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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 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>5. Creating sub-textures from an existing 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-image-loading.html" title="4. Loading image data into a texture"><link rel="next" href="textures-reflection.html" title="6. Creating a reflection of 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">5. Creating sub-textures from an existing texture</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="textures-image-loading.html">Prev</a> </td><th width="60%" align="center">Chapter 4. Textures</th><td width="20%" align="right"> <a accesskey="n" href="textures-reflection.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-sub-textures"></a>5. Creating sub-textures from an existing texture</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp61248992"></a>5.1. Problem</h3></div></div></div><p>You want to create a new <span class="type">ClutterTexture</span> that only
displays a rectangular sub-region of an existing texture.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp61250768"></a>5.2. Solution</h3></div></div></div><p>A possible way of achieving this is to retrieve the
<span class="type">CoglHandle</span> of the underlying Cogl texture of the existing
<span class="type">ClutterTexture</span>, create a new handle representing the
sub-region with <code class="function">cogl_texture_new_from_sub_texture()</code>
and finally populate a new <span class="type">ClutterTexture</span> with that handle.
</p><div class="informalexample"><pre class="programlisting">/* Create a new ClutterTexture that shows smiley.png */
image = clutter_texture_new_from_file ("smiley.png", NULL);
clutter_actor_get_size (image, &image_width, &image_height);
/* Grab the CoglHandle of the underlying Cogl texture */
texture = clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (image));
/* Create a new Cogl texture from the handle above. That new texture is a
* rectangular region from image, more precisely the northwest corner
* of the image */
sub_texture = cogl_texture_new_from_sub_texture (texture,
0, 0,
image_width / 2,
image_height / 2);
/* Finally, use the newly created Cogl texture to feed a new ClutterTexture
* and thus create a new actor that displays sub_texture */
sub_image = clutter_texture_new ();
clutter_texture_set_cogl_texture (CLUTTER_TEXTURE (sub_image), sub_texture);
/*
* You could have used the more straightforward g_object_new() function that
* can create an object and set some properties on it at the same time:
* sub_image = g_object_new (CLUTTER_TYPE_TEXTURE,
* "cogl-texture", sub_texture,
* NULL);
*/</pre></div><div class="screenshot"><div class="mediaobject"><img src="images/textures-sub-texture.png" alt="A texture and its sub-texture next to it"></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp61259616"></a>5.3. Discussion</h3></div></div></div><p>The key of this recipe is the Cogl handle that represents the
underlying texture, the actual array of pixels the GPU will use
when it's told to texture geometry.</p><p>From this handle, it's possible to create a new texture handle
that represents a rectangular region of the former texture. To do this
one must call <code class="function">cogl_texture_new_from_sub_texture()</code>
with the position and size of the said region. The interesting bit
about this function is that, when drawing either with the original
texture or with the new one, it's still the same GPU resource (pixels)
being used, meaning that creating a sub-texture doesn't use extra GPU
memory.</p><p>Once the sub-texture handle is created, the next step is
to create a new actor that will be able to draw it, namely a new
<span class="type">ClutterTexture</span>. You then need to tell the texture to
draw from the sub-texture.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The handle you can get from
<code class="function">clutter_texture_get_cogl_texture()</code> is effectively
the same texture than the first layer of the material retrieved by
<code class="function">clutter_texture_get_cogl_material()</code></p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp61265792"></a>5.4. Full example</h3></div></div></div><div class="example"><a name="textures-sub-texture"></a><p class="title"><b>Example 4.1. Creating a sub-texture from an existing texture</b></p><div class="example-contents"><pre class="programlisting">#include <clutter/clutter.h>
