LineArt: Smooth tolerance value for chaining.

smooth out jaggy lines with a given threshold. For each point in a stroke, the ones with in a given distance of its previous segment will be removed,
thus "zig-zag" artefacts can be cleaned up.

Reviewed By: Antonio Vazquez (antoniov)

Differential Revision: https://developer.blender.org/D12050

4 files changed, 41 insertions, 1 deletions

diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c b/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c
index 01488a8b2de..c5ccf1d8229 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c
@@ -587,6 +587,7 @@ static void chaining_panel_draw(const bContext *UNUSED(C), Panel *panel)
           is_geom ? IFACE_("Geometry Threshold") : NULL,
           ICON_NONE);
 
+  uiItemR(layout, ptr, "smooth_tolerance", UI_ITEM_R_SLIDER, NULL, ICON_NONE);
   uiItemR(layout, ptr, "split_angle", UI_ITEM_R_SLIDER, NULL, ICON_NONE);
 }
 
diff --git a/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h b/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h
index 134d9707ade..c00f34185dd 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h
+++ b/source/blender/gpencil_modifiers/intern/lineart/MOD_lineart.h
@@ -317,6 +317,8 @@ typedef struct LineartRenderBuffer {
   float chaining_image_threshold;
   float angle_splitting_threshold;
 
+  float chain_smooth_tolerance;
+
   /* FIXME(Yiming): Temporary solution for speeding up calculation by not including lines that
    * are not in the selected source. This will not be needed after we have a proper scene-wise
    * cache running because multiple modifiers can then select results from that without further
@@ -592,6 +594,7 @@ void MOD_lineart_chain_split_for_fixed_occlusion(LineartRenderBuffer *rb);
 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);
 
 int MOD_lineart_chain_count(const LineartEdgeChain *ec);
 void MOD_lineart_chain_clear_picked_flag(LineartCache *lc);
diff --git a/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c b/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c
index d86253e7fe0..8935bdd1870 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c
+++ b/source/blender/gpencil_modifiers/intern/lineart/lineart_chain.c
@@ -924,6 +924,34 @@ void MOD_lineart_chain_clear_picked_flag(LineartCache *lc)
   }
 }
 
+void MOD_lineart_smooth_chains(LineartRenderBuffer *rb, float tolerance)
+{
+  LISTBASE_FOREACH (LineartEdgeChain *, rlc, &rb->chains) {
+    LineartEdgeChainItem *next_eci;
+    for (LineartEdgeChainItem *eci = rlc->chain.first; eci; eci = next_eci) {
+      next_eci = eci->next;
+      LineartEdgeChainItem *eci2, *eci3, *eci4;
+
+      /* Not enough point to do simplify. */
+      if ((!(eci2 = eci->next)) || (!(eci3 = eci2->next))) {
+        continue;
+      }
+
+      /* No need to care for different line types/occlusion and so on, because at this stage they
+       * are all the same within a chain. */
+
+      /* If p3 is within the p1-p2 segment of a width of "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);
+          next_eci = eci;
+        }
+      }
+    }
+  }
+}
+
 /**
  * This should always be the last stage!, see the end of
  * #MOD_lineart_chain_split_for_fixed_occlusion().
diff --git a/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c b/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
index 725cc0741f0..5b878a4326f 100644
--- a/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
+++ b/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c
@@ -3056,8 +3056,9 @@ static LineartRenderBuffer *lineart_create_render_buffer(Scene *scene,
   rb->shift_y /= (1 + rb->overscan);
 
   rb->crease_threshold = cos(M_PI - lmd->crease_threshold);
-  rb->angle_splitting_threshold = lmd->angle_splitting_threshold;
   rb->chaining_image_threshold = lmd->chaining_image_threshold;
+  rb->angle_splitting_threshold = lmd->angle_splitting_threshold;
+  rb->chain_smooth_tolerance = lmd->chain_smooth_tolerance;
 
   rb->fuzzy_intersections = (lmd->calculation_flags & LRT_INTERSECTION_AS_CONTOUR) != 0;
   rb->fuzzy_everything = (lmd->calculation_flags & LRT_EVERYTHING_AS_CONTOUR) != 0;
@@ -4172,6 +4173,13 @@ bool MOD_lineart_compute_feature_lines(Depsgraph *depsgraph,
     /* This configuration ensures there won't be accidental lost of short unchained segments. */
     MOD_lineart_chain_discard_short(rb, MIN2(*t_image, 0.001f) - FLT_EPSILON);
 
+    if (rb->chain_smooth_tolerance > FLT_EPSILON) {
+      /* Keeping UI range of 0-1 for ease of read while scaling down the actual value for best
+       * effective range in image-space (Coordinate only goes from -1 to 1). This value is somewhat
+       * arbitrary, but works best for the moment.  */
+      MOD_lineart_smooth_chains(rb, rb->chain_smooth_tolerance / 50);
+    }
+
     if (rb->angle_splitting_threshold > FLT_EPSILON) {
       MOD_lineart_chain_split_angle(rb, rb->angle_splitting_threshold);
     }