Add auto-detect dpi method

If Xft.dpi value is not available, auto-detect value based on monitor using randr provided sizes.
Disable Xinerama and enable randr by default.
Also update dpi everytime the monitor changes.

config.mk

@@ -9,8 +9,12 @@ VERSION := $(shell git describe --tags)
 endif
 
 # Xinerama, comment if you don't want it
-XINERAMALIBS  = -lXinerama
+#XINERAMALIBS  = -lXinerama
-XINERAMAFLAGS = -DXINERAMA
+#XINERAMAFLAGS = -DXINERAMA
+
+# RANDR, comment if you don't want it
+XRANDRLIBS = -lXrandr
+XRANDRFLAGS = -DXRANDR
 
 # uncomment to disable parsing of dunstrc
 # or use "CFLAGS=-DSTATIC_CONFIG make" to build
@@ -22,7 +26,7 @@ ifeq (${PKG_CONFIG}, ${EMPTY})
 endif
 
 # flags
-CPPFLAGS += -D_DEFAULT_SOURCE -DVERSION=\"${VERSION}\" ${XINERAMAFLAGS} ${INIFLAGS}
+CPPFLAGS += -D_DEFAULT_SOURCE -DVERSION=\"${VERSION}\" ${XRANDRFLAGS} ${XINERAMAFLAGS} ${INIFLAGS}
 CFLAGS   += -g --std=gnu99 -pedantic -Wall -Wno-overlength-strings -Os ${STATIC} ${CPPFLAGS} ${EXTRACFLAGS}
 
 pkg_config_packs := dbus-1 x11 xscrnsaver \
@@ -37,7 +41,7 @@ endif
 # includes and libs
 INCS := $(shell ${PKG_CONFIG} --cflags ${pkg_config_packs})
 CFLAGS += ${INCS}
-LDFLAGS += -lm -L${X11LIB} -lXss ${XINERAMALIBS} $(shell ${PKG_CONFIG} --libs ${pkg_config_packs})
+LDFLAGS += -lm -L${X11LIB} -lXss ${XRANDRLIBS} ${XINERAMALIBS} $(shell ${PKG_CONFIG} --libs ${pkg_config_packs})
 
 # only make this an fatal error when where not cleaning
 ifneq (clean, $(MAKECMDGOALS))

src/x.c

@@ -7,7 +7,10 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <X11/Xresource.h>
-#ifdef XINERAMA
+#ifdef XRANDR
+#include <X11/extensions/Xrandr.h>
+#include <assert.h>
+#elif XINERAMA
 #include <X11/extensions/Xinerama.h>
 #include <assert.h>
 #endif
@@ -137,28 +140,6 @@ static color_t x_get_separator_color(colored_layout *cl, colored_layout *cl_next
         }
 }
 
-static void set_dpi_value()
-{
-        double dpi = 0.0;
-        XrmInitialize();
-        char * xRMS = XResourceManagerString(xctx.dpy);
-
-        if ( xRMS != NULL ) {
-                XrmDatabase xDB = XrmGetStringDatabase(xRMS);
-                char * xrmType;
-                XrmValue xrmValue;
-
-                if ( XrmGetResource(xDB, "Xft.dpi", NULL, &xrmType, &xrmValue))
-                        dpi = strtod(xrmValue.addr, NULL);
-
-        }
-
-        if (dpi > 0.0) {
-                PangoFontMap *font_map = pango_cairo_font_map_get_default();
-                pango_cairo_font_map_set_resolution((PangoCairoFontMap *) font_map, dpi);
-        }
-}
-
 static void x_cairo_setup(void)
 {
         cairo_ctx.surface = cairo_xlib_surface_create(xctx.dpy,
@@ -166,8 +147,6 @@ static void x_cairo_setup(void)
 
         cairo_ctx.context = cairo_create(cairo_ctx.surface);
 
-        set_dpi_value();
-
         cairo_ctx.desc = pango_font_description_from_string(settings.font);
 }
 
@@ -949,12 +928,80 @@ static Window get_focused_window(void)
         return focused;
 }
 
