Class: Vamp::Graphic::Context

Inherits:
Object
  • Object
show all
Extended by:
Forwardable
Defined in:
lib/vamp/graphic/context.rb

Overview

Graphic Context

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(dotter) ⇒ Context

Returns a new instance of Context.



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# File 'lib/vamp/graphic/context.rb', line 17

def initialize(dotter)
  @dotter = dotter
end

Instance Attribute Details

#dotter ⇒ Object (readonly)

can set a dot within [0, width] [0, height



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# File 'lib/vamp/graphic/context.rb', line 15

def dotter
  @dotter
end

Instance Method Details

#draw_line_direct(x0, y0, x1, y1) ⇒ Object

Bresenham’s line algorithm



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# File 'lib/vamp/graphic/context.rb', line 88

def draw_line_direct(x0, y0, x1, y1)
  dx = (x1 - x0).abs
  sx = x0 < x1 ? 1 : -1
  dy = -(y1 - y0).abs
  sy = y0 < y1 ? 1 : -1
  err = dx + dy
  while true
    dot(x0, y0)
    break if x0 == x1 && y0 == y1
    e2 = 2 * err
    if e2 > dy
      err += dy
      x0 += sx
    end
    if e2 < dx
      err += dx
      y0 += sy
    end
  end
  self
end

#line(x0, y0, x1, y1) ⇒ Object

Cohen–Sutherland clipping algorithm clips a line from P0 = (x0, y0) to P1 = (x1, y1) against a rectangle with diagonal from (xmin, ymin) to (xmax, ymax).



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# File 'lib/vamp/graphic/context.rb', line 24

def line(x0, y0, x1, y1)
  xmin = 0.0
  ymin = 0.0
  xmax = width - 1.0
  ymax = height - 1.0

  # compute outcodes for P0, P1, and whatever point lies outside the clip rectangle
  outcode0 = compute_out_code(x0, y0)
  outcode1 = compute_out_code(x1, y1)

  accept = false

  while true
    if 0 == (outcode0 | outcode1)     # Bitwise OR is 0. Trivially accept and get out of loop
      accept = true
      break
    elsif 0 != (outcode0 & outcode1)  # Bitwise AND is not 0. Trivially reject and get out of loop
      break
    else
      # failed both tests, so calculate the line segment to clip
      # from an outside point to an intersection with clip edge

      # At least one endpoint is outside the clip rectangle; pick it.
      outcodeOut = outcode0 != 0 ? outcode0 : outcode1


      # Now find the intersection point;
      # use formulas y = y0 + slope * (x - x0), x = x0 + (1 / slope) * (y - y0)
      if 0 != (outcodeOut & TOP)            # point is above the clip rectangle
        x = x0.to_f + (x1 - x0) * (ymax - y0) / (y1 - y0)
        y = ymax
      elsif (0 != outcodeOut & BOTTOM)      # point is below the clip rectangle
        x = x0.to_f + (x1 - x0) * (ymin - y0) / (y1 - y0)
        y = ymin
      elsif (0 != outcodeOut & RIGHT)       # point is to the right of clip rectangle
        y = y0.to_f + (y1 - y0) * (xmax - x0) / (x1 - x0)
        x = xmax
      elsif (0 != outcodeOut & LEFT)        # point is to the left of clip rectangle
        y = y0.to_f + (y1 - y0) * (xmin - x0) / (x1 - x0)
        x = xmin
      end

      # Now we move outside point to intersection point to clip
      # and get ready for next pass.
      if outcodeOut == outcode0
        x0 = x
        y0 = y
        outcode0 = compute_out_code(x0, y0)
      else
        x1 = x
        y1 = y
        outcode1 = compute_out_code(x1, y1)
      end
    end
  end
  if accept
    draw_line_direct (x0 + 0.5).to_i, (y0 + 0.5).to_i, (x1 + 0.5).to_i, (y1 + 0.5).to_i
  end
  self
end