1 files changed, 51 insertions, 3 deletions
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;
 }
 
 //