Add functions to draw widgets to a cairo surface

These are supposed to eventually replace the already-existing functions
in gears.surface which have a similar signature

Signed-off-by: Uli Schlachter <psychon@znc.in>

docs/config.ld

@@ -105,7 +105,6 @@ file = {
         '../lib/awful/startup_notification.lua',
         '../lib/gears/init.lua',
         '../lib/wibox/layout/init.lua',
-        '../lib/wibox/widget/init.lua',
         '../lib/wibox/container/init.lua',
 
         -- Ignore some parts of the widget library

lib/wibox/widget/init.lua

@@ -3,10 +3,12 @@
 -- @copyright 2010 Uli Schlachter
 -- @classmod wibox.widget
 ---------------------------------------------------------------------------
-local base = require("wibox.widget.base")
 
-return setmetatable({
-    base = base;
+local cairo = require("lgi").cairo
+local hierarchy = require("wibox.hierarchy")
+
+local widget = {
+    base = require("wibox.widget.base");
     textbox = require("wibox.widget.textbox");
     imagebox = require("wibox.widget.imagebox");
     background = require("wibox.widget.background");
@@ -17,6 +19,56 @@ return setmetatable({
     checkbox = require("wibox.widget.checkbox");
     piechart = require("wibox.widget.piechart");
     slider = require("wibox.widget.slider");
-}, {__call = function(_, args) return base.make_widget_declarative(args) end})
+}
+
+setmetatable(widget, {
+    __call = function(_, args)
+        return widget.base.make_widget_declarative(args)
+    end
+})
+
+--- Draw a widget directly to a given cairo context.
+-- This function creates a temporary `wibox.hierarchy` instance and uses that to
+-- draw the given widget once to the given cairo context.
+-- @tparam widget wdg A widget to draw
+-- @tparam cairo_context cr The cairo context to draw the widget on
+-- @tparam number width The width of the widget
+-- @tparam number height The height of the widget
+-- @tparam[opt={dpi=96}] table context The context information to give to the widget.
+function widget.draw_to_cairo_context(wdg, cr, width, height, context)
+    local function no_op() end
+    context = context or {dpi=96}
+    local h = hierarchy.new(context, wdg, width, height, no_op, no_op, {})
+    h:draw(context, cr)
+end
+
+--- Create an SVG file showing this widget.
+-- @tparam widget wdg A widget
+-- @tparam string path The output file path
+-- @tparam number width The surface width
+-- @tparam number height The surface height
+-- @tparam[opt={dpi=96}] table context The context information to give to the widget.
+function widget.draw_to_svg_file(wdg, path, width, height, context)
+    local img = cairo.SvgSurface.create(path, width, height)
+    local cr = cairo.Context(img)
+    widget.draw_to_cairo_context(wdg, cr, width, height, context)
+    img:finish()
+end
+
+--- Create a cairo image surface showing this widget.
+-- @tparam widget wdg A widget
+-- @tparam number width The surface width
+-- @tparam number height The surface height
+-- @param[opt=cairo.Format.ARGB32] format The surface format
+-- @tparam[opt={dpi=96}] table context The context information to give to the widget.
+-- @return The cairo surface
+function widget.draw_to_image_surface(wdg, width, height, format, context)
+    local img = cairo.ImageSurface(format or cairo.Format.ARGB32, width, height)
+    local cr = cairo.Context(img)
+    widget.draw_to_cairo_context(wdg, cr, width, height, context)
+    return img
+end
+
+return widget
 
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