negative width within geometry

See github issue #72

dunst.c

@@ -559,7 +559,11 @@ void draw_win(void)
                 width = 0;
         } else if (geometry.mask & WidthValue) {
                 /* fixed width */
-                width = geometry.w;
+                if (geometry.negative_width) {
+                        width = scr.dim.w - geometry.w;
+                } else {
+                        width = geometry.w;
+                }
         } else {
                 /* across the screen */
                 width = scr.dim.w;
@@ -1559,10 +1563,18 @@ int main(int argc, char *argv[])
         init_shortcut(&history_ks);
 
 
+        if (geom[0] == '-') {
+                geometry.negative_width = True;
+                geom++;
+        } else {
+                geometry.negative_width = False;
+        }
+
         geometry.mask = XParseGeometry(geom,
                                        &geometry.x, &geometry.y,
                                        &geometry.w, &geometry.h);
 
+
         screensaver_info = XScreenSaverAllocInfo();
 
         initdbus();

dunst.h

@@ -23,6 +23,7 @@ typedef struct _dimension_t {
         unsigned int h;
         unsigned int w;
         int mask;
+        int negative_width;
 } dimension_t;
 
 typedef struct _screen_info {

dunstrc

@@ -43,6 +43,8 @@
     # the window expands to the longest message displayed.
     # A positive x is measured from the left, a negative from the
     # right side of the screen.  Y is measured from the top and down respectevly.
+    # The width can be negative. In this case the actual width is the
+    # screen width minus the width defined in within the geometry option.
     geometry = "0x3-30+20"
 
     # The transparency of the window. range: [0; 100]