Realtime Compositor: Implement Anisotropic Kuwahara

This patch implements the Anisotropic Kuwahara filter for the realtime
compositor.

- [ ] Fix noisy minimum eigenvector.
- [ ] Expose Eccentricity and Sharpness to the user.

@@ -996,6 +996,8 @@ typedef struct NodeKuwaharaData {
   short size;
   short variation;
   int smoothing;

@@ -24,0 +31,4 @@
+
+GPU_SHADER_CREATE_INFO(compositor_kuwahara_anisotropic)
+    .local_group_size(16, 16)
+    .push_constant(Type::INT, "radius")

@@ -24,0 +32,4 @@
+GPU_SHADER_CREATE_INFO(compositor_kuwahara_anisotropic)
+    .local_group_size(16, 16)
+    .push_constant(Type::INT, "radius")
+    .push_constant(Type::FLOAT, "eccentricity")

@@ -0,0 +150,4 @@
+      vec2 rotated_disk_point = M_SQRT1_2 *
+                                vec2(disk_point.x - disk_point.y, disk_point.x + disk_point.y);
+
+      /* Finally, we compute the other every other 4 weights starting from the 45 degreed rotated

@@ -0,0 +1,40 @@
+#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
+

@@ -149,0 +237,4 @@
+   *
+   * Since the anisotropy is in the [0, 1] range, the factor tends to 1 as the eccentricity tends
+   * to infinity and tends to infinity when the eccentricity tends to zero. The stored eccentricity
+   * is in the range [0, 2], we map that to the range [infinity, 0.5] by taking the reciprocal,

@@ -101,0 +126,4 @@
+  /* Compute the overlap polynomial parameters for 8-sector ellipse based on the equations in
+   * section "3 Alternative Weighting Functions" of the polynomial weights paper. More on this
+   * later in the code. */
+  int number_of_sectors = 8;

@@ -0,0 +30,4 @@
+  /* Compute the first and second eigenvalues of the structure tensor using the equations in
+   * section "3.1 Orientation and Anisotropy Estimation" of the paper. */
+  float eigenvalue_first_term = (dxdx + dydy) / 2.0;
+  float eigenvalue_square_root_term = sqrt(pow(dxdx - dydy, 2.0) + 4.0 * pow(dxdy, 2.0)) / 2.0;

@@ -0,0 +87,4 @@
+  /* Compute the overlap polynomial parameters for 8-sector ellipse based on the equations in
+   * section "3 Alternative Weighting Functions" of the polynomial weights paper. More on this
+   * later in the code. */
+  int number_of_sectors = 8;

@@ -0,0 +14,4 @@
+
+  /* The weight kernels of the filter optimized for rotational symmetry described in section "3.2.1
+   * Gradient Calculation". */
+  float corner_weight = 0.182;

@@ -0,0 +33,4 @@
+
+  /* We encode the structure tensor in a vec4 using a column major storage order. */
+  vec4 structure_tensor = vec4(dot(x_partial_derivative, x_partial_derivative),
+                               dot(x_partial_derivative, y_partial_derivative),