HTML book-like pagination

Question

How can I split the content of a HTML file in screen-sized chunks to "paginate" it in a WebKit browser?

Each "page" should show a complete amount of text. This means that a line of text must not be cut in half in the top or bottom border of the screen.

Edit

This question was originally tagged "Android" as my intent is to build an Android ePub reader. However, it appears that the solution can be implemented just with JavaScript and CSS so I broadened the scope of the question to make it platform-independent.

Solution 1

Building on Dan's answer here is my solution for this problem, with which I was struggling myself until just now. (this JS works on iOS Webkit, no guarantees for android, but please let me know the results)

var desiredHeight;
var desiredWidth;
var bodyID = document.getElementsByTagName('body')[0];
totalHeight = bodyID.offsetHeight;
pageCount = Math.floor(totalHeight/desiredHeight) + 1;
bodyID.style.padding = 10; //(optional) prevents clipped letters around the edges
bodyID.style.width = desiredWidth * pageCount;
bodyID.style.height = desiredHeight;
bodyID.style.WebkitColumnCount = pageCount;

Hope this helps...

Solution 2

Speaking from experience, expect to put a lot of time into this, even for a barebones viewer. An ePub reader was actually first big project I took on when I started learning C#, but the ePub standard is definitely pretty complex.

You can find the latest version of the spec for ePub here: http://www.idpf.org/specs.htm which includes the OPS (Open Publication Structure), OPF (Open Packaging Format), and OCF (OEBPS Container Format).

Also, if it helps you at all, here is a link to the C# source code of the project I started on:

https://www.dropbox.com/sh/50kxcr29831t854/MDITIklW3I/ePub%20Test.zip

It's not fleshed out at all; I haven't played with this for months, but if I remember correctly, just stick an ePub in the debug directory, and when you run the program just type some part of the name (e.g. Under the Dome, just type "dome") and it will display the details of the book.

I had it working correctly for a few books, but any eBooks from Google Books broke it completely. They have a completely bizarre implementation of ePub (to me, at least) compared to books from other sources.

Anyway, hopefully some of the structural code in there might help you out!

Solution 3

I've had to code something like this too, and my (working) solution is this:

You have to apply these lines to the webview...

    webView_.getSettings().setUseWideViewPort(true);
    webView_.getSettings().setLayoutAlgorithm(LayoutAlgorithm.NARROW_COLUMNS);

Also, you have to inject some javascript. I've had tons of problems with the differents scales of my activity and the content rendered in the webview, so my solution doesn't take any kind of value from "outside".

    webView_.setWebViewClient(new WebViewClient(){

            public void onPageFinished(WebView view, String url) {
                injectJavascript();
            }

        });

[...]

    public void injectJavascript() {
        String js = "javascript:function initialize() { " +
                "var d = document.getElementsByTagName('body')[0];" +
                "var ourH = window.innerHeight; " +
                "var ourW = window.innerWidth; " + 
                "var fullH = d.offsetHeight; " +
                "var pageCount = Math.floor(fullH/ourH)+1;" +
                "var currentPage = 0; " +
                "var newW = pageCount*ourW; " +
                "d.style.height = ourH+'px';" +
                "d.style.width = newW+'px';" +
                "d.style.webkitColumnGap = '2px'; " +
                "d.style.margin = 0; " +
                "d.style.webkitColumnCount = pageCount;" +
                "}";
        webView_.loadUrl(js);
        webView_.loadUrl("javascript:initialize()");
    }

Enjoy :)

Solution 4

I recently attempted something similar to this and added some CSS styling to change the layout to horizontal instead of vertical. This gave me the desired effect without having to modify the content of the Epub in any way.

This code should work.

mWebView.setWebViewClient(new WebViewClient() {
    public void onPageFinished(WebView view, String url) {

        // Column Count is just the number of 'screens' of text. Add one for partial 'screens'
        int columnCount = Math.floor(view.getHeight() / view.getWidth())+1;

        // Must be expressed as a percentage. If not set then the WebView will not stretch to give the desired effect.
        int columnWidth = columnCount * 100;

        String js = "var d = document.getElementsByTagName('body')[0];" + 
            "d.style.WebkitColumnCount=" + columnCount + ";" + 
            "d.style.WebkitColumnWidth='" + columnWidth + "%';";
        mWebView.loadUrl("javascript:(function(){" + js + "})()");
    }
});

mWebView.loadUrl("file:///android_asset/chapter.xml");

So, basically you're injecting JavaScript to change the styling of the body element after the chapter has been loaded (very important). The only downfall to this approach is when you have images in the content the calculated column count goes askew. It shouldn't be too hard to fix though. My attempt was going to be injecting some JavaScript to add width and height attributes to all images in the DOM that don't have any.

