41 lines
1.1 KiB
Plaintext
41 lines
1.1 KiB
Plaintext
-- demo\rosetta\Bitmap_Circle.exw (runnable version)
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include ppm.e -- red, yellow, new_image(), write_ppm() -- (covers above requirements)
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function SetPx(sequence img, atom x, y, integer colour)
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if x>=1 and x<=length(img)
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and y>=1 and y<=length(img[x]) then
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img[x][y] = colour
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end if
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return img
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end function
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function Circle(sequence img, atom x, y, r, integer colour)
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atom x1 = -r,
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y1 = 0,
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err = 2-2*r
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if r>=0 then
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-- Bresenham algorithm
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while 1 do
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img = SetPx(img, x-x1, y+y1, colour)
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img = SetPx(img, x-y1, y-x1, colour)
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img = SetPx(img, x+x1, y-y1, colour)
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img = SetPx(img, x+y1, y+x1, colour)
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r = err
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if r>x1 then
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x1 += 1
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err += x1*2 + 1
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end if
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if r<=y1 then
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y1 += 1
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err += y1*2 + 1
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end if
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if x1>=0 then exit end if
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end while
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end if
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return img
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end function
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sequence img = new_image(400,300,yellow)
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img = Circle(img, 200, 150, 100, red)
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write_ppm("Circle.ppm",img)
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