pdfkit/lib/gradient.coffee

class PDFGradient
  constructor: (@doc) ->
    @stops = []
    @embedded = no
    @transform = [1, 0, 0, 1, 0, 0]
    @_colorSpace = 'DeviceRGB'
    
  stop: (pos, color, opacity = 1) ->
    opacity = Math.max(0, Math.min(1, opacity))
    @stops.push [pos, @doc._normalizeColor(color), opacity]
    return this
    
  embed: ->
    return if @embedded or @stops.length is 0
    @embedded = yes
    
    # if the last stop comes before 100%, add a copy at 100%
    last = @stops[@stops.length - 1]
    if last[0] < 1
      @stops.push [1, last[1], last[2]]
    
    bounds = []
    encode = []
    stops = []
    
    for i in [0...@stops.length - 1]
      encode.push 0, 1
      unless i + 2 is @stops.length
        bounds.push @stops[i + 1][0]
      
      fn = @doc.ref
        FunctionType: 2
        Domain: [0, 1]
        C0: @stops[i + 0][1]
        C1: @stops[i + 1][1]
        N: 1
        
      stops.push fn
      fn.end()
    
    # if there are only two stops, we don't need a stitching function
    if stops.length is 1
      fn = stops[0]
    else
      fn = @doc.ref
        FunctionType: 3 # stitching function
        Domain: [0, 1]
        Functions: stops
        Bounds: bounds
        Encode: encode
        
      fn.end()
        
    @id = 'Sh' + (++@doc._gradCount)
    
    # apply gradient transform to existing document ctm
    m = @doc._ctm.slice()
    [m0, m1, m2, m3, m4, m5] = m
    [m11, m12, m21, m22, dx, dy] = @transform
    m[0] = m0 * m11 + m2 * m12
    m[1] = m1 * m11 + m3 * m12
    m[2] = m0 * m21 + m2 * m22
    m[3] = m1 * m21 + m3 * m22
    m[4] = m0 * dx + m2 * dy + m4
    m[5] = m1 * dx + m3 * dy + m5

    shader = @shader fn
    shader.end()
    
    pattern = @doc.ref
      Type: 'Pattern'
      PatternType: 2
      Shading: shader
      Matrix: (+v.toFixed(5) for v in m)

    @doc.page.patterns[@id] = pattern
    pattern.end()
    
    if (@stops.some (stop) -> stop[2] < 1)
      grad = @opacityGradient()
      grad._colorSpace = 'DeviceGray'
      
      for stop in @stops
        grad.stop stop[0], [stop[2]]
        
      grad = grad.embed()
              
      group = @doc.ref
        Type: 'Group'
        S: 'Transparency'
        CS: 'DeviceGray'
        
      group.end()
      
      resources = @doc.ref
        ProcSet: ['PDF', 'Text', 'ImageB', 'ImageC', 'ImageI']
        Shading:
          Sh1: grad.data.Shading
          
      resources.end()
      
      form = @doc.ref
        Type: 'XObject'
        Subtype: 'Form'
        FormType: 1
        BBox: [0, 0, @doc.page.width, @doc.page.height]
        Group: group
        Resources: resources
      
      form.end "/Sh1 sh"
      
      sMask = @doc.ref
        Type: 'Mask'
        S: 'Luminosity'
        G: form
          
      sMask.end()
        
      gstate = @doc.ref
        Type: 'ExtGState'
        SMask: sMask
      
      @opacity_id = ++@doc._opacityCount
      name = "Gs#{@opacity_id}"
      
      @doc.page.ext_gstates[name] = gstate
      gstate.end()
    
    return pattern
      
  apply: (op) ->
    @embed() unless @embedded
    @doc.addContent "/#{@id} #{op}"
    
    if @opacity_id
      @doc.addContent "/Gs#{@opacity_id} gs"
      @doc._sMasked = true
    
class PDFLinearGradient extends PDFGradient
  constructor: (@doc, @x1, @y1, @x2, @y2) ->
    super
    
  shader: (fn) ->
    @doc.ref
      ShadingType: 2
      ColorSpace: @_colorSpace
      Coords: [@x1, @y1, @x2, @y2]
      Function: fn
      Extend: [true, true]
      
  opacityGradient: ->
    return new PDFLinearGradient(@doc, @x1, @y1, @x2, @y2)
    
class PDFRadialGradient extends PDFGradient
  constructor: (@doc, @x1, @y1, @r1, @x2, @y2, @r2) ->
    super
    
  shader: (fn) ->
    @doc.ref
      ShadingType: 3
      ColorSpace: @_colorSpace
      Coords: [@x1, @y1, @r1, @x2, @y2, @r2]
      Function: fn
      Extend: [true, true]
      
  opacityGradient: ->
    return new PDFRadialGradient(@doc, @x1, @y1, @r1, @x2, @y2, @r2)
      
module.exports = {PDFGradient, PDFLinearGradient, PDFRadialGradient}