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

1 files changed, 15 insertions, 5 deletions

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);
 }