Add simple drawing capability

Makefile

@@ -0,0 +1,6 @@
+TARGET=drawOnRoot
+SRC=main.c
+# DEBUG=-g
+DEBUG=
+$(TARGET): main.c
+	gcc -Wall -Wextra $(DEBUG) $(SRC) `pkg-config --cflags --libs cairo x11` -o $(TARGET)

main.c

@@ -0,0 +1,57 @@
+#include <assert.h>
+#include <stdio.h>
+#include <X11/Xlib.h>
+#include <X11/Xatom.h>
+#include <cairo.h>
+#include <cairo-xlib.h>
+
+int width, height;
+void draw(cairo_t *cr) {
+    int quarter_w = width / 4;
+    int quarter_h = height / 4;
+    cairo_set_source_rgb(cr, 1.0, 1.0, 0.0);
+    cairo_rectangle(cr, quarter_w, quarter_h, quarter_w * 2, quarter_h * 2);
+    cairo_fill(cr);
+}
+
+int main() {
+    Display *d = XOpenDisplay(NULL);
+    assert(d);
+
+    int s = DefaultScreen(d);
+    Window w = RootWindow(d, s);
+    XSync(d, False);
+    width = DisplayWidth(d, s);
+    height = DisplayHeight(d, s);
+    Pixmap pix;
+    int depth = DefaultDepth(d, s);
+    pix = XCreatePixmap(d, w, width, height, depth);
+    Atom prop_root;
+
+	prop_root = XInternAtom(d, "_XROOTPMAP_ID", False);
+
+    cairo_surface_t *surf = cairo_xlib_surface_create(d, pix,
+                                  DefaultVisual(d, s),
+                                  width, height);
+    cairo_t *cr = cairo_create(surf);
+    draw(cr);
+    XChangeProperty(d,   /* connection to x server */
+            w,    /* window whose property we want to change */
+            //prop_root = XInternAtom(disp2, "_XROOTPMAP_ID", False);
+            prop_root,   /* property name */
+            XA_PIXMAP, /* type of property */
+            32,         /* format of prop; can be 8, 16, 32 */
+            PropModeReplace,
+            (unsigned char*) &pix, /* actual data */
+            1         /* number of elements */
+            );
+
+	/* XSetWindowBackgroundPixmap(d, w, pix); // If we do not have compositor :) */
+    XClearWindow(d,w);
+    XFlush(d);
+    /* cairo_destroy(cr); */
+    /* cairo_surface_destroy(surf); */
+    /* XFreePixmap(d, pix); */
+    XCloseDisplay(d);
+    return 0;
+}