Use cairo for all drawing operations in i3bar.

fixes #1878

i3bar/include/cairo_util.h

@@ -0,0 +1,65 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ *
+ * © 2015 Ingo Bürk and contributors (see also: LICENSE)
+ *
+ * cairo_util.h: Utility for operations using cairo.
+ *
+ */
+#pragma once
+
+#include <cairo/cairo-xcb.h>
+
+/* Represents a color split by color channel. */
+typedef struct color_t {
+    double red;
+    double green;
+    double blue;
+
+    /* For compatibility, we also store the colorpixel for now. */
+    uint32_t colorpixel;
+} color_t;
+
+/* A wrapper grouping an XCB drawable and both a graphics context
+ * and the corresponding cairo objects representing it. */
+typedef struct surface_t {
+    /* The drawable which is being represented. */
+    xcb_drawable_t id;
+
+    // TODO remove this once i3 uses solely cairo for drawing operations
+    /* A classic XCB graphics context. This should not be used for
+     * drawing operations. */
+    xcb_gcontext_t gc;
+
+    /* A cairo surface representing the drawable. */
+    cairo_surface_t *surface;
+
+    /* The cairo object representing the drawale. In general,
+     * this is what one should use for any drawing operation. */
+    cairo_t *cr;
+} surface_t;
+
+/**
+ * Initialize the cairo surface to represent the given drawable.
+ *
+ */
+void cairo_surface_init(surface_t *surface, xcb_drawable_t drawable, int width, int height);
+
+/**
+ * Destroys the surface.
+ *
+ */
+void cairo_surface_free(surface_t *surface);
+
+/**
+ * Parses the given color in hex format to an internal color representation.
+ * Note that the input must begin with a hash sign, e.g., "#3fbc59".
+ *
+ */
+color_t cairo_hex_to_color(const char *color);
+
+/**
+ * Set the given color as the source color on the surface.
+ *
+ */
+void cairo_set_source_color(surface_t *surface, color_t color);