mirror of https://github.com/papermerge/mglib
84 lines
3.0 KiB
Python
84 lines
3.0 KiB
Python
class Step:
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# Q: What is ``Step`` and why it was a bad decision to introduce it?
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#
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# A: ``Step`` class is closely related to zooming in/zooming out
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# a specific page in the document in the frontend (javascript code).
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#
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# When user opens the document in document viewer, he/she actually
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# sees an image with text over it (text overlay). Text overlay is
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# created from hocr data. Very important point here, is that
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# text hocr data corresponds to (extracted, format jpeg) image of the page
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# of VERY SAME width/height. Again, hocr file and respective image file
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# of the page MUST HAVE SAME WIDTH AND HEIGHT.
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#
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# Each step is meant to be a specific zoom value of the page. Thus, step
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# 2, which corresonds to LIST[2] % = 75 % of the page initial logical size
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# of WIDTH_100p = 1240.
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# When user zooms in/zooms out - a new hocr file is downloaded
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# corresponding to that zoom step. As you may guess, user can zoom only
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# 125%, 100%, 75% and 50%. Value of 10% corresponds to thumbnail of the
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# document and does not count as 'real' step.
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#
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# Instead of doing this step thingy, it would have been better to drop
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# the entire step concept. Much better solution for zoom in/zoom out would
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# have been to download one SVG file for each page (instead of hocr) and
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# SVG file of respective page should contain embedded image
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# (binary jpeg; yes SVG format allows embedding of binary formats!) and
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# correctly mapped text overlay (built from hocr file). User later
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# can zoom in/zoom out using SVG transforations in frontend!
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#
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# The good things about SVG solutions are:
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#
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# * there will be 4X less OCR required (corresponding to
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# hOCR of each step minus thumbnail/10% step)
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# * will simplify front-end code as SVG (= hocr + jpeg) will be
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# generated on the on server side
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# * eliminate conept of Step entirely
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# (there will be only one SVG file per page)
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# * increase front-end and back-end performance as only one file SVG file
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# will be sent back and forth (from backend to frontend)
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#
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# width of a document when displayed as 100%.
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WIDTH_100p = 1240
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PERCENT = 100
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LIST = [125, 100, 75, 50, 10]
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# aspect ration for A4 paper is h = w * 1.41
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# for 100
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# 100 => w = 1240, h = 1748
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# 50 => w = 620, h = 874
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def __init__(self, current=1):
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self.current = current
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@property
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def width(self):
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p = self.percent / 100
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return int(p * Step.WIDTH_100p)
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@property
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def is_thumbnail(self):
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return self.percent < 50
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@property
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def is_for_hocr(self):
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return not self.is_thumbnail
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@property
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def percent(self):
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return Step.LIST[self.current]
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def __str__(self):
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return f"Step(percent={self.percent}, width={self.width})"
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def __repr__(self):
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return self.__str__()
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class Steps:
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def __init__(self):
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self.steps = [Step(0), Step(1), Step(2), Step(3), Step(4)]
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def __iter__(self):
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return iter(self.steps)
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