This is an event-based parser for
SVG path element data.
Each of the commands in a path string will generate a callback to a handler
proc specified at parser creation.
require 'svg_path_parser'
on_move = lambda{ |vo| puts "Hey! on_move received"}
on_line = lambda{|vo| puts "Hey! on_line received"}
on_curve = lambda{|vo| puts "Hey! on_curve received"}
on_quadratic = lambda{|vo| puts "Hey! on_quadratic received"}
on_arc = lambda{|vo| puts "Hey! on_arc received"}
on_close = lambda{|vo| puts "Hey! on_close received"}
parser = SvgPathParser::Impl.new :on_move => on_move,
:on_line => on_line,
:on_curve => on_curve,
:on_quadratic => on_quadratic,
:on_arc => on_arc,
:on_close => on_close
parser.parse(nil, "M5 5L10 10C15 15 0 0 20 20Q10 10 7 7A30 50 -45 1 1 30 30Z")
Hey! on_move received
Hey! on_line received
Hey! on_curve received
Hey! on_quadratic received
Hey! on_arc received
Hey! on_close received
=> nilYou only need to specify callbacks for the path commands you are interested in. All callbacks have default do-nothing lambdas that are invoked in response to the various commands.
The context object passed as the first argument is used to collect results of the parsing and needs to be modified by the callbacks to produce a meaningful result of the parsing. It is roughly analogous to a memo for the Array#inject method. It is returned as the result of the parse call.
In this example, we will convert curves to lines in an SVG path, but otherwise keep the path the same.
require 'svg_path_parser'
convert_to_line = lambda do |vo|
# a really bad conversion algorithm
vo.context << "L#{vo.dest_pt[0]} #{vo.dest_pt[1]}"
end
dupe_command = lambda do |vo|
vo.context << vo.command_str
end
parser = SvgPathParser::Impl.new :on_move => dupe_command,
:on_line => dupe_command,
:on_curve => convert_to_line,
:on_quadratic => convert_to_line,
:on_arc => convert_to_line,
:on_close => dupe_command
parser.parse("", "M5 5L10 10C15 15 0 0 20 20Q10 10 7 7A30 50 -45 1 1 30 30Z")
=> "M5 5L10 10L15.0 15.0L10.0 10.0L30.0 30.0Z"The argument lists for the callbacks can be pretty large, so I extracted them into events as follows:
DestinationEvent = Struct.new :command_str, :context, :current_pt, :dest_pt
CurveEvent = Struct.new :command_str, :context, :current_pt, :dest_pt, :control_1, :control_2
QuadraticEvent = Struct.new :command_str, :context, :current_pt, :dest_pt, :control
ArcEvent = Struct.new :command_str, :context, :current_pt, :x_radius, :y_radius, :x_rotation, :large_arc, :sweep, :dest_pt
CloseEvent = Struct.new :command_str, :context, :current_pt, :first_ptDestinationEvent is used for both move and line commands.
- This currently does not support the horizontal/vertical (H/V) line shortcuts.
- This currently does not support the shortcuts for stringing together sets of bezier or quadratic curves (S/T).
Both of these should be easy to implement.
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