LineArt: Stroke offset towards camera.

Allows the user to turn off in_front option for grease pencil object
and offset strokes towards camera to allow depth interaction of the
rest of the scene.

Reviewed By: Antonio Vazquez (antoniov)

Differential Revision: https://developer.blender.org/D12046

9 files changed, 121 insertions, 21 deletions

diff --git a/source/blender/editors/object/object_add.c b/source/blender/editors/object/object_add.c
index 629f40e0ae9..8fc1c119d0c 100644
--- a/source/blender/editors/object/object_add.c
+++ b/source/blender/editors/object/object_add.c
@@ -1323,6 +1323,7 @@ static int object_gpencil_add_exec(bContext *C, wmOperator *op)
   const bool use_in_front = RNA_boolean_get(op->ptr, "use_in_front");
   const bool use_lights = RNA_boolean_get(op->ptr, "use_lights");
   const int stroke_depth_order = RNA_enum_get(op->ptr, "stroke_depth_order");
+  const float stroke_depth_offset = RNA_float_get(op->ptr, "stroke_depth_offset");
 
   ushort local_view_bits;
   float loc[3], rot[3];
@@ -1454,6 +1455,7 @@ static int object_gpencil_add_exec(bContext *C, wmOperator *op)
         if (stroke_depth_order == GP_DRAWMODE_3D) {
           gpd->draw_mode = GP_DRAWMODE_3D;
         }
+        md->stroke_depth_offset = stroke_depth_offset;
       }
 
       break;
@@ -1491,9 +1493,10 @@ static void object_add_ui(bContext *UNUSED(C), wmOperator *op)
     uiItemR(layout, op->ptr, "use_lights", 0, NULL, ICON_NONE);
     uiItemR(layout, op->ptr, "use_in_front", 0, NULL, ICON_NONE);
     bool in_front = RNA_boolean_get(op->ptr, "use_in_front");
-    uiLayout *row = uiLayoutRow(layout, false);
-    uiLayoutSetActive(row, !in_front);
-    uiItemR(row, op->ptr, "stroke_depth_order", 0, NULL, ICON_NONE);
+    uiLayout *col = uiLayoutColumn(layout, false);
+    uiLayoutSetActive(col, !in_front);
+    uiItemR(col, op->ptr, "stroke_depth_offset", 0, NULL, ICON_NONE);
+    uiItemR(col, op->ptr, "stroke_depth_order", 0, NULL, ICON_NONE);
   }
 }
 
@@ -1532,9 +1535,18 @@ void OBJECT_OT_gpencil_add(wmOperatorType *ot)
   ot->prop = RNA_def_enum(ot->srna, "type", rna_enum_object_gpencil_type_items, 0, "Type", "");
   RNA_def_boolean(ot->srna,
                   "use_in_front",
-                  false,
-                  "In Front",
+                  true,
+                  "Show In Front",
                   "Show line art grease pencil in front of everything");
+  RNA_def_float(ot->srna,
+                "stroke_depth_offset",
+                0.05f,
+                0.0f,
+                0.0f,
+                "Stroke Offset",
+                "Stroke offset for the line art modifier",
+                0.0f,
+                0.5f);
   RNA_def_boolean(
       ot->srna, "use_lights", false, "Use Lights", "Use lights for this grease pencil object");
   RNA_def_enum(
@@ -1543,7 +1555,7 @@ void OBJECT_OT_gpencil_add(wmOperatorType *ot)
       rna_enum_gpencil_add_stroke_depth_order_items,
       GP_DRAWMODE_3D,
       "Stroke Depth Order",
-      "Defines how the strokes are ordered in 3D space for objects not displayed 'In Front'");
+      "Defines how the strokes are ordered in 3D space for objects not displayed 'In Front')");
 }
 
 /** \} */
diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c b/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c
index c5ccf1d8229..a7164e5bf2c 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c
@@ -160,12 +160,14 @@ static void generateStrokes(GpencilModifierData *md, Depsgraph *depsgraph, Objec
 
   LineartCache *local_lc = gpd->runtime.lineart_cache;
   if (!gpd->runtime.lineart_cache) {
-    MOD_lineart_compute_feature_lines(depsgraph, lmd, &gpd->runtime.lineart_cache);
+    MOD_lineart_compute_feature_lines(
+        depsgraph, lmd, &gpd->runtime.lineart_cache, (!(ob->dtx & OB_DRAW_IN_FRONT)));
     MOD_lineart_destroy_render_data(lmd);
   }
   else {
     if (!(lmd->flags & LRT_GPENCIL_USE_CACHE)) {
-      MOD_lineart_compute_feature_lines(depsgraph, lmd, &local_lc);
+      MOD_lineart_compute_feature_lines(
+          depsgraph, lmd, &local_lc, (!(ob->dtx & OB_DRAW_IN_FRONT)));
       MOD_lineart_destroy_render_data(lmd);
     }
     MOD_lineart_chain_clear_picked_flag(local_lc);
@@ -210,7 +212,8 @@ static void bakeModifier(Main *UNUSED(bmain),
     lmd->edge_types_override = lmd->edge_types;
     lmd->level_end_override = lmd->level_end;
 
