Example of a "transparent" wxTextCtrl under Windows

transparent_textctrl.cpp

#include <wx/app.h>
#include <wx/artprov.h>
#include <wx/custombgwin.h>
#include <wx/dcclient.h>
#include <wx/frame.h>
#include <wx/sizer.h>
#include <wx/textctrl.h>

#include <wx/msw/private.h>

struct CustomBackgroundFrame : public wxCustomBackgroundWindow<wxFrame> {
    CustomBackgroundFrame() {
        Create(nullptr, wxID_ANY, "Custom Background Frame");

        SetBackgroundBitmap(wxArtProvider::GetBitmap(wxART_QUESTION));
    }

    // This shouldn't be necessary in the future, but for now override it to
    // fix a bug with brush positioning in the current wxWidgets version.
    WXHBRUSH MSWGetBgBrushForChild(WXHDC hDC, wxWindowMSW *child) override
    {
        WXHBRUSH hbrush = MSWGetCustomBgBrush();
        if ( !hbrush )
            return 0;

        RECT rc;
        ::GetWindowRect(GetHwnd(), &rc);
        wxMapWindowPoints(GetHwnd(), GetHwndOf(child), &rc);
        ::SetBrushOrgEx((HDC)hDC, rc.left, rc.top, nullptr);

        return hbrush;
    }
};

struct TransparentTextCtrl : public wxTextCtrl {
    explicit TransparentTextCtrl(wxWindow* parent) :
        wxTextCtrl(parent, wxID_ANY, {}, {}, parent->FromDIP(wxSize(300, -1)), wxBORDER_NONE) {
        SetFont(wxFontInfo(20).Bold());
        SetForegroundColour(*wxYELLOW);

        Bind(wxEVT_SIZE, [this](wxSizeEvent& event) {
            auto size = event.GetSize();
            SetValue(wxString::Format("Size: %d x %d", size.x, size.y));
            Refresh();

            event.Skip();
        });
    }

    bool HasTransparentBackground() override { return true; }
};

struct TestApp : public wxApp {
    bool OnInit() override {
        auto f = new CustomBackgroundFrame();
        auto s = new wxBoxSizer(wxVERTICAL);

        s->AddStretchSpacer();
        s->Add(new TransparentTextCtrl(f), wxSizerFlags().Center());
        s->AddStretchSpacer();
        f->SetSizer(s);

        f->SetClientSize(f->FromDIP(wxSize(500, 300)));

        f->Show();
        return true;
    }
};

wxIMPLEMENT_APP(TestApp);