Class: SparkCanvas

Inherits:
Object
  • Object
show all
Defined in:
lib/spark_pr/spark_canvas.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(width, height, base_color = [0xFF,0xFF,0xFF]) ⇒ SparkCanvas

Returns a new instance of SparkCanvas.



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# File 'lib/spark_pr/spark_canvas.rb', line 16

def initialize(width,height,base_color=[0xFF,0xFF,0xFF])
  @canvas = []
  @height = height
  @width = width
  height.times{ @canvas << [base_color]*width }
  @color = [0,0,0,0xFF] #RGBA
end

Instance Attribute Details

#color ⇒ Object

Returns the value of attribute color.



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# File 'lib/spark_pr/spark_canvas.rb', line 13

def color
  @color
end

#height ⇒ Object (readonly)

Returns the value of attribute height.



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# File 'lib/spark_pr/spark_canvas.rb', line 14

def height
  @height
end

#width ⇒ Object (readonly)

Returns the value of attribute width.



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# File 'lib/spark_pr/spark_canvas.rb', line 14

def width
  @width
end

Instance Method Details

#blend(c1, c2) ⇒ Object

alpha blends two colors, using the alpha given by c2



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# File 'lib/spark_pr/spark_canvas.rb', line 25

def blend(c1, c2)
  (0..2).map{ |i| (c1[i]*(0xFF-c2[3]) + c2[i]*c2[3]) >> 8 }
end

#build_png_chunk(type, data) ⇒ Object 



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# File 'lib/spark_pr/spark_canvas.rb', line 106

def build_png_chunk(type,data)
  to_check = type + data
  [data.length].pack("N") + to_check + [Zlib.crc32(to_check)].pack("N")
end

#grayscale(c) ⇒ Object

calculate perceptive grayscale value



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# File 'lib/spark_pr/spark_canvas.rb', line 35

def grayscale(c)
  (c[0]*0.3 + c[1]*0.59 + c[2]*0.11).to_i
end

#intensity(c, i) ⇒ Object

calculate a new alpha given a 0-0xFF intensity



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# File 'lib/spark_pr/spark_canvas.rb', line 30

def intensity(c,i)
  [c[0],c[1],c[2],(c[3]*i) >> 8]
end

#line(x0, y0, x1, y1) ⇒ Object

draw an antialiased line google for “wu antialiasing”



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# File 'lib/spark_pr/spark_canvas.rb', line 53

def line(x0, y0, x1, y1)
  # clean params
  x0, y0, x1, y1 = x0.to_i, y0.to_i, x1.to_i, y1.to_i
  y0, y1, x0, x1 = y1, y0, x1, x0 if y0>y1
  sx = (dx = x1-x0) < 0 ? -1 : 1 ; dx *= sx ; dy = y1-y0

  # special cases
  x0.step(x1,sx) { |x| point x, y0 } and return if dy.zero?
  y0.upto(y1)    { |y| point x0, y } and return if dx.zero?
  x0.step(x1,sx) { |x| point x, y0; y0 += 1 } and return if dx==dy

  # main loops
  point x0, y0

  e_acc = 0
  if dy > dx
    e = (dx << 16) / dy
    y0.upto(y1-1) do
      e_acc_temp, e_acc = e_acc, (e_acc + e) & 0xFFFF
      x0 += sx if (e_acc <= e_acc_temp)
      point x0, (y0 += 1), intensity(@color,(w=0xFF-(e_acc >> 8)))
      point x0+sx, y0, intensity(@color,(0xFF-w))
    end
    point x1, y1
    return
  end

  e = (dy << 16) / dx
  x0.step(x1-sx,sx) do
    e_acc_temp, e_acc = e_acc, (e_acc + e) & 0xFFFF
    y0 += 1 if (e_acc <= e_acc_temp)
    point (x0 += sx), y0, intensity(@color,(w=0xFF-(e_acc >> 8)))
    point x0, y0+1, intensity(@color,(0xFF-w))
  end
  point x1, y1
end

#point(x, y, color = nil) ⇒ Object 



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# File 'lib/spark_pr/spark_canvas.rb', line 39

def point(x,y,color = nil)
  return if x<0 or y<0 or x>@width-1 or y>@height-1
  @canvas[y][x] = blend(@canvas[y][x], color || @color)
end

#polyline(arr) ⇒ Object 



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# File 'lib/spark_pr/spark_canvas.rb', line 90

def polyline(arr)
  (0...arr.size-1).each{ |i| line(arr[i][0], arr[i][1], arr[i+1][0], arr[i+1][1]) }
end

#rectangle(x0, y0, x1, y1) ⇒ Object 



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# File 'lib/spark_pr/spark_canvas.rb', line 44

def rectangle(x0, y0, x1, y1)
  x0, y0, x1, y1 = x0.to_i, y0.to_i, x1.to_i, y1.to_i
  x0, x1 = x1, x0 if x0 > x1
  y0, y1 = y1, y0 if y0 > y1
  x0.upto(x1) { |x| y0.upto(y1) { |y| point x, y } }
end

#to_ascii ⇒ Object 



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# File 'lib/spark_pr/spark_canvas.rb', line 111

def to_ascii
  chr = %w(M O # + ; - .) << ' '
  @canvas.map{ |r| r.map { |pt| chr[grayscale(pt) >> 5] }.join << "\n" }.join
end

#to_png ⇒ Object 



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# File 'lib/spark_pr/spark_canvas.rb', line 94

def to_png
  header = [137, 80, 78, 71, 13, 10, 26, 10].pack("C*")
  raw_data = @canvas.map { |row| [0] + row }.flatten.pack("C*")
  ihdr_data = [@canvas.first.length,@canvas.length,8,2,0,0,0].pack("NNCCCCC")

  header +
    build_png_chunk("IHDR", ihdr_data) +
    build_png_chunk("tRNS", ([ 0xFF ]*6).pack("C6")) +
    build_png_chunk("IDAT", Zlib::Deflate.deflate(raw_data)) +
    build_png_chunk("IEND", "")
end