-    MOD_lineart_compute_feature_lines(depsgraph, lmd, &gpd->runtime.lineart_cache);
+    MOD_lineart_compute_feature_lines(
+        depsgraph, lmd, &gpd->runtime.lineart_cache, (!(ob->dtx & OB_DRAW_IN_FRONT)));
     MOD_lineart_destroy_render_data(lmd);
   }
 
@@ -412,14 +415,23 @@ static void style_panel_draw(const bContext *UNUSED(C), Panel *panel)
 static void occlusion_panel_draw(const bContext *UNUSED(C), Panel *panel)
 {
   uiLayout *layout = panel->layout;
-  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, NULL);
+  PointerRNA ob_ptr;
+  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, &ob_ptr);
 
   const bool is_baked = RNA_boolean_get(ptr, "is_baked");
 
+  const bool use_multiple_levels = RNA_boolean_get(ptr, "use_multiple_levels");
+  const bool show_in_front = RNA_boolean_get(&ob_ptr, "show_in_front");
+
   uiLayoutSetPropSep(layout, true);
   uiLayoutSetEnabled(layout, !is_baked);
 
-  const bool use_multiple_levels = RNA_boolean_get(ptr, "use_multiple_levels");
+  if (!show_in_front) {
+    uiItemL(layout, IFACE_("Object is not in front"), ICON_INFO);
+  }
+
+  layout = uiLayoutColumn(layout, false);
+  uiLayoutSetActive(layout, show_in_front);
 
   uiItemR(layout, ptr, "use_multiple_levels", 0, IFACE_("Range"), ICON_NONE);
 
@@ -447,11 +459,14 @@ static bool anything_showing_through(PointerRNA *ptr)
 static void material_mask_panel_draw_header(const bContext *UNUSED(C), Panel *panel)
 {
   uiLayout *layout = panel->layout;
-  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, NULL);
+  PointerRNA ob_ptr;
+  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, &ob_ptr);
 
   const bool is_baked = RNA_boolean_get(ptr, "is_baked");
+  const bool show_in_front = RNA_boolean_get(&ob_ptr, "show_in_front");
+
   uiLayoutSetEnabled(layout, !is_baked);
-  uiLayoutSetActive(layout, anything_showing_through(ptr));
+  uiLayoutSetActive(layout, (!show_in_front) && anything_showing_through(ptr));
 
   uiItemR(layout, ptr, "use_material_mask", 0, IFACE_("Material Mask"), ICON_NONE);
 }
@@ -654,6 +669,27 @@ static void bake_panel_draw(const bContext *UNUSED(C), Panel *panel)
   uiItemO(col, NULL, ICON_NONE, "OBJECT_OT_lineart_clear_all");
 }
 
+static void composition_panel_draw(const bContext *UNUSED(C), Panel *panel)
+{
+  PointerRNA ob_ptr;
+  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, &ob_ptr);
+
+  uiLayout *layout = panel->layout;
+
+  const bool show_in_front = RNA_boolean_get(&ob_ptr, "show_in_front");
+
+  uiLayoutSetPropSep(layout, true);
+
+  if (show_in_front) {
+    uiItemL(layout, IFACE_("Object is shown in front"), ICON_ERROR);
+  }
+
+  uiLayout *row = uiLayoutRow(layout, false);
+  uiLayoutSetActive(row, !show_in_front);
+
+  uiItemR(row, ptr, "stroke_depth_offset", UI_ITEM_R_SLIDER, IFACE_("Depth Offset"), ICON_NONE);
+}
+
 static void panelRegister(ARegionType *region_type)
 {
   PanelType *panel_type = gpencil_modifier_panel_register(
@@ -682,6 +718,8 @@ static void panelRegister(ARegionType *region_type)
   gpencil_modifier_subpanel_register(
       region_type, "vgroup", "Vertex Weight Transfer", NULL, vgroup_panel_draw, panel_type);
   gpencil_modifier_subpanel_register(
+      region_type, "composition", "Composition", NULL, composition_panel_draw, panel_type);
+  gpencil_modifier_subpanel_register(
       region_type, "bake", "Bake", NULL, bake_panel_draw, panel_type);
 }
 
