Fix fl_read_image() under MacOS platform when GUI is rescaled.

This commit also simplifies the platform-dependent support of fl_read_image():
only Fl_XXX_Screen_Driver::read_win_rectangle() contains platform-specific
code to capture pixels from the current window or from an offscreen buffer.
Platform-independent function Fl_Screen_Driver::traverse_to_gl_subwindows()
captures subwindows that intersect with the area fl_read_image() targets.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12653 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

21 files changed, 214 insertions, 173 deletions

diff --git a/FL/Fl_Graphics_Driver.H b/FL/Fl_Graphics_Driver.H
index bd4a82326..27778da2f 100644
--- a/FL/Fl_Graphics_Driver.H
+++ b/FL/Fl_Graphics_Driver.H
@@ -395,6 +395,12 @@ public:
   virtual void font_name(int num, const char *name) {}
   /** Support function for Fl_Shared_Image drawing */
   virtual int draw_scaled(Fl_Image *img, int X, int Y, int W, int H);
+  /** Support function for fl_overlay_rect() and scaled GUI.
+   Defaut implementation may be enough */
+  virtual bool overlay_rect_unscaled();
+  /** Support function for fl_overlay_rect() and scaled GUI.
+   Defaut implementation may be enough */
+  virtual void overlay_rect(int x, int y, int w , int h) { loop(x, y, x+w-1, y, x+w-1, y+h-1, x, y+h-1); }
 };
 
 #ifndef FL_DOXYGEN
diff --git a/FL/Fl_Screen_Driver.H b/FL/Fl_Screen_Driver.H
index 00d3d763d..564b77754 100644
--- a/FL/Fl_Screen_Driver.H
+++ b/FL/Fl_Screen_Driver.H
@@ -3,7 +3,7 @@
 //
 // All screen related calls in a driver style class.
 //
-// Copyright 1998-2017 by Bill Spitzak and others.
+// Copyright 1998-2018 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
@@ -126,25 +126,23 @@ public:
 #if defined(FL_PORTING)
 #  pragma message "FL_PORTING: implement code to read RGB data from screen"
 #endif
-  /* Both member functions read_image() and read_win_rectangle() support
-   the public function fl_read_image() which captures pixel data either from
+  /* Member function read_win_rectangle() supports the public function
+   fl_read_image() which captures pixel data either from
    the current window or from an offscreen buffer.
 
-   A platform re-implements either read_image() or read_win_rectangle().
-   In the 1st case and for capture from a window, the returned pixel array 
+   With fl_read_image() and for capture from a window, the returned pixel array
    also contains data from any embedded sub-window.
-   In the 2nd case and for capture from a window, only data from the current 
-   window is collected, and read_image()'s default implementation captures 
-   pixels from any subwindow.
+   
+   In the case of read_win_rectangle() and for capture from a window, only data
+   from the current window is collected.
    
    A platform may also use its read_win_rectangle() implementation to capture
    window decorations (e.g., title bar). In that case, it is called by
    Fl_XXX_Window_Driver::capture_titlebar_and_borders().
    */
-  virtual uchar *read_image(uchar *p, int x, int y, int w, int h, int alpha);
-  virtual Fl_RGB_Image *read_win_rectangle(uchar *p, int X, int Y, int w, int h, int alpha) {return NULL;}
+  virtual Fl_RGB_Image *read_win_rectangle(int X, int Y, int w, int h) {return NULL;}
   static void write_image_inside(Fl_RGB_Image *to, Fl_RGB_Image *from, int to_x, int to_y);
-  static Fl_RGB_Image *traverse_to_gl_subwindows(Fl_Group *g, uchar *p, int x, int y, int w, int h, int alpha,
+  static Fl_RGB_Image *traverse_to_gl_subwindows(Fl_Group *g, int x, int y, int w, int h,
                                                  Fl_RGB_Image *full_img);
   // optional platform-specific key handling for Fl_Input widget
   // the default implementation may be enough
diff --git a/src/Fl_Graphics_Driver.cxx b/src/Fl_Graphics_Driver.cxx
index d7cb15031..05d609f14 100644
--- a/src/Fl_Graphics_Driver.cxx
+++ b/src/Fl_Graphics_Driver.cxx
@@ -221,6 +221,11 @@ unsigned Fl_Graphics_Driver::font_desc_size() {
   return (unsigned)sizeof(Fl_Fontdesc);
 }
 
+bool Fl_Graphics_Driver::overlay_rect_unscaled()
+{
+  return (scale() == int(scale()));
+}
+
 #ifndef FL_DOXYGEN
 Fl_Font_Descriptor::Fl_Font_Descriptor(const char* name, Fl_Fontsize Size) {
   next = 0;
diff --git a/src/Fl_Screen_Driver.cxx b/src/Fl_Screen_Driver.cxx
index b10aa13ac..2dffcd7a5 100644
--- a/src/Fl_Screen_Driver.cxx
+++ b/src/Fl_Screen_Driver.cxx
@@ -141,45 +141,22 @@ void Fl_Screen_Driver::compose_reset() {
   Fl::compose_state = 0;
 }
 