int
main (int argc, char **argv)
{
ClutterActor *stage, *image, *sub_image;
CoglHandle texture, sub_texture;
gfloat image_width, image_height;
/* Initialize Clutter */
if (clutter_init (NULL, NULL) != CLUTTER_INIT_SUCCESS)
return 1;
/* Get the default stage */
stage = clutter_stage_new ();
clutter_stage_set_title (CLUTTER_STAGE (stage), "Sub-texture");
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
/* Create a new ClutterTexture that shows smiley.png */
image = clutter_texture_new_from_file ("smiley.png", NULL);
clutter_actor_get_size (image, &image_width, &image_height);
clutter_actor_set_size (stage,
image_width * 3 / 2 + 30,
image_height + 20);
/* Grab the CoglHandle of the underlying Cogl texture */
texture = clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (image));
/* Create a new Cogl texture from the handle above. That new texture is a
* rectangular region from image, more precisely the northwest corner
* of the image */
sub_texture = cogl_texture_new_from_sub_texture (texture,
0, 0,
image_width / 2,
image_height / 2);
/* Finally, use the newly created Cogl texture to feed a new ClutterTexture
* and thus create a new actor that displays sub_texture */
sub_image = clutter_texture_new ();
clutter_texture_set_cogl_texture (CLUTTER_TEXTURE (sub_image), sub_texture);
/*
* You could have used the more straightforward g_object_new() function that
* can create an object and set some properties on it at the same time:
* sub_image = g_object_new (CLUTTER_TYPE_TEXTURE,
* "cogl-texture", sub_texture,
* NULL);
*/
/* Put the original image at (10,10) and the new sub image next to it */
clutter_actor_set_position (image, 10, 10);
clutter_actor_set_position (sub_image, 20 + image_width, 10);
/* Add both ClutterTexture to the stage */
clutter_container_add (CLUTTER_CONTAINER (stage), image, sub_image, NULL);
clutter_actor_show_all (stage);
clutter_main ();
return 0;
}</pre></div></div><br class="example-break"></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp61271744"></a>5.5. Going further</h3></div></div></div><p>Now that we know how to create sub-textures, it's time to make
something a bit more shiny with them. Let's animate them! In case you
have not heard about implicit animations in Clutter yet, it's a good
time to have a look at the animation section of this cookbook.
</p><p><video controls="controls" src="videos/textures-split-go.ogv"><a href="videos/textures-split-go.ogv"></a></video></p><div class="example"><a name="textures-split-go"></a><p class="title"><b>Example 4.2. Creating a sub-texture from an existing texture</b></p><div class="example-contents"><pre class="programlisting">#include <clutter/clutter.h>
/* Context will be used to carry interesting variables between functions */
typedef struct
{
ClutterActor *sub_nw, *sub_ne, *sub_sw, *sub_se;
gfloat image_width, image_height;
} Context;
/* Here, we animate the texture to go way by giving the new coordinates
* outside of the stage. We rotate the sub-textures around their anchor
* point (set in setup_sub() as well, it looks cool. */
static gboolean
go_away (gpointer data)
{
Context *context = data;
clutter_actor_animate (context->sub_nw, CLUTTER_EASE_OUT_CUBIC, 1500,
"x", -context->image_width,
"y", -context->image_height,
"rotation-angle-z", 2000.,
NULL);
clutter_actor_animate (context->sub_ne, CLUTTER_EASE_OUT_CUBIC, 1500,
"x", +context->image_width,
"y", -context->image_height,
"rotation-angle-z", 2000.,
NULL);
clutter_actor_animate (context->sub_sw, CLUTTER_EASE_OUT_CUBIC, 1500,
"x", -context->image_width,
"y", +context->image_height,
"rotation-angle-z", 2000.,
NULL);
clutter_actor_animate (context->sub_se, CLUTTER_EASE_OUT_CUBIC, 1500,
"x", -context->image_width,
"y", +context->image_height,
"rotation-angle-z", 2000.,
NULL);
return G_SOURCE_REMOVE; /* remove the timeout source */
}
/* We split the four sub-textures faking to be the big texture, moving them
* away by 10 pixels in each direction */
static gboolean
split (gpointer data)
{
Context *context = data;
gfloat x, y;
clutter_actor_get_position (context->sub_nw, &x, &y);
clutter_actor_animate (context->sub_nw, CLUTTER_EASE_OUT_CUBIC, 300,
"x", x - 10,
"y", y - 10,
NULL);
