OpenSubDiv: add support for an OpenGL evaluator

This evaluator is used in order to evaluate subdivision at render time, allowing for
faster renders of meshes with a subdivision surface modifier placed at the last
position in the modifier list.

When evaluating the subsurf modifier, we detect whether we can delegate evaluation
to the draw code. If so, the subdivision is first evaluated on the GPU using our own
custom evaluator (only the coarse data needs to be initially sent to the GPU), then,
buffers for the final `MeshBufferCache` are filled on the GPU using a set of
compute shaders. However, some buffers are still filled on the CPU side, if doing so
on the GPU is impractical (e.g. the line adjacency buffer used for x-ray, whose
logic is hardly GPU compatible).

This is done at the mesh buffer extraction level so that the result can be readily used
in the various OpenGL engines, without having to write custom geometry or tesselation
shaders.

We use our own subdivision evaluation shaders, instead of OpenSubDiv's vanilla one, in
order to control the data layout, and interpolation. For example, we store vertex colors
as compressed 16-bit integers, while OpenSubDiv's default evaluator only work for float
types.

In order to still access the modified geometry on the CPU side, for use in modifiers
or transform operators, a dedicated wrapper type is added `MESH_WRAPPER_TYPE_SUBD`.
Subdivision will be lazily evaluated via `BKE_object_get_evaluated_mesh` which will
create such a wrapper if possible. If the final subdivision surface is not needed on
the CPU side, `BKE_object_get_evaluated_mesh_no_subsurf` should be used.

Enabling or disabling GPU subdivision can be done through the user preferences (under
Viewport -> Subdivision).

See patch description for benchmarks.

Reviewed By: campbellbarton, jbakker, fclem, brecht, #eevee_viewport

Differential Revision: https://developer.blender.org/D12406

1 files changed, 94 insertions, 18 deletions

diff --git a/source/blender/blenkernel/intern/subdiv_eval.c b/source/blender/blenkernel/intern/subdiv_eval.c
index 0001eb8a205..9733a1498a6 100644
--- a/source/blender/blenkernel/intern/subdiv_eval.c
+++ b/source/blender/blenkernel/intern/subdiv_eval.c
@@ -28,6 +28,7 @@
 
 #include "BLI_bitmap.h"
 #include "BLI_math_vector.h"
+#include "BLI_task.h"
 #include "BLI_utildefines.h"
 
 #include "BKE_customdata.h"
@@ -38,7 +39,28 @@
 #include "opensubdiv_evaluator_capi.h"
 #include "opensubdiv_topology_refiner_capi.h"
 