-#ifdef XINERAMA
+static double get_xft_dpi_value()
+{
+        double dpi = 0.0;
+        XrmInitialize();
+        char * xRMS = XResourceManagerString(xctx.dpy);
+
+        if ( xRMS != NULL ) {
+                XrmDatabase xDB = XrmGetStringDatabase(xRMS);
+                char * xrmType;
+                XrmValue xrmValue;
+
+                if ( XrmGetResource(xDB, "Xft.dpi", NULL, &xrmType, &xrmValue))
+                        dpi = strtod(xrmValue.addr, NULL);
+
+        }
+
+        return dpi;
+}
+static void set_dpi_value(screen_info * scr, double dpi)
+{
+        if (dpi > 0.0) {
+                PangoFontMap *font_map = pango_cairo_font_map_get_default();
+                pango_cairo_font_map_set_resolution((PangoCairoFontMap *) font_map, dpi);
+        }
+#ifdef XRANDR
+        //fallback to auto-detect method
+        else {
+                dpi = (double)scr->dim.h * 25.4 / (double)scr->dim.mmh;
+                PangoFontMap *font_map = pango_cairo_font_map_get_default();
+                pango_cairo_font_map_set_resolution((PangoCairoFontMap *) font_map, dpi);
+        }
+#endif
+}
+
+#ifdef XRANDR
+static int lookup_active_screen(XRRMonitorInfo *info, int n, int x, int y)
+{
+        int ret = -1;
+        for (int i = 0; i < n; i++) {
+                if (INRECT(x, y, info[i].x, info[i].y,
+                        info[i].width, info[i].height)) {
+                        ret = i;
+                }
+        }
+
+        return ret;
+
+}
+#elif XINERAMA
+static int lookup_active_screen(XineramaScreenInfo * info, int n, int x, int y)
+{
+        int ret = -1;
+        for (int i = 0; i < n; i++) {
+                if (INRECT(x, y, info[i].x_org, info[i].y_org,
+                        info[i].width, info[i].height)) {
+                        ret = i;
+                }
+        }
+
+        return ret;
+}
+#endif
+
+
+#ifdef XRANDR
 /*
  * Select the screen on which the Window
  * should be displayed.
  */
+static int select_screen(XRRMonitorInfo *info, int n)
+#elif XINERAMA
 static int select_screen(XineramaScreenInfo * info, int info_len)
+#endif
+#if defined(XRANDR) || defined(XINERAMA)
 {
          int ret = 0;
          x_follow_setup_error_handler();
@@ -996,24 +1043,20 @@ static int select_screen(XineramaScreenInfo * info, int info_len)
                                                0, 0, &x, &y, &child_return);
                  }
 
-                for (int i = 0; i < info_len; i++) {
+                 ret = lookup_active_screen(info, n, x, y);
-                        if (INRECT(x, y, info[i].x_org,
+
-                                   info[i].y_org,
+                 if (ret > 0)
-                                   info[i].width, info[i].height)) {
-                                ret = i;
                         goto sc_cleanup;
-                        }
-                }
 
                  /* something seems to be wrong. Fallback to default */
                  ret = settings.monitor >=
                      0 ? settings.monitor : XDefaultScreen(xctx.dpy);
                  goto sc_cleanup;
          }
-sc_cleanup:
+ sc_cleanup:
          x_follow_tear_down_error_handler();
          return ret;
-}
+ }
 #endif
 
 /*
@@ -1022,7 +1065,24 @@ sc_cleanup:
  */
 static void x_screen_info(screen_info * scr)
 {
-#ifdef XINERAMA
+#ifdef XRANDR
+        int n;
+        XRRMonitorInfo	*m;
+
+        m = XRRGetMonitors(xctx.dpy, RootWindow(xctx.dpy, DefaultScreen(xctx.dpy)), true, &n);
+        int screen = select_screen(m, n);
+        if (screen >= n) {
+                /* invalid monitor, fallback to default */
+                screen = 0;
+        }
+
+        scr->dim.x = m[screen].x;
+        scr->dim.y = m[screen].y;
+        scr->dim.w = m[screen].width;
+        scr->dim.h = m[screen].height;
+        scr->dim.mmh = m[screen].mheight;
+        XRRFreeMonitors(m);
+#elif XINERAMA
         int n;
         XineramaScreenInfo *info;
         if ((info = XineramaQueryScreens(xctx.dpy, &n))) {
@@ -1051,6 +1111,12 @@ static void x_screen_info(screen_info * scr)
                 scr->dim.w = DisplayWidth(xctx.dpy, screen);
                 scr->dim.h = DisplayHeight(xctx.dpy, screen);
         }
+
+        //Update dpi
+        double dpi = 0.0;
+
+        dpi = get_xft_dpi_value();
+        set_dpi_value(scr, dpi);
 }
 
 void x_free(void)

src/x.h

@@ -16,6 +16,7 @@ typedef struct _dimension_t {
         int x;
         int y;
         unsigned int h;
+        unsigned int mmh;
         unsigned int w;
         int mask;
         int negative_width;