Looking for ideas to quickly flow content - javascript

I'm writing some code that wraps various content into columns of text (and images, videos, etc). The code works fine, but due to the algorithm I'm using it's rather slow, specifically this general logic:
add something (text for this example) to a column
check to see if column.scrollHeight > column.offsetHeight (this requires a DOM reflow)
if yes, start to binary split the text until it's shorter
Basically my issue is that I'm adding an unknown amount of text to a column, so after each chunk of text I check the column's scroll height which requires the browser to actively reflow the DOM in order to give me the correct scrollHeight. So I have 50-100 or more reflows in order to properly lay everything out.
Any general ideas on how to avoid most of these?

You could render the content multiple times. Since the first time would cache it, this should be fairly fast. The reason for the multiple rendering would be as follows.
Render the original content in a hidden area
Check to see what the column width is compared to content
Overlay the content over the column, but beneath the page. This
will cut off part of the content that is overflowing. You can accomplish with
z-indexing or with overflow: hidden;
Based on what the check from step 2 was, overlay a copy of the content with
the calculated offset in the next column in the same fashion, hiding the
extra content.
Keep track of the rendered content versus total content so you can tell how many
columns you need to do this to if there are multiple columns.

Maybe this is the same thing Travis J is suggesting, but I'm not sure, I don't quite understand his solution.
You could render everything first, on a single column, then loop through the elements top-down to know when to split, based on your desired column height versus each element's offsetTop plus height. When you find an element to break at, cache its position and go on. At the end you should have an array with the list of elements to break at, so you can actually split the content in columns.
Does this make any sense to you?

Related

Test simulated html element width with javascript

Use case
I want to detect if html tables get too wide, and if so, I want to flip the table header cells to become vertical (e.g. with writing-mode: vertical-lr;).
I want to update this on resize: If the viewport gets bigger, the text in the cells might become horizontal again.
The flip condition is whether the original table with horizontal labels would be wider than its container.
Question
How do I determine the width a table would have with horizontal labels, without changing the table itself?
Thoughts
My current idea would be to make an invisible copy of the table with horizontal labels, and use it as a "sensor". But I am afraid this will pollute the DOM and cause side effects somewhere. Also I would need to keep this copy updated all the time.
Is there a "best practice" or a known pattern to solve this problem?
It is actually quite simple:
We can change the css on the table during the script run. Once we query a property like element.width, this will cause a reflow during the script execution, but it won't cause a repaint. So this means we can do the test without the need for a cloned DOM element, and without visible changes.
See https://developers.google.com/speed/docs/insights/browser-reflow

How can I split HTML content into pages that fit the screen?

I'm making a book reader web application. From the server I get a long string with all of the book text in HTML format. It looks something like this:
<div><p>Alice was beginning....</p></div></div>to get very ... </div>
What I want is to split this text into pages. I want to get something like this:
<li id='page1'>... text ...</li>
<li id='page2'>... text ...</li>
...
A single page should fill the viewport. Users shouldn't be able to scroll the book text. Instead, they should be able to move between the pages using buttons.
I need some function to measure all content, split it into pieces of same maximum height, and tag the pieces with page numbers. It must also take into account pictures and long paragraphs (which may not fit on a single page).
How can I accomplish all of this?
To find out the dimensions of each bit of content, you'd have to let the browser actually render it and then measure it. Additionally, if you want to break in the middle of flow (e.g. in the middle of a paragraph), things get pretty difficult. (You cannot measure individual characters/words without wrapping them in elements.) You'd also have to disable zoom, etc., so that your measurements have some lasting meaning. All in all, HTML rendering engines are specifically tailored to render flow content, which is pretty much the opposite to paged content.
However, there are some approaches to paging, you could take, neither of which actually deals with rendering the whole text and taking measurements.
Scroll Override
One approach I'd try would be to simply
render all text into a container,
style the container in such a way that the scrollbar is not visible (e.g. by pushing it off the screen),
disable manual scrolling, and
provide "paging" buttons that programatically scroll by exactly the height of your "page".
This solution has the advantage of being simple to implement, but it's not perfect. Images can be rendered across the break and the user wouldn't be able to see them whole.
Columns
The only other approach I could think of at short notice is using columns. You'd have to
render all text into a container,
style the container to be "infinitely" wide and have "infinite" number of columns, each the width of the page,
absolutely position the container in its parent,
make your "paging" buttons move the container horizontally by the width of the page.
This solution needs modern browsers with support for columns, but using columns solves the problem of properly breaking flow content into pages. I'd recommend trying this first, if at all possible.

