New member function Fl_Image_Surface::mask(Fl_RGB_Image*)

11 files changed, 425 insertions, 3 deletions

diff --git a/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H b/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H
index 8677a920f..e55f051d7 100644
--- a/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H
+++ b/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H
@@ -68,6 +68,7 @@ public:
   cairo_t *cr() { return cairo_; }
   PangoLayout *pango_layout() {return pango_layout_;}
   void set_cairo(cairo_t *c, float f = 0);
+  static cairo_pattern_t *calc_cairo_mask(const Fl_RGB_Image *rgb);
 
   void check_status(void);
 
diff --git a/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx b/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx
index cda328c17..40264c757 100644
--- a/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx
+++ b/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx
@@ -1517,4 +1517,41 @@ void Fl_Cairo_Graphics_Driver::focus_rect(int x, int y, int w, int h)
   surface_needs_commit();
 }
 
+
+cairo_pattern_t *Fl_Cairo_Graphics_Driver::calc_cairo_mask(const Fl_RGB_Image *rgb) {
+  int i, j, d = rgb->d(), w = rgb->data_w(), h = rgb->data_h(), ld = rgb->ld();
+  int bytesperrow = cairo_format_stride_for_width(CAIRO_FORMAT_A1, w);
+  if (!ld) ld = d * w;
+  unsigned u;
+  uchar byte, onebit;
+  // build a CAIRO_FORMAT_A1 surface covering the non-black part of the image
+  uchar* bits = new uchar[h*bytesperrow]; // to store the surface data
+  for (i = 0; i < h; i++) {
+    const uchar* alpha = (const uchar*)*rgb->data() + i * ld;
+    uchar *p = (uchar*)bits + i * bytesperrow;
+    byte = 0;
+    onebit = 1;
+    for (j = 0; j < w; j++) {
+      u = *alpha;
+      u += *(alpha+1);
+      u += *(alpha+2);
+      if (u > 0) { // if the pixel is not black
+        byte |= onebit; // turn on the corresponding bit of the bitmap
+      }
+      onebit = onebit << 1; // move the single set bit one position to the left
+      if (onebit == 0 || j == w-1) {
+        onebit = 1;
+        *p++ = byte; // store in bitmap one pack of bits
+        byte = 0;
+      }
+      alpha += d; // point to next rgb pixel
+    }
+  }
+  cairo_surface_t *mask_surf = cairo_image_surface_create_for_data(bits,
+    CAIRO_FORMAT_A1, w, h, bytesperrow);
+  cairo_pattern_t *mask_pattern = cairo_pattern_create_for_surface(mask_surf);
+  cairo_surface_destroy(mask_surf);
+  return mask_pattern;
+}
+
 #endif // USE_PANGO
diff --git a/src/drivers/GDI/Fl_GDI_Graphics_Driver.H b/src/drivers/GDI/Fl_GDI_Graphics_Driver.H
index 4d1f45c82..03371c8c4 100644
--- a/src/drivers/GDI/Fl_GDI_Graphics_Driver.H
+++ b/src/drivers/GDI/Fl_GDI_Graphics_Driver.H
@@ -70,6 +70,7 @@ public:
 
   // --- bitmap stuff
   static HBITMAP create_bitmask(int w, int h, const uchar *array); // NOT virtual
+  static HBITMAP calc_HBITMAP_mask(Fl_RGB_Image *mask);
   void delete_bitmask(fl_uintptr_t bm) FL_OVERRIDE;
   HBITMAP create_alphamask(int w, int h, int d, int ld, const uchar *array);
   void draw_unscaled(const char* str, int n, int x, int y) FL_OVERRIDE;
diff --git a/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.H b/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.H
index d44d57cd6..129a4ecbc 100644
--- a/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.H
+++ b/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.H
@@ -26,6 +26,12 @@ class Fl_GDI_Image_Surface_Driver : public Fl_Image_Surface_Driver {
 public:
   HWND pre_window;
   int _savedc;
+  void mask(const Fl_RGB_Image *) FL_OVERRIDE;
+  struct shape_data_type {
+    HBITMAP background;
+    uchar *vBits;
+    Fl_RGB_Image* mask;
+  } *shape_data_;
   Fl_GDI_Image_Surface_Driver(int w, int h, int high_res, Fl_Offscreen off);
   ~Fl_GDI_Image_Surface_Driver();
   void set_current() FL_OVERRIDE;
diff --git a/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx b/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx
index 5a4d5ada7..7e1c2f24e 100644
--- a/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx
+++ b/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx
@@ -19,6 +19,7 @@
 #include "../WinAPI/Fl_WinAPI_Screen_Driver.H"
 #include "Fl_GDI_Image_Surface_Driver.H"
 #include <FL/platform.H>
+#include <FL/Fl_Bitmap.H>
 #include <windows.h>
 
