GPencil and Annotation: Use cached depth to perform depth testing operations

Operations such as erasing with occlusion and drawing on the surface
require reading the depth buffer.

However, this is being done with minimal efficiency.

Currently, to read the depth corresponding to each point of the new stroke,
a ReadPixel is called to send a message to the GPU and read the depth of
the corresponding pixel in the VRAM.

The communication between GPU and CPU is known to be a slow operation so
it is good to be avoided.

Therefore, save the entire depth buffer in a cache to be read directly
from the RAM.

(Also the `ED_view3d_autodist_depth` and `ED_view3d_autodist_depth_seg` have
been removed since they are no longer used).

Reviewed By: antoniov, fclem

Differential Revision: https://developer.blender.org/D10894

8 files changed, 65 insertions, 42 deletions

diff --git a/source/blender/editors/gpencil/annotate_paint.c b/source/blender/editors/gpencil/annotate_paint.c
index ba603cdd6ec..bdb4e485373 100644
--- a/source/blender/editors/gpencil/annotate_paint.c
+++ b/source/blender/editors/gpencil/annotate_paint.c
@@ -123,6 +123,8 @@ typedef struct tGPsdata {
   ARegion *region;
   /** needed for GP_STROKE_2DSPACE. */
   View2D *v2d;
+  /** For operations that require occlusion testing. */
+  ViewDepths *depths;
   /** for using the camera rect within the 3d view. */
   rctf *subrect;
   rctf subrect_data;
@@ -972,12 +974,13 @@ static void annotation_stroke_newfrombuffer(tGPsdata *p)
 
       depth_arr = MEM_mallocN(sizeof(float) * gpd->runtime.sbuffer_used, "depth_points");
 
+      const ViewDepths *depths = p->depths;
       for (i = 0, ptc = gpd->runtime.sbuffer; i < gpd->runtime.sbuffer_used; i++, ptc++, pt++) {
         round_v2i_v2fl(mval_i, &ptc->x);
 
-        if ((ED_view3d_autodist_depth(p->region, mval_i, depth_margin, depth_arr + i) == 0) &&
-            (i && (ED_view3d_autodist_depth_seg(
-                       p->region, mval_i, mval_prev, depth_margin + 1, depth_arr + i) == 0))) {
+        if ((ED_view3d_depth_read_cached(depths, mval_i, depth_margin, depth_arr + i) == 0) &&
+            (i && (ED_view3d_depth_read_cached_seg(
+                       depths, mval_i, mval_prev, depth_margin + 1, depth_arr + i) == 0))) {
           interp_depth = true;
         }
         else {
@@ -1086,7 +1089,10 @@ static bool annotation_stroke_eraser_is_occluded(tGPsdata *p,
     const int mval_i[2] = {x, y};
     float mval_3d[3];
 
-    if (ED_view3d_autodist_simple(p->region, mval_i, mval_3d, 0, NULL)) {
+    float p_depth;
+    if (ED_view3d_depth_read_cached(p->depths, mval_i, 0, &p_depth)) {
+      ED_view3d_depth_unproject_v3(p->region, mval_i, (double)p_depth, mval_3d);
+
       const float depth_mval = ED_view3d_calc_depth_for_comparison(rv3d, mval_3d);
       const float depth_pt = ED_view3d_calc_depth_for_comparison(rv3d, &pt->x);
 
@@ -1211,7 +1217,8 @@ static void annotation_stroke_doeraser(tGPsdata *p)
     if (p->flags & GP_PAINTFLAG_V3D_ERASER_DEPTH) {
       View3D *v3d = p->area->spacedata.first;
       view3d_region_operator_needs_opengl(p->win, p->region);
-      ED_view3d_depth_override(p->depsgraph, p->region, v3d, NULL, V3D_DEPTH_NO_GPENCIL, NULL);
+      ED_view3d_depth_override(
+          p->depsgraph, p->region, v3d, NULL, V3D_DEPTH_NO_GPENCIL, &p->depths);
     }
   }
 