Hope it helps.

-Dan

Solution 5

I was able to improve Nacho's solution to get horizontal swipe paging effect with WebView. You can find solution here and example code.

Edit:

Solution code.

MainActivity.java

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
        WebView.setWebContentsDebuggingEnabled(true);
    }
    wv = (HorizontalWebView) findViewById(R.id.web_view);
    wv.getSettings().setJavaScriptEnabled(true);
    wv.setWebViewClient(new WebViewClient() {

        public void onPageFinished(WebView view, String url) {
            injectJavascript();
        }
    });

    wv.setWebChromeClient(new WebChromeClient() {
        @Override
        public boolean onJsAlert(WebView view, String url, String message, JsResult result) {
            int pageCount = Integer.parseInt(message);
            wv.setPageCount(pageCount);
            result.confirm();
            return true;
        }
    });
    wv.loadUrl("file:///android_asset/ch03.html");   // now it will not fail here
}

private void injectJavascript() {
    String js = "function initialize(){\n" +
            "    var d = document.getElementsByTagName('body')[0];\n" +
            "    var ourH = window.innerHeight;\n" +
            "    var ourW = window.innerWidth;\n" +
            "    var fullH = d.offsetHeight;\n" +
            "    var pageCount = Math.floor(fullH/ourH)+1;\n" +
            "    var currentPage = 0;\n" +
            "    var newW = pageCount*ourW;\n" +
            "    d.style.height = ourH+'px';\n" +
            "    d.style.width = newW+'px';\n" +
            "    d.style.margin = 0;\n" +
            "    d.style.webkitColumnCount = pageCount;\n" +
            "    return pageCount;\n" +
            "}";
    wv.loadUrl("javascript:" + js);
    wv.loadUrl("javascript:alert(initialize())");
}

In my WebChromeClient's onJsAlert get the number of horizontal pages which i pass to the custom HorizontalWebView to implement paging effect

HorizontalWebView.java

public class HorizontalWebView extends WebView {
    private float x1 = -1;
    private int pageCount = 0;

    public HorizontalWebView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                x1 = event.getX();
                break;
            case MotionEvent.ACTION_UP:
                float x2 = event.getX();
                float deltaX = x2 - x1;
                if (Math.abs(deltaX) > 100) {
                    // Left to Right swipe action
                    if (x2 > x1) {
                        turnPageLeft();
                        return true;
                    }

                    // Right to left swipe action
                    else {
                        turnPageRight();
                        return true;
                    }

                }
                break;
        }
        return true;
    }

    private int current_x = 0;

    private void turnPageLeft() {
        if (getCurrentPage() > 0) {
            int scrollX = getPrevPagePosition();
            loadAnimation(scrollX);
            current_x = scrollX;
            scrollTo(scrollX, 0);
        }
    }

    private int getPrevPagePosition() {
        int prevPage = getCurrentPage() - 1;
        return (int) Math.ceil(prevPage * this.getMeasuredWidth());
    }

    private void turnPageRight() {
        if (getCurrentPage() < pageCount - 1) {
            int scrollX = getNextPagePosition();
            loadAnimation(scrollX);
            current_x = scrollX;
            scrollTo(scrollX, 0);
        }
    }

    private void loadAnimation(int scrollX) {
        ObjectAnimator anim = ObjectAnimator.ofInt(this, "scrollX",
                current_x, scrollX);
        anim.setDuration(500);
        anim.setInterpolator(new LinearInterpolator());
        anim.start();
    }

    private int getNextPagePosition() {
        int nextPage = getCurrentPage() + 1;
        return (int) Math.ceil(nextPage * this.getMeasuredWidth());
    }

    public int getCurrentPage() {
        return (int) (Math.ceil((double) getScrollX() / this.getMeasuredWidth()));
    }

    public void setPageCount(int pageCount) {
        this.pageCount = pageCount;
    }
}

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Comments

[hpique]

And how can I know where to split based on the screen and font size?

[hpique]

+1 Couldn't make this to work, but I think it has pointed me in the right direction.

[Kanak Vaghela]

Can you please guide me how to implement this in webview? or can you post whole code for this? Thanks in advance.

[Midhun Sivaraj]

This works. How can i scroll to next column on a button click?

[Jmorvan]

@Midhun, $("body").animate({scrollLeft: window.innerWidth*<your col index>});

[Milan Sheth]

@Dan can you share me your css style. Pagination works for me but need css for the same. Please post your css. Thanks in advance.

[Illya Bublyk]

how to use this code for page pagination on scroll?

[Srikar Reddy]

This is working great but there is one issue. I'm able to scroll down and there is lots of extra space at the bottom. How can remove this extra space?

[Srikar Reddy]

What is the use of currentPage variable which is inside the js string?