To use gegl:transform, you need to create the transformation matrix yourself. There are plenty of tutorials for learning how to create transformation matrices online.

Then, do this to set the node's property:

1. When you create your matrix, place it in a GeglMatrix3 struct. It contains one member named coeff, which is a 3x3 array of doubles for the matrix values.
2. Turn the matrix into a string with gchar* gegl_matrix3_to_string (GeglMatrix3 *matrix);
3. Set this string as the property "transform" on your gegl:transform node with gegl_node_set.
4. Free the string from (2) with g_free

Anyway, I hope this helps! Feel free to ask if you have any issues.

-- drawoc

On Sun, Sep 29, 2013 at 6:06 AM, beee wrote:

Hi,

I want to apply perspective effects on an image. But I can't find an operation for it. I thought maybe I can do it with gegl:transform. But I don't know which parameters should use.

Please help. Thanks!

Regards.

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Sorry, I've been busy, and I forgot to reply to this.

Gegl doesn't have any built-in operations for gradients right now, but you can code your own, either as operations, or that operate on gegl buffers.

There are some operations for gradients that are in gegl's source tree, but they're marked as experimental, and they aren't built by default. You can build them if you build gegl with --enable-workshop. Their code is here:
operations/workshop/linear-gradient.c operations/workshop/radial-gradient.c

I haven't looked at them closely, so I can't vouch for whether their code is correct or not, and when operations are maked experimental like this, there's often something slightly wrong with them. Still, they might be a good starting point.

On Tue, Oct 8, 2013 at 2:14 AM, beee wrote:

Dear Michael,

Thanks for your kindly help. I have another question: How can I fill a region with gradient color using gegl?

Best Regards. At 2013-09-29 21:55:00,"Michael Henning" wrote:

To use gegl:transform, you need to create the transformation matrix yourself. There are plenty of tutorials for learning how to create transformation matrices online.

Then, do this to set the node's property:

1. When you create your matrix, place it in a GeglMatrix3 struct. It contains one member named coeff, which is a 3x3 array of doubles for the matrix values.
2. Turn the matrix into a string with gchar* gegl_matrix3_to_string (GeglMatrix3 *matrix);
3. Set this string as the property "transform" on your gegl:transform node with gegl_node_set.
4. Free the string from (2) with g_free

Anyway, I hope this helps! Feel free to ask if you have any issues.

-- drawoc

On Sun, Sep 29, 2013 at 6:06 AM, beee wrote:

Hi,

I want to apply perspective effects on an image. But I can't find an operation for it. I thought maybe I can do it with gegl:transform. But I don't know which parameters should use.

Please help. Thanks!

Regards.

_______________________________________________ gegl-developer-list mailing list
List address: gegl-developer-list@gnome.org List membership: https://mail.gnome.org/mailman/listinfo/gegl-developer-list