@@ -1499,6 +1506,9 @@ static void annotation_session_cleanup(tGPsdata *p)
 
 static void annotation_session_free(tGPsdata *p)
 {
+  if (p->depths) {
+    ED_view3d_depths_free(p->depths);
+  }
   MEM_freeN(p);
 }
 
diff --git a/source/blender/editors/gpencil/gpencil_fill.c b/source/blender/editors/gpencil/gpencil_fill.c
index 1b69947b294..9860c75f290 100644
--- a/source/blender/editors/gpencil/gpencil_fill.c
+++ b/source/blender/editors/gpencil/gpencil_fill.c
@@ -127,6 +127,8 @@ typedef struct tGPDfill {
   struct bGPDstroke *gps_mouse;
   /** Pointer to report messages. */
   struct ReportList *reports;
+  /** For operations that require occlusion testing. */
+  struct ViewDepths *depths;
   /** flags */
   short flag;
   /** avoid too fast events */
@@ -1374,7 +1376,7 @@ static void gpencil_get_depth_array(tGPDfill *tgpf)
     /* need to restore the original projection settings before packing up */
     view3d_region_operator_needs_opengl(tgpf->win, tgpf->region);
     ED_view3d_depth_override(
-        tgpf->depsgraph, tgpf->region, tgpf->v3d, NULL, V3D_DEPTH_NO_GPENCIL, NULL);
+        tgpf->depsgraph, tgpf->region, tgpf->v3d, NULL, V3D_DEPTH_NO_GPENCIL, &tgpf->depths);
 
     /* Since strokes are so fine, when using their depth we need a margin
      * otherwise they might get missed. */
@@ -1385,6 +1387,7 @@ static void gpencil_get_depth_array(tGPDfill *tgpf)
     int interp_depth = 0;
     int found_depth = 0;
 
+    const ViewDepths *depths = tgpf->depths;
     tgpf->depth_arr = MEM_mallocN(sizeof(float) * totpoints, "depth_points");
 
     for (i = 0, ptc = tgpf->sbuffer; i < totpoints; i++, ptc++) {
@@ -1392,11 +1395,9 @@ static void gpencil_get_depth_array(tGPDfill *tgpf)
       int mval_i[2];
       round_v2i_v2fl(mval_i, &ptc->x);
 
-      if ((ED_view3d_autodist_depth(tgpf->region, mval_i, depth_margin, tgpf->depth_arr + i) ==
-           0) &&
-          (i &&
-           (ED_view3d_autodist_depth_seg(
-                tgpf->region, mval_i, mval_prev, depth_margin + 1, tgpf->depth_arr + i) == 0))) {
+      if ((ED_view3d_depth_read_cached(depths, mval_i, depth_margin, tgpf->depth_arr + i) == 0) &&
+          (i && (ED_view3d_depth_read_cached_seg(
+                     depths, mval_i, mval_prev, depth_margin + 1, tgpf->depth_arr + i) == 0))) {
         interp_depth = true;
       }
       else {
@@ -1771,6 +1772,11 @@ static void gpencil_fill_exit(bContext *C, wmOperator *op)
       ED_region_draw_cb_exit(tgpf->region->type, tgpf->draw_handle_3d);
     }
 
+    /* Remove depth buffer in cache. */
+    if (tgpf->depths) {
+      ED_view3d_depths_free(tgpf->depths);
+    }
+
     /* finally, free memory used by temp data */
     MEM_freeN(tgpf);
   }
diff --git a/source/blender/editors/gpencil/gpencil_intern.h b/source/blender/editors/gpencil/gpencil_intern.h
index b6730cb123b..3f3fd4fff39 100644
--- a/source/blender/editors/gpencil/gpencil_intern.h
+++ b/source/blender/editors/gpencil/gpencil_intern.h
@@ -155,6 +155,8 @@ typedef struct tGPDprimitive {
   struct Material *material;
   /** current brush */
   struct Brush *brush;
+  /** For operations that require occlusion testing. */
+  struct ViewDepths *depths;
 
   /** Settings to pass to gp_points_to_xy(). */
   GP_SpaceConversion gsc;
diff --git a/source/blender/editors/gpencil/gpencil_paint.c b/source/blender/editors/gpencil/gpencil_paint.c
index 3e9f22f25d3..f37f2cd549f 100644
--- a/source/blender/editors/gpencil/gpencil_paint.c
+++ b/source/blender/editors/gpencil/gpencil_paint.c
@@ -161,6 +161,8 @@ typedef struct tGPsdata {
   ARegion *region;
   /** needed for GP_STROKE_2DSPACE. */
   View2D *v2d;
+  /** For operations that require occlusion testing. */
+  ViewDepths *depths;
   /** for using the camera rect within the 3d view. */
   rctf *subrect;
   rctf subrect_data;
@@ -1090,14 +1092,16 @@ static void gpencil_stroke_newfrombuffer(tGPsdata *p)
       int found_depth = 0;
 
       depth_arr = MEM_mallocN(sizeof(float) * gpd->runtime.sbuffer_used, "depth_points");
+
+      const ViewDepths *depths = p->depths;
       int i;
       for (i = 0, ptc = gpd->runtime.sbuffer; i < gpd->runtime.sbuffer_used; i++, ptc++, pt++) {
 
         round_v2i_v2fl(mval_i, &ptc->x);
 
