Class: Compass::Canvas::Backend::Cairo

Inherits:
Base
  • Object
show all
Defined in:
lib/canvas/backend/cairo.rb

Overview

Cairo backend implementation.

Instance Attribute Summary collapse

Attributes inherited from Base

#file, #height, #width

Instance Method Summary collapse

Methods inherited from Base

#execute, #initialize, #to_s, #value

Constructor Details

This class inherits a constructor from Compass::Canvas::Backend::Base

Instance Attribute Details

#surface ⇒ ::Cairo::ImageSurface

Returns The internal image surface.

Returns:

  • (::Cairo::ImageSurface) —

    The internal image surface.



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# File 'lib/canvas/backend/cairo.rb', line 7

def surface
  @surface
end

Instance Method Details

#begin_canvas ⇒ Object

Creates a new ImageSurface and binds a new context to it.



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# File 'lib/canvas/backend/cairo.rb', line 53

def begin_canvas
  if @width && @height
    @surface = ::Cairo::ImageSurface.new(::Cairo::FORMAT_ARGB32, @width, @height)
  else
    @surface = ::Cairo::ImageSurface.from_png(@file)
  end
  bind_context
end

#execute_one(action, *args) ⇒ Object

Executes a single action on the context bound to the surface.



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# File 'lib/canvas/backend/cairo.rb', line 63

def execute_one(action, *args)
  case action
  when Compass::Canvas::Actions::MOVE
    @context.move_to(*args)
  when Compass::Canvas::Actions::LINE
    @context.line_to(*args)
  when Compass::Canvas::Actions::CURVE
    @context.curve_to(*args)
  when Compass::Canvas::Actions::QUADRATIC_CURVE
    x1, y1, x2, y2 = args
    x, y = @context.current_point
    @context.curve_to(
      x  + 2.0 / 3.0 * (x1 - x),  y  + 2.0 / 3.0 * (y1 - y),
      x2 + 2.0 / 3.0 * (x1 - x2), y2 + 2.0 / 3.0 * (y1 - y2),
      x2, y2
    )
  when Compass::Canvas::Actions::ARC
    @context.arc(*args)
  when Compass::Canvas::Actions::ARC_REVERSE
    @context.arc_negative(*args)
  when Compass::Canvas::Actions::PAINT
    @context.paint(*args)
  when Compass::Canvas::Actions::STROKE
    @context.stroke_preserve(*args)
  when Compass::Canvas::Actions::FILL
    @context.fill_preserve(*args)
  when Compass::Canvas::Actions::LINE_WIDTH
    @context.set_line_width(*args)
  when Compass::Canvas::Actions::PUSH
    @context.push_group
  when Compass::Canvas::Actions::POP
    @context.pop_group_to_source
  when Compass::Canvas::Actions::STORE
    @sources.push(@context.source)
  when Compass::Canvas::Actions::RETRIEVE
    @context.set_source(@sources.pop)
  when Compass::Canvas::Actions::GROUP
    @context.new_sub_path
  when Compass::Canvas::Actions::CLIP
    @context.clip_preserve
  when Compass::Canvas::Actions::UNCLIP
    @context.reset_clip
  when Compass::Canvas::Actions::CLOSE
    @context.close_path
  when Compass::Canvas::Actions::RESET
    @context.new_path
  when Compass::Canvas::Actions::SAVE
    @context.save
  when Compass::Canvas::Actions::RESTORE
    @context.restore
  when Compass::Canvas::Actions::ANTIALIAS
    @context.set_antialias(constant('ANTIALIAS', args))
  when Compass::Canvas::Actions::FILL_RULE
    @context.set_fill_rule(constant('FILL_RULE', args))
  when Compass::Canvas::Actions::TOLERANCE
    @context.set_tolerance(*args)
  when Compass::Canvas::Actions::LINE_CAP
    @context.set_line_cap(constant('LINE_CAP', args))
  when Compass::Canvas::Actions::LINE_JOIN
    @context.set_line_join(constant('LINE_JOIN', args))
  when Compass::Canvas::Actions::MITER_LIMIT
    @context.set_miter_limit(*args)
  when Compass::Canvas::Actions::DASH_PATTERN
    # If at least two lengths exist, create a new pattern
    if args.length > 1
      @context.set_dash(args)
    # Otherwise return to a solid stroke
    else
      @context.set_dash(nil, 0)
    end
  when Compass::Canvas::Actions::TRANSLATE
    @context.translate(*args)
  when Compass::Canvas::Actions::SCALE
    @context.scale(*args)
  when Compass::Canvas::Actions::ROTATE
    @context.rotate(*args)
  when Compass::Canvas::Actions::TRANSFORM
    @context.transform(::Cairo::Matrix.new(*args))
  when Compass::Canvas::Actions::MASK
    type = args.shift
    if type.is_a?(Compass::Canvas::Backend::Cairo)
      surface = type.execute.surface
      if args.length == 1
        pattern = ::Cairo::SurfacePattern.new(surface)
        pattern.set_extend(constant('EXTEND', args))
        @context.mask(pattern)
      else
        x = args.shift if args.length > 0
        y = args.shift if args.length > 0
        @context.mask(surface, x || 0, y || 0)
      end
    elsif type == Compass::Canvas::Actions::RETRIEVE
      @context.mask(@sources.pop)
    else
      raise Compass::Canvas::Exception.new("(#{self.class}.#{action}) Unsupported canvas, Cairo can only mask with Cairo: #{type.inspect}")
    end
  when Compass::Canvas::Actions::BRUSH
    type = args.shift
    case type
    when Compass::Canvas::Constants::SOLID
      components = args.shift
      @context.set_source_rgba(*components)
    when Compass::Canvas::Constants::LINEAR, Compass::Canvas::Constants::RADIAL
      coordinates = args.shift
      stops       = args.shift
      gradient    = ::Cairo::const_get("#{ type.to_s.sub(/^\w/) { |s| s.capitalize } }Pattern").new(*coordinates)
      stops.each { |value| gradient.add_color_stop_rgba(*value) }
      @context.set_source(gradient)
    when Compass::Canvas::Constants::CANVAS
      canvas = args.shift
      if canvas.is_a?(Compass::Canvas::Backend::Cairo)
        pattern = ::Cairo::SurfacePattern.new(canvas.execute.surface)
        pattern.set_extend(constant('EXTEND', args)) if args.length > 0
        @context.set_source(pattern)
      else
        raise Compass::Canvas::Exception.new("(#{self.class}.#{action}) Unsupported canvas, Cairo can only paint with Cairo: #{canvas.inspect}")
      end
    else
      raise Compass::Canvas::Exception.new("(#{self.class}.#{action}) Unsupported type (supported types are 'solid', 'linear', 'radial'): #{type.inspect}")
    end
  when Compass::Canvas::Actions::SLOW_BLUR
    radius = args.shift
    @context.pseudo_blur(radius) do
      execute_actions(args)
    end
  else
    raise Compass::Canvas::Exception.new("(#{self.class}) '#{action}' is not supported.")
  end
end

