gltransformation: implement pivot point for rotation and scale

https://bugzilla.gnome.org/show_bug.cgi?id=744763

Add a pivot vector for setting the origin of rotations and scales.

With the pivot point the rotation and scale operations can have
different origins. This adds the ability to rotate around different points.
Currently the default (0, 0) pivot point is possible,
a rotation around the center, and zooming into and out of the center.

With an pivot point this is optional.
I defined the following image coordinates for the pivot point:

	 (-1,1) ------------------------- (1,1)
		|			|
		|			|
		|			|
		|	  (0,0)		|
		|			|
		|			|
		|			|
	(-1,-1) ------------------------- (1,-1)

Example:

	Rotate the video at the bottom left corner

	gst-launch-1.0 videotestsrc \
			! gltransformation \
		 		scale-x=0.5 \
				scale-y=0.5 \
				rotation-z=25.0 \
				pivot-x=-1.0 \
				pivot-y=-1.0 \
			! glimagesink

The pivot-z option defines the pivot point in 3D space.
This only affects rotation, since we have no Z data to scale.
With this option a video can be rotated around a point in 3D space.

Example:

	Rotate around point behind the video:

    	gst-launch-1.0 videotestsrc \
			! gltransformation \
				rotation-x=10.0 \
				pivot-z=-4.0 \
			! glimagesink

ext/gl/gstgltransformation.c

@@ -67,7 +67,10 @@ enum
   PROP_ROTATION_Z,
   PROP_SCALE_X,
   PROP_SCALE_Y,
-  PROP_MVP
+  PROP_MVP,
+  PROP_PIVOT_X,
+  PROP_PIVOT_Y,
+  PROP_PIVOT_Z,
 };
 
 #define DEBUG_INIT \
@@ -196,6 +199,27 @@ gst_gl_transformation_class_init (GstGLTransformationClass * klass)
           "Scale multiplier for the Y-Axis.",
           0.0, G_MAXFLOAT, 1.0, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  /* Pivot */
+  g_object_class_install_property (gobject_class, PROP_PIVOT_X,
+      g_param_spec_float ("pivot-x", "X Pivot",
+          "Rotation pivot point X coordinate, where 0 is the center,"
+          " -1 the lef +1 the right boarder and <-1, >1 outside.",
+          -G_MAXFLOAT, G_MAXFLOAT, 0.0,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
+  g_object_class_install_property (gobject_class, PROP_PIVOT_Y,
+      g_param_spec_float ("pivot-y", "Y Pivot",
+          "Rotation pivot point X coordinate, where 0 is the center,"
+          " -1 the lef +1 the right boarder and <-1, >1 outside.",
+          -G_MAXFLOAT, G_MAXFLOAT, 0.0,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
+  g_object_class_install_property (gobject_class, PROP_PIVOT_Z,
+      g_param_spec_float ("pivot-z", "Z Pivot",
+          "Relevant for rotation in 3D space. You look into the negative Z axis direction",
+          -G_MAXFLOAT, G_MAXFLOAT, 0.0,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   /* MVP */
   g_object_class_install_property (gobject_class, PROP_MVP,
       g_param_spec_boxed ("mvp-matrix",
@@ -237,6 +261,13 @@ gst_gl_transformation_build_mvp (GstGLTransformation * transformation)
       transformation->ytranslation * 2.0,
       transformation->ztranslation * 2.0);
 
+  graphene_point3d_t pivot_vector =
+      GRAPHENE_POINT3D_INIT (-transformation->xpivot * transformation->aspect,
+      transformation->ypivot,
+      -transformation->zpivot);
+
+  graphene_point3d_t negative_pivot_vector;
+
   graphene_matrix_t model_matrix;
   graphene_matrix_t projection_matrix;
   graphene_matrix_t view_matrix;
@@ -250,9 +281,14 @@ gst_gl_transformation_build_mvp (GstGLTransformation * transformation)
   graphene_vec3_init (&center, 0.f, 0.f, 0.f);
   graphene_vec3_init (&up, 0.f, 1.f, 0.f);
 
-  graphene_matrix_init_scale (&model_matrix,
+  /* Translate into pivot origin */
+  graphene_matrix_init_translate (&model_matrix, &pivot_vector);
+
+  /* Scale */
+  graphene_matrix_scale (&model_matrix,
       transformation->xscale, transformation->yscale, 1.0f);
 
+  /* Rotation */
   graphene_matrix_rotate (&model_matrix,
       transformation->xrotation, graphene_vec3_x_axis ());
   graphene_matrix_rotate (&model_matrix,
@@ -260,6 +296,11 @@ gst_gl_transformation_build_mvp (GstGLTransformation * transformation)
   graphene_matrix_rotate (&model_matrix,
       transformation->zrotation, graphene_vec3_z_axis ());
 
+  /* Translate back from pivot origin */
+  graphene_point3d_scale (&pivot_vector, -1.0, &negative_pivot_vector);
+  graphene_matrix_translate (&model_matrix, &negative_pivot_vector);
+
+  /* Translation */
   graphene_matrix_translate (&model_matrix, &translation_vector);
 
   if (transformation->ortho) {
@@ -316,6 +357,15 @@ gst_gl_transformation_set_property (GObject * object, guint prop_id,
     case PROP_SCALE_Y:
       filter->yscale = g_value_get_float (value);
       break;
+    case PROP_PIVOT_X:
+      filter->xpivot = g_value_get_float (value);
+      break;
+    case PROP_PIVOT_Y:
+      filter->ypivot = g_value_get_float (value);
+      break;
+    case PROP_PIVOT_Z:
+      filter->zpivot = g_value_get_float (value);
+      break;
     case PROP_MVP:
       if (g_value_get_boxed (value) != NULL)
         filter->mvp_matrix = *((graphene_matrix_t *) g_value_get_boxed (value));
@@ -365,6 +415,15 @@ gst_gl_transformation_get_property (GObject * object, guint prop_id,
     case PROP_SCALE_Y:
       g_value_set_float (value, filter->yscale);
       break;
+    case PROP_PIVOT_X:
+      g_value_set_float (value, filter->xpivot);
+      break;
+    case PROP_PIVOT_Y:
+      g_value_set_float (value, filter->ypivot);
+      break;
+    case PROP_PIVOT_Z:
+      g_value_set_float (value, filter->zpivot);
+      break;
     case PROP_MVP:
       g_value_set_boxed (value, (gconstpointer) & filter->mvp_matrix);
       break;

ext/gl/gstgltransformation.h

@@ -60,6 +60,10 @@ struct _GstGLTransformation
     gfloat ytranslation;
     gfloat ztranslation;
 
+    gfloat xpivot;
+    gfloat ypivot;
+    gfloat zpivot;
+
     /* perspective */
     gfloat fov;
     gfloat aspect;