Sculpt: Hardness brush property

The hardness property moves the brush falloff towards the edges, making
the brush sharper.

This should be the intended way to control the brush falloff instead of
tweaking the falloff curve manually, as it can be mapped to pressure to
make the falloff variable during the stroke.
It is also a good idea to show in the UI that the custom curves is an
advance features and it should almost never be modified when sculpting/
painting unless you want to create some advanced effects. By modifying
the curves freely it is really easy to break the brushes and make them
produce artifacts. This needs to be done in a later after merging the
pending projects to reorganize all the brush properties accordingly.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D6902

release/scripts/startup/bl_ui/properties_paint_common.py

@@ -536,6 +536,7 @@ def brush_settings(layout, context, brush, popover=False):
 
         # normal_radius_factor
         layout.prop(brush, "normal_radius_factor", slider=True)
+        layout.prop(brush, "hardness", slider=True)
 
         # auto_smooth_factor and use_inverse_smooth_pressure
         if capabilities.has_auto_smooth:

source/blender/editors/sculpt_paint/sculpt.c

@@ -1953,8 +1953,20 @@ float tex_strength(SculptSession *ss,
     }
   }
 
+  /* Hardness. */
+  float final_len = len;
+  const float hardness = br->hardness;
+  float p = len / cache->radius;
+  if (p < hardness) {
+    final_len = 0.0f;
+  }
+  else {
+    p = (p - hardness) / (1.0f - hardness);
+    final_len = p * cache->radius;
+  }
+
   /* Falloff curve. */
-  avg *= BKE_brush_curve_strength(br, len, cache->radius);
+  avg *= BKE_brush_curve_strength(br, final_len, cache->radius);
   avg *= frontface(br, cache->view_normal, vno, fno);
 
   /* Paint mask. */

source/blender/makesdna/DNA_brush_defaults.h

@@ -102,6 +102,7 @@
     .sculpt_tool = SCULPT_TOOL_DRAW, \
     .pose_smooth_iterations = 4, \
     .pose_ik_segments = 1, \
+    .hardness = 0.0f, \
  \
     /* A kernel radius of 1 has almost no effect (T63233). */ \
     .blur_kernel_radius = 2, \

source/blender/makesdna/DNA_brush_types.h

@@ -326,7 +326,7 @@ typedef struct Brush {
   char mask_tool;
   /** Active grease pencil tool. */
   char gpencil_tool;
-  char _pad1[1];
+  char _pad1[5];
 
   float autosmooth_factor;
 
@@ -344,6 +344,8 @@ typedef struct Brush {
   float texture_sample_bias;
 
   int curve_preset;
+  float hardness;
+
   int automasking_flags;
 
   /* Factor that controls the shape of the brush tip by rounding the corners of a square. */

source/blender/makesrna/intern/rna_brush.c

@@ -2012,6 +2012,13 @@ static void rna_def_brush(BlenderRNA *brna)
                            "Area to apply deformation falloff to the effects of the simulation");
   RNA_def_property_update(prop, 0, "rna_Brush_update");
 
+  prop = RNA_def_property(srna, "hardness", PROP_FLOAT, PROP_FACTOR);
+  RNA_def_property_float_sdna(prop, NULL, "hardness");
+  RNA_def_property_range(prop, 0.0f, 1.0f);
+  RNA_def_property_ui_text(
+      prop, "Hardness", "How close the brush falloff starts from the edge of the brush");
+  RNA_def_property_update(prop, 0, "rna_Brush_update");
+
   prop = RNA_def_property(srna, "auto_smooth_factor", PROP_FLOAT, PROP_FACTOR);
   RNA_def_property_float_sdna(prop, NULL, "autosmooth_factor");
   RNA_def_property_float_default(prop, 0);