PngSupport.vala 5.8 KB
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/* Copyright 2016 Software Freedom Conservancy Inc.
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 *
 * This software is licensed under the GNU LGPL (version 2.1 or later).
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 * See the COPYING file in this distribution.
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 */

class PngFileFormatProperties : PhotoFileFormatProperties {
    private static string[] KNOWN_EXTENSIONS = { "png" };
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    private static string[] KNOWN_MIME_TYPES = { "image/png" };
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    private static PngFileFormatProperties instance = null;
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    public static void init() {
        instance = new PngFileFormatProperties();
    }
    
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    public static PngFileFormatProperties get_instance() {
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        return instance;
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    }
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    public override PhotoFileFormat get_file_format() {
        return PhotoFileFormat.PNG;
    }
    
    public override PhotoFileFormatFlags get_flags() {
        return PhotoFileFormatFlags.NONE;
    }
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    public override string get_user_visible_name() {
        return _("PNG");
    }

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    public override string get_default_extension() {
        return KNOWN_EXTENSIONS[0];
    }
    
    public override string[] get_known_extensions() {
        return KNOWN_EXTENSIONS;
    }
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    public override string get_default_mime_type() {
        return KNOWN_MIME_TYPES[0];
    }
    
    public override string[] get_mime_types() {
        return KNOWN_MIME_TYPES;
    }
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}

public class PngSniffer : GdkSniffer {
    private const uint8[] MAGIC_SEQUENCE = { 137, 80, 78, 71, 13, 10, 26, 10 };

    public PngSniffer(File file, PhotoFileSniffer.Options options) {
        base (file, options);
    }

    private static bool is_png_file(File file) throws Error {
        FileInputStream instream = file.read(null);

        uint8[] file_lead_sequence = new uint8[MAGIC_SEQUENCE.length];

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        instream.read(file_lead_sequence, null);
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        for (int i = 0; i < MAGIC_SEQUENCE.length; i++) {
            if (file_lead_sequence[i] != MAGIC_SEQUENCE[i])
                return false;
        }

        return true;
    }

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    public override DetectedPhotoInformation? sniff(out bool is_corrupted) throws Error {
        // Rely on GdkSniffer to detect corruption
        is_corrupted = false;
        
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        if (!is_png_file(file))
            return null;
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        DetectedPhotoInformation? detected = base.sniff(out is_corrupted);
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        if (detected == null)
            return null;
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        return (detected.file_format == PhotoFileFormat.PNG) ? detected : null;
    }
}

public class PngReader : GdkReader {
    public PngReader(string filepath) {
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        base (filepath, PhotoFileFormat.PNG);
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    }
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    public override Gdk.Pixbuf scaled_read(Dimensions full, Dimensions scaled) throws Error {
        Gdk.Pixbuf result = null;
        /* if we encounter a situation where there are two orders of magnitude or more of
           difference between the full image size and the scaled size, and if the full image
           size has five or more decimal digits of precision, Gdk.Pixbuf.from_file_at_scale( ) can
           fail due to what appear to be floating-point round-off issues. This isn't surprising,
           since 32-bit floats only have 6-7 decimal digits of precision in their mantissa. In
           this case, we prefetch the image at a larger scale and then downsample it to the
           desired scale as a post-process step. This short-circuits Gdk.Pixbuf's buggy
           scaling code. */
        if (((full.width > 9999) || (full.height > 9999)) && ((scaled.width < 100) ||
             (scaled.height < 100))) {
            Dimensions prefetch_dimensions = full.get_scaled_by_constraint(1000,
                ScaleConstraint.DIMENSIONS);
                                  
            result = new Gdk.Pixbuf.from_file_at_scale(get_filepath(), prefetch_dimensions.width,
                prefetch_dimensions.height, false);

            result = result.scale_simple(scaled.width, scaled.height, Gdk.InterpType.HYPER);
        } else {
            result = new Gdk.Pixbuf.from_file_at_scale(get_filepath(), scaled.width,
                scaled.height, false);
        }

        return result;
    }
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}

public class PngWriter : PhotoFileWriter {
    public PngWriter(string filepath) {
        base (filepath, PhotoFileFormat.PNG);
    }
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    public override void write(Gdk.Pixbuf pixbuf, Jpeg.Quality quality) throws Error {
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        pixbuf.save(get_filepath(), "png", "compression", "9", null);
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    }
}

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public class PngMetadataWriter : PhotoFileMetadataWriter {
    public PngMetadataWriter(string filepath) {
        base (filepath, PhotoFileFormat.PNG);
    }
    
    public override void write_metadata(PhotoMetadata metadata) throws Error {
        metadata.write_to_file(get_file());
    }
}

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public class PngFileFormatDriver : PhotoFileFormatDriver {
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    private static PngFileFormatDriver instance = null;
    
    public static void init() {
        instance = new PngFileFormatDriver();
        PngFileFormatProperties.init();
    }
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    public static PngFileFormatDriver get_instance() {
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        return instance;
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    }
    
    public override PhotoFileFormatProperties get_properties() {
        return PngFileFormatProperties.get_instance();
    }
    
    public override PhotoFileReader create_reader(string filepath) {
        return new PngReader(filepath);
    }
    
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    public override bool can_write_image() {
        return true;
    }
    
    public override bool can_write_metadata() {
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        return true;
    }
    
    public override PhotoFileWriter? create_writer(string filepath) {
        return new PngWriter(filepath);
    }
    
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    public override PhotoFileMetadataWriter? create_metadata_writer(string filepath) {
        return new PngMetadataWriter(filepath);
    }
    
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    public override PhotoFileSniffer create_sniffer(File file, PhotoFileSniffer.Options options) {
        return new PngSniffer(file, options);
    }
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    public override PhotoMetadata create_metadata() {
        return new PhotoMetadata();
    }
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}