[gnome-photos/wip/rishi/buffer-decoder: 2/11] gegl: Add a function to calculate the inverse Jacobian for zooming

[Debarshi Ray <debarshir src gnome org>]

commit c6012a937cd7ec3b93c8229069ad1a6350601362
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.
    
    Bump minimum GEGL version to 0.4.10.
    
    https://gitlab.gnome.org/GNOME/gnome-photos/issues/63

 configure.ac                  |  2 +-
 meson.build                   |  2 +-
 src/photos-gegl.c             | 20 +++++++++++
 src/photos-gegl.h             |  4 +++
 tests/unit/photos-test-gegl.c | 84 +++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 110 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index d9026d00..f269f0c7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -42,7 +42,7 @@ CAIRO_MIN_VERSION=1.14.0
 DAZZLE_MIN_VERSION=3.26.0
 GDATA_MIN_VERSION=0.15.2
 GDK_PIXBUF_MIN_VERSION=2.36.8
-GEGL_MIN_VERSION=0.4.0
+GEGL_MIN_VERSION=0.4.10
 GEXIV2_MIN_VERSION=0.10.8
 GFBGRAPH_MIN_VERSION=0.2.1
 GLIB_MIN_VERSION=2.57.2
diff --git a/meson.build b/meson.build
index 1e461517..d459fd98 100644
--- a/meson.build
+++ b/meson.build
@@ -151,7 +151,7 @@ libgd_dep = libgd.get_variable('libgd_dep')
 babl_dep = dependency('babl')
 cairo_dep = dependency('cairo', version: '>= 1.14.0')
 gdk_pixbuf_dep = dependency('gdk-pixbuf-2.0', version: '>= 2.36.8')
-gegl_dep = dependency('gegl-0.4', version: '>= 0.4.0')
+gegl_dep = dependency('gegl-0.4', version: '>= 0.4.10')
 geocode_glib_dep = dependency('geocode-glib-1.0')
 gexiv_dep = dependency('gexiv2', version: '>= 0.10.8')
 gio_dep = dependency('gio-2.0')
diff --git a/src/photos-gegl.c b/src/photos-gegl.c
index 186f1613..44efaef4 100644
--- a/src/photos-gegl.c
+++ b/src/photos-gegl.c
@@ -694,6 +694,26 @@ photos_gegl_init_fishes (void)
 }
 
 
+void
+photos_gegl_inverse_jacobian_zoom (GeglBufferMatrix2 *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];
+}
+
+
 GdkPixbuf *
 photos_gegl_pixbuf_new_from_buffer (GeglBuffer *buffer)
 {
diff --git a/src/photos-gegl.h b/src/photos-gegl.h
index 550a1dd8..42649e89 100644
--- a/src/photos-gegl.h
+++ b/src/photos-gegl.h
@@ -53,6 +53,10 @@ void             photos_gegl_init                         (void);
 
 void             photos_gegl_init_fishes                  (void);
 
+void             photos_gegl_inverse_jacobian_zoom        (GeglBufferMatrix2 *out_inverse_jacobian,
+                                                           gdouble zoom_x,
+                                                           gdouble zoom_y);
+
 GdkPixbuf       *photos_gegl_pixbuf_new_from_buffer       (GeglBuffer *buffer);
 
 void             photos_gegl_processor_process_async      (GeglProcessor *processor,
diff --git a/tests/unit/photos-test-gegl.c b/tests/unit/photos-test-gegl.c
index 986a3bf4..943c5779 100644
--- a/tests/unit/photos-test-gegl.c
+++ b/tests/unit/photos-test-gegl.c
@@ -438,6 +438,19 @@ photos_test_gegl_buffer_check_zoom (PhotosTestGeglFixture *fixture, double zoom,
 }
 
 
+static void
+photos_test_gegl_check_inverse_jacobian (gdouble zoom_x, gdouble zoom_y, GeglBufferMatrix2 *reference)
+{
+  GeglBufferMatrix2 inverse_jacobian;
+
+  photos_gegl_inverse_jacobian_zoom (&inverse_jacobian, zoom_y, zoom_y);
+  g_assert_cmpfloat_with_epsilon (inverse_jacobian.coeff[0][0], reference->coeff[0][0], PHOTOS_EPSILON);
+  g_assert_cmpfloat_with_epsilon (inverse_jacobian.coeff[0][1], reference->coeff[0][1], PHOTOS_EPSILON);
+  g_assert_cmpfloat_with_epsilon (inverse_jacobian.coeff[1][0], reference->coeff[1][0], PHOTOS_EPSILON);
+  g_assert_cmpfloat_with_epsilon (inverse_jacobian.coeff[1][1], reference->coeff[1][1], PHOTOS_EPSILON);
+}
+
+
 static void
 photos_test_gegl_buffer_apply_orientation_bottom_0 (PhotosTestGeglFixture *fixture, gconstpointer user_data)
 {
@@ -771,6 +784,71 @@ photos_test_gegl_buffer_zoom_out_1 (PhotosTestGeglFixture *fixture, gconstpointe
 }
 
