Asset: Dropping Material assets on material slot under mouse cursor.

This patch allows dropping material assets from material slot under the mouse
cursor. Before this change the material slot had to be hand-picked from the
properties panel.

For consistency it is chosen to do this in any shading mode as the tooltip shows
what is exactly going to happen during release.

The feature also works for other object types than Meshes as it uses the drawn surface on the
GPU to detect the material slots. Performance of this patch has been tested with AMD GCN3.0
cards and are very responsive.

Reviewed By: fclem, Severin

Differential Revision: https://developer.blender.org/D12190

5 files changed, 69 insertions, 16 deletions

diff --git a/source/blender/draw/DRW_engine.h b/source/blender/draw/DRW_engine.h
index 8a35ab2aeb9..a125a13eaf9 100644
--- a/source/blender/draw/DRW_engine.h
+++ b/source/blender/draw/DRW_engine.h
@@ -110,6 +110,7 @@ void DRW_draw_select_loop(struct Depsgraph *depsgraph,
                           bool use_obedit_skip,
                           bool draw_surface,
                           bool use_nearest,
+                          const bool do_material_sub_selection,
                           const struct rcti *rect,
                           DRW_SelectPassFn select_pass_fn,
                           void *select_pass_user_data,
diff --git a/source/blender/draw/engines/basic/basic_engine.c b/source/blender/draw/engines/basic/basic_engine.c
index c120df7e897..87f5c6f5857 100644
--- a/source/blender/draw/engines/basic/basic_engine.c
+++ b/source/blender/draw/engines/basic/basic_engine.c
@@ -25,9 +25,12 @@
 
 #include "DRW_render.h"
 
+#include "BKE_object.h"
 #include "BKE_paint.h"
 #include "BKE_particle.h"
 
+#include "BLI_alloca.h"
+
 #include "DNA_particle_types.h"
 
 #include "GPU_shader.h"
@@ -80,6 +83,7 @@ typedef struct BASIC_PrivateData {
   DRWShadingGroup *depth_shgrp[2];
   DRWShadingGroup *depth_shgrp_cull[2];
   DRWShadingGroup *depth_hair_shgrp[2];
+  bool use_material_slot_selection;
 } BASIC_PrivateData; /* Transient data */
 
 /* Functions */
@@ -131,6 +135,8 @@ static void basic_cache_init(void *vedata)
     stl->g_data = MEM_callocN(sizeof(*stl->g_data), __func__);
   }
 
+  stl->g_data->use_material_slot_selection = DRW_state_is_material_select();
+
   /* Twice for normal and in front objects. */
   for (int i = 0; i < 2; i++) {
     DRWState clip_state = (draw_ctx->sh_cfg == GPU_SHADER_CFG_CLIPPED) ? DRW_STATE_CLIP_PLANES : 0;
@@ -155,6 +161,38 @@ static void basic_cache_init(void *vedata)
   }
 }
 
+/* TODO(fclem): DRW_cache_object_surface_material_get needs a refactor to allow passing NULL
+ * instead of gpumat_array. Avoiding all this boilerplate code. */
+static struct GPUBatch **basic_object_surface_material_get(Object *ob)
+{
+  const int materials_len = DRW_cache_object_material_count_get(ob);
+  struct GPUMaterial **gpumat_array = BLI_array_alloca(gpumat_array, materials_len);
+  memset(gpumat_array, 0, sizeof(*gpumat_array) * materials_len);
+
+  return DRW_cache_object_surface_material_get(ob, gpumat_array, materials_len);
+}
+
+static void basic_cache_populate_particles(void *vedata, Object *ob)
+{
+  const bool do_in_front = (ob->dtx & OB_DRAW_IN_FRONT) != 0;
+  BASIC_StorageList *stl = ((BASIC_Data *)vedata)->stl;
+  for (ParticleSystem *psys = ob->particlesystem.first; psys != NULL; psys = psys->next) {
+    if (!DRW_object_is_visible_psys_in_active_context(ob, psys)) {
+      continue;
+    }
+    ParticleSettings *part = psys->part;
+    const int draw_as = (part->draw_as == PART_DRAW_REND) ? part->ren_as : part->draw_as;
+    if (draw_as == PART_DRAW_PATH) {
+      struct GPUBatch *hairs = DRW_cache_particles_get_hair(ob, psys, NULL);
+      if (stl->g_data->use_material_slot_selection) {
+        const short material_slot = part->omat;
+        DRW_select_load_id(ob->runtime.select_id | (material_slot << 16));
+      }
+      DRW_shgroup_call(stl->g_data->depth_hair_shgrp[do_in_front], hairs, NULL);
+    }
+  }
+}
+
 static void basic_cache_populate(void *vedata, Object *ob)
 {
   BASIC_StorageList *stl = ((BASIC_Data *)vedata)->stl;
@@ -165,24 +203,13 @@ static void basic_cache_populate(void *vedata, Object *ob)
     return;
   }
 
