From de6c6501f0eec38287222f0e9e641cf3fed18eba Mon Sep 17 00:00:00 2001
From: YimingWu <xp8110@outlook.com>
Date: Thu, 24 Jun 2021 13:15:09 +0800
Subject: LineArt: Bound box visibility check when loading

This patch enables bound box check when loading geometry
into line art. Works with overscan as well. Will discard
object if its bbox completely lies in one side of the
clipping space frustum.

Reviewed by: Sebastian Parborg (zeddb)

Differential Revision: https://developer.blender.org/D11545
---
 .../gpencil_modifiers/intern/lineart/lineart_cpu.c | 59 +++++++++++++++++++---
 1 file changed, 53 insertions(+), 6 deletions(-)

diff --git a/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c b/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
index c00bd7c1cb5..0b5003e5f2d 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
+++ b/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
@@ -43,6 +43,7 @@
 #include "BKE_gpencil_modifier.h"
 #include "BKE_material.h"
 #include "BKE_mesh.h"
+#include "BKE_object.h"
 #include "BKE_pointcache.h"
 #include "BKE_scene.h"
 #include "DEG_depsgraph_query.h"
@@ -1903,6 +1904,41 @@ static void lineart_geometry_load_assign_thread(LineartObjectLoadTaskInfo *olti_
   use_olti->pending = obi;
 }
 
+static bool lineart_geometry_check_visible(double (*model_view_proj)[4], Object *use_ob)
+{
+  BoundBox *bb = BKE_object_boundbox_get(use_ob);
+  if (!bb) {
+    /* For lights and empty stuff there will be no bbox. */
+    return false;
+  }
+
+  double co[8][4];
+  double tmp[3];
+  for (int i = 0; i < 8; i++) {
+    copy_v3db_v3fl(co[i], bb->vec[i]);
+    copy_v3_v3_db(tmp, co[i]);
+    mul_v4_m4v3_db(co[i], model_view_proj, tmp);
+  }
+
+  bool cond[6] = {true, true, true, true, true, true};
+  /* Beause for a point to be inside clip space, it must satisfy -Wc <= XYCc <= Wc, here if all
+   * verts falls to the same side of the clip space border, we know it's outside view. */
+  for (int i = 0; i < 8; i++) {
+    cond[0] &= (co[i][0] < -co[i][3]);
+    cond[1] &= (co[i][0] > co[i][3]);
+    cond[2] &= (co[i][1] < -co[i][3]);
+    cond[3] &= (co[i][1] > co[i][3]);
+    cond[4] &= (co[i][2] < -co[i][3]);
+    cond[5] &= (co[i][2] > co[i][3]);
+  }
+  for (int i = 0; i < 6; i++) {
+    if (cond[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
 static void lineart_main_load_geometries(
     Depsgraph *depsgraph,
     Scene *scene,
@@ -1923,6 +1959,7 @@ static void lineart_main_load_geometries(
   if (G.debug_value == 4000) {
     t_start = PIL_check_seconds_timer();
   }
+  int bound_box_discard_count = 0;
 
   if (cam->type == CAM_PERSP) {
     if (fit == CAMERA_SENSOR_FIT_VERT && asp > 1) {
@@ -1974,16 +2011,27 @@ static void lineart_main_load_geometries(
     }
 
     Object *use_ob = DEG_get_evaluated_object(depsgraph, ob);
+    /* Prepare the matrix used for transforming this specific object (instance). This has to be
+     * done before mesh boundbox check because the function needs that.  */
+    mul_m4db_m4db_m4fl_uniq(obi->model_view_proj, rb->view_projection, ob->obmat);
+    mul_m4db_m4db_m4fl_uniq(obi->model_view, rb->view, ob->obmat);
 
-    if (!(use_ob->type == OB_MESH || use_ob->type == OB_MBALL || use_ob->type == OB_CURVE ||
-          use_ob->type == OB_SURF || use_ob->type == OB_FONT)) {
+    if (!ELEM(use_ob->type, OB_MESH, OB_MBALL, OB_CURVE, OB_SURF, OB_FONT)) {
       continue;
     }
+
+    if (!lineart_geometry_check_visible(obi->model_view_proj, use_ob)) {
+      if (G.debug_value == 4000) {
+        bound_box_discard_count++;
+      }
+      continue;
+    }
+
     if (use_ob->type == OB_MESH) {
       use_mesh = use_ob->data;
     }
     else {
-      use_mesh = BKE_mesh_new_from_object(NULL, use_ob, false, true);
+      use_mesh = BKE_mesh_new_from_object(depsgraph, use_ob, true, true);
     }
 
     /* In case we still can not get any mesh geometry data from the object */
@@ -1995,9 +2043,7 @@ static void lineart_main_load_geometries(
       obi->free_use_mesh = true;
     }
 
-    /* Prepare the matrix used for transforming this specific object (instance).  */
-    mul_m4db_m4db_m4fl_uniq(obi->model_view_proj, rb->view_projection, ob->obmat);
-    mul_m4db_m4db_m4fl_uniq(obi->model_view, rb->view, ob->obmat);
+    /* Make normal matrix.  */
     float imat[4][4];
     invert_m4_m4(imat, ob->obmat);
     transpose_m4(imat);
@@ -2041,6 +2087,7 @@ static void lineart_main_load_geometries(
   if (G.debug_value == 4000) {
     double t_elapsed = PIL_check_seconds_timer() - t_start;
     printf("Line art loading time: %lf\n", t_elapsed);
+    printf("Discarded %d object from bound box check\n", bound_box_discard_count);
   }
 }
 
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