cairo: add BEMENU_SCALE env variable

Allows overriding the scaling factor for bemenu

README.md

@@ -73,6 +73,7 @@ All dependencies are searched with `pkg-config`
 | BEMENU_BACKEND   | Force backend by name                   | x11, wayland, curses |
 | BEMENU_RENDERER  | Force backend by loading a .so file     | Path to the .so file |
 | BEMENU_RENDERERS | Override the backend search path        | Path to a directory  |
+| BEMENU_SCALE     | Override the rendering scale factor     | Float value          |
 
 ## About Wayland support
 

lib/renderers/wayland/wayland.c

@@ -263,7 +263,13 @@ recreate_windows(const struct bm_menu *menu, struct wayland *wayland)
 
         struct window *window = calloc(1, sizeof(struct window));
         window->bottom = menu->bottom;
-        window->scale = output->scale;
+
+        const char *scale = getenv("BEMENU_SCALE");
+        if (scale) {
+            window->scale = fmax(strtof(scale, NULL), 1.0f);
+        } else {
+            window->scale = output->scale;
+        }
 
         if (!bm_wl_window_create(window, wayland->display, wayland->shm, output->output, wayland->layer_shell, surface))
             free(window);

lib/renderers/x11/window.c

@@ -21,7 +21,12 @@ create_buffer(struct window *window, struct buffer *buffer, int32_t width, int32
 
     cairo_xlib_surface_set_size(surf, width, height);
 
-    buffer->cairo.scale = 1;
+    const char *scale = getenv("BEMENU_SCALE");
+    if (scale) {
+        buffer->cairo.scale = fmax(strtof(scale, NULL), 1.0f);
+    } else {
+        buffer->cairo.scale = 1;
+    }
 
     if (!bm_cairo_create_for_surface(&buffer->cairo, surf)) {
         cairo_surface_destroy(surf);

man/bemenu.1

@@ -224,3 +224,9 @@ Force backend by loading a .so file.
 .RS
 Override the backend search path.
 .RE
+
+.TP
+.B BEMENU_SCALE
+.RS
+Override the rendering scale factor.
+.RE