-        if ((ED_view3d_autodist_depth(p->region, mval_i, depth_margin, depth_arr + i) == 0) &&
-            (i && (ED_view3d_autodist_depth_seg(
-                       p->region, mval_i, mval_prev, depth_margin + 1, depth_arr + i) == 0))) {
+        if ((ED_view3d_depth_read_cached(depths, mval_i, depth_margin, depth_arr + i) == 0) &&
+            (i && (ED_view3d_depth_read_cached_seg(
+                       depths, mval_i, mval_prev, depth_margin + 1, depth_arr + i) == 0))) {
           interp_depth = true;
         }
         else {
@@ -1346,7 +1350,10 @@ static bool gpencil_stroke_eraser_is_occluded(
     /* calculate difference matrix if parent object */
     BKE_gpencil_layer_transform_matrix_get(p->depsgraph, obact, gpl, diff_mat);
 
-    if (ED_view3d_autodist_simple(p->region, mval_i, mval_3d, 0, NULL)) {
+    float p_depth;
+    if (ED_view3d_depth_read_cached(p->depths, mval_i, 0, &p_depth)) {
+      ED_view3d_depth_unproject_v3(p->region, mval_i, (double)p_depth, mval_3d);
+
       const float depth_mval = ED_view3d_calc_depth_for_comparison(rv3d, mval_3d);
 
       mul_v3_m4v3(fpt, diff_mat, &pt->x);
@@ -1733,7 +1740,7 @@ static void gpencil_stroke_doeraser(tGPsdata *p)
   if ((gp_settings != NULL) && (gp_settings->flag & GP_BRUSH_OCCLUDE_ERASER)) {
     View3D *v3d = p->area->spacedata.first;
     view3d_region_operator_needs_opengl(p->win, p->region);
-    ED_view3d_depth_override(p->depsgraph, p->region, v3d, NULL, V3D_DEPTH_NO_GPENCIL, NULL);
+    ED_view3d_depth_override(p->depsgraph, p->region, v3d, NULL, V3D_DEPTH_NO_GPENCIL, &p->depths);
   }
 
   /* loop over all layers too, since while it's easy to restrict editing to
@@ -2087,6 +2094,9 @@ static void gpencil_session_free(tGPsdata *p)
   if (p->rng != NULL) {
     BLI_rng_free(p->rng);
   }
+  if (p->depths != NULL) {
+    ED_view3d_depths_free(p->depths);
+  }
 
   MEM_freeN(p);
 }
diff --git a/source/blender/editors/gpencil/gpencil_primitive.c b/source/blender/editors/gpencil/gpencil_primitive.c
index f8cfc130e35..7382aca9a87 100644
--- a/source/blender/editors/gpencil/gpencil_primitive.c
+++ b/source/blender/editors/gpencil/gpencil_primitive.c
@@ -795,15 +795,16 @@ static void gpencil_primitive_update_strokes(bContext *C, tGPDprimitive *tgpi)
                              (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE) ?
                                  V3D_DEPTH_GPENCIL_ONLY :
                                  V3D_DEPTH_NO_GPENCIL,
-                             NULL);
+                             &tgpi->depths);
 
     depth_arr = MEM_mallocN(sizeof(float) * gps->totpoints, "depth_points");
+    const ViewDepths *depths = tgpi->depths;
     tGPspoint *ptc = &points2D[0];
     for (int i = 0; i < gps->totpoints; i++, ptc++) {
       round_v2i_v2fl(mval_i, &ptc->x);
-      if ((ED_view3d_autodist_depth(tgpi->region, mval_i, depth_margin, depth_arr + i) == 0) &&
-          (i && (ED_view3d_autodist_depth_seg(
-                     tgpi->region, mval_i, mval_prev, depth_margin + 1, depth_arr + i) == 0))) {
+      if ((ED_view3d_depth_read_cached(depths, mval_i, depth_margin, depth_arr + i) == 0) &&
+          (i && (ED_view3d_depth_read_cached_seg(
+                     depths, mval_i, mval_prev, depth_margin + 1, depth_arr + i) == 0))) {
         interp_depth = true;
       }
       else {
@@ -1154,6 +1155,11 @@ static void gpencil_primitive_exit(bContext *C, wmOperator *op)
       BLI_rng_free(tgpi->rng);
     }
 