diff --git a/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h b/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h
index c00f34185dd..d170a6033fa 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h
+++ b/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h
@@ -595,13 +595,15 @@ void MOD_lineart_chain_connect(LineartRenderBuffer *rb);
 void MOD_lineart_chain_discard_short(LineartRenderBuffer *rb, const float threshold);
 void MOD_lineart_chain_split_angle(LineartRenderBuffer *rb, float angle_threshold_rad);
 void MOD_lineart_smooth_chains(LineartRenderBuffer *rb, float tolerance);
+void MOD_lineart_chain_offset_towards_camera(LineartRenderBuffer *rb, float dist);
 
 int MOD_lineart_chain_count(const LineartEdgeChain *ec);
 void MOD_lineart_chain_clear_picked_flag(LineartCache *lc);
 
 bool MOD_lineart_compute_feature_lines(struct Depsgraph *depsgraph,
                                        struct LineartGpencilModifierData *lmd,
-                                       LineartCache **cached_result);
+                                       struct LineartCache **cached_result,
+                                       bool enable_stroke_offset);
 
 struct Scene;
 
diff --git a/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c b/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c
index 8935bdd1870..57eeeb96541 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c
+++ b/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c
@@ -926,9 +926,9 @@ void MOD_lineart_chain_clear_picked_flag(LineartCache *lc)
 
 void MOD_lineart_smooth_chains(LineartRenderBuffer *rb, float tolerance)
 {
-  LISTBASE_FOREACH (LineartEdgeChain *, rlc, &rb->chains) {
+  LISTBASE_FOREACH (LineartEdgeChain *, ec, &rb->chains) {
     LineartEdgeChainItem *next_eci;
-    for (LineartEdgeChainItem *eci = rlc->chain.first; eci; eci = next_eci) {
+    for (LineartEdgeChainItem *eci = ec->chain.first; eci; eci = next_eci) {
       next_eci = eci->next;
       LineartEdgeChainItem *eci2, *eci3, *eci4;
 
@@ -944,7 +944,7 @@ void MOD_lineart_smooth_chains(LineartRenderBuffer *rb, float tolerance)
       if (dist_to_line_segment_v2(eci3->pos, eci->pos, eci2->pos) < tolerance) {
         /* And if p4 is on the extension of p1-p2 , we remove p3. */
         if ((eci4 = eci3->next) && (dist_to_line_v2(eci4->pos, eci->pos, eci2->pos) < tolerance)) {
-          BLI_remlink(&rlc->chain, eci3);
+          BLI_remlink(&ec->chain, eci3);
           next_eci = eci;
         }
       }
@@ -1008,3 +1008,35 @@ void MOD_lineart_chain_split_angle(LineartRenderBuffer *rb, float angle_threshol
     }
   }
 }
+
+void MOD_lineart_chain_offset_towards_camera(LineartRenderBuffer *rb, float dist)
+{
+  float dir[3];
+  float cam[3];
+  float view[3];
+  float view_clamp[3];
+  copy_v3fl_v3db(cam, rb->camera_pos);
+  copy_v3fl_v3db(view, rb->view_vector);
+  if (rb->cam_is_persp) {
+    LISTBASE_FOREACH (LineartEdgeChain *, ec, &rb->chains) {
+      LISTBASE_FOREACH (LineartEdgeChainItem *, eci, &ec->chain) {
+        sub_v3_v3v3(dir, cam, eci->gpos);
+        float orig_len = len_v3(dir);
+        normalize_v3(dir);
+        mul_v3_fl(dir, MIN2(dist, orig_len - rb->near_clip));
+        add_v3_v3(eci->gpos, dir);
+      }
+    }
+  }
+  else {
+    LISTBASE_FOREACH (LineartEdgeChain *, ec, &rb->chains) {
+      LISTBASE_FOREACH (LineartEdgeChainItem *, eci, &ec->chain) {
+        sub_v3_v3v3(dir, cam, eci->gpos);
+        float len_lim = dot_v3v3(view, dir) - rb->near_clip;
+        normalize_v3_v3(view_clamp, view);
+        mul_v3_fl(view_clamp, MIN2(dist, len_lim));
+        add_v3_v3(eci->gpos, view_clamp);
+      }
+    }
+  }
+}
diff --git a/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c b/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
index 6660da79b40..f8dda2f9174 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
+++ b/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
@@ -4076,7 +4076,8 @@ static LineartBoundingArea *lineart_bounding_area_next(LineartBoundingArea *this
  */
 bool MOD_lineart_compute_feature_lines(Depsgraph *depsgraph,
                                        LineartGpencilModifierData *lmd,
-                                       LineartCache **cached_result)
+                                       LineartCache **cached_result,
+                                       bool enable_stroke_depth_offset)
 {
   LineartRenderBuffer *rb;
   Scene *scene = DEG_get_evaluated_scene(depsgraph);
@@ -4189,6 +4190,10 @@ bool MOD_lineart_compute_feature_lines(Depsgraph *depsgraph,
       MOD_lineart_chain_split_angle(rb, rb->angle_splitting_threshold);
     }
 