-uchar *Fl_Screen_Driver::read_image(uchar *p, int X, int Y, int w, int h, int alpha) {
-  uchar *image_data = NULL;
-  Fl_RGB_Image *img;
-  if (fl_find(fl_window) == 0) { // read from off_screen buffer
-    img = read_win_rectangle(p, X, Y, w, h, alpha);
-    if (!img) {
-      return NULL;
-    }
-    img->alloc_array = 1;
-  } else {
-    img = traverse_to_gl_subwindows(Fl_Window::current(), p, X, Y, w, h, alpha, NULL);
-  }
-  if (img) {
-    if (img->w() != w) {
-      Fl_RGB_Image *img2 = (Fl_RGB_Image*)img->copy(w, h);
-      delete img;
-      img = img2;
-    }
-    img->alloc_array = 0;
-    image_data = (uchar*)img->array;
-    delete img;
-  }
-  return image_data;
-}
-
 void Fl_Screen_Driver::write_image_inside(Fl_RGB_Image *to, Fl_RGB_Image *from, int to_x, int to_y)
 /* Copy the image "from" inside image "to" with its top-left angle at coordinates to_x, to_y.
-Image depth can differ between "to" and "from".
+Image depths can differ between "to" and "from".
 */
 {
   int to_ld = (to->ld() == 0? to->w() * to->d() : to->ld());
   int from_ld = (from->ld() == 0? from->w() * from->d() : from->ld());
   uchar *tobytes = (uchar*)to->array + to_y * to_ld + to_x * to->d();
   const uchar *frombytes = from->array;
+  int need_alpha = (from->d() == 3 && to->d() == 4);
   for (int i = 0; i < from->h(); i++) {
     if (from->d() == to->d()) memcpy(tobytes, frombytes, from->w() * from->d());
     else {
       for (int j = 0; j < from->w(); j++) {
         memcpy(tobytes + j * to->d(), frombytes + j * from->d(), from->d());
+        if (need_alpha) *(tobytes + j * to->d() + 3) = 0xff;
       }
     }
     tobytes += to_ld;
@@ -193,45 +170,31 @@ Image depth can differ between "to" and "from".
  
  Arguments when this function is initially called:
  g: a window or GL window
- p: as in fl_read_image()
  x,y,w,h: a rectangle in window g's coordinates
- alpha: as in fl_read_image()
  full_img: NULL
  
  Arguments when this function recursively calls itself:
  g: an Fl_Group
- p: as above
  x,y,w,h: a rectangle in g's coordinates if g is a window, or in g's parent window coords if g is a group
- alpha: as above
  full_img: NULL, or a previously captured image that encompasses the x,y,w,h rectangle and that
  will be partially overwritten with the new capture
  
