Add a 'Stamp' widget.

Place one or multiple stamps on scanned pages in defined locations.

A stamp is understood here as
 - a transparent text in a transparent frame with no borders
 - an opaque text on an opaque background with no borders.

Stamp parameters:
 - text
 - font
 - foreground colour
 - background colour
 - angle of rotation
 - transparency.

Locations:
 - centre
 - cardinal directions
 - inter-cardinal directions.

Resources/StampWidget/StampWorker.cpp

@@ -0,0 +1,121 @@
+// /*
+//  * File:   StampWorker.cpp
+//  * Author: Saleem Edah-Tally - nmset@yandex.com
+//  * License : CeCILL-C
+//  * Copyright Saleem Edah-Tally - © 2025
+//  *
+//  * Created on 02 07 2025, 21:23
+//  */
+
+#include "StampWorker.h"
+#include <math.h> // M_PI
+
+wxImage StampWorker::CreateStamp(StampDescriptor * descriptor, int scanResolution)
+{
+  /*
+   * Rescale the font point size of the stamp according to the scan resolution.
+   * Exclude rescaling on v4l that does not have a resolution parameter.
+   */
+  wxFont dcFont(descriptor->font);
+  double scale = (scanResolution > 0)
+              ? (double) scanResolution / 72.0
+              :1.0;
+  
+  wxCoord extentWidth, extentHeight, textLineHeight;
+  {
+    wxMemoryDC dc;
+    if (scale != 1.0)
+      dcFont.SetFractionalPointSize(descriptor->font.GetFractionalPointSize() * scale);
+    dc.SetFont(dcFont); // Mandatory despite set below.
+    dc.GetMultiLineTextExtent(descriptor->text, &extentWidth, &extentHeight, &textLineHeight, &dcFont);
+  }
+  wxBitmap bmp;
+  // bmp.UseAlpha(true); // Not mandatory.
+  bmp.Create(extentWidth, extentHeight); // Memo: See CreateWithDIPSize
+  wxImage img0, img;
+
+  wxMemoryDC dc(bmp);
+  dc.SetFont(dcFont);
+  if (descriptor->transparent)
+  {
+    // +++, Use the red channel only: used by ConvertColourToAlpha().
+    // The chosen value is inversely proportional to the transparency of the text itself.
+    dc.SetTextForeground(wxColour(128, 0, 0)); // A good mean is reasonable.
+    dc.SetBackgroundMode(wxBRUSHSTYLE_TRANSPARENT);
+  }
+  else
+  {
+    dc.SetTextForeground(descriptor->foregroundColour);
+    dc.SetTextBackground(descriptor->backgroundColour);
+    dc.SetBackgroundMode(wxBRUSHSTYLE_SOLID);
+  }
+  
+  dc.DrawText(descriptor->text, wxPoint(0, 0));
+  
+  img0 = bmp.ConvertToImage();
+  if (!descriptor->transparent)
+    img0.InitAlpha(); // So that there is no dark surrounding if it is rotated.
+
+  img = img0.Rotate((M_PI / 180.0) * descriptor->rotationAngle, wxPoint(0, 0));
+  if (descriptor->transparent)
+  {
+    img.ConvertColourToAlpha(descriptor->foregroundColour.GetRed(),
+                            descriptor->foregroundColour.GetGreen(),
+                            descriptor->foregroundColour.GetBlue()); // The target colour is passed in.
+    img.ChangeSaturation(-0.7); // Slightly better looking.
+  }
+  
+  return img;
+}
+
+void StampWorker::StampBackground(wxImage& background,
+                                  const wxImage& stamp, int location)
+{
+  // Simply pasting the stamp on the background, i.e., the scanned page.
+  wxPoint bgCentre(background.GetWidth() / 2, background.GetHeight() / 2);
+  wxPoint stampCentre(stamp.GetWidth() / 2, stamp.GetHeight() / 2);
+  int x = 0, y = 0;
+  switch (location)
+  {
+  case NORTH:
+    x = bgCentre.x - stampCentre.x;
+    y = 0;
+    break;
+  case SOUTH:
+    x = bgCentre.x - stampCentre.x;
+    y = background.GetHeight() - stamp.GetHeight();
+    break;
+  case EAST:
+    x = background.GetWidth() - stamp.GetWidth();
+    y = bgCentre.y - stampCentre.y;
+    break;
+  case WEST:
+    x = 0;
+    y = bgCentre.y - stampCentre.y;
+    break;
+  case NORTH_EAST:
+    x = background.GetWidth() - stamp.GetWidth();
+    y = 0;
+    break;
+  case NORTH_WEST:
+    x = 0;
+    y = 0;
+    break;
+  case SOUTH_EAST:
+    x = background.GetWidth() - stamp.GetWidth();
+    y = background.GetHeight() - stamp.GetHeight();
+    break;
+  case SOUTH_WEST:
+    x = 0;
+    y = background.GetHeight() - stamp.GetHeight();
+    break;
+  default: // CENTRE
+    x = bgCentre.x - stampCentre.x;
+    y = bgCentre.y - stampCentre.y;
+    break;
+  }
+  
+  wxPoint stampLocation(x, y);
+  background.Paste(stamp, stampLocation.x, stampLocation.y, wxIMAGE_ALPHA_BLEND_COMPOSE);
+}
+