Mirrored Text

[rsb]

Is there a way to draw mirrored text to a wxDC object.

I tried the wxMirrorDC class but it didn't work. I also tried the SetLayoutDirection method and
it didn't work either.

Thank you.

Using:
- wxWidgets 3.1.0
- Window 7 Professional
- Visual Studio 2015.

[doublemax]

Code: Select all

  void OnPaint( wxPaintEvent &evt )
  {
    wxPaintDC pdc(this);

    wxGraphicsContext *gc = wxGraphicsContext::Create( pdc );
    wxGraphicsFont gf = gc->CreateFont( 24, "Lucida Sans Unicode" );
    gc->SetFont(gf);

    // normal text
    gc->DrawText("some text", 150,30 );

    wxGraphicsMatrix gmc = gc->CreateMatrix();
    gmc.Scale( -1.0, 1.0 );
    gc->SetTransform( gmc );

    // mirrored text
    // beware that coordinates are affected by the negative x-scale, too
    gc->DrawText("some text", -130, 30 );
    delete gc;
  }

I tried the same with the wPaintDC directly, but it didn't work.

I'm also not sure if this would work on all platforms. Tested on Windows only.

[New Pagodi]

In addition to the above, you can use a transformation matrix for the DC itself without wrapping it into a graphics context first. For example to mirror across the line x=50, you could do something like

Code: Select all

    wxAffineMatrix2D mat = dc.GetTransformMatrix();
    mat.Translate(50, 0);
    mat.Mirror();
    dc.SetTransformMatrix(mat);
    dc.DrawText("Hello",0,0);
    dc.ResetTransformMatrix();

To mirror across the line y=50, you would change this slightly to

Code: Select all

    wxAffineMatrix2D mat=dc.GetTransformMatrix();
    mat.Translate(0, 50);
    mat.Mirror(wxVERTICAL);
    dc.SetTransformMatrix(mat);
    dc.DrawText("Hello",0,0);
    dc.ResetTransformMatrix();

[rsb]

Thank you both, I'll try and let you know.

[rsb]

We're not drawing inside a paint event handler so I couldn't use the first option.

The second worked well when mirroring around the x or y axis.

How would the second option work for text displayed at a 45 degree rotation
or anything other than 0, 90, 180, 270.

Thanks.

[New Pagodi]

You can use the Rotate method to add a rotation factor to the matrix.

Just remember that when dealing with matrices, the order of operation matters. For example, this code:

Code: Select all

    mat.Translate(50, 50);
    mat.Mirror(wxVERTICAL);
    mat.Rotate(45*3.14/180);
    dc.SetTransformMatrix(mat);
    dc.DrawText("Hello",0,0);

results in:

mirror_then_rotate.png (694 Bytes) Viewed 1526 times

And changing the order slightly:

Code: Select all

    mat.Translate(50, 50);
    mat.Rotate(45*3.14/180);
    mat.Mirror(wxVERTICAL);
    dc.SetTransformMatrix(mat);
    dc.DrawText("Hello",0,0);

results in:

rotate_then_mirror.png (651 Bytes) Viewed 1526 times

[rsb]

Thank you.