 
@@ -35,10 +36,16 @@ Fl_GDI_Image_Surface_Driver::Fl_GDI_Image_Surface_Driver(int w, int h, int high_
   driver(Fl_Graphics_Driver::newMainGraphicsDriver());
   if (d != 1 && high_res) ((Fl_GDI_Graphics_Driver*)driver())->scale(d);
   origin.x = origin.y = 0;
+  shape_data_ = NULL;
 }
 
 
 Fl_GDI_Image_Surface_Driver::~Fl_GDI_Image_Surface_Driver() {
+  if (shape_data_ && shape_data_->background) {
+    DeleteObject(shape_data_->background);
+    delete shape_data_->mask;
+    free(shape_data_);
+  }
   if (offscreen && !external_offscreen) DeleteObject((HBITMAP)offscreen);
   delete driver();
 }
@@ -67,6 +74,43 @@ void Fl_GDI_Image_Surface_Driver::untranslate() {
 
 Fl_RGB_Image* Fl_GDI_Image_Surface_Driver::image()
 {
+  if (shape_data_ && shape_data_->background) {
+    // get the offscreen size in pixels
+    HDC gc = fl_makeDC((HBITMAP)offscreen);
+    BITMAPINFO bmi;
+    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
+    bmi.bmiHeader.biCompression = BI_RGB;
+    bmi.bmiHeader.biPlanes = 1;
+    bmi.bmiHeader.biBitCount = 0;
+    bmi.bmiHeader.biSizeImage = 0;
+    GetDIBits(gc, (HBITMAP)offscreen, 0, 0, NULL, &bmi, DIB_RGB_COLORS);
+    int W = bmi.bmiHeader.biWidth;
+    int H = bmi.bmiHeader.biHeight;
+    int line_size = ((3*W+3)/4) * 4;
+
+    // read bits of main offscreen
+    uchar *dib_src = new uchar[line_size * H];
+    bmi.bmiHeader.biWidth = W;
+    bmi.bmiHeader.biHeight = H;
+    bmi.bmiHeader.biCompression = BI_RGB;
+    bmi.bmiHeader.biBitCount = 24;
+    GetDIBits(gc, (HBITMAP)offscreen, 0, H,
+                       dib_src, &bmi, DIB_RGB_COLORS);
+        
+    // draw above the secondary offscreen the main offscreen masked by shape_data_->mask
+    GdiFlush();
+    Fl_Image_Surface_Driver::copy_with_mask(shape_data_->mask, shape_data_->vBits, dib_src, ((3*W+3)/4) * 4, true);
+    delete shape_data_->mask;
+    delete[] dib_src;
+
+    // write bits of main offscreen
+    SetDIBits(gc, (HBITMAP)offscreen, 0, H, shape_data_->vBits, &bmi, DIB_RGB_COLORS);
+    DeleteDC(gc);
+    DeleteObject(shape_data_->background);
+    shape_data_->background = NULL;
+    free(shape_data_);
+    shape_data_ = NULL;
+   }
   Fl_RGB_Image *image = Fl::screen_driver()->read_win_rectangle( 0, 0, width, height, 0);
   return image;
 }
@@ -81,3 +125,45 @@ void Fl_GDI_Image_Surface_Driver::end_current()
   fl_window = pre_window;
   Fl_Surface_Device::end_current();
 }
+
+
+void Fl_GDI_Image_Surface_Driver::mask(const Fl_RGB_Image *mask) {
+  shape_data_ =  (struct shape_data_type*)calloc(1, sizeof(struct shape_data_type));
+  // get the offscreen size in pixels
+  HDC gc = fl_makeDC((HBITMAP)offscreen);
+  BITMAPINFO bmi;
+  bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
+  bmi.bmiHeader.biCompression = BI_RGB;
+  bmi.bmiHeader.biPlanes = 1;
+  bmi.bmiHeader.biBitCount = 0;
+  bmi.bmiHeader.biSizeImage = 0;
+
+  GetDIBits(gc, (HBITMAP)offscreen, 0, 0, NULL, &bmi, DIB_RGB_COLORS);
+  int W = bmi.bmiHeader.biWidth;
+  int H = bmi.bmiHeader.biHeight;
+  
+  shape_data_->mask = Fl_Image_Surface_Driver::RGB3_to_RGB1(mask, W, H);
+  
+  // duplicate current offscreen content to new offscreen
+  int line_size = ((3*W+3)/4) * 4;
+  uchar *dib = new uchar[line_size * H];  // create temporary buffer to read DIB
+  bmi.bmiHeader.biWidth = W;
+  bmi.bmiHeader.biHeight = H;
+  bmi.bmiHeader.biCompression = BI_RGB;
+  bmi.bmiHeader.biBitCount = 24;
+  
+  GetDIBits(gc, (HBITMAP)offscreen, 0, H, dib, &bmi, DIB_RGB_COLORS);
+  
+  HDC background_gc = CreateCompatibleDC(gc);
+  shape_data_->background = 
+    CreateDIBSection(background_gc, &bmi, DIB_RGB_COLORS,
+                     (void**)&shape_data_->vBits, NULL, 0);
+  if (!shape_data_->background) {
+    Fl::error("CreateDIBSection error=%lu", GetLastError());
+  }
+  memcpy(shape_data_->vBits, dib, H * line_size);
+  delete[] dib;
+  DeleteDC(background_gc);
+  DeleteDC(gc);
+}
+
diff --git a/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.H b/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.H
index b6f58ec8f..69e00dfd0 100644
--- a/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.H
+++ b/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.H
@@ -21,6 +21,11 @@
 #include <FL/platform.H>
 
