naughty: Correctly handle rowstride on icons

The notification spec allow sending icons as data with a dbus message. The
rowstride for this can be set which means there can be bytes after each row of
icon data which must be ignored.

Before this commit, naughty wasn't properly ignoring these garbage bytes which
resulted in weird notifications.

Thanks to dadrc for reporting that gmusicbrowser's notifications didn't work.

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

lib/naughty.lua.in

@@ -538,25 +538,37 @@ if capi.dbus then
                 -- icon_data is an array:
                 -- 1 -> width, 2 -> height, 3 -> rowstride, 4 -> has alpha
                 -- 5 -> bits per sample, 6 -> channels, 7 -> data
+                local width, height, rowstride = hints.icon_data[1], hints.icon_data[2], hints.icon_data[3]
 
                 local imgdata = ""
+                local format, bpp
                 -- If has alpha (ARGB32)
                 if hints.icon_data[6] == 4 then
-                    for i = 1, #hints.icon_data[7], 4 do
+                    format, bpp = cairo.Format.ARGB32, 4
-                        imgdata = imgdata .. hints.icon_data[7]:sub(i, i + 2):reverse()
-                        imgdata = imgdata .. hints.icon_data[7]:sub(i + 3, i + 3)
-                    end
                 -- If has not alpha (RGB24)
                 elseif hints.icon_data[6] == 3 then
-                    for i = 1, #hints.icon_data[7], 3 do
+                    format, bpp = cairo.Format.RGB24, 3
+                end
+                -- Figure out some stride magic (cairo dictates rowstride)
+                local stride = cairo.Format.stride_for_width(format, width)
+                local append = string.format("%c", 0):rep(stride - 4 * width)
+                local offset = 0
+                -- Now convert each row on its own
+                for y = 1, height do
+                    for i = 1 + offset, width * bpp + offset, bpp do
                         imgdata = imgdata .. hints.icon_data[7]:sub(i, i + 2):reverse()
-                        imgdata = imgdata .. string.format("%c", 255) -- alpha is 255
+                        if bpp == 4 then
+                            imgdata = imgdata .. hints.icon_data[7]:sub(i + 3, i + 3)
+                        else
+                            imgdata = imgdata .. string.format("%c", 255)
                         end
                     end
-                if imgdata then
+                    -- Handle rowstride, offset is stride for the input, append for output
-                    args.icon = cairo.ImageSurface.create_for_data(imgdata,
+                    offset = offset + rowstride
-                        cairo.Format.ARGB32, hints.icon_data[1], hints.icon_data[2], hints.icon_data[1] * 4)
+                    imgdata = imgdata .. append
                 end
+                args.icon = cairo.ImageSurface.create_for_data(imgdata, format,
+                    width, height, stride)
             end
             if replaces_id and replaces_id ~= "" and replaces_id ~= 0 then
                 args.replaces_id = replaces_id