#load_dependencies ⇒ Object

Loads the cairo gem dependency. If it is not on $LOAD_PATH, attempts to load RubyGems.



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# File 'lib/canvas/backend/cairo.rb', line 11

def load_dependencies
  begin
    require 'cairo'
  rescue LoadError
    require 'rubygems'
    begin
      require 'cairo'
    rescue LoadError
      puts "Compass::Canvas\n_______________\n\n"
      puts "Unable to load Cairo backend. Please install it with the following command:\n\n"
      puts "  gem install cairo\n\n"
      puts "For more information, please visit https://github.com/rcairo/rcairo"
      raise
    end
  end
end

#property(name) ⇒ Object

Reads a property of the Cairo backend.

This can be used to obtain information about the width/height of the surface as well as the current point’s X/Y coordinates.

Parameters:

  • name (String) —

    The property name.

Returns:

  • (Object) —

    The property value, or nil if it doesn’t exist.



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# File 'lib/canvas/backend/cairo.rb', line 35

def property(name)
  execute
  case name
  when :width;  return @surface.width
  when :height; return @surface.height
  when :x;      return @context.current_point[0]
  when :y;      return @context.current_point[1]
  else return nil
  end
end

#read_canvas ⇒ Object

Creates a new ImageSurface from a file



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# File 'lib/canvas/backend/cairo.rb', line 47

def read_canvas
  @surface = ::Cairo::ImageSurface.from_png(@file)
  bind_context
end

#to_blob ⇒ Object

Serializes the ImageSurface to a String.



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# File 'lib/canvas/backend/cairo.rb', line 194

def to_blob
  stream = StringIO.new
  @surface.write_to_png(stream)
  stream.string
end