[gst-devel] have written new "effect" for geometrictransform

[thiagossantos at gmail.com]

On Thu, Sep 2, 2010 at 9:45 AM, Bert Douglas <bertd at tplogic.com> wrote:

> Hi All,
>
> I have written a new "effect" for geometrictransform.  It does image
> rotation.
> The code is appended below.
> If there is any interest, I will do the work to push it upstream.
> But I need a mentor to help guide the way.
>
> On the code itself.
> I modified the "circle" element, to do rotation.
> The changes were confined to the "map" function.
> I used the same parameters, but with different meaning.
>

Great! I can help you getting this in. Can you provide this as a git patch
in bugzilla?

In case you've never done this before, I could guide you through the details
so you'd learn how to do it. I'm available on #gstreamer on freenode as
'thiagoss'. You can talk to me there or send me a private mail.


>
> Thanks,
> Bert Douglas
>
> ------------------------------------------------------------------------
>
> static gboolean
> circle_map (GstGeometricTransform * gt, gint x, gint y, gdouble * in_x,
>     gdouble * in_y)
> {
>   //GstCircleGeometricTransform *cgt = GST_CIRCLE_GEOMETRIC_TRANSFORM_CAST
> (gt);
>   GstCircle *circle = GST_CIRCLE_CAST (gt);
>
>   gint w, h;
>   gdouble pad, sa;
>   gdouble cix, ciy, cox, coy;   // centers, in/out x/y
>   gdouble ai, ao, ar;           // angles, in/out/rotate  (radians)
>   gdouble r;                    // radius
>   gdouble xi, yi, xo, yo;       // positions in/out x/y
>
>   // input and output image height and width
>   w = gt->width;
>   h = gt->height;
>
>   // our parameters
>   pad = circle->height;         // padding on bottom and right of input
> image
>   ar = circle->angle * M_PI / 180.0;    // angle of rotation, degrees to
> radians
>   sa = circle->spread_angle;    // not used
>
>   // get in and out centers
>   cox = 0.5 * w;
>   coy = 0.5 * h;
>   cix = 0.5 * (w - pad);
>   ciy = 0.5 * (h - pad);
>
>   // convert output image position to polar form
>   xo = x - cox;
>   yo = y - coy;
>   ao = atan2 (yo, xo);
>   r = sqrt (xo * xo + yo * yo);
>
>   // perform rotation backward to get input image rotation
>   // this seems wrong, but rotation from in-->out is counterclockwise
>   ai = ao + ar;
>
>   // back to rectangular for input image position
>   xi = r * cos (ai);
>   yi = r * sin (ai);
>
>   // restore center offset, return values to caller
>   *in_x = xi + cix;
>   *in_y = yi + ciy;
>
>   GST_DEBUG_OBJECT (circle, "Inversely mapped %d %d into %lf %lf",
>       x, y, *in_x, *in_y);
>
>   return TRUE;
> }
>
>
>
>
>
>
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-- 
Thiago Sousa Santos
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