  Return value:
- An Fl_RGB_Image* of depth 4 if alpha>0 or 3 if alpha = 0 containing the captured pixels.
+ An Fl_RGB_Image*, the depth of which is platform-dependent, containing the captured pixels.
  */
-Fl_RGB_Image *Fl_Screen_Driver::traverse_to_gl_subwindows(Fl_Group *g, uchar *p, int x, int y, int w, int h, int alpha,
+Fl_RGB_Image *Fl_Screen_Driver::traverse_to_gl_subwindows(Fl_Group *g, int x, int y, int w, int h,
                                                           Fl_RGB_Image *full_img)
 {
   if ( g->as_gl_window() ) {
     Fl_Plugin_Manager pm("fltk:device");
     Fl_Device_Plugin *pi = (Fl_Device_Plugin*)pm.plugin("opengl.device.fltk.org");
     if (!pi) return full_img;
-    Fl_RGB_Image *img = pi->rectangle_capture(g, x, y, w, h);
-    if (full_img) full_img = img;
-    else {
-      uchar *data = ( p ? p : new uchar[img->w() * img->h() * (alpha?4:3)] );
-      full_img = new Fl_RGB_Image(data, img->w(), img->h(), alpha?4:3);
-      if (!p) full_img->alloc_array = 1;
-      if (alpha) memset(data, alpha, img->w() * img->h() * 4);
-      write_image_inside(full_img, img, 0, 0);
-      delete img;
-    }
+    full_img = pi->rectangle_capture(g, x, y, w, h);
   }
   else if ( g->as_window() && (!full_img || (g->window() && g->window()->as_gl_window())) ) {
     // the starting window or one inside a GL window
     if (full_img) g->as_window()->make_current();
-    int alloc_img = (full_img != NULL || p == NULL); // false means use p, don't alloc new memory for image
-    full_img = Fl::screen_driver()->read_win_rectangle( (alloc_img ? NULL : p), x, y, w, h, alpha);
+    full_img = Fl::screen_driver()->read_win_rectangle(x, y, w, h);
   }
   int n = g->children();
   for (int i = 0; i < n; i++) {
@@ -249,8 +212,8 @@ Fl_RGB_Image *Fl_Screen_Driver::traverse_to_gl_subwindows(Fl_Group *g, uchar *p,
       if (origin_y + height > c->y() + c->h()) height = c->y() + c->h() - origin_y;
       if (origin_y + height > y + h) height = y + h - origin_y;
       if (width > 0 && height > 0) {
-        Fl_RGB_Image *img = traverse_to_gl_subwindows(c->as_window(), p, origin_x - c->x(),
-                                                      origin_y - c->y(), width, height, alpha, full_img);
+        Fl_RGB_Image *img = traverse_to_gl_subwindows(c->as_window(),  origin_x - c->x(),
+                                                      origin_y - c->y(), width, height, full_img);
         if (img == full_img) continue;
         int top;
         if (c->as_gl_window()) {
@@ -264,7 +227,7 @@ Fl_RGB_Image *Fl_Screen_Driver::traverse_to_gl_subwindows(Fl_Group *g, uchar *p,
         delete img;
       }
     }
-    else traverse_to_gl_subwindows(c->as_group(), p, x, y, w, h, alpha, full_img);
+    else traverse_to_gl_subwindows(c->as_group(), x, y, w, h, full_img);
   }
   return full_img;
 }
diff --git a/src/Fl_Widget_Surface.cxx b/src/Fl_Widget_Surface.cxx
index 7adc4361e..64f86d9ed 100644
--- a/src/Fl_Widget_Surface.cxx
+++ b/src/Fl_Widget_Surface.cxx
@@ -157,7 +157,7 @@ void Fl_Widget_Surface::print_window_part(Fl_Window *win, int x, int y, int w, i
   win->show();
   Fl::check();
   win->driver()->flush(); // makes the window current
-  Fl_RGB_Image *img = Fl_Screen_Driver::traverse_to_gl_subwindows(win, NULL, x, y, w, h, 0, NULL);
+  Fl_RGB_Image *img = Fl_Screen_Driver::traverse_to_gl_subwindows(win, x, y, w, h, NULL);
   Fl_Shared_Image *shared = Fl_Shared_Image::get(img);
   shared->scale(w, h, 1, 1);
   if (save_front != win) save_front->show();
diff --git a/src/Fl_win32.cxx b/src/Fl_win32.cxx
index 74b2f317b..0a8e399b9 100644
--- a/src/Fl_win32.cxx
+++ b/src/Fl_win32.cxx
@@ -2710,17 +2710,17 @@ void Fl_WinAPI_Window_Driver::capture_titlebar_and_borders(Fl_Shared_Image *&top
   // capture the 4 window sides from screen
   Fl_WinAPI_Screen_Driver *dr = (Fl_WinAPI_Screen_Driver *)Fl::screen_driver();
   if (htop) {
-    r_top = dr->read_win_rectangle_unscaled(NULL, r.left, r.top, r.right - r.left, htop, 0);
+    r_top = dr->read_win_rectangle_unscaled(r.left, r.top, r.right - r.left, htop);
     top = Fl_Shared_Image::get(r_top);
     if (DWMscaling != 1)
       top->scale(ww, htop / DWMscaling, 0, 1);
   }
   if (wsides) {
-    r_left = dr->read_win_rectangle_unscaled(NULL, r.left, r.top + htop, wsides, h() * scaling, 0);
+    r_left = dr->read_win_rectangle_unscaled(r.left, r.top + htop, wsides, h() * scaling);
     left = Fl_Shared_Image::get(r_left);
-    r_right = dr->read_win_rectangle_unscaled(NULL, r.right - wsides, r.top + htop, wsides, h() * scaling, 0);
+    r_right = dr->read_win_rectangle_unscaled(r.right - wsides, r.top + htop, wsides, h() * scaling);
     right = Fl_Shared_Image::get(r_right);
-    r_bottom = dr->read_win_rectangle_unscaled(NULL, r.left, r.bottom - hbottom, ww, hbottom, 0);
+    r_bottom = dr->read_win_rectangle_unscaled(r.left, r.bottom - hbottom, ww, hbottom);
     bottom = Fl_Shared_Image::get(r_bottom);
     if (scaling != 1) {
       left->scale(wsides, h(), 0, 1);
diff --git a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H
index 12d93b9e8..077416823 100644
--- a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H
+++ b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H
@@ -4,7 +4,7 @@
 // Definition of Apple Cocoa Screen interface
 // for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2010-2017 by Bill Spitzak and others.
+// Copyright 2010-2018 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
@@ -40,6 +40,7 @@
 
 class Fl_Window;
 class Fl_Input;
+class Fl_RGB_Image;
 
 class FL_EXPORT Fl_Cocoa_Screen_Driver : public Fl_Screen_Driver 
 {
@@ -87,7 +88,6 @@ public:
   int insertion_point_location(int *px, int *py, int *pheight);
   virtual int dnd(int use_selection);
   virtual int compose(int &del);
-  virtual uchar *read_image(uchar *p, int x, int y, int w, int h, int alpha);
   virtual int input_widget_handle_key(int key, unsigned mods, unsigned shift, Fl_Input *input);
   virtual int get_mouse(int &x, int &y);
   virtual void enable_im();
@@ -100,6 +100,7 @@ public:
   virtual APP_SCALING_CAPABILITY rescalable() { return SYSTEMWIDE_APP_SCALING; }
   virtual float scale(int n) {return scale_;}
   virtual void scale(int n, float f) { scale_ = f;}
+  virtual Fl_RGB_Image *read_win_rectangle(int X, int Y, int w, int h);
   virtual int run_also_windowless();
   virtual int wait_also_windowless(double delay);
 private:
diff --git a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
index 213995126..d46879932 100644
--- a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
+++ b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
@@ -256,70 +256,6 @@ int Fl_Cocoa_Screen_Driver::compose(int &del) {
   return 1;
 }
 