clutter_actor_get_position (context->sub_ne, &x, &y);
clutter_actor_animate (context->sub_ne, CLUTTER_EASE_OUT_CUBIC, 300,
"x", x + 10,
"y", y - 10,
NULL);
clutter_actor_get_position (context->sub_sw, &x, &y);
clutter_actor_animate (context->sub_sw, CLUTTER_EASE_OUT_CUBIC, 300,
"x", x - 10,
"y", y + 10,
NULL);
clutter_actor_get_position (context->sub_se, &x, &y);
clutter_actor_animate (context->sub_se, CLUTTER_EASE_OUT_CUBIC, 300,
"x", x + 10,
"y", y + 10,
NULL);
/* In 500ms the textures will flee! */
clutter_threads_add_timeout (500, go_away, context);
return G_SOURCE_REMOVE; /* remove the timeout source */
}
static ClutterActor *
setup_sub (CoglHandle texture,
gint image_width,
gint image_height,
gint t_x,
gint t_y,
gint t_width,
gint t_height)
{
CoglHandle sub_texture;
ClutterActor *sub_image;
/* Create a new sub-texture from textures */
sub_texture = cogl_texture_new_from_sub_texture (texture,
t_x, t_y,
t_width, t_height);
/* Create the corresponding ClutterTexture */
sub_image = g_object_new (CLUTTER_TYPE_TEXTURE,
"cogl-texture", sub_texture,
NULL);
/* Set the anchor point in the middle of each sub_image so the position and
* rotation of the textures are relative to that point */
clutter_actor_set_anchor_point (sub_image, image_width / 4, image_height / 4);
return sub_image;
}
#define IMAGE "smiley.png"
int
main (int argc,
char **argv)
{
gfloat image_width, image_height, stage_width, stage_height;
ClutterActor *stage, *image;
GError *error = NULL;
CoglHandle texture;
Context context;
if (clutter_init (NULL, NULL) != CLUTTER_INIT_SUCCESS)
return 1;
stage = clutter_stage_new ();
clutter_actor_get_size (stage, &stage_width, &stage_height);
clutter_stage_set_title (CLUTTER_STAGE (stage), "Animate sub-textures");
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
/* Load smiley.png, creating a new ClutterTexture, get its size and the
* Cogl texture handle */
image = clutter_texture_new_from_file (IMAGE, &error);
if (error != NULL)
{
g_warning ("Could not load " IMAGE ": %s", error->message);
g_clear_error (&error);
return 1;
}
clutter_actor_get_size (image, &image_width, &image_height);
texture = clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (image));
/* Create four sub-textures from image, actually splitting the image in
* four */
context.sub_nw = setup_sub (texture, image_width, image_height,
0, 0, image_width / 2 , image_height / 2);
context.sub_ne = setup_sub (texture, image_width, image_height,
image_width / 2 , 0,
image_width / 2, image_height / 2);
context.sub_sw = setup_sub (texture, image_width, image_height,
0.f, image_height / 2,
image_width / 2, image_height / 2);
context.sub_se = setup_sub (texture, image_width, image_height,
image_width / 2, image_height / 2,
image_width / 2, image_height / 2);
/* We don't need the image anymore as we won't display it and as
* cogl_texture_new_from_sub_texture() keeps a reference to the underlying
* texture ressource */
g_object_unref (image);
/* Position the sub-texures in the middle of the screen, recreating the
* original texture */
clutter_actor_set_position (context.sub_nw,
stage_width / 2 - image_width / 4,
stage_height / 2 - image_height / 4);
clutter_actor_set_position (context.sub_ne,
stage_width / 2 + image_width / 4,
stage_height / 2 - image_height / 4);
clutter_actor_set_position (context.sub_sw,
stage_width / 2 - image_width / 4,
stage_height / 2 + image_height / 4);
clutter_actor_set_position (context.sub_se,
stage_width / 2 + image_width / 4,
stage_height / 2 + image_height / 4);
/* Add the four sub-textures to the stage */
clutter_container_add (CLUTTER_CONTAINER (stage), context.sub_nw,
context.sub_ne, context.sub_sw, context.sub_se, NULL);
clutter_actor_show_all (stage);
context.image_width = image_width;
context.image_height = image_height;
/* In two seconds, we'll split the texture! */
clutter_threads_add_timeout (2000, split, &context);
clutter_main ();
return 0;
}</pre></div></div><br class="example-break"></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="textures-image-loading.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-reflection.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">4. Loading image data into a texture </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 6. Creating a reflection of a texture</td></tr></table></div></body></html>
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