 class Fl_Quartz_Image_Surface_Driver : public Fl_Image_Surface_Driver {
+private:
+# if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
+  CGImageRef mask_;
+  void mask(const Fl_RGB_Image *) FL_OVERRIDE;
+#endif
   void end_current() FL_OVERRIDE;
 public:
   FLWindow *pre_window;
diff --git a/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.cxx b/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.cxx
index 451078484..fb522745a 100644
--- a/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.cxx
+++ b/src/drivers/Quartz/Fl_Quartz_Image_Surface_Driver.cxx
@@ -1,7 +1,7 @@
 //
 // Draw-to-image code for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2018 by Bill Spitzak and others.
+// Copyright 1998-2023 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -23,6 +23,9 @@
 
 
 Fl_Quartz_Image_Surface_Driver::Fl_Quartz_Image_Surface_Driver(int w, int h, int high_res, Fl_Offscreen off) : Fl_Image_Surface_Driver(w, h, high_res, off) {
+# if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
+  mask_ = NULL;
+#endif
   int W = w, H = h;
   float s = 1;
   if (high_res) {
@@ -49,6 +52,12 @@ Fl_Quartz_Image_Surface_Driver::Fl_Quartz_Image_Surface_Driver(int w, int h, int
 }
 
 Fl_Quartz_Image_Surface_Driver::~Fl_Quartz_Image_Surface_Driver() {
+# if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
+  if (mask_) {
+    CGImageRelease(mask_);
+  }
+#endif
+  if (offscreen) CGContextRestoreGState((CGContextRef)offscreen);
   if (offscreen && !external_offscreen) {
     void *data = CGBitmapContextGetData((CGContextRef)offscreen);
     free(data);
@@ -56,6 +65,7 @@ Fl_Quartz_Image_Surface_Driver::~Fl_Quartz_Image_Surface_Driver() {
   }
   delete driver();
 }
+ 
 
 void Fl_Quartz_Image_Surface_Driver::set_current() {
   Fl_Surface_Device::set_current();
@@ -63,6 +73,15 @@ void Fl_Quartz_Image_Surface_Driver::set_current() {
   driver()->gc((CGContextRef)offscreen);
   fl_window = 0;
   ((Fl_Quartz_Graphics_Driver*)driver())->high_resolution( CGBitmapContextGetWidth((CGContextRef)offscreen) > (size_t)width );
+# if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
+  if (mask_) {
+    int W, H;
+    printable_rect(&W, &H);
+    CGContextSaveGState((CGContextRef)offscreen);
+    CGContextClipToMask((CGContextRef)offscreen, CGRectMake(0,0,W,H), mask_); // 10.4
+    CGContextSaveGState((CGContextRef)offscreen);
+  }
+# endif
 }
 
 void Fl_Quartz_Image_Surface_Driver::translate(int x, int y) {
@@ -79,6 +98,13 @@ void Fl_Quartz_Image_Surface_Driver::untranslate() {
 Fl_RGB_Image* Fl_Quartz_Image_Surface_Driver::image()
 {
   CGContextFlush((CGContextRef)offscreen);
+# if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
+  if (mask_) {
+    CGContextRestoreGState((CGContextRef)offscreen);
+    CGImageRelease(mask_);
+    mask_ = NULL;
+  }
+#endif
   int W = (int)CGBitmapContextGetWidth((CGContextRef)offscreen);
   int H = (int)CGBitmapContextGetHeight((CGContextRef)offscreen);