+    /* Remove depth buffer in cache. */
+    if (tgpi->depths) {
+      ED_view3d_depths_free(tgpi->depths);
+    }
+
     MEM_freeN(tgpi);
   }
 
diff --git a/source/blender/editors/gpencil/gpencil_utils.c b/source/blender/editors/gpencil/gpencil_utils.c
index d3640c6eebd..c4319fd7ee2 100644
--- a/source/blender/editors/gpencil/gpencil_utils.c
+++ b/source/blender/editors/gpencil/gpencil_utils.c
@@ -979,7 +979,7 @@ bool gpencil_point_xy_to_3d(const GP_SpaceConversion *gsc,
  * to 3D coordinates.
  *
  * \param point2D: The screen-space 2D point data to convert.
- * \param depth: Depth array (via #ED_view3d_autodist_depth()).
+ * \param depth: Depth array (via #ED_view3d_depth_read_cached()).
  * \param r_out: The resulting 2D point data.
  */
 void gpencil_stroke_convertcoords_tpoint(Scene *scene,
diff --git a/source/blender/editors/include/ED_view3d.h b/source/blender/editors/include/ED_view3d.h
index ebf3316a509..f9ccd916327 100644
--- a/source/blender/editors/include/ED_view3d.h
+++ b/source/blender/editors/include/ED_view3d.h
@@ -609,12 +609,8 @@ bool ED_view3d_autodist_simple(struct ARegion *region,
                                float mouse_worldloc[3],
                                int margin,
                                const float *force_depth);
-bool ED_view3d_autodist_depth(struct ARegion *region, const int mval[2], int margin, float *depth);
-bool ED_view3d_autodist_depth_seg(struct ARegion *region,
-                                  const int mval_sta[2],
-                                  const int mval_end[2],
-                                  int margin,
-                                  float *depth);
+bool ED_view3d_depth_read_cached_seg(
+    const ViewDepths *vd, const int mval_sta[2], const int mval_end[2], int margin, float *depth);
 
 /* select */
 #define MAXPICKELEMS 2500
diff --git a/source/blender/editors/space_view3d/view3d_utils.c b/source/blender/editors/space_view3d/view3d_utils.c
index e09453b9957..dab1b55072a 100644
--- a/source/blender/editors/space_view3d/view3d_utils.c
+++ b/source/blender/editors/space_view3d/view3d_utils.c
@@ -1094,17 +1094,10 @@ bool ED_view3d_autodist_simple(ARegion *region,
   return ED_view3d_unproject_v3(region, centx, centy, depth, mouse_worldloc);
 }
 
-bool ED_view3d_autodist_depth(ARegion *region, const int mval[2], int margin, float *depth)
-{
-  *depth = view_autodist_depth_margin(region, mval, margin);
-
-  return (*depth != FLT_MAX);
-}
-
 static bool depth_segment_cb(int x, int y, void *userData)
 {
   struct {
-    ARegion *region;
+    const ViewDepths *vd;
     int margin;
     float depth;
   } *data = userData;
@@ -1114,27 +1107,25 @@ static bool depth_segment_cb(int x, int y, void *userData)
   mval[0] = x;
   mval[1] = y;
 
-  depth = view_autodist_depth_margin(data->region, mval, data->margin);
-
-  if (depth != FLT_MAX) {
+  if (ED_view3d_depth_read_cached(data->vd, mval, data->margin, &depth)) {
     data->depth = depth;
     return false;
   }
   return true;
 }
 
-bool ED_view3d_autodist_depth_seg(
-    ARegion *region, const int mval_sta[2], const int mval_end[2], int margin, float *depth)
+bool ED_view3d_depth_read_cached_seg(
+    const ViewDepths *vd, const int mval_sta[2], const int mval_end[2], int margin, float *depth)
 {
   struct {
-    ARegion *region;
+    const ViewDepths *vd;
     int margin;
     float depth;
   } data = {NULL};
   int p1[2];
   int p2[2];
 
-  data.region = region;
+  data.vd = vd;
   data.margin = margin;
   data.depth = FLT_MAX;
 
@@ -1691,6 +1682,8 @@ bool ED_view3d_depth_read_cached(const ViewDepths *vd,
     return true;
   }
 
+  /* GPencil and Anotations also need the returned depth value to be high so that it is invalid. */
+  *r_depth = FLT_MAX;
   return false;
 }