Multi-monitor support

Use BUZZLOCKER_MONITOR_NUM to specify which monitor you want the locker to appear on. 0 is the primary one

5 files changed, 88 insertions, 30 deletions

diff --git a/README.md b/README.md
index db1887c..b39b6cb 100644
--- a/README.md
+++ b/README.md
@@ -38,4 +38,8 @@ XSECURELOCK_AUTH=/usr/local/bin/auth_buzzlocker xsecurelock
 
 So every time you run `xsecurelock` by itself, it will use buzzlocker as the GUI.
 
+## Configuration
+If you have multiple monitors, buzzlocker will appear only on whatever the primary monitor is (according 
+to XRandR). If you want to override this behavior, set the environment variable `BUZZLOCKER_MONITOR_NUM`
+to whichever monitor you wish to have buzzlocker appear on. 
 
diff --git a/meson.build b/meson.build
index 0e639c4..e74d74d 100644
--- a/meson.build
+++ b/meson.build
@@ -14,6 +14,7 @@ sources = [
 
 dependencies = [
   dependency('x11'),
+  dependency('xrandr'),
   dependency('cairo'),
   dependency('librsvg-2.0'),
   dependency('pangocairo'),
diff --git a/src/main.c b/src/main.c
index 3eebc55..82439e6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -17,9 +17,6 @@
 
 static const int kXSecureLockCharFD = 0;
 
-static const int kDefaultWidth = 1024;
-static const int kDefaultHeight = 768;
-
 static const char *kDefaultFont = "Input Mono 22";
 
 static inline saver_state_t* saver_state(void *c)
@@ -326,7 +323,10 @@ static int runloop(cairo_surface_t *surface)
     };
     schedule_animation(&state, logo_animation);
 
-    x11_get_display_bounds(&state.canvas_width, &state.canvas_height);
+    x11_display_bounds_t bounds;
+    x11_get_display_bounds(get_preferred_monitor_num(), &bounds);
+    state.canvas_width = bounds.width;
+    state.canvas_height = bounds.height;
 
     // Docs say this must be called whenever the size of the window changes
     cairo_xlib_surface_set_size(surface, state.canvas_width, state.canvas_height);
@@ -370,10 +370,7 @@ static int runloop(cairo_surface_t *surface)
 
 int main(int argc, char **argv)
 {
-    int default_width = kDefaultWidth;
-    int default_height = kDefaultHeight;
-
-    cairo_surface_t *surface = x11_helper_acquire_cairo_surface(default_width, default_height);
+    cairo_surface_t *surface = x11_helper_acquire_cairo_surface();
     if (surface == NULL) {
         fprintf(stderr, "Error creating cairo surface\n");
         exit(1);
diff --git a/src/x11_support.c b/src/x11_support.c
index 3683b5a..9f924d7 100644
--- a/src/x11_support.c
+++ b/src/x11_support.c
@@ -6,46 +6,89 @@
 
 #include "x11_support.h"
 
+#include <X11/extensions/Xrandr.h> 
 #include <stdio.h>
 #include <stdlib.h>
 
 static Window __window = { 0 };
 static Display *__display = NULL;
 
-static Window get_window_from_environment_or_make_one(Display *display, int width, int height)
+static void x11_get_display_bounds_w(Window window, unsigned int monitor_num, x11_display_bounds_t *out_bounds);
+
+static Window get_window_from_environment_or_make_one(Display *display, int *out_width, int *out_height)
 {
     Window window;
 
+    Window root_window = DefaultRootWindow(__display);
     const char *env_window = getenv("XSCREENSAVER_WINDOW");
     if (env_window != NULL && env_window[0] != 0) {
         char *endptr = NULL;
         unsigned long long number = strtoull(env_window, &endptr, 0);
-        window = (Window)number;
-    } else {
-        // Presumably this is for debugging
-        Window root_window = DefaultRootWindow(__display);
-        window = XCreateSimpleWindow(
-                display,        // display
-                root_window,    // parent window
-                0, 0,           // x, y
-                width,          // width
-                height,         // height
-                0,              // border_width
-                0,              // border
-                0               // background
-        );
+        root_window = (Window)number;
     }
 