-uchar *                                       // O - Pixel buffer or NULL if failed
-Fl_Cocoa_Screen_Driver::read_image(uchar *p,	// I - Pixel buffer or NULL to allocate
-                                   int   x,		// I - Left position
-                                   int   y,		// I - Top position
-                                   int   w,		// I - Width of area to read
-                                   int   h,		// I - Height of area to read
-                                   int   alpha)// I - Alpha value for image (0 for none)
-{
-  uchar *base;
-  int rowBytes, delta;
-  float s = 1;
-  int ori_w = w, ori_h = h;
-  if (fl_window == NULL) { // reading from an offscreen buffer
-    CGContextRef src = (CGContextRef)Fl_Surface_Device::surface()->driver()->gc();  // get bitmap context
-    base = (uchar *)CGBitmapContextGetData(src);  // get data
-    if(!base) return NULL;
-    int sw = CGBitmapContextGetWidth(src);
-    int sh = CGBitmapContextGetHeight(src);
-    if( (sw - x < w) || (sh - y < h) )  return NULL;
-    rowBytes = CGBitmapContextGetBytesPerRow(src);
-    delta = CGBitmapContextGetBitsPerPixel(src)/8;
-    Fl_Image_Surface *imgs = (Fl_Image_Surface*)Fl_Surface_Device::surface();
-    int fltk_w, fltk_h;
-    imgs->printable_rect(&fltk_w, &fltk_h);
-    s = sw / float(fltk_w);
-    x *= s; y *= s; w *= s; h *= s;
-    if (x + w > sw) w = sw - x;
-    if (y + h > sh) h = sh - y;
-  }
-  else { // reading from current window
-    Fl_Cocoa_Window_Driver *d = Fl_Cocoa_Window_Driver::driver(Fl_Window::current());
-    base = d->bitmap_from_window_rect(x,y,w,h,&delta);
-    if (!base) return NULL;
-    rowBytes = delta*w;
-    x = y = 0;
-  }
-  // Allocate the image data array as needed...
-  int d = alpha ? 4 : 3;
-  if (!p) p = new uchar[w * h * d];
-  // Initialize the default colors/alpha in the whole image...
-  memset(p, alpha, w * h * d);
-  // Copy the image from the off-screen buffer to the memory buffer.
-  int idx, idy;	// Current X & Y in image
-  uchar *pdst, *psrc;
-  for (idy = y, pdst = p; idy < h + y; idy ++) {
-    for (idx = 0, psrc = base + idy * rowBytes + x * delta; idx < w; idx ++, psrc += delta, pdst += d) {
-      pdst[0] = psrc[0];  // R
-      pdst[1] = psrc[1];  // G
-      pdst[2] = psrc[2];  // B
-    }
-  }
-  if (fl_window != NULL) delete[] base;
-  if (s != 1) {
-    Fl_RGB_Image *rgb = new Fl_RGB_Image(p, w, h, alpha ? 4 : 3);
-    rgb->alloc_array = 1;
-    Fl_RGB_Image *rgb2 = (Fl_RGB_Image*)rgb->copy(ori_w, ori_h);
-    rgb2->alloc_array = 0;
-    delete rgb;
-    p = (uchar*)rgb2->array;
-    delete rgb2;
-  }
-  return p;
-}
-
 
 int Fl_Cocoa_Screen_Driver::input_widget_handle_key(int key, unsigned mods, unsigned shift, Fl_Input *input)
 {
@@ -401,6 +337,67 @@ void Fl_Cocoa_Screen_Driver::offscreen_size(Fl_Offscreen off, int &width, int &h
   height = CGBitmapContextGetHeight(off);
 }
 
+Fl_RGB_Image *Fl_Cocoa_Screen_Driver::read_win_rectangle(int X, int Y, int w, int h)
+{
+  int bpp, bpr, depth = 4;
+  uchar *base, *p;
+  if (!fl_window) { // read from offscreen buffer
+    float s = 1;
+    CGContextRef src = (CGContextRef)Fl_Surface_Device::surface()->driver()->gc();  // get bitmap context
+    base = (uchar *)CGBitmapContextGetData(src);  // get data
+    if(!base) return NULL;
+    int sw = CGBitmapContextGetWidth(src);
+    int sh = CGBitmapContextGetHeight(src);
+    if( (sw - X < w) || (sh - Y < h) )  return NULL;
+    bpr = CGBitmapContextGetBytesPerRow(src);
+    bpp = CGBitmapContextGetBitsPerPixel(src)/8;
+    Fl_Image_Surface *imgs = (Fl_Image_Surface*)Fl_Surface_Device::surface();
+    int fltk_w, fltk_h;
+    imgs->printable_rect(&fltk_w, &fltk_h);
+    s = sw / float(fltk_w);
+    X *= s; Y *= s; w *= s; h *= s;
+    if (X + w > sw) w = sw - X;
+    if (Y + h > sh) h = sh - Y;
+    // Copy the image from the off-screen buffer to the memory buffer.
+    int idx, idy;  // Current X & Y in image
+    uchar *pdst, *psrc;
+    p = new uchar[w * h * depth];
+    for (idy = Y, pdst = p; idy < h + Y; idy ++) {
+      for (idx = 0, psrc = base + idy * bpr + X * bpp; idx < w; idx ++, psrc += bpp, pdst += depth) {
+        pdst[0] = psrc[0];  // R
+        pdst[1] = psrc[1];  // G
+        pdst[2] = psrc[2];  // B
+      }
+    }
+    bpr = 0;
+  } else { // read from window
+    Fl_Cocoa_Window_Driver *d = Fl_Cocoa_Window_Driver::driver(Fl_Window::current());
+    CGImageRef cgimg = d->CGImage_from_window_rect(X, Y, w, h);
+    if (!cgimg) {
+      return NULL;
+    }
+    w = CGImageGetWidth(cgimg);
+    h = CGImageGetHeight(cgimg);
+    Fl_Image_Surface *surf = new Fl_Image_Surface(w, h);
+    Fl_Surface_Device::push_current(surf);
+    ((Fl_Quartz_Graphics_Driver*)fl_graphics_driver)->draw_CGImage(cgimg, 0, 0, w, h, 0, 0, w, h);
+    CGContextRef gc = (CGContextRef)fl_graphics_driver->gc();
+    w = CGBitmapContextGetWidth(gc);
+    h = CGBitmapContextGetHeight(gc);
+    bpr = CGBitmapContextGetBytesPerRow(gc);
+    bpp = CGBitmapContextGetBitsPerPixel(gc)/8;
+    base = (uchar*)CGBitmapContextGetData(gc);
+    p = new uchar[bpr * h];
+    memcpy(p, base, bpr * h);
+    Fl_Surface_Device::pop_current();
+    delete surf;
+    CFRelease(cgimg);
+  }
+  Fl_RGB_Image *rgb = new Fl_RGB_Image(p, w, h, depth, bpr);
+  rgb->alloc_array = 1;
+  return rgb;
+}
+
 //
 // End of "$Id$".
 //
diff --git a/src/drivers/Cocoa/Fl_Cocoa_Window_Driver.H b/src/drivers/Cocoa/Fl_Cocoa_Window_Driver.H
index 08a8ce42c..ef64799c9 100644
--- a/src/drivers/Cocoa/Fl_Cocoa_Window_Driver.H
+++ b/src/drivers/Cocoa/Fl_Cocoa_Window_Driver.H
@@ -88,7 +88,6 @@ public:
   CGRect* subRect() { return subRect_; } // getter
   void subRect(CGRect *r) { subRect_ = r; } // setter
   static void destroy(FLWindow*);
-  unsigned char *bitmap_from_window_rect(int x, int y, int w, int h, int *bytesPerPixel);
   CGImageRef CGImage_from_window_rect(int x, int y, int w, int h);
 
