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Rotating an Image by an Arbitrary Angle

#Rotating an image by an arbitrary angle
#REMOVED O'Hare (gtg377h@mail.gatech.edu)
#CS1315
#June 1, 2004

def rotate(source, target, angle):

  #defining the rotation matrix that we all know and love
  #   [  cos(theta)    sin(theta)  ]
  #   [  -sin(theta)   cos(theta)  ]
  rma = cos(angle)
  rmb = sin(angle)
  rmc = -1 * rmb
  rmd = rma
  # rather than actually making a 2x2 array, I jREMOVEDt made 4 variables that will
  # be referenced to and I'll do the matrix operations manually

  #we're going to loop through the target image
  for x in range(1, getWidth(target)+1):
    for y in range(1, getHeight(target)+1):

      # denoting the top left pixel as (1,1) isn't real good for doing rotations
      # therefore, I'm going to redefine another coordinate system where the center of
      # the image is (0,0) and negative coordinates will be utilized.
      xcor = x - int(getWidth(target)/2)
      ycor = y - int(getHeight(target)/2)


      # now I'm going to take these coordinates and rotate them REMOVEDing
      # the rotational matrix. These new coordinates (sx, sy) will be 
      # REMOVEDed to determine which color to look for in the source picture
      sx = xcor * rma + ycor * rmb + getWidth(source)/2
      sy = xcor * rmc + ycor * rmd + getHeight(source)/2
      # the beauty of this method is that when you loop through the 
      # target image, you will know that there will always be a coresponding 
      # color on the source image. If I were to loop through the source image
      # coordinates, then I wouldn't be guaranteed a 1 to 1 corelation of pixels
      # and there'll probably be an even distribution of "holes" in the final image


      # if the rotated coordinates goes off the bounds of the source image, 
      # then ignore this loop and go on to the next one. 
      if ((sx < 1) or (sx > getWidth(source))) or ((sy < 1) or (sy > getHeight(source))):
        pass
      else:
        # if not, then find the source color and plot it on the target image
        color = getColor(getPixel(source, int(sx), int(sy)))
        setColor(getPixel(target, x, y), color)

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• Tutorials last edited on 30 November 2006 at 7:35 pm by r40h103.res.gatech.edu