 
+static void
+photos_test_gegl_inverse_jacobian_zoom_0 (void)
+{
+  GeglBufferMatrix2 inverse_jacobian;
+
+  inverse_jacobian.coeff[0][0] = 0.714285714;
+  inverse_jacobian.coeff[0][1] = 0.0;
+  inverse_jacobian.coeff[1][0] = 0.0;
+  inverse_jacobian.coeff[1][1] = 0.714285714;
+  photos_test_gegl_check_inverse_jacobian (1.4, 1.4, &inverse_jacobian);
+}
+
+
+static void
+photos_test_gegl_inverse_jacobian_zoom_1 (void)
+{
+  GeglBufferMatrix2 inverse_jacobian;
+
+  inverse_jacobian.coeff[0][0] = 0.25;
+  inverse_jacobian.coeff[0][1] = 0.0;
+  inverse_jacobian.coeff[1][0] = 0.0;
+  inverse_jacobian.coeff[1][1] = 0.25;
+  photos_test_gegl_check_inverse_jacobian (4.0, 4.0, &inverse_jacobian);
+}
+
+
+static void
+photos_test_gegl_inverse_jacobian_zoom_2 (void)
+{
+  GeglBufferMatrix2 inverse_jacobian;
+
+  inverse_jacobian.coeff[0][0] = 1.0;
+  inverse_jacobian.coeff[0][1] = 0.0;
+  inverse_jacobian.coeff[1][0] = 0.0;
+  inverse_jacobian.coeff[1][1] = 1.0;
+  photos_test_gegl_check_inverse_jacobian (1.0, 1.0, &inverse_jacobian);
+}
+
+
+static void
+photos_test_gegl_inverse_jacobian_zoom_3 (void)
+{
+  GeglBufferMatrix2 inverse_jacobian;
+
+  inverse_jacobian.coeff[0][0] = 1.66666667;
+  inverse_jacobian.coeff[0][1] = 0.0;
+  inverse_jacobian.coeff[1][0] = 0.0;
+  inverse_jacobian.coeff[1][1] = 1.66666667;
+  photos_test_gegl_check_inverse_jacobian (0.6, 0.6, &inverse_jacobian);
+}
+
+
+static void
+photos_test_gegl_inverse_jacobian_zoom_4 (void)
+{
+  GeglBufferMatrix2 inverse_jacobian;
+
+  inverse_jacobian.coeff[0][0] = 4.0;
+  inverse_jacobian.coeff[0][1] = 0.0;
+  inverse_jacobian.coeff[1][0] = 0.0;
+  inverse_jacobian.coeff[1][1] = 4.0;
+  photos_test_gegl_check_inverse_jacobian (0.25, 0.25, &inverse_jacobian);
+}
+
+
 static void
 photos_test_gegl_legacy_convert_between_buffer_pixbuf_0 (PhotosTestGeglFixture *fixture, gconstpointer 
user_data)
 {
@@ -1100,6 +1178,12 @@ main (gint argc, gchar *argv[])
               photos_test_gegl_buffer_zoom_out_1,
               photos_test_gegl_teardown);
 
+  g_test_add_func ("/gegl/inverse-jacobian-zoom-0", photos_test_gegl_inverse_jacobian_zoom_0);
+  g_test_add_func ("/gegl/inverse-jacobian-zoom-1", photos_test_gegl_inverse_jacobian_zoom_1);
+  g_test_add_func ("/gegl/inverse-jacobian-zoom-2", photos_test_gegl_inverse_jacobian_zoom_2);
+  g_test_add_func ("/gegl/inverse-jacobian-zoom-3", photos_test_gegl_inverse_jacobian_zoom_3);
+  g_test_add_func ("/gegl/inverse-jacobian-zoom-4", photos_test_gegl_inverse_jacobian_zoom_4);
+
   g_test_add ("/gegl/legacy/convert-between-buffer-pixbuf-0",
               PhotosTestGeglFixture,
               NULL,