Use Xft.dpi for DPI if available.

[i3/i3] / libi3 / dpi.c

diff --git a/libi3/dpi.c b/libi3/dpi.c
index 897e6e4016a362645f96ee84bd032b577ed0015f..f105ef9aed710189529b247433037df0d26a1bac 100644 (file)
--- a/libi3/dpi.c
+++ b/libi3/dpi.c
@@ -7,6 +7,61 @@
  */
 #include "libi3.h"
 #include <math.h>
+#include <stdlib.h>
+#include <xcb/xcb_xrm.h>
+
+static long dpi;
+
+static long init_dpi_fallback(void) {
+    return (double)root_screen->height_in_pixels * 25.4 / (double)root_screen->height_in_millimeters;
+}
+
+/*
+ * Initialize the DPI setting.
+ * This will use the 'Xft.dpi' X resource if available and fall back to
+ * guessing the correct value otherwise.
+ */
+void init_dpi(void) {
+    xcb_xrm_database_t *database = NULL;
+
+    if (conn == NULL) {
+        goto init_dpi_end;
+    }
+
+    database = xcb_xrm_database_from_default(conn);
+    if (database == NULL) {
+        ELOG("Failed to open the resource database.\n");
+        goto init_dpi_end;
+    }
+
+    char *resource;
+    xcb_xrm_resource_get_string(database, "Xft.dpi", NULL, &resource);
+    if (resource == NULL) {
+        DLOG("Resource Xft.dpi not specified, skipping.\n");
+        goto init_dpi_end;
+    }
+
+    char *endptr;
+    dpi = strtol(resource, &endptr, 10);
+    if (dpi == LONG_MAX || dpi == LONG_MIN || dpi < 0 || *endptr != '\0' || endptr == resource) {
+        ELOG("Xft.dpi = %s is an invalid number and couldn't be parsed.\n", resource);
+        dpi = 0;
+        goto init_dpi_end;
+    }
+
+    DLOG("Found Xft.dpi = %ld.\n", dpi);
+
+init_dpi_end:
+    if (database != NULL) {
+        xcb_xrm_database_free(database);
+    }
+
+    if (dpi == 0) {
+        DLOG("Using fallback for calculating DPI.\n");
+        dpi = init_dpi_fallback();
+        DLOG("Using dpi = %ld\n", dpi);
+    }
+}
 
 /*
  * Convert a logical amount of pixels (e.g. 2 pixels on a “standard” 96 DPI
@@ -21,8 +76,6 @@ int logical_px(const int logical) {
         return logical;
     }
 
-    const int dpi = (double)root_screen->height_in_pixels * 25.4 /
-                    (double)root_screen->height_in_millimeters;
     /* There are many misconfigurations out there, i.e. systems with screens
      * whose dpi is in fact higher than 96 dpi, but not significantly higher,
      * so software was never adapted. We could tell people to reconfigure their