IE vs. Firefox, image.src swapping, offline vs online?

Discussion in 'Javascript' started by cjl, Nov 9, 2005.

  1. cjl

    cjl Guest

    I have a website which allows people to view interesting radiology
    cases. It is for teaching radiology residents. It is designed to run
    in fullscreen or 'kiosk' mode, at 1024 x 768 resolution only.

    I designed it with firefox (plus the autohide extension) in mind, but
    also want to support IE.

    Online and offline it works great in Firefox. Offline it also works
    great in IE. The problem is with IE online. I allow the user to cycle
    through images with either the page up / page down keys, or with the
    mouse wheel, or toggle 'cine' mode with the space bar.

    I preload all the images before cycling through them. However, when
    viewing it online with IE, cycling through images is slow to the point
    that it appears to be downloading them each time.

    I am swapping images with a function that re-assigns the 'src' of an
    image element.

    Any thoughts?

    cjl, Nov 9, 2005
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  2. It would be prudent if you posted at least the URL of the script
    you are referring to as the above website does not include one.

    It would also be prudent if you did not serve XHTML als text/html
    but HTML as text/html (since XHTML [as application/xhtml+xml] is
    not supported by IE).

    Thomas 'PointedEars' Lahn, Nov 9, 2005
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  3. cjl

    cjl Guest

    Of course. Sorry. Here it is:

    The code is complicated, and poorly written, but basically I am
    preloading lots of high resolution images, and it's working in Firefox,
    but not in IE 6.
    I'm not sure I understand this comment. Are you referring to the

    cjl, Nov 10, 2005
  4. cjl

    aundro Guest

    No, he's talking about the HTTP Content-Type header sent by the
    webserver. This is rather low-level stuff (that means: JS is not
    responsible or capable to change that), but IE indeed doesn't seem to
    like documents that are served as application/xhtml+xml.
    (I discovered that while toying with VML)
    aundro, Nov 10, 2005
  5. It's better than I have come to expect of such scripts, yet there are
    some possibilities of improvement left. For example, you need the
    reference to the element with ID 'right_image' very often. It is
    highly inefficient to obtain that reference every time it is needed
    with document.getElementById('right_image'); the reference can be
    stored in a variable once and that variable can be used instead.

    Maybe IE's current cache size is just not big enough?
    Exactly. As Internet Explorer does not support XHTML, such markup
    is subject to error-correction where the SGML NET delimiter is ignored
    (in HTML, <br /> is equivalent to <br>&gt;). Firefox and all other
    Mozilla/5.0 based user agents support XHTML, however to have it parsed
    as XHTML and not as error-corrected HTML, it has to be served with
    the proper XHTML Content-Type: application/xhtml+xml. Unfortunately,
    IE does not accept responses with this Content-Type since it does not
    understand XHTML. There are other ramifications in using XHTML, such
    as that document.write() cannot be used since it is not properly
    implemented in the XHTML DOM although specified for XHTML 1.0 Transitional
    in W3C DOM Level 2 HTML. So nowadays it is still best to not use XHTML
    at all if not needed (for example when embedding SVG or MathML).


    Thomas 'PointedEars' Lahn, Nov 10, 2005
  6. cjl

    cjl Guest

    Thank you, I will make this change.
    This doesn't seem to be the problem. Let me elaborate. No matter what
    the size of the cache is, or the cache settings are, when I dynamically
    change the 'src' of an image to a preloaded image in Internet Explorer
    there is network activity (I think it is checking to see of the
    requested image is the same as the one in the cache). Firefox doesn't
    do this, and swaps the image with the preloaded image with no network
    activity, and very quickly.

    Is there something wrong with the way that I preload images? Or is it
    something wrong with the headers my servers sends, as detailed here:

    Is there something happening where image 'src's created statically
    (explicitly) are appropriately handled, by dynamic 'src's (generated by
    variables) are rechecked before being displayed?

    Any help would be greatly appreciated.
    cjl, Nov 10, 2005
  7. cjl

    cjl Guest

    OK, I'm stumped.

    Other scripts which dynamically swap the .src of an image object to a
    'variable named' preloaded image do not make IE 6 check the network
    against the cache, but my script does.

    I am either preloading incorrectly (althought it works in Firefox) or I
    am image swapping incorrectly (although it works in Firefox).


    cjl, Nov 10, 2005
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