   int bpr = (int)CGBitmapContextGetBytesPerRow((CGContextRef)offscreen);
@@ -101,6 +127,54 @@ Fl_RGB_Image* Fl_Quartz_Image_Surface_Driver::image()
 
 void Fl_Quartz_Image_Surface_Driver::end_current()
 {
+# if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
+  if (mask_) {
+    CGContextRestoreGState((CGContextRef)offscreen);
+    CGContextRestoreGState((CGContextRef)offscreen);
+  }
+# endif
   fl_window = pre_window;
   Fl_Surface_Device::end_current();
 }
+
+
+# if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
+
+static void MyProviderReleaseData (void *info, const void *data, size_t size) {
+  delete[] (uchar*)data;
+}
+
+
+void Fl_Quartz_Image_Surface_Driver::mask(const Fl_RGB_Image *img) {
+  if (!&CGContextClipToMask) return;
+  int W = (int)CGBitmapContextGetWidth((CGContextRef)offscreen);
+  int H = (int)CGBitmapContextGetHeight((CGContextRef)offscreen);
+  bool using_copy = false;
+  if (W != img->data_w() || H != img->data_h()) {
+    Fl_RGB_Image *copy = (Fl_RGB_Image*)img->copy(W, H);
+    img = copy;
+    using_copy = true;
+  }
+  
+  int i, d = img->d(), w = img->data_w(), h = img->data_h();
+  // reverse top and bottom and convert to gray scale if img->d() == 3 and complement bits
+  int bytes_per_row = (img->ld() ? img->ld() : w * d);
+  uchar *from = new uchar[w * h];
+  for ( i = 0; i < h; i++) {
+    const uchar *p = img->array + bytes_per_row * i;
+    const uchar *last = p + bytes_per_row;
+    uchar *q = from + (h - 1 - i) * w;
+    while (p < last) {
+      unsigned u = *p++;
+      u += *p++;
+      u += *p++;
+      *q++ = ~(u/3);
+    }
+  }
+  CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, from, w * h, MyProviderReleaseData);
+  mask_ = CGImageMaskCreate(w, h, 8, 8, w, provider, NULL, false);
+  CFRelease(provider);
+  if (using_copy) delete img;
+}
+
+#endif
diff --git a/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.H b/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.H
index 285222ced..ae32ac3df 100644
--- a/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.H
+++ b/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.H
@@ -25,6 +25,12 @@ class Fl_Wayland_Image_Surface_Driver : public Fl_Image_Surface_Driver {
 public:
   Fl_Wayland_Image_Surface_Driver(int w, int h, int high_res, Fl_Offscreen off);
   ~Fl_Wayland_Image_Surface_Driver();
+  void mask(const Fl_RGB_Image *) FL_OVERRIDE;
+  struct shape_data_type {
+    double scale;
+    cairo_pattern_t *mask_pattern_;
+    cairo_t *bg_cr;
+  } *shape_data_;
   void set_current() FL_OVERRIDE;
   void translate(int x, int y) FL_OVERRIDE;
   void untranslate() FL_OVERRIDE;
diff --git a/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.cxx b/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.cxx
index 83419e5b2..f25fe025d 100644
--- a/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.cxx
+++ b/src/drivers/Wayland/Fl_Wayland_Image_Surface_Driver.cxx
@@ -22,6 +22,7 @@
 