   // --- window data
diff --git a/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx b/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx
index 573bca696..453a5f600 100644
--- a/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx
+++ b/src/drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx
@@ -92,7 +92,7 @@ void Fl_GDI_Image_Surface_Driver::untranslate() {
 
 Fl_RGB_Image* Fl_GDI_Image_Surface_Driver::image()
 {
-  Fl_RGB_Image *image = Fl::screen_driver()->read_win_rectangle(NULL, 0, 0, width, height, 0);
+  Fl_RGB_Image *image = Fl::screen_driver()->read_win_rectangle( 0, 0, width, height);
   return image;
 }
 
diff --git a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
index 60a261e94..b23817d46 100644
--- a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
+++ b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
@@ -184,6 +184,8 @@ protected:
 #else
   void descriptor_init(const char* name, Fl_Fontsize Size, Fl_Quartz_Font_Descriptor *d);
 #endif
+  virtual bool overlay_rect_unscaled() {return false; }
+  virtual void overlay_rect(int x, int y, int w , int h);
 };
 
 class Fl_Quartz_Printer_Graphics_Driver : public Fl_Quartz_Graphics_Driver {
diff --git a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx
index 3a83b94d6..8153f4e78 100644
--- a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx
+++ b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx
@@ -173,6 +173,30 @@ void Fl_Quartz_Graphics_Driver::loop(int x, int y, int x1, int y1, int x2, int y
   if (quartz_line_width_ > 1.5f) CGContextSetShouldAntialias(gc_, false);
 }
 
+// returns y of horizontal line corresponding to pixels of current window
+// read by Fl_Cocoa_Screen_Driver::read_win_rectangle(  -,  y, -, 1)
+// when GUI is scaled by s
+static float overlay_y(int y, float s, int H) {
+  int a, b, c;
+  a = int(H*s) - (y+1)*s; // in Cocoa units from window bottom
+  c = (s > 1 ? s : 1); // height of pixels read in Cocoa units
+  b = H*s - (a+c); // top of read image from window top in Cocoa units
+  return b/s; // top of read image from window top in FLTK units
+}
+
+void Fl_Quartz_Graphics_Driver::overlay_rect(int x, int y, int w , int h) {
+  float s = scale();
+  CGContextSetLineWidth(gc_, 0.01);
+  int H = Fl_Window::current()->h();
+  CGContextMoveToPoint(gc_, x, overlay_y(y, s, H));
+  CGContextAddLineToPoint(gc_, x+w-1, overlay_y(y, s, H));
+  CGContextAddLineToPoint(gc_, x+w-1, overlay_y(y+h-1, s, H));
+  CGContextAddLineToPoint(gc_, x, overlay_y(y+h-1, s, H));
+  CGContextClosePath(gc_);
+  CGContextStrokePath(gc_);
+  CGContextSetLineWidth(gc_, quartz_line_width_);
+}
+
 void Fl_Quartz_Graphics_Driver::polygon(int x, int y, int x1, int y1, int x2, int y2) {
   CGContextSetShouldAntialias(gc_, true);
   CGContextMoveToPoint(gc_, x, y);
diff --git a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H
index e28fb791a..b5d238ba9 100644
--- a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H
+++ b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H
@@ -4,7 +4,7 @@
 // Definition of MSWindows Win32/64 Screen interface
 // for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2010-2016 by Bill Spitzak and others.
+// Copyright 2010-2018 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
@@ -79,8 +79,8 @@ public:
   virtual void remove_timeout(Fl_Timeout_Handler cb, void *argp);
   virtual int dnd(int unused);
   virtual int compose(int &del);
-  virtual Fl_RGB_Image *read_win_rectangle(uchar *p, int X, int Y, int w, int h, int alpha);
-  Fl_RGB_Image *read_win_rectangle_unscaled(uchar *p, int X, int Y, int w, int h, int alpha);
+  virtual Fl_RGB_Image *read_win_rectangle(int X, int Y, int w, int h);
+  Fl_RGB_Image *read_win_rectangle_unscaled(int X, int Y, int w, int h);
   virtual int get_mouse(int &x, int &y);
   virtual void enable_im();
   virtual void disable_im();
diff --git a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx
index 9373d345d..f44fa7a3c 100644
--- a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx
+++ b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx
@@ -496,24 +496,21 @@ int Fl_WinAPI_Screen_Driver::compose(int &del) {
 
