EEVEE Next: GI surfels debug display

First step to help with the GI implementation development.

@@ -142,6 +142,7 @@ set(SRC
   engines/eevee_next/eevee_depth_of_field.cc
   engines/eevee_next/eevee_engine.cc
   engines/eevee_next/eevee_film.cc
+  engines/eevee_next/eevee_gi.cc

@@ -448,6 +450,8 @@ set(GLSL_SRC
   engines/eevee_next/shaders/eevee_geom_gpencil_vert.glsl
   engines/eevee_next/shaders/eevee_geom_mesh_vert.glsl
   engines/eevee_next/shaders/eevee_geom_world_vert.glsl
+  engines/eevee_next/shaders/eevee_gi_debug_surfels_vert.glsl

@@ -119,6 +119,7 @@
 #define LIGHT_BUF_SLOT 1
 #define LIGHT_ZBIN_BUF_SLOT 2
 #define LIGHT_TILE_BUF_SLOT 3
+#define GI_SURFEL_BUF_SLOT 4

@@ -0,0 +28,4 @@
+void GI::init()
+{
+  if (debug_surfels_sh_ == nullptr) {
+    debug_surfels_sh_ = GPU_shader_create_from_info_name("eevee_gi_debug_surfels");

@@ -0,0 +8,4 @@
+
+class Instance;
+
+class GI {

@@ -51,3 +55,4 @@
   /**
    * Show tiles depending on their status.
    */
+

@@ -822,2 +827,4 @@
 /** \} */
 
+/* -------------------------------------------------------------------- */
+/** \name GI

@@ -824,0 +830,4 @@
+/** \name GI
+ * \{ */
+
+struct Surfel {

@@ -824,0 +831,4 @@
+ * \{ */
+
+struct Surfel {
+  float3 position;

@@ -0,0 +6,4 @@
+  surfel_index = gl_InstanceID;
+  Surfel surfel = surfels_buf[surfel_index];
+
+  const vec3 verts[4] = vec3[4](vec3(-1, 1, 0), vec3(-1, -1, 0), vec3(1, 1, 0), vec3(1, -1, 0));

@@ -303,7 +303,6 @@ if(WITH_METAL_BACKEND)
   list(APPEND SRC ${METAL_SRC})
 endif()
 
-

@@ -824,0 +830,4 @@
+/** \name GI
+ * \{ */
+
+struct Surfel {

@@ -119,6 +119,7 @@
 #define LIGHT_BUF_SLOT 1
 #define LIGHT_ZBIN_BUF_SLOT 2
 #define LIGHT_TILE_BUF_SLOT 3
+#define GI_SURFEL_BUF_SLOT 4

@@ -119,6 +119,7 @@
 #define LIGHT_BUF_SLOT 1
 #define LIGHT_ZBIN_BUF_SLOT 2
 #define LIGHT_TILE_BUF_SLOT 3
+#define GI_SURFEL_BUF_SLOT 4

@@ -824,0 +830,4 @@
+/** \name GI
+ * \{ */
+
+struct Surfel {