Refactor window positioning and surface rendering into x.c

Move the double-buffering implementation and the x_win_call move into
x.c so we only need to call x_display_surface for each draw.

This isolates all uses of the cairo context and root surface outside of
x.c which will help to add support for other display servers.

src/draw.c

@@ -1,9 +1,7 @@
 #include "draw.h"
 
-#include <X11/Xutil.h> // Temporary
 #include <assert.h>
 #include <cairo.h>
-#include <cairo-xlib.h> // Temporary
 #include <math.h>
 #include <pango/pango-attributes.h>
 #include <pango/pango-font.h>
@@ -556,15 +554,8 @@ void draw(void)
         GSList *layouts = create_layouts(win->c_ctx);
 
         struct dimensions dim = calculate_dimensions(layouts);
-        int width = dim.w;
-        int height = dim.h;
-        int win_x, win_y;
 
-        cairo_surface_t *image_surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
-
-        calc_window_pos(dim.w, dim.h, &win_x, &win_y);
-        x_win_move(win_x, win_y, width, height);
-        cairo_xlib_surface_set_size(win->root_surface, width, height);
+        cairo_surface_t *image_surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, dim.w, dim.h);
 
         bool first = true;
         for (GSList *iter = layouts; iter; iter = iter->next) {
@@ -576,11 +567,8 @@ void draw(void)
                 first = false;
         }
 
-        cairo_set_source_surface(win->c_ctx, image_surface, 0, 0);
-        cairo_paint(win->c_ctx);
-        cairo_show_page(win->c_ctx);
-
-        XFlush(xctx.dpy);
+        calc_window_pos(dim.w, dim.h, &dim.x, &dim.y);
+        x_display_surface(image_surface, win, &dim);
 
         cairo_surface_destroy(image_surface);
         free_layouts(layouts);

src/x11/x.c

@@ -44,28 +44,37 @@ static int x_shortcut_tear_down_error_handler(void);
 static void setopacity(Window win, unsigned long opacity);
 static void x_handle_click(XEvent ev);
 
-void x_win_move(int x, int y, int width, int height)
+static void x_win_move(window_x11 *win, int x, int y, int width, int height)
 {
-        // Previous dimensions of the window to avoid calling X11 if no change
-        // is needed
-        static struct dimensions window_dim = { 0 };
-
         /* move and resize */
-        if (x != window_dim.x || y != window_dim.y) {
+        if (x != win->dim.x || y != win->dim.y) {
                 XMoveWindow(xctx.dpy, win->xwin, x, y);
 
-                window_dim.x = x;
-                window_dim.y = y;
+                win->dim.x = x;
+                win->dim.y = y;
         }
 
-        if (width != window_dim.w || height != window_dim.h) {
+        if (width != win->dim.w || height != win->dim.h) {
                 XResizeWindow(xctx.dpy, win->xwin, width, height);
 
-                window_dim.h = height;
-                window_dim.w = width;
+                win->dim.h = height;
+                win->dim.w = width;
         }
 }
 
+void x_display_surface(cairo_surface_t *srf, window_x11 *win, const struct dimensions *dim)
+{
+        x_win_move(win, dim->x, dim->y, dim->w, dim->h);
+        cairo_xlib_surface_set_size(win->root_surface, dim->w, dim->h);
+
+        cairo_set_source_surface(win->c_ctx, srf, 0, 0);
+        cairo_paint(win->c_ctx);
+        cairo_show_page(win->c_ctx);
+
+        XFlush(xctx.dpy);
+
+}
+
 static void setopacity(Window win, unsigned long opacity)
 {
         Atom _NET_WM_WINDOW_OPACITY =

src/x11/x.h

@@ -58,10 +58,10 @@ extern xctx_t xctx;
 
 /* window */
 window_x11 *x_win_create(void);
-void x_win_move(int x, int y, int width, int height);
 void x_win_hide(void);
 void x_win_show(void);
 void x_win_destroy(window_x11 *win);
+void x_display_surface(cairo_surface_t *srf, window_x11 *win, const struct dimensions *dim);
 
 /* shortcut */
 void x_shortcut_init(keyboard_shortcut *shortcut);