 
 Fl_RGB_Image *                                                  // O - image or NULL if failed
-Fl_WinAPI_Screen_Driver::read_win_rectangle(uchar *p,		// I - Pixel buffer or NULL to allocate
+Fl_WinAPI_Screen_Driver::read_win_rectangle(
                                             int   X,		// I - Left position
                                             int   Y,		// I - Top position
                                             int   w,		// I - Width of area to read
-                                            int   h,		// I - Height of area to read
-                                            int   alpha) 	// I - Alpha value for image (0 for none)
+                                            int   h)		// I - Height of area to read
 {
   float s = Fl_Surface_Device::surface()->driver()->scale();
-  return read_win_rectangle_unscaled(p, X*s, Y*s, w*s, h*s, alpha);
+  return read_win_rectangle_unscaled(X*s, Y*s, w*s, h*s);
 }
 
-Fl_RGB_Image *Fl_WinAPI_Screen_Driver::read_win_rectangle_unscaled(uchar *p, int X, int Y, int w, int h, int alpha)
+Fl_RGB_Image *Fl_WinAPI_Screen_Driver::read_win_rectangle_unscaled(int X, int Y, int w, int h)
 {
-  int	d;			// Depth of image
-  
-  // Allocate the image data array as needed...
-  d = alpha ? 4 : 3;
-  
+  int	d = 3;			// Depth of image
+  int alpha = 0; uchar *p = NULL;
+  // Allocate the image data array as needed...  
   const uchar *oldp = p;
   if (!p) p = new uchar[w * h * d];
   
diff --git a/src/drivers/X11/Fl_X11_Screen_Driver.H b/src/drivers/X11/Fl_X11_Screen_Driver.H
index 6ceca775c..78a0510a5 100644
--- a/src/drivers/X11/Fl_X11_Screen_Driver.H
+++ b/src/drivers/X11/Fl_X11_Screen_Driver.H
@@ -4,7 +4,7 @@
 // Definition of X11 Screen interface
 // for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2010-2017 by Bill Spitzak and others.
+// Copyright 2010-2018 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
@@ -93,7 +93,7 @@ public:
   virtual int compose(int &del);
   virtual void compose_reset();
   virtual int text_display_can_leak();
-  virtual Fl_RGB_Image *read_win_rectangle(uchar *p, int X, int Y, int w, int h, int alpha);
+  virtual Fl_RGB_Image *read_win_rectangle(int X, int Y, int w, int h);
   virtual int get_mouse(int &x, int &y);
   virtual void enable_im();
   virtual void disable_im();
diff --git a/src/drivers/X11/Fl_X11_Screen_Driver.cxx b/src/drivers/X11/Fl_X11_Screen_Driver.cxx
index 6b253931d..7f6dc5528 100644
--- a/src/drivers/X11/Fl_X11_Screen_Driver.cxx
+++ b/src/drivers/X11/Fl_X11_Screen_Driver.cxx
@@ -750,7 +750,7 @@ extern "C" {
   }
 }
 
-Fl_RGB_Image *Fl_X11_Screen_Driver::read_win_rectangle(uchar *p, int X, int Y, int w, int h, int alpha)
+Fl_RGB_Image *Fl_X11_Screen_Driver::read_win_rectangle(int X, int Y, int w, int h)
 {
   XImage	*image;		// Captured image
   int		i, maxindex;	// Looping vars
@@ -862,14 +862,14 @@ Fl_RGB_Image *Fl_X11_Screen_Driver::read_win_rectangle(uchar *p, int X, int Y, i
   printf("map_entries      = %d\n", fl_visual->visual->map_entries);
 #endif // DEBUG
   
-  d = alpha ? 4 : 3;
-  
+  d = 3;
+  uchar *p = NULL;
   // Allocate the image data array as needed...
   const uchar *oldp = p;
   if (!p) p = new uchar[w * h * d];
   
   // Initialize the default colors/alpha in the whole image...
-  memset(p, alpha, w * h * d);
+  memset(p, 0, w * h * d);
   