 Fl_Wayland_Image_Surface_Driver::Fl_Wayland_Image_Surface_Driver(int w, int h,
       int high_res, Fl_Offscreen off) : Fl_Image_Surface_Driver(w, h, high_res, off) {
+  shape_data_ = NULL;
   float s = 1;
   int d = 1;
   if (!off) {
@@ -51,6 +52,19 @@ Fl_Wayland_Image_Surface_Driver::Fl_Wayland_Image_Surface_Driver(int w, int h,
 
 
 Fl_Wayland_Image_Surface_Driver::~Fl_Wayland_Image_Surface_Driver() {
+  if (shape_data_) {
+    cairo_surface_t *surf;
+    cairo_pattern_get_surface(shape_data_->mask_pattern_, &surf);
+    unsigned char *bits = cairo_image_surface_get_data(surf);
+    cairo_pattern_destroy(shape_data_->mask_pattern_);
+    delete[] bits;
+    struct Fl_Wayland_Graphics_Driver::draw_buffer *off_ =
+    Fl_Wayland_Graphics_Driver::offscreen_buffer((Fl_Offscreen)shape_data_->bg_cr);
+    delete[] off_->buffer;
+    free(off_);
+    cairo_destroy(shape_data_->bg_cr);
+    free(shape_data_);
+  }
   if (offscreen && !external_offscreen) {
     struct Fl_Wayland_Graphics_Driver::draw_buffer *buffer =
       Fl_Wayland_Graphics_Driver::offscreen_buffer(offscreen);
@@ -91,10 +105,38 @@ void Fl_Wayland_Image_Surface_Driver::untranslate() {
 
