Android etc1tool png image conversion pkm and zipalign Introduction

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I. Introduction

We continue to summarize our learningbasics, warming up to the past.

This article documents the introduction and use of the android etc1 tool.
This article documents the introduction and use of the android zipalign command.

Two, etc1tool

etc1tool is a command line utility that can be used to encode PNG images into the ETC1 Compression Standard Format (PKM) and decode ETC1 compressed images back into PNG.

Simply put, png and pkm image formats are converted to each other.

Files in pkm format in android can be read in the assets directory.

2.1. Usage

etc1tool infile [--help | --encode | --encodeNoHeader | --decode] [--showDifference
diff-file] [-o outfile]

options (as in computer software settings)	clarification
infile	The input file to be compressed.
–help	Outputs usage information.
–encode	Creates an ETC1 file from a PNG file. If no mode is specified, this will be the default mode for this tool.
–encodeNoHeader	Creates the original ETC1 data file (without headers) from a PNG file.
–decode	Creates a PNG file from an ETC1 file.
–showDifference diff-file	Writes the difference between the original image and the encoded image to diff-file. this option is only valid when encoding.
-o outfile	Specifies the name of the output file. If outfile is not specified, the name of the output file will consist of the name of the input file with the appropriate suffix (.pkm or .png).

etc1tool

III. zipalign

zipalign is a zip archive alignment tool that helps ensure that all uncompressed files in an archive are aligned relative to the beginning of the file.

This is done automatically if you build with Android Studio using the Android Gradle Plugin (AGP).

The following section focuses on the use of custom build systems:

3.1 Utilization

If your APK contains shared libraries (.so files), use -p to make sure they are aligned with the 4KiB page boundaries appropriate for mmap(2).
For other files (whose alignment is determined by zipalign’s mandatory alignment parameter), Android Studio will align to 4 bytes on 32-bit and 64-bit systems.

To align infile.apk and save it as outfile.apk, run the following command:

zipalign -p -f -v 4 infile.apk outfile.apk

To verify the alignment of existing.apk, use the following command. If you are building with Android Studio or AGP, you should use this command to verify that the APK is aligned.

zipalign -c -v 4 existing.apk

options (as in computer software settings)	clarification
-c	Checks alignment only (does not modify the file).
-f	Overwrite existing output files.
-h	Displays tool help.
-p	Aligns uncompressed .so files to pages.
-v	Detailed output.
-z	Use Zopfli to recompress.

zipalign

IV. Recommended reading

Java Column

SQL Column

Data Structures and Algorithms

Android Learning Column