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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>3. Maintaining the aspect ratio when loading an image into a texture</title><link rel="stylesheet" type="text/css" href="style.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="The Clutter Cookbook"><link rel="up" href="textures.html" title="Chapter 4. Textures"><link rel="prev" href="textures-drawing-with-cairo.html" title="2. Drawing 2D graphics onto a texture"><link rel="next" href="textures-image-loading.html" title="4. Loading image data into a texture"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">3. Maintaining the aspect ratio when loading an
image into a texture</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="textures-drawing-with-cairo.html">Prev</a> </td><th width="60%" align="center">Chapter 4. Textures</th><td width="20%" align="right"> <a accesskey="n" href="textures-image-loading.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="textures-aspect-ratio"></a>3. Maintaining the aspect ratio when loading an
image into a texture</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp40637820"></a>3.1. Problem</h3></div></div></div><p>You want want to load an image into a texture
and scale it, while retaining the underlying image's aspect ratio.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp40638604"></a>3.2. Solution</h3></div></div></div><p>Set the texture to keep the aspect ratio of the
underlying image (so it doesn't distort when it's scaled); use
the actor's <span class="property">request-mode</span> property to set
the correct geometry management (see the discussion section); then
resize the texture along one dimension (height or width).
Now, when an image is loaded into the texture, the image is
scaled to fit the set height or width; the other dimension
is automatically scaled by the same factor so the image fits
the texture:</p><div class="informalexample"><pre class="programlisting">ClutterActor *texture;
texture = clutter_texture_new ();
clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (texture), TRUE);
/*
* this setting means the height of the scaled image is based on its width;
* it's not strictly necessary to set this, as this is the default
*/
clutter_actor_set_request_mode (texture, CLUTTER_REQUEST_HEIGHT_FOR_WIDTH);
/* set the width, which causes height to be scaled by the same factor */
clutter_actor_set_width (texture, 300);
clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
"/path/to/image.jpg",
NULL);</pre></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp43543804"></a>3.3. Discussion</h3></div></div></div><p>The <span class="property">request-mode</span> for an actor
determines how geometry requisition is performed; in this case, this
includes how scaling is applied if you change the actor's
width or height. There are two possible values for
request-mode:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>If set to <code class="constant">CLUTTER_REQUEST_HEIGHT_FOR_WIDTH</code>
(the default), changing the width causes the height
to be scaled by the same factor as the width.</p></li><li class="listitem"><p>If set to <code class="constant">CLUTTER_REQUEST_WIDTH_FOR_HEIGHT</code>,
changing the height causes the width to be scaled by the
same factor as the height.</p></li></ol></div><p>In the example above, the texture is set to keep its
aspect ratio then fixed to a width of 300 pixels; the
request-mode is set to <code class="constant">CLUTTER_REQUEST_HEIGHT_FOR_WIDTH</code>.
If a standard, photo-sized image in landscape orientation were
loaded into it (2848 pixels wide x 2136 high), it would be scaled
down to 300 pixels wide; then, its height would be scaled by the
same factor as the width (i.e. scaled down to 225 pixels).</p><p>With request-mode set to
<code class="constant">CLUTTER_REQUEST_WIDTH_FOR_HEIGHT</code>,
you would get the same effect by setting the height first;
then, computation of the width for the scaled image would be
based on the scaling factor applied to its height instead.</p><p>You can work out which side of the source image is longest using
<code class="function">clutter_texture_base_size()</code> to get its
width and height. This can be useful when trying to scale images
with different orientations to fit into uniform rows or columns:</p><div class="informalexample"><pre class="programlisting">gint width;
gint height;
clutter_texture_get_base_size (CLUTTER_TEXTURE (texture), &width, &height);</pre></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>If you explicitly set the size (both width and height)
of a texture with <code class="function">clutter_actor_set_size()</code> (or
with <code class="function">clutter_actor_set_width()</code> and
<code class="function">clutter_actor_set_height()</code>), any
image loaded into the texture is automatically stretched/shrunk to
fit the texture. This is the case regardless of any other settings
(like whether to keep aspect ratio).</p></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Since a texture can scale down its contents, its minimum
preferred size is 0.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="textures-drawing-with-cairo.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="textures.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="textures-image-loading.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2. Drawing 2D graphics onto a texture </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 4. Loading image data into a texture</td></tr></table></div></body></html>
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