef __APPLE__
 //    ctrlMask |= wxMOD_RAW_CONTROL;

src/slic3r/GUI/Gizmos/GLGizmoBase.cpp

@@ -145,6 +145,7 @@ GLGizmoBase::GLGizmoBase(GLCanvas3D& parent, const std::string& icon_filename, u
     , m_hover_id(-1)
     , m_dragging(false)
     , m_imgui(wxGetApp().imgui())
+    , m_first_input_window_render(true)
 {
     ::memcpy((void*)m_base_color, (const void*)DEFAULT_BASE_COLOR, 4 * sizeof(float));
     ::memcpy((void*)m_drag_color, (const void*)DEFAULT_DRAG_COLOR, 4 * sizeof(float));
@@ -273,6 +274,18 @@ std::string GLGizmoBase::format(float value, unsigned int decimals) const
     return Slic3r::string_printf("%.*f", decimals, value);
 }
 
+void GLGizmoBase::render_input_window(float x, float y, float bottom_limit)
+{
+    on_render_input_window(x, y, bottom_limit);
+    if (m_first_input_window_render)
+    {
+        // for some reason, the imgui dialogs are not shown on screen in the 1st frame where they are rendered, but show up only with the 2nd rendered frame
+        // so, we forces another frame rendering the first time the imgui window is shown
+        m_parent.set_as_dirty();
+        m_first_input_window_render = false;
+    }
+}
+
 // Produce an alpha channel checksum for the red green blue components. The alpha channel may then be used to verify, whether the rgb components
 // were not interpolated by alpha blending or multi sampling.
 unsigned char picking_checksum_alpha_channel(unsigned char red, unsigned char green, unsigned char blue)

src/slic3r/GUI/Gizmos/GLGizmoBase.hpp

@@ -99,6 +99,7 @@ protected:
     float m_highlight_color[4];
     mutable std::vector<Grabber> m_grabbers;
     ImGuiWrapper* m_imgui;
+    bool m_first_input_window_render;
 
 public:
     GLGizmoBase(GLCanvas3D& parent, const std::string& icon_filename, unsigned int sprite_id);
@@ -144,7 +145,7 @@ public:
 
     void render() const { on_render(); }
     void render_for_picking() const { on_render_for_picking(); }
-    void render_input_window(float x, float y, float bottom_limit) { on_render_input_window(x, y, bottom_limit); }
+    void render_input_window(float x, float y, float bottom_limit);
 
 protected:
     virtual bool on_init() = 0;

src/slic3r/GUI/Gizmos/GLGizmoCut.cpp

@@ -141,6 +141,7 @@ void GLGizmoCut::on_render_input_window(float x, float y, float bottom_limit)
     m_imgui->set_next_window_pos(x, y, ImGuiCond_Always);
 
     m_imgui->set_next_window_bg_alpha(0.5f);
+
     m_imgui->begin(_(L("Cut")), ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoCollapse);
 
     ImGui::PushItemWidth(m_imgui->scaled(5.0f));