+    if (enable_stroke_depth_offset && lmd->stroke_depth_offset > FLT_EPSILON) {
+      MOD_lineart_chain_offset_towards_camera(rb, lmd->stroke_depth_offset);
+    }
+
     /* Finally transfer the result list into cache. */
     memcpy(&lc->chains, &rb->chains, sizeof(ListBase));
 
diff --git a/source/blender/gpencil_modifiers/intern/lineart/lineart_ops.c b/source/blender/gpencil_modifiers/intern/lineart/lineart_ops.c
index 988c90483a6..b74499daf6b 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/lineart_ops.c
+++ b/source/blender/gpencil_modifiers/intern/lineart/lineart_ops.c
@@ -118,12 +118,12 @@ static bool bake_strokes(Object *ob,
   }
   LineartCache *local_lc = *lc;
   if (!(*lc)) {
-    MOD_lineart_compute_feature_lines(dg, lmd, lc);
+    MOD_lineart_compute_feature_lines(dg, lmd, lc, (!(ob->dtx & OB_DRAW_IN_FRONT)));
     MOD_lineart_destroy_render_data(lmd);
   }
   else {
     if (is_first || (!(lmd->flags & LRT_GPENCIL_USE_CACHE))) {
-      MOD_lineart_compute_feature_lines(dg, lmd, &local_lc);
+      MOD_lineart_compute_feature_lines(dg, lmd, &local_lc, (!(ob->dtx & OB_DRAW_IN_FRONT)));
       MOD_lineart_destroy_render_data(lmd);
     }
     MOD_lineart_chain_clear_picked_flag(local_lc);
diff --git a/source/blender/makesdna/DNA_gpencil_modifier_defaults.h b/source/blender/makesdna/DNA_gpencil_modifier_defaults.h
index 11299ae9717..1ad884bee8f 100644
--- a/source/blender/makesdna/DNA_gpencil_modifier_defaults.h
+++ b/source/blender/makesdna/DNA_gpencil_modifier_defaults.h
@@ -319,6 +319,7 @@
     .angle_splitting_threshold = DEG2RAD(60.0f), \
     .chaining_image_threshold = 0.001f, \
     .chain_smooth_tolerance = 0.2f,\
+    .stroke_depth_offset = 0.05,\
   }
 
 #define _DNA_DEFAULT_LengthGpencilModifierData \
diff --git a/source/blender/makesdna/DNA_gpencil_modifier_types.h b/source/blender/makesdna/DNA_gpencil_modifier_types.h
index c7a93080f7c..6ea07163ca8 100644
--- a/source/blender/makesdna/DNA_gpencil_modifier_types.h
+++ b/source/blender/makesdna/DNA_gpencil_modifier_types.h
@@ -1042,7 +1042,6 @@ typedef struct LineartGpencilModifierData {
 
   /** Strength for smoothing jagged chains. */
   float chain_smooth_tolerance;
-  int _pad1;
 
   /* CPU mode */
   float chaining_image_threshold;
@@ -1053,6 +1052,9 @@ typedef struct LineartGpencilModifierData {
   /* #eLineArtGPencilModifierFlags, modifier internal state. */
   int flags;
 
+  /* Move strokes towards camera to avoid clipping while preserve depth for the viewport. */
+  float stroke_depth_offset;
+
   /* Runtime data. */
 
   /* Because we can potentially only compute features lines once per modifier stack (Use Cache), we
diff --git a/source/blender/makesrna/intern/rna_gpencil_modifier.c b/source/blender/makesrna/intern/rna_gpencil_modifier.c
index 631d5822c5e..29689a2b281 100644
--- a/source/blender/makesrna/intern/rna_gpencil_modifier.c
+++ b/source/blender/makesrna/intern/rna_gpencil_modifier.c
@@ -3200,6 +3200,14 @@ static void rna_def_modifier_gpencillineart(BlenderRNA *brna)
                            "separate stroke for each overlapping type");
   RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
 
+  prop = RNA_def_property(srna, "stroke_depth_offset", PROP_FLOAT, PROP_DISTANCE);
+  RNA_def_property_ui_text(prop,
+                           "Stroke Depth Offset",
+                           "Move strokes slightly towards the camera to avoid clipping while "
+                           "preserve depth for the viewport");
+  RNA_def_property_ui_range(prop, 0.0f, 0.5f, 0.001f, 4);
+  RNA_def_property_update(prop, NC_SCENE, "rna_GpencilModifier_update");
+
   prop = RNA_def_property(srna, "source_type", PROP_ENUM, PROP_NONE);
   RNA_def_property_enum_items(prop, modifier_lineart_source_type);
   RNA_def_property_ui_text(prop, "Source Type", "Line art stroke source type");