The function `isWebpAnimated` checks whether a given WebP image file...

The function isWebpAnimated checks whether a given WebP image file is an animated WebP or not. Here's a detailed breakdown of what the code does:

1. Input and Result Initialization:

   • The function accepts a single argument, $fn, which is the file path to a WebP image.
   • It initializes a variable $result to false. This will later hold whether the WebP file is animated or not.

2. Open the File:

   • The file specified by $fn is opened in binary read mode using fopen.

3. Check for WebP Extended Header:

   • Using fseek, the file pointer is moved to the 12th byte.

   • It reads 4 bytes starting from this position using fread. For a WebP file, these 4 bytes will tell whether the file uses the "extended" WebP format (indicated by the string VP8X).

   • If the 4 bytes equal VP8X, the file uses the extended WebP format, in which case further checks are performed.

4. Check the Animation Flag:

   • If the file is a WebP extended format (VP8X), the function moves the file pointer to the 20th byte using fseek.

   • It reads 1 byte from this position using fread. This byte contains a series of bits, one of which (the second bit) is the animation flag.

   • The function extracts this flag by:

     • Using ord($myByte) to convert the byte to an integer.
     • Shifting right by 1 bit (>> 1) to target the second bit.
     • Using bitwise AND (& 1) to isolate whether the second bit is set.

   • If the second bit is set, it means the WebP file is animated, and $result is set to true.

5. Close the File:

   • The function closes the file using fclose, ensuring no file resource leaks.

6. Return the Result:

   • The function returns the value of $result, which is true if the WebP file is animated and false otherwise.

Summary:

This function determines whether a WebP file is an animated WebP by checking the animation flag in the file's header if the file uses the extended WebP format (VP8X). It does this by reading specific bytes from the file, interpreting the format, and checking the relevant flag bit.