 
 Fl_RGB_Image* Fl_Wayland_Image_Surface_Driver::image() {
+  if (shape_data_ && shape_data_->mask_pattern_) {
+    // draw above the secondary offscreen the main offscreen masked by mask_pattern_
+    cairo_t *c = ((Fl_Cairo_Graphics_Driver*)driver())->cr();
+    cairo_pattern_t *paint_pattern = cairo_pattern_create_for_surface(cairo_get_target(c));
+    cairo_set_source(shape_data_->bg_cr, paint_pattern);
+    cairo_mask(shape_data_->bg_cr, shape_data_->mask_pattern_);
+    cairo_pattern_destroy(paint_pattern);
+    // copy secondary offscreen to the main offscreen
+    cairo_pattern_t *pat = cairo_pattern_create_for_surface(cairo_get_target(shape_data_->bg_cr));
+    cairo_scale(c, shape_data_->scale, shape_data_->scale);
+    cairo_set_source(c, pat),
+    cairo_paint(c);
+    cairo_pattern_destroy(pat);
+    // delete secondary offscreen
+    cairo_surface_t *surf;
+    cairo_pattern_get_surface(shape_data_->mask_pattern_, &surf);
+    unsigned char *bits = cairo_image_surface_get_data(surf);
+    cairo_pattern_destroy(shape_data_->mask_pattern_);
+    delete[] bits;
+    struct Fl_Wayland_Graphics_Driver::draw_buffer *off_ =
+    Fl_Wayland_Graphics_Driver::offscreen_buffer((Fl_Offscreen)shape_data_->bg_cr);
+    delete[] off_->buffer;
+    free(off_);
+    cairo_destroy(shape_data_->bg_cr);
+    free(shape_data_);
+    shape_data_ = NULL;
+  }
+  
   // Convert depth-4 image in draw_buffer to a depth-3 image while exchanging R and B colors
   struct Fl_Wayland_Graphics_Driver::draw_buffer *off_buf =
     Fl_Wayland_Graphics_Driver::offscreen_buffer(offscreen);
-  int height = off_buf->data_size / off_buf->stride;
+  int height = int(off_buf->data_size / off_buf->stride);
   uchar *rgb = new uchar[off_buf->width * height * 3];
   uchar *p = rgb;
   uchar *q;
@@ -111,3 +153,34 @@ Fl_RGB_Image* Fl_Wayland_Image_Surface_Driver::image() {
   image->alloc_array = 1;
   return image;
 }
+
+
+void Fl_Wayland_Image_Surface_Driver::mask(const Fl_RGB_Image *mask) {
+  bool using_copy = false;
+  shape_data_ =  (struct shape_data_type*)calloc(1, sizeof(struct shape_data_type));
+  int W, H;
+  struct Fl_Wayland_Graphics_Driver::draw_buffer *off_buf =
+  Fl_Wayland_Graphics_Driver::offscreen_buffer(offscreen);
+  W = off_buf->width;
+  H = (int)(off_buf->data_size / off_buf->stride);
+  if (W != mask->data_w() || H != mask->data_h()) {
+    Fl_RGB_Image *copy = (Fl_RGB_Image*)mask->copy(W, H);
+    mask = copy;
+    using_copy = true;
+  }
+  shape_data_->mask_pattern_ = Fl_Cairo_Graphics_Driver::calc_cairo_mask(mask);
+  //duplicate current offscreen content to new cairo_t* shape_data_->bg_cr
+  int width, height;
+  printable_rect(&width, &height);
+  struct Fl_Wayland_Graphics_Driver::draw_buffer *off_ =
+  (struct Fl_Wayland_Graphics_Driver::draw_buffer*)calloc(1,
+                                                          sizeof(struct Fl_Wayland_Graphics_Driver::draw_buffer));
+  Fl_Wayland_Graphics_Driver::cairo_init(off_, W, H,
+                                         cairo_format_stride_for_width(CAIRO_FORMAT_RGB24, W),
+                                         CAIRO_FORMAT_RGB24);
+  cairo_set_user_data(off_->cairo_, &Fl_Wayland_Graphics_Driver::key, off_, NULL);
+  shape_data_->bg_cr = off_->cairo_;
+  memcpy(off_->buffer, off_buf->buffer, off_buf->data_size);
+  shape_data_->scale = double(width) / W;
+  if (using_copy) delete mask;
+}
diff --git a/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.H b/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.H
index ab702840d..382daf886 100644
--- a/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.H
+++ b/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.H
@@ -1,7 +1,7 @@
 //
 // Draw-to-image code for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2022 by Bill Spitzak and others.
+// Copyright 2022-2023 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -32,8 +32,19 @@ public:
   void translate(int x, int y) FL_OVERRIDE;
   void untranslate() FL_OVERRIDE;
   Fl_RGB_Image *image() FL_OVERRIDE;
+  void mask(const Fl_RGB_Image *) FL_OVERRIDE;
 #if FLTK_USE_CAIRO
   cairo_t *cairo_;
+  struct shape_data_type {
+    double scale;
+    cairo_pattern_t *mask_pattern_;
+    cairo_t *bg_cr;
+  } *shape_data_;
+#else
+  struct shape_data_type {
+    Pixmap background;
+    Fl_RGB_Image* mask;
+  } *shape_data_;
 #endif
 };
 