-bool BKE_subdiv_eval_begin(Subdiv *subdiv)
+/* ============================  Helper Function ============================ */
+
+static eOpenSubdivEvaluator opensubdiv_evalutor_from_subdiv_evaluator_type(
+    eSubdivEvaluatorType evaluator_type)
+{
+  switch (evaluator_type) {
+    case SUBDIV_EVALUATOR_TYPE_CPU: {
+      return OPENSUBDIV_EVALUATOR_CPU;
+    }
+    case SUBDIV_EVALUATOR_TYPE_GLSL_COMPUTE: {
+      return OPENSUBDIV_EVALUATOR_GLSL_COMPUTE;
+    }
+  }
+  BLI_assert_msg(0, "Unknown evaluator type");
+  return OPENSUBDIV_EVALUATOR_CPU;
+}
+
+/* ======================  Main Subdivision Evaluation ====================== */
+
+bool BKE_subdiv_eval_begin(Subdiv *subdiv,
+                           eSubdivEvaluatorType evaluator_type,
+                           OpenSubdiv_EvaluatorCache *evaluator_cache)
 {
   BKE_subdiv_stats_reset(&subdiv->stats, SUBDIV_STATS_EVALUATOR_CREATE);
   if (subdiv->topology_refiner == NULL) {
@@ -47,8 +69,11 @@ bool BKE_subdiv_eval_begin(Subdiv *subdiv)
     return false;
   }
   if (subdiv->evaluator == NULL) {
+    eOpenSubdivEvaluator opensubdiv_evaluator_type =
+        opensubdiv_evalutor_from_subdiv_evaluator_type(evaluator_type);
     BKE_subdiv_stats_begin(&subdiv->stats, SUBDIV_STATS_EVALUATOR_CREATE);
-    subdiv->evaluator = openSubdiv_createEvaluatorFromTopologyRefiner(subdiv->topology_refiner);
+    subdiv->evaluator = openSubdiv_createEvaluatorFromTopologyRefiner(
+        subdiv->topology_refiner, opensubdiv_evaluator_type, evaluator_cache);
     BKE_subdiv_stats_end(&subdiv->stats, SUBDIV_STATS_EVALUATOR_CREATE);
     if (subdiv->evaluator == NULL) {
       return false;
@@ -80,6 +105,9 @@ static void set_coarse_positions(Subdiv *subdiv,
       BLI_BITMAP_ENABLE(vertex_used_map, loop->v);
     }
   }
+  /* Use a temporary buffer so we do not upload vertices one at a time to the GPU. */
+  float(*buffer)[3] = MEM_mallocN(sizeof(float[3]) * mesh->totvert, "subdiv tmp coarse positions");
+  int manifold_vertex_count = 0;
   for (int vertex_index = 0, manifold_vertex_index = 0; vertex_index < mesh->totvert;
        vertex_index++) {
     if (!BLI_BITMAP_TEST_BOOL(vertex_used_map, vertex_index)) {
@@ -93,13 +121,49 @@ static void set_coarse_positions(Subdiv *subdiv,
       const MVert *vertex = &mvert[vertex_index];
       vertex_co = vertex->co;
     }
-    subdiv->evaluator->setCoarsePositions(subdiv->evaluator, vertex_co, manifold_vertex_index, 1);
+    copy_v3_v3(&buffer[manifold_vertex_index][0], vertex_co);
     manifold_vertex_index++;
+    manifold_vertex_count++;
   }
+  subdiv->evaluator->setCoarsePositions(
+      subdiv->evaluator, &buffer[0][0], 0, manifold_vertex_count);
   MEM_freeN(vertex_used_map);
+  MEM_freeN(buffer);
+}
+
+/* Context which is used to fill face varying data in parallel. */
+typedef struct FaceVaryingDataFromUVContext {
+  OpenSubdiv_TopologyRefiner *topology_refiner;
+  const Mesh *mesh;
+  const MLoopUV *mloopuv;
+  float (*buffer)[2];
+  int layer_index;
+} FaceVaryingDataFromUVContext;
+
+static void set_face_varying_data_from_uv_task(void *__restrict userdata,
+                                               const int face_index,
+                                               const TaskParallelTLS *__restrict UNUSED(tls))
+{
+  FaceVaryingDataFromUVContext *ctx = userdata;
+  OpenSubdiv_TopologyRefiner *topology_refiner = ctx->topology_refiner;
+  const int layer_index = ctx->layer_index;
+  const Mesh *mesh = ctx->mesh;
+  const MPoly *mpoly = &mesh->mpoly[face_index];
+  const MLoopUV *mluv = &ctx->mloopuv[mpoly->loopstart];
+
+  /* TODO(sergey): OpenSubdiv's C-API converter can change winding of
+   * loops of a face, need to watch for that, to prevent wrong UVs assigned.
+   */
+  const int num_face_vertices = topology_refiner->getNumFaceVertices(topology_refiner, face_index);
+  const int *uv_indices = topology_refiner->getFaceFVarValueIndices(
+      topology_refiner, face_index, layer_index);
+  for (int vertex_index = 0; vertex_index < num_face_vertices; vertex_index++, mluv++) {
+    copy_v2_v2(ctx->buffer[uv_indices[vertex_index]], mluv->uv);
+  }
 }
 
