From: shawn bright <nephish@...>
Date: 2008-02-20T05:21:48+09:00
Subject: RMagick and circle problem

Hello all, i am back with this one.

my problem is that i am trying to draw a line on a circle that will
indicate a certain angle.
kinda like the hands on a clock. I have a line image that i rotate
around and then superimpose upon the circle image that i draw.

The problem is that when the line image is rotated, it is shorter than
the circle.

here is the code.
#!/usr/bin/ruby

require 'RMagick'

def gps_image(r)
  # fetches the image file

  gps_image = Magick::Image.read('line_stop.png').first
  gps_image.background_color = 'none'

  angle = 45
  gps_image.rotate!(angle)

  factor = (r.to_i * 2)
  gps_image.crop_resized!(factor, factor, Magick::CenterGravity)
  gps_image.write("site.site_name.png")

  return gps_image
end

def circle_image
  r = 45
  #start with a bare canvas (square 2 times the radius of circle) the
extra two pixels is to not cut any of the border
  canvas = Magick::Image.new((2 * r) +2, (2*r) +2,
Magick::HatchFill.new('transparent', 'transparent'))

  # draw the circle
  gc = Magick::Draw.new
  gc.stroke('red')
  gc.stroke_width(1)
  # fill in the inside
  color = 'blue'
  gc.fill(color)
  gc.fill_opacity(0.3)
  gc.circle(r, r, 0, r)

  # put our circle on the canvas
  image = gc.draw(canvas)

  # place the line for gps circles
  gps_image = gps_image(r)
  canvas.composite!(gps_image, 0, 0, Magick::OverCompositeOp)

  # write the image out as a file
  canvas.write("circle.png")
end

circle_image()

Everything is ok if the image is 90, 180, 270, or 0 degrees, but the
more i stray toward 45 degrees or so, the smaller the line comes out
on the image.

the image used here ( line_stop.png) is just a transparent image with
a line drawn on it in the middle. ( my clock hand )

thanks for any tips.

shawn