+    // Figure out which monitor this is supposed to go on
+    const unsigned int preferred_monitor = get_preferred_monitor_num();
+    x11_display_bounds_t bounds;
+    x11_get_display_bounds_w(root_window, preferred_monitor, &bounds);
+
+    window = XCreateSimpleWindow(
+            display,        // display
+            root_window,    // parent window
+            bounds.x,       // x 
+            bounds.y,       // y
+            bounds.width,   // width
+            bounds.height,  // height
+            0,              // border_width
+            0,              // border
+            0               // background
+    );
+
+    *out_width = bounds.width;
+    *out_height = bounds.height;
     return window;
 }
 
-void x11_get_display_bounds(int *width, int *height)
+void x11_get_display_bounds(unsigned int monitor_num, x11_display_bounds_t *out_bounds)
 {
-    *width = DisplayWidth(__display, DefaultScreen(__display));
-    *height = DisplayHeight(__display, DefaultScreen(__display));
+    x11_get_display_bounds_w(__window, monitor_num, out_bounds);
+}
+
+static void x11_get_display_bounds_w(Window window, unsigned int monitor_num, x11_display_bounds_t *out_bounds)
+{
+    int num_monitors = 0;
+    XRRMonitorInfo *monitor_infos = XRRGetMonitors(__display, window, True, &num_monitors);
+    if (num_monitors == 0) {
+        fprintf(stderr, "FATAL: Couldn't get monitor info from XRandR!\n");
+        exit(1);
+    }
+
+    unsigned int idx = monitor_num;
+    if (idx > num_monitors) {
+        fprintf(stderr, "WARNING: Specified monitor number is greater than the number of connected monitors!\n");
+        idx = 0;
+    }
+
+    XRRMonitorInfo *monitor = &monitor_infos[idx];
+    out_bounds->x = monitor->x;
+    out_bounds->y = monitor->y;
+    out_bounds->width = monitor->width;
+    out_bounds->height = monitor->height;
+}
+
+unsigned int get_preferred_monitor_num()
+{
+    const char *preferred_monitor = getenv("BUZZLOCKER_MONITOR_NUM");
+    if (preferred_monitor != NULL && preferred_monitor[0] != 0) {
+        char *endptr = NULL;
+        unsigned long int result = strtoul(preferred_monitor, &endptr, 0);
+        return result;
+    }
+
+    return 0;
 }
 
-cairo_surface_t* x11_helper_acquire_cairo_surface(int width, int height)
+cairo_surface_t* x11_helper_acquire_cairo_surface()
 {
     __display = XOpenDisplay(NULL);
     if (__display == NULL) {
@@ -54,7 +97,8 @@ cairo_surface_t* x11_helper_acquire_cairo_surface(int width, int height)
     }
 
     // Create (or get) window
-    __window = get_window_from_environment_or_make_one(__display, width, height);
+    int width, height;
+    __window = get_window_from_environment_or_make_one(__display, &width, &height);
 
     // Enable key events
     XSelectInput(__display, __window, ButtonPressMask | KeyPressMask | StructureNotifyMask);
diff --git a/src/x11_support.h b/src/x11_support.h
index 6421f4b..9007602 100644
--- a/src/x11_support.h
+++ b/src/x11_support.h
@@ -12,10 +12,22 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 
-void x11_get_display_bounds(int *width, int *height);
+typedef struct {
+    int x;
+    int y;
+    int width;
+    int height;
+} x11_display_bounds_t;
+
+// Get the preferred monitor number (via BUZZLOCKER_MONITOR_NUM environment variable)
+// Returns 0 (the primary one) if not set 
+unsigned int get_preferred_monitor_num();
+
+// Get the bounds for the specified monitor num (via XRandR)
+void x11_get_display_bounds(unsigned int monitor_num, x11_display_bounds_t *out_bounds);
 
 // Sets up a window and returns a cairo_surface to draw onto
-cairo_surface_t* x11_helper_acquire_cairo_surface(int width, int height);
+cairo_surface_t* x11_helper_acquire_cairo_surface();
 
 // Cleanup
 void x11_helper_destroy_surface(cairo_surface_t *surface);