Multiple Dynamic Columns

I'm trying to create a column-based, blog layout. I want the text to wrap to a new column when it hits the bottom of the page. At it's very simplest form something like, when the column height == the_height_of_the_wrapper then column-count++.
The problem with something like that would be the text would be distributed evenly. Also, that would rely on css columns and I want something a bit more browser-friendly. Are there any existing plugins for this functionality or anywhere I can get some ideas?
If anyone is familiar with any of the text-heavy windows 8 "metro" apps (such as the news one) that's the kind of layout I'm trying to mimic.
As i noticed in comments, you cannot use column-count there. But there is solution, check this one please: Continuing overflowed text in a different div?
Alternatively. You can apply a fixed height (even a percentage will work) to the wrapper the columns will fill appropriately. (example: w3schools.com/css3/tryit.asp?filename=trycss3_column-count). It even seems as though you don't have to specify a fixed column count as it appears to create extra columns as the content dictates.

Set DIV height so text is not cut or sliced horizontally

Is there any JS/CSS/jQuery magic I can work to identify whether the last visible bit of content in a div is being cut off, and slightly increase/decrease the DIV's height to prevent the cut off text?
Our system allows the user to enter "elements" containing XHTML (using a Telerik Edit control). We have an ElementList page, where we show all the user-entered elements. However, since the user-entered XHTML can be very large, on the list page we only want to show the first 3 lines of each. So I set the DIV containing the XHTML to a specific height equal to 3 rows of text, and set overflow: hidden. So far, so good.
However, since the user can enter XHTML, they can create tables with padding (or otherwise diverge from standard text height). The text within those cells appears to be sliced off horizontally, due to the combination of height and overflow: hidden. Our requirements person doesn't like the look of this; but of course we cannot restrict the XHTML editable by the end user.
Here is a JSFiddle example of the issue.
This question is not a duplicate of:
"Stopping cut off text in variable height div..." as that question involves "webkit-line-clamp" which is irrelevant to my situation. (and in any case, that question was never answered)
"Cut text by height, no truncate" as that question is about a DIV containing pure text; my DIV contains XHTML. You'll note in the JSFiddle that I'm already sizing the DIV height using the em measurement.
This issue has me completely baffled - I'm hoping the SO community can come to my rescue!
UPDATE:
Ultimately, I suspect this cannot be resolved using HTML/JS/jQuery. In fact, you can craft a table (or series of DIVs) with gradually increasing top-margins, such that there's no way to avoid slicing at least one of them.
Thanks to all for their responses. I'm marking one as an answer, because in my opinion, it's a particularly simple/elegant workaround.
This is not the solution you were looking for, but it might be a good design workaround.
I put a white gradient in the bottom of the div, so that it creates sort of a "visual ellipsis"
Take a look: http://jsfiddle.net/robertofrega/LkYjs/3/
It is not as ugly as when the text is simply cut.
Your trouble is coming from overflow:hidden;. This line is doing exactly what you tell it to do, namely hiding the overflow. Can you use overflow-y: auto or something like that? That along with a grippy (like SO uses on its text areas), should help you out.
Instead of having overflow:hidden, you could set it to auto and then check for the presence of a scrollbar upon submission of the content. See this thread:
detect elements overflow using jquery
Try CSS3 property: text-overflow and set it to ellipsis, the default value is clip

get div current (rendered) width with javascript

Hey, Ive got an php script dragging some images from a database and displaying them using float:left; so they go left to right.
However unless in the css i define i width for the container they jump down onto a 2nd line.
So the question IS!
How for the life of me could I get it to figure out the width of the content and then set the width attribute via javascript all on the one load.
I did have a slight worry that this wouldnt be easily possible as it wud have had to render the images/layout first to get a width before then adjusting it.
Ideas please people!! x
Your question has to do with how the flows of floats work...
If two images are floated and the sum of their widths is wider than the containing element, they will wrap (similar to the way words in a paragraph wrap).
Visual references describing the flow of "float"ed elements (way too difficult to describe in a few words):
http://css.maxdesign.com.au/floatutorial/introduction.htm

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