Add getframe function for opengl based toolkits (bug #48195) * graphics.in.h (graphics_toolkit::get_pixels, base_graphics_toolkit::get_pixels): new virtual methods * graphics.cc (F__get_frame__): new function. * Backend.h/cc (Backend::get_pixels): implement new method * ObjectProxy.h/cc (ObjectProxy::get_pixels): new method, invoke directly Figure object slotGetPixels in Qt::BlockingQueuedConnection mode * Figure.h/cc (Figure::slotGetPixels): new public slot * Canvas.h (Canvas::getPixels, Canvas::do_getPixels): new methods * GLCanvas.h/cc (GLCanvas::do_getPixels): reimplemented method, use opengl_renderer to draw object and get_pixels * __init_fltk__.cc (fltk_graphics_toolkit::get_pixels, figure_manager::get_pixels, figure_manager::do_get_pixels, plot_window::get_pixels, OpenGL_fltk::get_pixels): new methods * gl-renderer.h/cc (opengl_renderer::get_pixels): new method, read pixels in the current opengl scene * getframe.m: new function file * image.txi: add getframe doc * NEWS: announce new function

--- a/libgui/graphics/Canvas.h	Sat May 27 09:59:32 2017 -0700
+++ b/libgui/graphics/Canvas.h	Tue May 23 15:01:27 2017 +0200
@@ -71,12 +71,15 @@
     virtual void toggleGrid (const graphics_handle& handle) = 0;
     virtual void autoAxes (const graphics_handle& handle) = 0;
 
+    virtual uint8NDArray getPixels (void) { return do_getPixels (m_handle); };
+
   protected:
     virtual void draw (const graphics_handle& handle) = 0;
     virtual void drawZoomBox (const QPoint& p1, const QPoint& p2) = 0;
     virtual void resize (int x, int y, int width, int height) = 0;
     virtual graphics_object selectFromAxes (const graphics_object& ax,
                                             const QPoint& pt) = 0;
+    virtual uint8NDArray do_getPixels (const graphics_handle& handle) = 0;
 
   protected:
     Canvas (const graphics_handle& handle)