 static void set_face_varying_data_from_uv(Subdiv *subdiv,
+                                          const Mesh *mesh,
                                           const MLoopUV *mloopuv,
                                           const int layer_index)
 {
@@ -107,25 +171,37 @@ static void set_face_varying_data_from_uv(Subdiv *subdiv,
   OpenSubdiv_Evaluator *evaluator = subdiv->evaluator;
   const int num_faces = topology_refiner->getNumFaces(topology_refiner);
   const MLoopUV *mluv = mloopuv;
-  /* TODO(sergey): OpenSubdiv's C-API converter can change winding of
-   * loops of a face, need to watch for that, to prevent wrong UVs assigned.
-   */
-  for (int face_index = 0; face_index < num_faces; face_index++) {
-    const int num_face_vertices = topology_refiner->getNumFaceVertices(topology_refiner,
-                                                                       face_index);
-    const int *uv_indices = topology_refiner->getFaceFVarValueIndices(
-        topology_refiner, face_index, layer_index);
-    for (int vertex_index = 0; vertex_index < num_face_vertices; vertex_index++, mluv++) {
-      evaluator->setFaceVaryingData(evaluator, layer_index, mluv->uv, uv_indices[vertex_index], 1);
-    }
-  }
+
+  const int num_fvar_values = topology_refiner->getNumFVarValues(topology_refiner, layer_index);
+  /* Use a temporary buffer so we do not upload UVs one at a time to the GPU. */
+  float(*buffer)[2] = MEM_mallocN(sizeof(float[2]) * num_fvar_values, "temp UV storage");
+
+  FaceVaryingDataFromUVContext ctx;
+  ctx.topology_refiner = topology_refiner;
+  ctx.layer_index = layer_index;
+  ctx.mloopuv = mluv;
+  ctx.mesh = mesh;
+  ctx.buffer = buffer;
+
+  TaskParallelSettings parallel_range_settings;
+  BLI_parallel_range_settings_defaults(&parallel_range_settings);
+  parallel_range_settings.min_iter_per_thread = 1;
+
+  BLI_task_parallel_range(
+      0, num_faces, &ctx, set_face_varying_data_from_uv_task, &parallel_range_settings);
+
+  evaluator->setFaceVaryingData(evaluator, layer_index, &buffer[0][0], 0, num_fvar_values);
+
+  MEM_freeN(buffer);
 }
 
 bool BKE_subdiv_eval_begin_from_mesh(Subdiv *subdiv,
                                      const Mesh *mesh,
-                                     const float (*coarse_vertex_cos)[3])
+                                     const float (*coarse_vertex_cos)[3],
+                                     eSubdivEvaluatorType evaluator_type,
+                                     OpenSubdiv_EvaluatorCache *evaluator_cache)
 {
-  if (!BKE_subdiv_eval_begin(subdiv)) {
+  if (!BKE_subdiv_eval_begin(subdiv, evaluator_type, evaluator_cache)) {
     return false;
   }
   return BKE_subdiv_eval_refine_from_mesh(subdiv, mesh, coarse_vertex_cos);
@@ -146,7 +222,7 @@ bool BKE_subdiv_eval_refine_from_mesh(Subdiv *subdiv,
   const int num_uv_layers = CustomData_number_of_layers(&mesh->ldata, CD_MLOOPUV);
   for (int layer_index = 0; layer_index < num_uv_layers; layer_index++) {
     const MLoopUV *mloopuv = CustomData_get_layer_n(&mesh->ldata, CD_MLOOPUV, layer_index);
-    set_face_varying_data_from_uv(subdiv, mloopuv, layer_index);
+    set_face_varying_data_from_uv(subdiv, mesh, mloopuv, layer_index);
   }
   /* Update evaluator to the new coarse geometry. */
   BKE_subdiv_stats_begin(&subdiv->stats, SUBDIV_STATS_EVALUATOR_REFINE);