-  bool do_in_front = (ob->dtx & OB_DRAW_IN_FRONT) != 0;
-
   const DRWContextState *draw_ctx = DRW_context_state_get();
   if (ob != draw_ctx->object_edit) {
-    for (ParticleSystem *psys = ob->particlesystem.first; psys != NULL; psys = psys->next) {
-      if (!DRW_object_is_visible_psys_in_active_context(ob, psys)) {
-        continue;
-      }
-      ParticleSettings *part = psys->part;
-      const int draw_as = (part->draw_as == PART_DRAW_REND) ? part->ren_as : part->draw_as;
-      if (draw_as == PART_DRAW_PATH) {
-        struct GPUBatch *hairs = DRW_cache_particles_get_hair(ob, psys, NULL);
-        DRW_shgroup_call(stl->g_data->depth_hair_shgrp[do_in_front], hairs, NULL);
-      }
-    }
+    basic_cache_populate_particles(vedata, ob);
   }
 
   /* Make flat object selectable in ortho view if wireframe is enabled. */
+  const bool do_in_front = (ob->dtx & OB_DRAW_IN_FRONT) != 0;
   if ((draw_ctx->v3d->overlay.flag & V3D_OVERLAY_WIREFRAMES) ||
       (draw_ctx->v3d->shading.type == OB_WIRE) || (ob->dtx & OB_DRAWWIRE) || (ob->dt == OB_WIRE)) {
     int flat_axis = 0;
@@ -211,9 +238,25 @@ static void basic_cache_populate(void *vedata, Object *ob)
     DRW_shgroup_call_sculpt(shgrp, ob, false, false);
   }
   else {
-    struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
-    if (geom) {
-      DRW_shgroup_call(shgrp, geom, ob);
+    if (stl->g_data->use_material_slot_selection && BKE_object_supports_material_slots(ob)) {
+      struct GPUBatch **geoms = basic_object_surface_material_get(ob);
+      if (geoms) {
+        const int materials_len = DRW_cache_object_material_count_get(ob);
+        for (int i = 0; i < materials_len; i++) {
+          if (geoms[i] == NULL) {
+            continue;
+          }
+          const short material_slot_select_id = i + 1;
+          DRW_select_load_id(ob->runtime.select_id | (material_slot_select_id << 16));
+          DRW_shgroup_call(shgrp, geoms[i], ob);
+        }
+      }
+    }
+    else {
+      struct GPUBatch *geom = DRW_cache_object_surface_get(ob);
+      if (geom) {
+        DRW_shgroup_call(shgrp, geom, ob);
+      }
     }
   }
 }
diff --git a/source/blender/draw/intern/DRW_render.h b/source/blender/draw/intern/DRW_render.h
index 6639a100af9..660a4adaf51 100644
--- a/source/blender/draw/intern/DRW_render.h
+++ b/source/blender/draw/intern/DRW_render.h
@@ -731,6 +731,7 @@ void DRW_select_load_id(uint id);
 /* Draw State */
 bool DRW_state_is_fbo(void);
 bool DRW_state_is_select(void);
+bool DRW_state_is_material_select(void);
 bool DRW_state_is_depth(void);
 bool DRW_state_is_image_render(void);
 bool DRW_state_is_scene_render(void);
diff --git a/source/blender/draw/intern/draw_manager.c b/source/blender/draw/intern/draw_manager.c
index 9590a4aa7ee..aca645acc09 100644
--- a/source/blender/draw/intern/draw_manager.c
+++ b/source/blender/draw/intern/draw_manager.c
@@ -2232,6 +2232,7 @@ void DRW_draw_select_loop(struct Depsgraph *depsgraph,
                           bool use_obedit_skip,
                           bool draw_surface,
                           bool UNUSED(use_nearest),
+                          const bool do_material_sub_selection,
                           const rcti *rect,
                           DRW_SelectPassFn select_pass_fn,
                           void *select_pass_user_data,
@@ -2299,6 +2300,7 @@ void DRW_draw_select_loop(struct Depsgraph *depsgraph,
 
   DST.viewport = viewport;
   DST.options.is_select = true;
+  DST.options.is_material_select = do_material_sub_selection;
   drw_task_graph_init();
   /* Get list of enabled engines */
   if (use_obedit) {
@@ -2776,6 +2778,11 @@ bool DRW_state_is_select(void)
   return DST.options.is_select;
 }
 
+bool DRW_state_is_material_select(void)
+{
+  return DST.options.is_material_select;
+}
+
 bool DRW_state_is_depth(void)
 {
   return DST.options.is_depth;
diff --git a/source/blender/draw/intern/draw_manager.h b/source/blender/draw/intern/draw_manager.h
index 1747ca752c7..c09126c98ef 100644
--- a/source/blender/draw/intern/draw_manager.h
+++ b/source/blender/draw/intern/draw_manager.h
@@ -553,6 +553,7 @@ typedef struct DRWManager {
 
   struct {
     uint is_select : 1;
+    uint is_material_select : 1;
     uint is_depth : 1;
     uint is_image_render : 1;
     uint is_scene_render : 1;