diff --git a/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx b/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx
index bcaf7d46a..87e55b417 100644
--- a/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx
+++ b/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx
@@ -17,6 +17,7 @@
 #include <FL/platform.H>
 #include "Fl_Xlib_Image_Surface_Driver.H"
 #include "../../Fl_Screen_Driver.H"
+#include <stdlib.h>
 #if FLTK_USE_CAIRO
 #  include <cairo-xlib.h>
 #  include "../Cairo/Fl_X11_Cairo_Graphics_Driver.H"
@@ -37,6 +38,7 @@ Fl_Xlib_Image_Surface_Driver::Fl_Xlib_Image_Surface_Driver(int w, int h, int hig
     }
     offscreen = (Fl_Offscreen)XCreatePixmap(fl_display, RootWindow(fl_display, fl_screen), w, h, fl_visual->depth);
   }
+  shape_data_ = NULL;
 #if FLTK_USE_CAIRO
   driver(new Fl_X11_Cairo_Graphics_Driver());
   cairo_surface_t *s = cairo_xlib_surface_create(fl_display, offscreen, fl_visual->visual, w, h);
@@ -52,7 +54,24 @@ Fl_Xlib_Image_Surface_Driver::Fl_Xlib_Image_Surface_Driver(int w, int h, int hig
 
 Fl_Xlib_Image_Surface_Driver::~Fl_Xlib_Image_Surface_Driver() {
 #if FLTK_USE_CAIRO
+  if (shape_data_) {
+    cairo_surface_t *surf;
+    cairo_pattern_get_surface(shape_data_->mask_pattern_, &surf);
+    unsigned char *bits = cairo_image_surface_get_data(surf);
+    cairo_pattern_destroy(shape_data_->mask_pattern_);
+    delete[] bits;
+    Pixmap p = cairo_xlib_surface_get_drawable(cairo_get_target(shape_data_->bg_cr));
+    XFreePixmap(fl_display, p);
+    cairo_destroy(shape_data_->bg_cr);
+    free(shape_data_);
+  }
   cairo_destroy(cairo_);
+#else
+  if (shape_data_) {
+    XFreePixmap(fl_display, shape_data_->background);
+    delete shape_data_->mask;
+    free(shape_data_);
+  }
 #endif
   if (offscreen && !external_offscreen) XFreePixmap(fl_display, (Pixmap)offscreen);
   delete driver();
@@ -84,14 +103,117 @@ void Fl_Xlib_Image_Surface_Driver::untranslate() {
 #endif
 }
 
+
 Fl_RGB_Image* Fl_Xlib_Image_Surface_Driver::image()
 {
+  if (shape_data_) {
+#if FLTK_USE_CAIRO
+    // draw above the secondary offscreen the main offscreen masked by mask_pattern_
+    cairo_t *c = ((Fl_Cairo_Graphics_Driver*)driver())->cr();
+    cairo_pattern_t *paint_pattern = cairo_pattern_create_for_surface(cairo_get_target(c));
+    cairo_set_source(shape_data_->bg_cr, paint_pattern);
+    cairo_mask(shape_data_->bg_cr, shape_data_->mask_pattern_);
+    cairo_pattern_destroy(paint_pattern);
+    // copy secondary offscreen to the main offscreen
+    cairo_pattern_t *pat = cairo_pattern_create_for_surface(cairo_get_target(shape_data_->bg_cr));
+    cairo_scale(c, shape_data_->scale, shape_data_->scale);
+    cairo_set_source(c, pat),
+    cairo_paint(c);
+    cairo_pattern_destroy(pat);
+    // delete secondary offscreen
+    cairo_surface_t *surf;
+    cairo_pattern_get_surface(shape_data_->mask_pattern_, &surf);
+    unsigned char *bits = cairo_image_surface_get_data(surf);
+    cairo_pattern_destroy(shape_data_->mask_pattern_);
+    delete[] bits;
+    Pixmap p = cairo_xlib_surface_get_drawable(cairo_get_target(shape_data_->bg_cr));
+    XFreePixmap(fl_display, p);
+    cairo_destroy(shape_data_->bg_cr);
+#else // !FLTK_USE_CAIRO
+  // draw the main offscreen masked by shape_data_->mask above the background offscreen
+    int w, h;
+    printable_rect(&w, &h);
+    Fl_RGB_Image *img_main = Fl::screen_driver()->read_win_rectangle(0, 0, w, h, 0);
+    fl_window = shape_data_->background; // temporary change
+    Fl_RGB_Image *img_background = Fl::screen_driver()->read_win_rectangle(0, 0, w, h, 0);
+    fl_window = offscreen;
+    Fl_Image_Surface_Driver::copy_with_mask(shape_data_->mask, 
+                                            (uchar*)img_background->array,
+                                            (uchar*)img_main->array,
+                                            3 * shape_data_->mask->w(), false);
+    delete img_main;
+  // copy background offscreen to main offscreen
+    float s = driver()->scale();
+    driver()->scale(1);
+    fl_draw_image(img_background->array, 0, 0,
+                  img_background->data_w(), img_background->data_h());
+    driver()->scale(s);
+    delete img_background;
+  // delete background offscreen
+    XFreePixmap(fl_display, shape_data_->background);
+    delete shape_data_->mask;
+#endif // FLTK_USE_CAIRO
+    free(shape_data_);
+    shape_data_ = NULL;
+}
   Fl_RGB_Image *image = Fl::screen_driver()->read_win_rectangle(0, 0, width, height, 0);
   return image;
 }
 
