[gnome-photos/wip/rishi/buffer-decoder: 7/15] gegl: Add a function to calculate the inverse Jacobian for zooming

[Debarshi Ray <debarshir src gnome org>]

commit b2a49c03654c133a48af26270a6f5ac3cb1936e5
Author: Debarshi Ray <debarshir gnome org>
Date:   Mon Sep 24 11:36:21 2018 +0200

    gegl: Add a function to calculate the inverse Jacobian for zooming
    
    This will be necessary to support arbitrary downscales, without keeping
    the aspect ratio, in the new codec API for GeglBuffer. It is something
    that every codec will need and is, therefore, useful to have as a
    separate utility function.
    
    https://gitlab.gnome.org/GNOME/gnome-photos/issues/63

 src/photos-gegl.c | 20 ++++++++++++++++++++
 src/photos-gegl.h |  4 ++++
 2 files changed, 24 insertions(+)
---
diff --git a/src/photos-gegl.c b/src/photos-gegl.c
index 7788b758..f7b38ec5 100644
--- a/src/photos-gegl.c
+++ b/src/photos-gegl.c
@@ -650,6 +650,26 @@ photos_gegl_init_fishes (void)
 }
 
 
+void
+photos_gegl_inverse_jacobian_zoom (GeglMatrix2 *inverse_jacobian, gdouble zoom_x, gdouble zoom_y)
+{
+  GeglMatrix3 tmp;
+
+  g_return_if_fail (inverse_jacobian != NULL);
+
+  gegl_matrix3_identity (&tmp);
+  tmp.coeff[0][0] = zoom_x;
+  tmp.coeff[1][1] = zoom_y;
+
+  gegl_matrix3_invert (&tmp);
+
+  inverse_jacobian->coeff[0][0] = tmp.coeff[0][0];
+  inverse_jacobian->coeff[0][1] = tmp.coeff[0][1];
+  inverse_jacobian->coeff[1][0] = tmp.coeff[1][0];
+  inverse_jacobian->coeff[1][1] = tmp.coeff[1][1];
+}
+
+
 static gboolean
 photos_gegl_processor_process_idle (gpointer user_data)
 {
diff --git a/src/photos-gegl.h b/src/photos-gegl.h
index d902300b..5e49169c 100644
--- a/src/photos-gegl.h
+++ b/src/photos-gegl.h
@@ -51,6 +51,10 @@ void             photos_gegl_init                         (void);
 
 void             photos_gegl_init_fishes                  (void);
 
+void             photos_gegl_inverse_jacobian_zoom        (GeglMatrix2 *out_inverse_jacobian,
+                                                           gdouble zoom_x,
+                                                           gdouble zoom_y);
+
 void             photos_gegl_processor_process_async      (GeglProcessor *processor,
                                                            GCancellable *cancellable,
                                                            GAsyncReadyCallback callback,