EEVEE-Next: Irradiance Bake: Virtual Offset

This implement virtual offset as described in the reference material.

A quick prepass runs before the baking to offset the samples away
from any surface that could potentially make bad samples.

In order to speedup the process, we create cluster list of surfels
near each irradiance grid point. This allow access to neighboring
surfels that can contribute to the virtual offset which should
never be more than half a cell wide.

@@ -99,0 +111,4 @@
+   */
+  float min_distance_to_surface_ = 0.05f;
+  /**
+   * Maximum distance from the grid sample point a recording location.

@@ -0,0 +1,5 @@
+

@@ -0,0 +22,4 @@
+    Surfel surfel = surfel_buf[surfel_id];
+
+    vec3 probe_to_surfel = surfel.position - P;
+    float surfel_dist = length(probe_to_surfel);

@@ -0,0 +75,4 @@
+    vec3 probe_to_surfel = surfel.position - P;
+    float surf_dist = dot(offset_direction, probe_to_surfel);
+    /* Do not consider surfels that are outside of search radius. */
+    if (surf_dist > search_radius) {

@@ -19,1 +20,4 @@
 }
+
+/**
+ * Return the coresponding cluster index in the `cluster_list_tx` for a given world position.