+
 void Fl_Xlib_Image_Surface_Driver::end_current()
 {
   fl_window = pre_window;
   Fl_Surface_Device::end_current();
 }
+
+
+#if FLTK_USE_CAIRO
+
+void Fl_Xlib_Image_Surface_Driver::mask(const Fl_RGB_Image *mask) {
+  bool using_copy = false;
+  shape_data_ =  (struct shape_data_type*)calloc(1, sizeof(struct shape_data_type));
+  int W, H;
+  cairo_t *c = ((Fl_Cairo_Graphics_Driver*)driver())->cr();
+  cairo_surface_t *c_surface = cairo_get_target(c);
+  W = cairo_xlib_surface_get_width(c_surface);
+  H = cairo_xlib_surface_get_height(c_surface);
+  if (W != mask->data_w() || H != mask->data_h()) {
+    Fl_RGB_Image *copy = (Fl_RGB_Image*)mask->copy(W, H);
+    mask = copy;
+    using_copy = true;
+  }
+  shape_data_->mask_pattern_ = Fl_Cairo_Graphics_Driver::calc_cairo_mask(mask);
+  //duplicate current offscreen content to new cairo_t* shape_data_->bg_cr
+  int width, height;
+  printable_rect(&width, &height);
+  Pixmap pxm = XCreatePixmap(fl_display, RootWindow(fl_display, fl_screen), W, H, fl_visual->depth);
+  cairo_surface_t *background = cairo_xlib_surface_create(fl_display, pxm, fl_visual->visual, W, H);
+  shape_data_->bg_cr = cairo_create(background);
+  cairo_surface_destroy(background);
+  cairo_surface_flush(c_surface);
+  cairo_pattern_t *pat = cairo_pattern_create_for_surface(c_surface);
+  cairo_set_source(shape_data_->bg_cr, pat),
+  cairo_paint(shape_data_->bg_cr);
+  cairo_pattern_destroy(pat);
+  shape_data_->scale = double(width) / W;
+  if (using_copy) delete mask;
+}
+
+#else
+
+void Fl_Xlib_Image_Surface_Driver::mask(const Fl_RGB_Image *mask) {
+  shape_data_ =  (struct shape_data_type*)calloc(1, sizeof(struct shape_data_type));
+  // get dimensions
+  int W, H;
+  Fl::screen_driver()->offscreen_size(offscreen, W, H);
+  // compute depth-1 mask
+  shape_data_->mask = Fl_Image_Surface_Driver::RGB3_to_RGB1(mask, W, H);
+
+  // duplicate current offscreen content to new, background offscreen
+  shape_data_->background = XCreatePixmap(fl_display, RootWindow(fl_display, fl_screen), W, H, fl_visual->depth);
+  driver()->restore_clip();
+  XCopyArea(fl_display, (Pixmap)offscreen, shape_data_->background, (GC)driver()->gc(), 0, 0, W, H,  0, 0);
+}
+
+#endif // FLTK_USE_CAIRO