share

ENGINEERING

2min read

How to take a screenshot with 50KB memory left

Taking a screenshot on Android is quite a trivial task. There are numerous methods and you can find a lot of code samples on the Internet. The problem is that each of them requires at least as much memory as Android needs to store the image before saving it to the sdcard. While developing Apphance for Android it quickly became apparent that we need a better approach. Especially when we have to take a screenshot in case of frequent crashes caused by OutOfMemoryError.

Our method is very simple - we split the screen into parts. Then create the screenshot by drawing the screen in bit-by-bit using a small, pre-allocated Canvas object. When we started working on a prototype, we thought that it will be extremely slow due to multiple draw calls. The results showed something different. The code is very simple:

View view = getWindow().getDecorView().getRootView();
int width = view.getWidth(), height = view.getHeight();
while (true) {
    try {
        Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        for (int y = 0; y < view.getHeight() / height; y++) {
            for (int x = 0; x < view.getWidth() / width; x++) {
                canvas.save();
                canvas.translate(-x * width, -y * height);
                view.draw(canvas);
                canvas.restore();
            }
        }
        bitmap.recycle();
        break;
    } catch (OutOfMemoryError e) {
        if (width > height) {
            width /= 2;
        } else {
            height /= 2;
        }
    }
}

In a loop we’re trying to allocate required amount of memory. If it’s not possible, we split the image in half and try once again. Then we draw small parts onto the bitmap.

Taking a 1-part screenshot takes 170ms on Galaxy Nexus. 2-part takes 70ms and 32-part only 50ms. Why?

  • Allocating a 3.5MB, continuous block of memory takes a lot of time.
  • Each view, which would be drawn outside the screenshot can be quickly detected and rejected.
  • Drawing cache helps a lot.

The results are very promising. Using this method we can take a screenshot using ~50KB of memory, which is very little for managed language. The only thing left is how to merge the parts. During the merging we have to allocate a block of memory for the screenshot. The bitmap will be used in another Activity. Theoretically Android should free the memory used by the previous Activity and give us enough space so that restoring complete bitmap wouldn’t be a problem. Unfortunately the os frees memory with a delay and we cannot ever be sure when it happens.

We can pass a screenshot as a simple structure:

public class Screenshot implements Serializable {
    List<File> files;
    int width, height;
}

Such lightweight object can be passed just through the Intent. In the next Activity we will just have to read all parts, allocate enough memory for the screenshot and draw all the images on the screenshot bitmap in a loop. But, we still have an OutOfMemoryError. Apparently the solution is very simple. Each process shares memory between Activities, but if we don’t want to wait for freeing memory, we can run an another process. We just have to add a simple flag to the Activity declaration in the manifest. In such way we can take a screenshot and pass it on without worrying about lack of memory in our Activity.

share


MarcinSenior Software Engineer

LEARN MORE

Contact us if you have any questions regarding the article or just want to chat about technology, our services, job offers and more!

POLIDEA NEWSLETTER

Sign in and expect sharp insights, recommendations, ebooks and fascinating project stories delivered to your inbox

The controller of the personal data that you are about to provide in the above form will be Polidea sp. z o.o. with its registered office in Warsaw at ul. Przeskok 2, 00-032 Warsaw, KRS number: 0000330954, tel.: 0048 795 536 436, email: hello@polidea.com (“Polidea”). We will process your personal data based on our legitimate interest and/or your consent. Providing your personal data is not obligatory, but necessary for Polidea to respond to you in relation to your question and/or request. If you gave us consent to call you on the telephone, you may revoke the consent at any time by contacting Polidea via telephone or email. You can find detailed information about the processing of your personal data in relation to the above contact form, including your rights relating to the processing, HERE.

Data controller:

The controller of your personal data is Polidea sp. z o.o. with its registered office in Warsaw at ul. Przeskok 2, 00-032 Warsaw, KRS number: 0000330954, tel.: [0048795536436], email: [hello@polidea.com] (“Polidea”)

Purpose and legal bases for processing:

 

Used abbreviations:

GDPR – Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016
on the protection of natural persons with regard to the processing of personal data and on the free movement
of such data, and repealing Directive 95/46/EC (General Data Protection Regulation)

ARES – Polish Act on Rendering Electronic Services dated 18 July 2002

TL – Polish Telecommunications Law dated 16 July 2004

1)        sending to the given email address a newsletter including information on Polidea’s new projects, products, services, organised events and/or general insights from the mobile app business world |art. 6.1 a) GDPR, art. 10.2 ARES and art. 172.1 TL (upon your consent)

Personal data:name, email address

2)       statistical, analytical and reporting purposes |art. 6. 1 f) GDPR (based on legitimate interests pursued by Polidea, consisting in analysing the way our services are used and adjusting them to our clients’ needs, as well as developing new services)

Personal data:name, email address

Withdrawal of consent:

You may withdraw your consent to process your personal data at any time.

Withdrawal of the consent is possible solely in the scope of processing performed based on the consent. Polidea is authorised to process your personal data after you withdraw your consent if it has another legal basis for the processing, for the purposes covered by that legal basis.

Categories of recipients:

Your personal data may be shared with:

1)       authorised employees and/or contractors of Polidea

2)       persons or entities providing particular services to Polidea (accounting, legal, IT, marketing and advertising services) – in the scope required for those persons or entities to provide those services to Polidea

 

Retention period:

1)       For the purpose of sending newsletter to the given email address – for as long as the relevant consent is not withdrawn

2)       For statistical, analytical and reporting purposes – for as long as the relevant consent is not withdrawn

Your rights:

 

Used abbreviation:

GDPR – Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016
on the protection of natural persons with regard to the processing of personal data and on the free movement
of such data, and repealing Directive 95/46/EC (General Data Protection Regulation)

According to GDPR, you have the following rights relating to the processing of your personal data, exercised by contacting Polidea via [e-mail, phone].

1)       to access to your personal data (art. 15 GDPR) by requesting sharing and/or sending a copy of all your personal data processed by Polidea

2)       to request rectification of inaccurate personal data
(art. 16 GDPR) by indicating the data requiring rectification

3)       to request erasure of your persona data (art. 17 GDPR); Polidea has the rights to refuse erasing the personal data in specific circumstances provided by law

4)       to request restriction of processing of your personal data (art. 18 GDPR) by indicating the data which should be restricted

5)       to move your personal data (art. 20 GDPR) by requesting preparation and transfer by Polidea of the personal data that you provided to Polidea to you or another controller in a structured, commonly used machine-readable format

6)       to object to processing your personal data conducted based on art. 6.1 e) or f) GDPR, on grounds relating to your particular situation (art. 21 GDPR)

7)       to lodge a complaint with a supervisory authority,
in particular in the EU member state of your habitual residence, place of work or place of the alleged infringement if you consider that the processing
of personal data relating to you infringes the GDPR
(art. 77.1 GDPR)

No obligation to provide data:

Providing your personal data is not obligatory, but necessary for Polidea to provide you the newsletter service

Refusal to provide the above data will result in inability to receive the newsletter service.

Profiling

In the process of providing the newsletter service, we make decisions in an automated way, including profiling, based on the data you provide.

 

“Profiling” means automated processing of personal data consisting of the use of your personal data to evaluate certain personal aspects relating to you, in particular to analyze or predict aspects concerning your personal preferences and interests.

 

The automated decisions are taken based on the analysis of clicked and viewed content. They affect the targeting of specific newsletter content to selected users registered to receive the newsletter service, based on the anticipated interests of the recipient.