   // Check that we have valid mask/shift values...
   if (!image->red_mask && image->bits_per_pixel > 12) {
diff --git a/src/drivers/X11/Fl_X11_Window_Driver.cxx b/src/drivers/X11/Fl_X11_Window_Driver.cxx
index 5612ce4df..b89688b47 100644
--- a/src/drivers/X11/Fl_X11_Window_Driver.cxx
+++ b/src/drivers/X11/Fl_X11_Window_Driver.cxx
@@ -413,22 +413,22 @@ void Fl_X11_Window_Driver::capture_titlebar_and_borders(Fl_Shared_Image*& top, F
   htop /= s; wsides /= s;
   fl_window = parent;
   if (htop) {
-    r_top = Fl::screen_driver()->read_win_rectangle(NULL, 0, 0, - (w() + 2 * wsides), htop, 0);
+    r_top = Fl::screen_driver()->read_win_rectangle(0, 0, - (w() + 2 * wsides), htop);
     top = Fl_Shared_Image::get(r_top);
     top->scale(w() + 2 * wsides, htop, 0, 1);
   }
   if (wsides) {
-    r_left = Fl::screen_driver()->read_win_rectangle(NULL, 0, htop, -wsides, h(), 0);
+    r_left = Fl::screen_driver()->read_win_rectangle(0, htop, -wsides, h());
     if (r_left) {
       left =  Fl_Shared_Image::get(r_left);
       left->scale(wsides, h(), 0, 1);
     }
-    r_right = Fl::screen_driver()->read_win_rectangle(NULL, w() + wsides, htop, -wsides, h(), 0);
+    r_right = Fl::screen_driver()->read_win_rectangle(w() + wsides, htop, -wsides, h());
     if (r_right) {
       right = Fl_Shared_Image::get(r_right);
       right->scale(wsides, h(), 0, 1);
     }
-    r_bottom = Fl::screen_driver()->read_win_rectangle(NULL, 0, htop + h(), -(w() + 2*wsides), hbottom, 0);
+    r_bottom = Fl::screen_driver()->read_win_rectangle(0, htop + h(), -(w() + 2*wsides), hbottom);
     if (r_bottom) {
       bottom = Fl_Shared_Image::get(r_bottom);
       bottom->scale(w() + 2*wsides, wsides, 0, 1);
diff --git a/src/drivers/Xlib/Fl_Xlib_Copy_Surface_Driver.cxx b/src/drivers/Xlib/Fl_Xlib_Copy_Surface_Driver.cxx
index 73a69109b..74a5022f4 100644
--- a/src/drivers/Xlib/Fl_Xlib_Copy_Surface_Driver.cxx
+++ b/src/drivers/Xlib/Fl_Xlib_Copy_Surface_Driver.cxx
@@ -67,7 +67,7 @@ Fl_Xlib_Copy_Surface_Driver::~Fl_Xlib_Copy_Surface_Driver() {
   driver()->pop_clip();
   bool need_push = (Fl_Surface_Device::surface() != this);
   if (need_push) Fl_Surface_Device::push_current(this);
-  Fl_RGB_Image *rgb = Fl::screen_driver()->read_win_rectangle(NULL, 0, 0, width, height, 0);
+  Fl_RGB_Image *rgb = Fl::screen_driver()->read_win_rectangle(0, 0, width, height);
   if (need_push) Fl_Surface_Device::pop_current();
   Fl_X11_Screen_Driver::copy_image(rgb->array, rgb->w(), rgb->h(), 1);
   delete rgb;
diff --git a/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx b/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx
index 0d3383cc5..c5bcce9af 100644
--- a/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx
+++ b/src/drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx
@@ -80,7 +80,7 @@ void Fl_Xlib_Image_Surface_Driver::untranslate() {
 
 Fl_RGB_Image* Fl_Xlib_Image_Surface_Driver::image()
 {
-  Fl_RGB_Image *image = Fl::screen_driver()->read_win_rectangle(NULL, 0, 0, width, height, 0);
+  Fl_RGB_Image *image = Fl::screen_driver()->read_win_rectangle(0, 0, width, height);
   return image;
 }
 
