Class: Raster

Inherits:
Object
  • Object
show all
Defined in:
lib/skrift/raster.rb

Defined Under Namespace

Classes: Cell, Vector

Instance Method Summary collapse

Constructor Details

#initialize(width, height) ⇒ Raster

Returns a new instance of Raster.



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# File 'lib/skrift/raster.rb', line 11

def initialize width, height
  @width = width
  @height = height
  @cells = (0..(width*height-1)).map { Cell[0.0,0.0] }
end

Instance Method Details

#draw_line(origin, goal) ⇒ Object

Draws a line into the buffer. Uses a custom 2D raycasting algorithm to do so.



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# File 'lib/skrift/raster.rb', line 30

def draw_line(origin, goal)
  prev_distance = 0.0
  num_steps = 0
  delta = goal-origin
  dir_x = delta[0] <=> 0
  dir_y = delta[1] <=> 0
  next_crossing = Vector[0.0,0.0]
  pixel = Vector[0,0]
  return if dir_y == 0

  crossing_incr_x = dir_x != 0 ? (1.0 / delta[0]).abs : 1.0
  crossing_incr_y = (1.0 / delta[1]).abs

  if dir_x == 0
    pixel[0] = origin[0].floor
    next_crossing[0] = 100.0
  else
    if dir_x > 0
      pixel[0] = origin[0].floor
      next_crossing[0] = crossing_incr_x - (origin[0] - pixel[0]) * crossing_incr_x
      num_steps += goal[0].ceil - origin[0].floor - 1
    else
      pixel[0] = origin[0].ceil - 1
      next_crossing[0] = (origin[0] - pixel[0]) * crossing_incr_x
      num_steps += origin[0].ceil - goal[0].floor - 1
    end
  end

  if dir_y > 0
    pixel[1] = origin[1].floor
    next_crossing[1] = crossing_incr_y - (origin[1] - pixel[1]) * crossing_incr_y
    num_steps += goal[1].ceil - origin[1].floor - 1
  else
    pixel[1] = origin[1].ceil - 1
    next_crossing[1] = (origin[1] - pixel[1]) * crossing_incr_y
    num_steps += origin[1].ceil - goal[1].floor - 1
  end

  next_distance = next_crossing.min
  half_delta_x = 0.5 * delta[0]
  setcell = ->(nd) do
    x_average = origin[0] + (prev_distance + nd) * half_delta_x - pixel[0]
    y_difference = (nd - prev_distance).to_f * delta[1]
    cell = @cells[pixel[1] * @width + pixel[0]]
    cell.cover += y_difference
    cell.area  += (1.0 - x_average) * y_difference
  end
  num_steps.times do
    setcell.call(next_distance)
    prev_distance = next_distance
    along_x = next_crossing[0] < next_crossing[1]
    pixel += along_x ? Vector[dir_x,0] : Vector[0,dir_y]
    next_crossing += along_x ? Vector[crossing_incr_x, 0.0] : [0.0, crossing_incr_y]
    next_distance = next_crossing.min
  end
  setcell.call(1.0)
end

#post_process ⇒ Object

Integrate the values in the buffer to arrive at the final grayscale image.



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# File 'lib/skrift/raster.rb', line 18

def post_process
  accum = 0.0
  (@width*@height).times.collect do |i|
    cell = @cells[i]
    value = (accum + cell.area).abs
    value = [value, 1.0].min * 255.0 + 0.5
    accum += cell.cover
    value.to_i & 0xff
  end
end