forked from AuroraMiddleware/gtk
289 lines
6.7 KiB
Plaintext
289 lines
6.7 KiB
Plaintext
<!-- ##### SECTION Title ##### -->
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The GdkPixbuf Structure
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<!-- ##### SECTION Short_Description ##### -->
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Information that describes an image.
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<!-- ##### SECTION Long_Description ##### -->
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<para>
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The <structname>GdkPixbuf</structname> structure contains
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information that describes an image in memory.
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</para>
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<section id="image-data">
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<title>Image Data</title>
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<para>
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Image data in a pixbuf is stored in memory in uncompressed,
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packed format. Rows in the image are stored top to bottom, and
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in each row pixels are stored from left to right. There may be
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padding at the end of a row. The "rowstride" value of a pixbuf,
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as returned by gdk_pixbuf_get_rowstride(), indicates the number
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of bytes between rows.
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</para>
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<example id="put-pixel">
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<title>put_pixel(<!-- -->) example</title>
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<para>
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The following code illustrates a simple put_pixel(<!-- -->)
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function for RGB pixbufs with 8 bits per channel with an alpha
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channel. It is not included in the gdk-pixbuf library for
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performance reasons; rather than making several function calls
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for each pixel, your own code can take shortcuts.
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</para>
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<programlisting>
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static void
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put_pixel (GdkPixbuf *pixbuf, int x, int y, guchar red, guchar green, guchar blue, guchar alpha)
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{
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int width, height, rowstride, n_channels;
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guchar *pixels, *p;
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n_channels = gdk_pixbuf_get_n_channels (pixbuf);
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g_assert (gdk_pixbuf_get_colorspace (pixbuf) == GDK_COLORSPACE_RGB);
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g_assert (gdk_pixbuf_get_bits_per_sample (pixbuf) == 8);
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g_assert (gdk_pixbuf_get_has_alpha (pixbuf));
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g_assert (n_channels == 4);
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width = gdk_pixbuf_get_width (pixbuf);
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height = gdk_pixbuf_get_height (pixbuf);
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g_assert (x >= 0 && x < width);
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g_assert (y >= 0 && y < height);
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rowstride = gdk_pixbuf_get_rowstride (pixbuf);
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pixels = gdk_pixbuf_get_pixels (pixbuf);
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p = pixels + y * rowstride + x * n_channels;
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p[0] = red;
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p[1] = green;
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p[2] = blue;
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p[3] = alpha;
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}
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</programlisting>
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<para>
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This function will not work for pixbufs with images that are
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other than 8 bits per sample or channel, but it will work for
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most of the pixbufs that GTK+ uses.
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</para>
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</example>
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<note>
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<para>
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If you are doing memcpy() of raw pixbuf data, note that the
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last row in the pixbuf may not be as wide as the full
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rowstride, but rather just as wide as the pixel data needs to
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be. That is, it is unsafe to do <literal>memcpy (dest,
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pixels, rowstride * height)</literal> to copy a whole pixbuf.
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Use gdk_pixbuf_copy() instead, or compute the width in bytes
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of the last row as <literal>width * ((n_channels *
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bits_per_sample + 7) / 8)</literal>.
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</para>
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</note>
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</section>
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<!-- ##### SECTION See_Also ##### -->
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<para>
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</para>
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<!-- ##### ENUM GdkPixbufError ##### -->
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<para>
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An error code in the #GDK_PIXBUF_ERROR domain. Many &gdk-pixbuf;
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operations can cause errors in this domain, or in the #G_FILE_ERROR
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domain.
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</para>
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@GDK_PIXBUF_ERROR_CORRUPT_IMAGE: An image file was broken somehow.
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@GDK_PIXBUF_ERROR_INSUFFICIENT_MEMORY: Not enough memory.
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@GDK_PIXBUF_ERROR_BAD_OPTION: A bad option was passed to a pixbuf save module.
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@GDK_PIXBUF_ERROR_UNKNOWN_TYPE: Unknown image type.
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@GDK_PIXBUF_ERROR_UNSUPPORTED_OPERATION: Don't know how to perform the
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given operation on the type of image at hand.
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@GDK_PIXBUF_ERROR_FAILED: Generic failure code, something went wrong.
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<!-- ##### MACRO GDK_PIXBUF_ERROR ##### -->
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<para>
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Error domain used for pixbuf operations. Indicates that the error code
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will be in the #GdkPixbufError enumeration. See #GError for
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information on error domains and error codes.
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</para>
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<!-- ##### ENUM GdkColorspace ##### -->
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<para>
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This enumeration defines the color spaces that are supported by
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the &gdk-pixbuf; library. Currently only RGB is supported.
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</para>
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@GDK_COLORSPACE_RGB: Indicates a red/green/blue additive color space.
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<!-- ##### ENUM GdkPixbufAlphaMode ##### -->
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<para>
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These values can be passed to
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gdk_pixbuf_render_to_drawable_alpha() to control how the alpha
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channel of an image should be handled. This function can create a
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bilevel clipping mask (black and white) and use it while painting
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the image. In the future, when the X Window System gets an alpha
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channel extension, it will be possible to do full alpha
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compositing onto arbitrary drawables. For now both cases fall
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back to a bilevel clipping mask.
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</para>
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@GDK_PIXBUF_ALPHA_BILEVEL: A bilevel clipping mask (black and white)
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will be created and used to draw the image. Pixels below 0.5 opacity
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will be considered fully transparent, and all others will be
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considered fully opaque.
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@GDK_PIXBUF_ALPHA_FULL: For now falls back to #GDK_PIXBUF_ALPHA_BILEVEL.
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In the future it will do full alpha compositing.
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<!-- ##### STRUCT GdkPixbuf ##### -->
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<para>
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This is the main structure in the &gdk-pixbuf; library. It is
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used to represent images. It contains information about the
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image's pixel data, its color space, bits per sample, width and
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height, and the rowstride (the number of bytes between the start of
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one row and the start of the next).
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</para>
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<!-- ##### ARG GdkPixbuf:bits-per-sample ##### -->
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<para>
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</para>
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<!-- ##### ARG GdkPixbuf:colorspace ##### -->
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<para>
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</para>
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<!-- ##### ARG GdkPixbuf:has-alpha ##### -->
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<para>
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</para>
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<!-- ##### ARG GdkPixbuf:height ##### -->
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<para>
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</para>
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<!-- ##### ARG GdkPixbuf:n-channels ##### -->
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<para>
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</para>
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<!-- ##### ARG GdkPixbuf:pixels ##### -->
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<para>
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</para>
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<!-- ##### ARG GdkPixbuf:rowstride ##### -->
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<para>
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</para>
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<!-- ##### ARG GdkPixbuf:width ##### -->
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<para>
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</para>
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<!-- ##### FUNCTION gdk_pixbuf_get_colorspace ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_get_n_channels ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_get_has_alpha ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_get_bits_per_sample ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_get_pixels ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_get_width ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_get_height ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_get_rowstride ##### -->
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<para>
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</para>
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@pixbuf:
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@Returns: <!--
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Local variables:
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mode: sgml
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sgml-parent-document: ("../gdk-pixbuf.sgml" "book" "refsect2" "")
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End:
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-->
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<!-- ##### FUNCTION gdk_pixbuf_get_option ##### -->
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<para>
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</para>
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@pixbuf:
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@key:
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@Returns:
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<!--
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Local variables:
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mode: sgml
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sgml-parent-document: ("../gdk-pixbuf.sgml" "book" "refsect2")
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End:
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-->
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