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cookbook: Use GdkPixbuf instead of getting data from a texture

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Rewrote example for single texture + COGL to use
a GdkPixbuf to load images, rather than reading data
out of another CoglTexture.

The data is then loaded from the pixbuf to a region of
the CoglTexture (as before).
This commit is contained in:
Elliot Smith 2010-08-18 16:02:51 +01:00
parent c207820bef
commit 444d315078
1 changed files with 78 additions and 77 deletions
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155
doc/cookbook/textures.xml
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@ -1187,7 +1187,7 @@ clutter_state_set_state (transitions, "show-top");
different dimensions, the <emphasis>source</emphasis> will
appear distorted.</para>
<para>There are a few ways you can remedy this:</para>
<para>There are a couple of ways you can remedy this:</para>
<orderedlist>
@ -1209,91 +1209,92 @@ clutter_state_set_state (transitions, "show-top");
</listitem>
<listitem>
<para>If the bounds of the images you're going to be loading
are known (i.e. you know the greatest width and height
of all the images you're going to load), you can size
the <type>ClutterTexture</type> to those bounds.</para>
<para>Use GdkPixbuf (or similar) to load the images into a temporary
data structure. (GdkPixbuf works well for this as it can resize
the image while retaining its aspect ratio.) Then load the data from
the pixbuf into a <emphasis>region</emphasis> of a
<type>CoglTexture</type> which has the same dimensions as
the <type>ClutterTexture</type>.</para>
<para>Then, as you load each image (e.g. you could do this in the
<para>Here's an example of how you can rewrite the
<function>load_cogl_texture()</function> function of
the <link linkend="textures-crossfade-example-2">code
example</link>):</para>
the <link linkend="textures-crossfade-example-2">single
texture example</link> to do this:</para>
<itemizedlist>
<listitem>
<para>Load the image into a temporary
<type>CoglTexture</type> (e.g. called
<varname>filetex</varname>). Then use the
<type>CoglTexture</type> API to get the data from it.
For example:</para>
<informalexample>
<programlisting>
<informalexample>
<programlisting>
<![CDATA[
/* load texture from a file */
CoglHandle *filetex = cogl_texture_new_from_file (FOX_FILE,
COGL_TEXTURE_NO_SLICING,
COGL_PIXEL_FORMAT_ANY,
NULL);
/* requires this extra include */
#include <gdk-pixbuf/gdk-pixbuf.h>
CoglPixelFormat format = cogl_texture_get_format (filetex);
guint rowstride = cogl_texture_get_rowstride (filetex);
guint width = cogl_texture_get_width (filetex);
guint height = cogl_texture_get_height (filetex);
static CoglHandle
load_cogl_texture (const char *type,
const char *file,
const guint texture_width,
const guint texture_height)
{
GError *error = NULL;
/* allocate memory large enough for the data */
gint size = cogl_texture_get_data (filetex, format, 0, NULL);
guchar *data = g_new0 (guchar, size);
/*
* Load image data from a file into a GdkPixbuf,
* but constrained to the size of the target ClutterTexture;
* aspect ratio is maintained
*
* texture_width and texture_height are set elsewhere to
* the width and height of the ClutterTexture
*/
GdkPixbuf *pixbuf = gdk_pixbuf_new_from_file_at_size (file,
texture_width,
texture_height,
&error);
/* get the data from the texture */
cogl_texture_get_data (filetex,
format,
rowstride,
data);
if (error != NULL)
{
g_print ("Unable to load %s image: %s\n", type, error->message);
g_error_free (error);
exit (EXIT_FAILURE);
}
guint rowstride = gdk_pixbuf_get_rowstride (pixbuf);
guint width = gdk_pixbuf_get_width (pixbuf);
guint height = gdk_pixbuf_get_height (pixbuf);
guchar *data = gdk_pixbuf_get_pixels (pixbuf);
CoglPixelFormat format = COGL_PIXEL_FORMAT_RGB_888;
if (gdk_pixbuf_get_has_alpha (pixbuf) == TRUE)
format = COGL_PIXEL_FORMAT_RGBA_8888;
/* CoglTexture with the same dimensions as the ClutterTexture */
CoglHandle *tex = cogl_texture_new_with_size (texture_width,
texture_height,
COGL_TEXTURE_NO_SLICING,
format);
/*
* load the texture data into a region of the full-sized texture;
* the size of the region is set from the size of the image data
* (as resized by GdkPixbuf)
*/
cogl_texture_set_region (tex,
0, 0, /* from top-left corner of the pixbuf */
(texture_width - width) / 2, /* center on the CoglTexture */
(texture_height - height) / 2, /* center on the CoglTexture */
width, height,
width, height,
format,
rowstride,
data);
return tex;
}
]]>
</programlisting>
</informalexample>
</listitem>
<listitem>
<para>Create another <type>CoglTexture</type> as
large as the <type>ClutterTexture</type> (i.e. big enough
to fit any image you're going to load). Then copy the
data from <varname>filetex</varname> into a region of
it. For example:</para>
</programlisting>
</informalexample>
<informalexample>
<programlisting>
<![CDATA[
/* COGL texture which is the same size as the ClutterTexture */
CoglHandle *tex = cogl_texture_new_with_size (clutter_texture_width,
clutter_texture_height,
COGL_TEXTURE_NO_SLICING,
format);
/* copy the texture data (from filetex) into a region of the full-sized texture */
cogl_texture_set_region (tex,
0, 0, 0, 0,
clutter_texture_width,
clutter_texture_height,
width,
height,
format,
rowstride,
data);
]]>
</programlisting>
</informalexample>
<para>Because you're copying the image data from the
file into a region of the <type>CoglTexture</type>
that's the same size as the image data, it won't be
distorted. However, it's worth stressing that the
<type>ClutterTexture</type> needs to be as wide as
the widest image and as tall as the tallest, so
all the images can be accommodated. Otherwise this
works, but images might be clipped.</para>
</listitem>
</itemizedlist>
<para>Because you're copying the image data from the
file into a region of the <type>CoglTexture</type>
that's the same size as the image data in the pixbuf, it isn't
distorted.</para>
</listitem>