Improve OpenGL rendering on high resolution screens with Qt 5 (bug #49053) * FigureWindow.cc/h (FigureWindow::figureWindowShown): New signal (FigureWindow::showEvent): Overload QMainWindow::showEvent to also emit figureWindowShown signal. * Figure.cc/h (Figure::figureWindowShown): New slot. Set the figure object __device_pixel_ratio__ property and connect the window's screenChanged signal to Figure::screenChanged slot. (Figure::screenChanged): New slot. Update the figure object's __device_pixel_ratio__ property. * GLCanvas.cc (GLCanvas::draw, GLCanvas::selectFromAxes) scale the opengl_rederer's viewport with the correct __device_pixel_ratio__ * gl-render.cc/h (opengl_renderer::m_devpixratio): New data member to store the current screen's __device_pixel_ratio__ (opengl_renderer::draw_figure): Set m_devpixratio. (opengl_renderer::setup_opengl_transformation,::draw_text_background, ::opengl_renderer::init_marker): Scale width and height of the figure when setting up glOrtho transform. (opengl_renderer::draw_image): Scale zoom factors when using glPixelZoom (opengl_renderer::set_font): Scale font size. (opengl_renderer::set_linewidth): Scale line width. * graphics.cc (device_pixel_ratio): New static function to get the ancestor figure's __devive_pixel_ratio__. (axes::properties::update_font, text::properties::update_font): Scale font size. (axes::properties::get_ticklabel_extents): Scale tick labels size. (text::properties::get_extent): Scale text size. (figure::properties::update_text_pos): New mehtod to update the position of axes objects annotations and text objects. * graphics.in.h (figure::properties::__device_pixel_ratio__, figure::properties::update__device_pixel_ratio__): New property and updater. (axes::properties::update_font, text::properties::update_font, text::properties::update_text_extent): Make methods public so that update_text_pos can access them. * acinclude.m4: Determine if QScreen::devicePixelRatio is present in the Qt library in use. * print.m: set __device_pixel_ratio__ to 1 when printing.

--- a/libinterp/corefcn/gl-render.h	Fri Sep 14 18:47:23 2018 +0200
+++ b/libinterp/corefcn/gl-render.h	Sat Sep 15 09:43:48 2018 +0200
@@ -244,6 +244,9 @@
 
     // Indicate we are drawing for selection purpose
     bool selecting;
+
+    // Factor used for translating Octave pixels to actual device pixels
+    double m_devpixratio;
   private:
     class patch_tesselator;
   };