diff --git a/src/fl_overlay.cxx b/src/fl_overlay.cxx
index c1a8e2d32..8e095a962 100644
--- a/src/fl_overlay.cxx
+++ b/src/fl_overlay.cxx
@@ -57,7 +57,7 @@ static void draw_current_rect() {
   int old = SetROP2(fl_graphics_driver->gc(), R2_NOT);
   fl_rect(px, py, pw, ph);
   SetROP2(fl_graphics_driver->gc(), old);
-# elif defined(__APPLE_) // PORTME: Fl_Window_Driver - platform overlay
+# elif defined(__APPLE__)
   // warning: Quartz does not support xor drawing
   // Use the Fl_Overlay_Window instead.
   fl_color(FL_WHITE);
@@ -66,8 +66,8 @@ static void draw_current_rect() {
 #  error unsupported platform
 # endif
 #else
-  float s = fl_graphics_driver->scale();
-  if (s == int(s)) {
+  bool unscaled = fl_graphics_driver->overlay_rect_unscaled();
+  if (unscaled) {
     if (bgN) { free(bgN); bgN = 0L; }
     if (bgS) { free(bgS); bgS = 0L; }
     if (bgE) { free(bgE); bgE = 0L; }
@@ -79,29 +79,29 @@ static void draw_current_rect() {
     if (s_bgW) { s_bgW->release(); s_bgW = 0; }
   }
   if (pw>0 && ph>0) {
-    if (s == int(s)) {
+    if (unscaled) {
       bgE = fl_read_image(0L, px+pw-1, py, 1, ph);
       bgW = fl_read_image(0L, px, py, 1, ph);
       bgS = fl_read_image(0L, px, py+ph-1, pw, 1);
       bgN = fl_read_image(0L, px, py, pw, 1);
     } else {
       Fl_RGB_Image *tmp;
-      tmp = Fl::screen_driver()->read_win_rectangle(NULL, px+pw-1, py, 1, ph, 0);
+      tmp = Fl::screen_driver()->read_win_rectangle( px+pw-1, py, 1, ph);
       if(tmp && tmp->w() && tmp->h()) {
         s_bgE = Fl_Shared_Image::get(tmp);
         s_bgE->scale(1, ph,0,1);
       }
-      tmp = Fl::screen_driver()->read_win_rectangle(NULL, px, py, 1, ph, 0);
+      tmp = Fl::screen_driver()->read_win_rectangle( px, py, 1, ph);
       if(tmp && tmp->w() && tmp->h()) {
         s_bgW = Fl_Shared_Image::get(tmp);
         s_bgW->scale(1, ph,0,1);
       }
-      tmp = Fl::screen_driver()->read_win_rectangle(NULL, px, py+ph-1, pw, 1, 0);
+      tmp = Fl::screen_driver()->read_win_rectangle( px, py+ph-1, pw, 1);
       if(tmp && tmp->w() && tmp->h()) {
         s_bgS = Fl_Shared_Image::get(tmp);
         s_bgS->scale(pw, 1,0,1);
       }
-      tmp = Fl::screen_driver()->read_win_rectangle(NULL, px, py, pw, 1, 0);
+      tmp = Fl::screen_driver()->read_win_rectangle( px, py, pw, 1);
       if(tmp && tmp->w() && tmp->h()) {
         s_bgN = Fl_Shared_Image::get(tmp);
         s_bgN->scale(pw, 1,0,1);
@@ -112,12 +112,13 @@ static void draw_current_rect() {
   }
   fl_color(FL_WHITE);
   fl_line_style(FL_SOLID);
-  if (s == int(s)) fl_rect(px, py, pw, ph);
-  else fl_loop(px, py, px+pw-1, py, px+pw-1, py+ph-1, px, py+ph-1);
+  if (unscaled) fl_rect(px, py, pw, ph);
+  else fl_graphics_driver->overlay_rect(px, py, pw, ph);
+
   fl_color(FL_BLACK);
   fl_line_style(FL_DOT);
-  if (s == int(s)) fl_rect(px, py, pw, ph);
-  else fl_loop(px, py, px+pw-1, py, px+pw-1, py+ph-1, px, py+ph-1);
+  if (unscaled) fl_rect(px, py, pw, ph);
+  else fl_graphics_driver->overlay_rect(px, py, pw, ph);
   fl_line_style(FL_SOLID);
 #endif // USE_XOR
 }
@@ -130,8 +131,8 @@ static void erase_current_rect() {
   draw_current_rect();
 # endif
 #else
-  float s = fl_graphics_driver->scale();
-  if (s == int(s)) {
+  bool unscaled = fl_graphics_driver->overlay_rect_unscaled();
+  if (unscaled) {
     if (bgN) fl_draw_image(bgN, bgx, bgy, bgw, 1);
     if (bgS) fl_draw_image(bgS, bgx, bgy+bgh-1, bgw, 1);
     if (bgW) fl_draw_image(bgW, bgx, bgy, 1, bgh);
diff --git a/src/fl_read_image.cxx b/src/fl_read_image.cxx
index e7d91b865..d3d32877f 100644
--- a/src/fl_read_image.cxx
+++ b/src/fl_read_image.cxx
@@ -3,7 +3,7 @@
 //
 // X11 image reading routines for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2016 by Bill Spitzak and others.
+// Copyright 1998-2018 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
@@ -17,6 +17,7 @@
 //
 
 #include <FL/Fl.H>
+#include <FL/platform.H>
 #include <FL/Fl_Screen_Driver.H>
 
 /**
@@ -36,8 +37,55 @@
  and the value that is placed in the alpha channel. If 0, no alpha
  channel is generated.
  */
-uchar *fl_read_image(uchar *p, int X, int Y, int W, int H, int alpha) {
-  return Fl::screen_driver()->read_image(p, X, Y, W, H, alpha);
+uchar *fl_read_image(uchar *p, int X, int Y, int w, int h, int alpha) {
+  uchar *image_data = NULL;
+  Fl_RGB_Image *img;
+  if (fl_find(fl_window) == 0) { // read from off_screen buffer
+    img = Fl::screen_driver()->read_win_rectangle(X, Y, w, h);
+    if (!img) {
+      return NULL;
+    }
+    img->alloc_array = 1;
+  } else {
+    img = Fl::screen_driver()->traverse_to_gl_subwindows(Fl_Window::current(), X, Y, w, h, NULL);
+  }
+  int depth = alpha ? 4 : 3;
+  if (img->d() != depth) {
+    uchar *data = new uchar[img->w() * img->h() * depth];
+    if (depth == 4) memset(data, alpha, img->w() * img->h() * depth);
+    uchar *d = data;
+    const uchar *q;
+    int ld = img->ld() ? img->ld() : img->w() * img->d();
+    for (int r = 0; r < img->h(); r++) {
+      q = img->array + r * ld;
+      for (int c = 0; c < img->w(); c++) {
+        d[0] = q[0];
+        d[1] = q[1];
+        d[2] = q[2];
+        d += depth; q += img->d();
+      }
+    }
+    Fl_RGB_Image *img2 = new Fl_RGB_Image(data, img->w(), img->h(), depth);
+    img2->alloc_array = 1;
+    delete img;
+    img = img2;
+  }
+  if (img) {
+    if (img->w() != w || img->h() != h) {
+      Fl_RGB_Image *img2 = (Fl_RGB_Image*)img->copy(w, h);
+      delete img;
+      img = img2;
+    }
+    img->alloc_array = 0;
+    image_data = (uchar*)img->array;
+    delete img;
+  }
+  if (p && image_data) {
+    memcpy(p, image_data, w * h * depth);
+    delete[] image_data;
+    image_data = p;
+  }
+  return image_data;
 }
 
 //