Ability to capture a scrolling web page
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#13 Ability to capture a scrolling web page
It would be great to have the ability to capture the full length of a web page, beyond what fits on a single screen. The way to implement this would be:
* use the current capture frame selector to select the visible part of the web page to be captured
* check some option to capture a scrolling page
* write the result to a single image file
This implies xvidcap would need a way to scroll the page without human intervention.
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(update)
I have no idea how to implement this ...
been thinking about it and can only think of two ways to
address it:
1) capture individual frames and implement some logic that
actually
understands the image data and can determine how the
frames should be
cut and pasted together.
This I would atm rule out as way out of scope!
2) grab the mouse and find out by how many pixels the mouse
moves
in a vertical direction between to captured frames. For a
move down
cut the lower portion of that height and paste to the
bottom of the
previous frame (scrolling up, the other way arount).
PROBLEM: the pixels by which the mouse pointer moves may
not be
the amount of pixels the web page scrolls. Let's say your
browser is
200 pixels high and the page is 5000 pixels, then moving
the mouse
by 20 pixels will move the page by 500 pixels.
And since there is no way of knowing for an external
application how
the ratio scrollbar increment:page scroll increment I
have no idea
of how to solve this issue.
Karl.
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Would it be possible to implement this for a single program, say Mozilla
Firebird (which is cross-platform)?
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Well,
How do I ask Mozilla (or Firebird [or any other application,
which is just
the point]) for the ratio between the scroll bar and the
actual height of
the web-page in pixels?
(How do I even know the height of the scroll bar ... when I
can only ask
X for the height of the window and don't know which toolbars
the user
has visible or which theme the user has selected?)
Of course one could build an interface into Mozilla to
return such
numbers, but I'd regard this as quite out of scope.
Karl.
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Capturing a scrolling page is an interesting puzzle that can be left for
later. Let me just put down some thoughts for the record.
Capturing by scrolling is relevant only if there is a scrollbar, and this can
be controlled by the mouse. Could xvidcap take control of the mouse,
position it on the scrollbar, click and hold, initialize the capture by
moving the scrollbar to the top, begin capture, and scroll to the bottom?
Xvidcap would need two pieces of information: the height of the (visible)
window (let's call it x), and the height of the entire page (y).
The ratio between these is represented in the height (z) of the scrollbar,
so that z:x :: x:y. I don't think this varies by theme. You can find out
from X what x is, but you still need to know either y or z.
After moving the scrollbar to the top, xvidcap would simply capture the
first window, move the scrollbar down by its own height (z pixels),
capture and append the next window again, and so on y/x times.
All it needs to know is the height of the scrollbar or the height of the full
page -- once it knows one of these it can infer the other. And it needs
the ability to click, hold, and move the scrollbar.
What do you think? Is there no way to get the value of either y or z? Or
am I missing something?
Cheers,
David
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This seems almost out of scope to me...