High resolution screen shot in Android

问题:

Is there any way to get a high resolution screen shot of a certain view in an activity.

I want to convert html content of my webview to PDF. For that I tried to take screen shot of the webview content and then converted it to PDF using itext. The resulted PDF is not in much more clarity.

My code:

    protected void takeimg() {
    Picture picture = mWebView.capturePicture();
    Bitmap b = Bitmap.createBitmap(picture.getWidth(), picture.getHeight(),
            Bitmap.Config.ARGB_8888);
    Canvas c = new Canvas(b);
    picture.draw(c);

    // byte[] bt = b.getNinePatchChunk();

    // Bitmap b;
    // View v1 = mWebView.getRootView();
    // v1.setDrawingCacheEnabled(true);
    // b = Bitmap.createBitmap(v1.getDrawingCache());
    // v1.setDrawingCacheEnabled(false);

    FileOutputStream fos = null;
    try {
        File root = new File(Environment.getExternalStorageDirectory(),
                "Sample");

        if (!root.exists()) {
            root.mkdir();
        }
        String sdcardhtmlpath = root.getPath().toString() + "/"
                + "temp_1.png";

        fos = new FileOutputStream(sdcardhtmlpath);
        // fos = openFileOutput("samsp_1.jpg", MODE_WORLD_WRITEABLE);
        if (fos != null) {
            b.compress(Bitmap.CompressFormat.PNG, 100, fos);

            // fos.write(bt);
            fos.close();
        }
    } catch (Exception e) {
        Log.e("takeimg", e.toString());
        e.printStackTrace();

    }
}


protected void pdfimg() {
    Document mydoc = new Document(PageSize.A3);
    try {
        File root = new File(Environment.getExternalStorageDirectory(),
                "Sample");

        if (!root.exists()) {
            root.mkdir();
        }
        String sdcardhtmlpath = root.getPath().toString() + "/";
        mydoc.setMargins(0, 0, 0, 0);
        PdfWriter.getInstance(mydoc, new FileOutputStream(sdcardhtmlpath
                + PDFfilename));
        mydoc.open();
        Image image1 = Image.getInstance(sdcardhtmlpath + "temp_1.jpg");
        image1.scalePercent(95f);

        mydoc.add(image1);
        // mydoc.newPage();

        mydoc.close();
    } catch (Exception e) {
        Log.e("pdi name", e.toString());
    }
}

回答1:

Update: See Edit 3 for an answer to op's original question

There are two options:

1. Use a library to convert the HTML to PDF. This is by far the best option, since it will (probably) preserve text as vectors.

2. Get a high resolution render of the HTML and save it as a PNG (not PDF surely!).

For HTML to PDF, wkhtmltopdf looks like a good option, but it relies on Qt which you can't really use on Android. There are some other libraries but I doubt they do the PDF rendering very well.

For getting a high-res webview, you could try creating your own WebView and calling onMeasure(...) and onLayout(...) and pass appropriate parameters so the view is really big. Then call onDraw(myOwnCanvas) and the webview will draw itself to your canvas, which can be backed by a Bitmap using Canvas.setBitmap().

You can probably copy the state into the new WebView using something like

screenshotterWebview.onRestoreInstanceState(mWebView.onSaveInstanceState());

Orrr it may even be possible to use the same WebView, just temporarily resize it to be large, onDraw() it to your canvas, and resize it back again. That's getting very hacky though!

You might run into memory issues if you make it too big.

Edit 1

I thought of a third, exactly-what-you-want option, but it's kind of hardcore. You can create a custom Canvas, that writes to a PDF. In fact, it is almost easy, because underlying Canvas is Skia, which actually includes a PDF backend. Unfortunately you don't get access to it on Android, so you'll basically have to build your own copy of it on Android (there are instructions), and duplicate/override all the Canvas methods to point to your Skia instead of Androids. Note that there is a tempting Picture.writeToStream() method which serializes the Skia data, but unfortunately this format is not forwards or backwards compatible so if you use it your code will probably only work on a few versions of Android.

I'll update if/when I have fully working code.

Edit 2

Actually it is impossible to make your own "intercepting" Canvas. I started doing it and went through the tedious process of serializing all function calls. A few you can't do because they are hidden, but those didn't look important. But right at the end I came to serializing Path only to discover that it is write-only. That seems like a killer to me, so the only option is to interpret the result of Picture.writeToStream(). Fortunately there are only two versions of that format in use, and they are nearly identical.

Edit 3 - Really simple way to get a high resolution Bitmap of a view

Ok, it turns out just getting a high res bitmap of a view (which can be the entire app) is trivial. Here is how to get double resolution. Obviously all the bitmaps look a bit crap, but the text is rendered at full resolution:

View window = activity.getWindow().getDecorView()

Canvas bitmapCanvas = new Canvas();
Bitmap bitmap = Bitmap.createBitmap(window.getWidth()*2, window.getHeight()*2, Bitmap.Config.ARGB_8888);

bitmapCanvas.setBitmap(bitmap);
bitmapCanvas.scale(2.0f, 2.0f);
window.draw(bitmapCanvas);

bitmap.compress(Bitmap.CompressFormat.PNG, 0, myOutputStream);

Works like a charm. I've now given up on getting a PDF screenshot with vector text. It's certainly possible, but very difficult. Instead I am working on getting a high-res PSD where each draw operation is a separate layer, which should be much easier.

Edit 4

Woa this is getting a bit long, but success! I've generated an .xcf (GIMP) and PDF where each layer is a different canvas drawing operation. It's not quite as fine-grained as I was expecting, but still, pretty useful!

Actually my code just outputs full-size PNGs and I used "Open as layers..." and "Autocrop layer" in GIMP to make these files, but of course you can do that in code if you like. I think I will turn this into a blog post.

Download the GIMP or Photoshop demo file (rendered at 3x resolution).

回答2:

When you capture the view, just screen bound will capture ( due to control weight and android render pipeline ).

Capturing screenshot for converting to PDF is tricky way. I think two way is more reasonable solutions.

Solution #1

Write a parser ( it's simple ) to convert webview content ( that is HTML ) to iText format.
You can refer to this article for more information.
http://www.vogella.com/articles/JavaPDF/article.html

Also to write a parser you can use REGEX and provide your own methods like parseTable, parseImage, ...

Solution #2 Internet Required

Provide a URL ( or webservice ) to convert HTML to PDF using PHP or C# that has a lot of nice libraries. Next you can send download link to the Client ( Android Device ).

So you can also dynamically add some Tags, Banners, ... to the PDF from server side.

回答3:

Screen Shot is nothing but picture of your device display which usually depend upon your phone absolute pixels, if your phone is 480x800 screen shot will be same and generally applicable for all scenarios.

回答4:

Sure, Use this:

Bitmap bitmap;
View v1 = MyView.getRootView();
v1.setDrawingCacheEnabled(true);
bitmap = Bitmap.createBitmap(v1.getDrawingCache());
v1.setDrawingCacheEnabled(false);

Here MyView is the View you need a screenshot of.