Use GDK methods to retrieve the actual screen DPI

gtk-gui.c:
+ added the method get_screen_dpi() that uses a simple
formula to retrieve the actual screen DPI
display.h:
+ use get_screen_dpi() in the SCALE_PRINT macro

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

2 files changed, 12 insertions, 2 deletions

diff --git a/display.h b/display.h
index 4fed339ac..83f8ada8f 100644
--- a/display.h
+++ b/display.h
@@ -3,12 +3,12 @@
 
 #include <cairo.h>
 
-#define DPI_SCREEN 72.0
 #define SCALE_SCREEN 1.0
-#define SCALE_PRINT (1.0 / DPI_SCREEN)
+#define SCALE_PRINT (1.0 / get_screen_dpi())
 
 extern void repaint_dive(void);
 extern void do_print(void);
+extern gdouble get_screen_dpi(void);
 
 /* Plot info with smoothing, velocity indication
  * and one-, two- and three-minute minimums and maximums */
diff --git a/gtk-gui.c b/gtk-gui.c
index e009f5ac0..20a2da824 100644
--- a/gtk-gui.c
+++ b/gtk-gui.c
@@ -2020,3 +2020,13 @@ void set_dc_nickname(struct dive *dive)
 		dc = dc->next;
 	}
 }
+
+gdouble get_screen_dpi(void)
+{
+	const gdouble mm_per_inch = 25.4;
+	GdkScreen *scr = gdk_screen_get_default();
+	gdouble h_mm = gdk_screen_get_height_mm(scr);
+	gdouble h = gdk_screen_get_height(scr);
+	gdouble dpi_h = floor((h / h_mm) * mm_per_inch);
+	return dpi_h;
+}