mirror of
https://gitlab.gnome.org/GNOME/gtk.git
synced 2025-01-12 21:40:19 +00:00
Added a section on how to compute pixel offsets for
2004-01-06 Federico Mena Quintero <federico@ximian.com> * gdk-pixbuf/tmpl/gdk-pixbuf.sgml: Added a section on how to compute pixel offsets for gdk_pixbuf_get_pixels().
This commit is contained in:
Federico Mena Quintero
Federico Mena Quintero
parent
65fa5b0f98
commit
9d6ed04dff
@ -15,6 +15,11 @@ Wed Jan 7 01:26:07 2004 Matthias Clasen <maclas@gmx.de>
|
|||||||
|
|
||||||
* gdk-pixbuf/gdk-pixbuf-sections.txt: Add gdk_pixbuf_get_file_info.
|
* gdk-pixbuf/gdk-pixbuf-sections.txt: Add gdk_pixbuf_get_file_info.
|
||||||
|
|
||||||
|
2004-01-06 Federico Mena Quintero <federico@ximian.com>
|
||||||
|
|
||||||
|
* gdk-pixbuf/tmpl/gdk-pixbuf.sgml: Added a section on how to
|
||||||
|
compute pixel offsets for gdk_pixbuf_get_pixels().
|
||||||
|
|
||||||
Mon Dec 29 01:40:20 2003 Matthias Clasen <maclas@gmx.de>
|
Mon Dec 29 01:40:20 2003 Matthias Clasen <maclas@gmx.de>
|
||||||
|
|
||||||
* gtk/gtk-sections.txt: Add gtk_accel_map_{un,}lock_path.
|
* gtk/gtk-sections.txt: Add gtk_accel_map_{un,}lock_path.
|
||||||
|
|||||||
@ -11,6 +11,81 @@ Information that describes an image.
|
|||||||
information that describes an image in memory.
|
information that describes an image in memory.
|
||||||
</para>
|
</para>
|
||||||
|
|
||||||
|
<section id="image-data">
|
||||||
|
<title>Image Data</title>
|
||||||
|
|
||||||
|
<para>
|
||||||
|
Image data in a pixbuf is stored in memory in uncompressed,
|
||||||
|
packed format. Rows in the image are stored top to bottom, and
|
||||||
|
in each row pixels are stored from left to right. There may be
|
||||||
|
padding at the end of a row. The "rowstride" value of a pixbuf,
|
||||||
|
as returned by gdk_pixbuf_get_rowstride(), indicates the number
|
||||||
|
of bytes between rows.
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<example id="put-pixel">
|
||||||
|
<title>put_pixel() example</title>
|
||||||
|
|
||||||
|
<para>
|
||||||
|
The following code illustrates a simple put_pixel() function
|
||||||
|
for RGB pixbufs with 8 bits per channel with an alpha channel.
|
||||||
|
It is not included in the gdk-pixbuf library for performance
|
||||||
|
reasons; rather than making several function calls for each
|
||||||
|
pixel, your own code can take shortcuts.
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<programlisting>
|
||||||
|
static void
|
||||||
|
put_pixel (GdkPixbuf *pixbuf, int x, int y, guchar red, guchar green, guchar blue, guchar alpha)
|
||||||
|
{
|
||||||
|
int width, height, rowstride, n_channels;
|
||||||
|
guchar *pixels, *p;
|
||||||
|
|
||||||
|
n_channels = gdk_pixbuf_get_n_channels (pixbuf);
|
||||||
|
|
||||||
|
g_assert (gdk_pixbuf_get_colorspace (pixbuf) == GDK_COLORSPACE_RGB);
|
||||||
|
g_assert (gdk_pixbuf_get_bits_per_sample (pixbuf) == 8);
|
||||||
|
g_assert (gdk_pixbuf_get_has_alpha (pixbuf));
|
||||||
|
g_assert (n_channels == 4);
|
||||||
|
|
||||||
|
width = gdk_pixbuf_get_width (pixbuf);
|
||||||
|
height = gdk_pixbuf_get_height (pixbuf);
|
||||||
|
|
||||||
|
g_assert (x >= 0 && x < width);
|
||||||
|
g_assert (y >= 0 && y < height);
|
||||||
|
|
||||||
|
rowstride = gdk_pixbuf_get_rowstride (pixbuf);
|
||||||
|
pixels = gdk_pixbuf_get_pixels (pixbuf);
|
||||||
|
|
||||||
|
p = pixels + y * rowstride + x * n_channels;
|
||||||
|
p[0] = red;
|
||||||
|
p[1] = green;
|
||||||
|
p[2] = blue;
|
||||||
|
p[3] = alpha;
|
||||||
|
}
|
||||||
|
</programlisting>
|
||||||
|
|
||||||
|
<para>
|
||||||
|
This function will not work for pixbufs with images that are
|
||||||
|
other than 8 bits per sample or channel, but it will work for
|
||||||
|
most of the pixbufs that GTK+ uses.
|
||||||
|
</para>
|
||||||
|
</example>
|
||||||
|
|
||||||
|
<note>
|
||||||
|
<para>
|
||||||
|
If you are doing memcpy() of raw pixbuf data, note that the
|
||||||
|
last row in the pixbuf may not be as wide as the full
|
||||||
|
rowstride, but rather just as wide as the pixel data needs to
|
||||||
|
be. That is, it is unsafe to do <literal>memcpy (dest,
|
||||||
|
pixels, rowstride * height)</literal> to copy a whole pixbuf.
|
||||||
|
Use gdk_pixbuf_copy() instead, or compute the width in bytes
|
||||||
|
of the last row as <literal>width * ((n_channels *
|
||||||
|
bits_per_sample + 7) / 8)</literal>.
|
||||||
|
</para>
|
||||||
|
</note>
|
||||||
|
</section>
|
||||||
|
|
||||||
<!-- ##### SECTION See_Also ##### -->
|
<!-- ##### SECTION See_Also ##### -->
|
||||||
<para>
|
<para>
|
||||||
</para>
|
</para>
|
||||||
@ -76,6 +151,46 @@ In the future it will do full alpha compositing.
|
|||||||
</para>
|
</para>
|
||||||
|
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:bits-per-sample ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:colorspace ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:has-alpha ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:height ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:n-channels ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:pixels ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:rowstride ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
|
<!-- ##### ARG GdkPixbuf:width ##### -->
|
||||||
|
<para>
|
||||||
|
|
||||||
|
</para>
|
||||||
|
|
||||||
<!-- ##### FUNCTION gdk_pixbuf_get_colorspace ##### -->
|
<!-- ##### FUNCTION gdk_pixbuf_get_colorspace ##### -->
|
||||||
<para>
|
<para>
|
||||||
|
|
||||||
@ -163,3 +278,9 @@ End:
|
|||||||
@Returns:
|
@Returns:
|
||||||
|
|
||||||
|
|
||||||
|
<!--
|
||||||
|
Local variables:
|
||||||
|
mode: sgml
|
||||||
|
sgml-parent-document: ("../gdk-pixbuf.sgml" "book" "refsect2")
|
||||||
|
End:
|
||||||
|
-->
|
||||||
|
|||||||
Loading…
Reference in New Issue
Block a user