Fix T67939: GPencil Noise modifier wrong random calculation

There were several problems in the old random calculation:

* Different result in the viewport and render.
* Noise "pop" in some frames. 
* Random number was calculated every time the file was opened, so get different results.

Now, instead to calculate the random numbers when n number of frames changed, the random values are calculated using a unique seed by stroke.

Also, a new Seed parameter has been added and this adds more control in the noise generated. This value can be animated and get more variations.

Differential Revision: http://developer.blender.org/D5393

release/scripts/startup/bl_ui/properties_data_modifier.py

@@ -1685,6 +1685,9 @@ class DATA_PT_gpencil_modifiers(ModifierButtonsPanel, Panel):
         row = col.row()
         row.enabled = md.random
         row.prop(md, "step")
+        row = col.row()
+        row.enabled = md.random
+        row.prop(md, "seed")
         col.prop(md, "full_stroke")
         col.prop(md, "move_extreme")
 

source/blender/gpencil_modifiers/intern/MOD_gpencilnoise.c

@@ -26,10 +26,9 @@
 #include "BLI_utildefines.h"
 
 #include "BLI_math_vector.h"
+#include "BLI_hash.h"
 #include "BLI_rand.h"
 
-#include "PIL_time.h"
-
 #include "DNA_meshdata_types.h"
 #include "DNA_scene_types.h"
 #include "DNA_object_types.h"
@@ -58,20 +57,7 @@ static void initData(GpencilModifierData *md)
   gpmd->layername[0] = '\0';
   gpmd->vgname[0] = '\0';
   gpmd->step = 1;
-  gpmd->scene_frame = -999999;
-  gpmd->gp_frame = -999999;
-
-  gpmd->vrand1 = 1.0;
-  gpmd->vrand2 = 1.0;
-}
-
-static void freeData(GpencilModifierData *md)
-{
-  NoiseGpencilModifierData *mmd = (NoiseGpencilModifierData *)md;
-
-  if (mmd->rng != NULL) {
-    BLI_rng_free(mmd->rng);
-  }
+  gpmd->seed = 0;
 }
 
 static void copyData(const GpencilModifierData *md, GpencilModifierData *target)
@@ -85,21 +71,6 @@ static bool dependsOnTime(GpencilModifierData *md)
   return (mmd->flag & GP_NOISE_USE_RANDOM) != 0;
 }
 
-/* Get the lower number of frame for all layers. */
-static int get_lower_frame(bGPdata *gpd)
-{
-  int init = 99999;
-  for (bGPDlayer *gpl = gpd->layers.first; gpl; gpl = gpl->next) {
-    if (gpl->frames.first) {
-      bGPDframe *gpf = gpl->frames.first;
-      if (gpf->framenum < init) {
-        init = gpf->framenum;
-      }
-    }
-  }
-  return init;
-}
-
 /* aply noise effect based on stroke direction */
 static void deformStroke(
     GpencilModifierData *md, Depsgraph *depsgraph, Object *ob, bGPDlayer *gpl, bGPDstroke *gps)
@@ -111,26 +82,10 @@ static void deformStroke(
   float normal[3];
   float vec1[3], vec2[3];
   int sc_frame = 0;
-  int sc_diff = 0;
+  int stroke_seed = 0;
   const int def_nr = defgroup_name_index(ob, mmd->vgname);
   const float unit_v3[3] = {1.0f, 1.0f, 1.0f};
 
-  Object *object_eval = DEG_get_evaluated_object(depsgraph, ob);
-  GpencilModifierData *md_eval = BKE_gpencil_modifiers_findByName(object_eval, md->name);
-  NoiseGpencilModifierData *mmd_eval = (NoiseGpencilModifierData *)md_eval;
-  bGPdata *gpd = (bGPdata *)ob->data;
-
-  /* Random generator, only init once. (it uses eval to get same value in render) */
-  if (mmd_eval->rng == NULL) {
-    uint rng_seed = (uint)(PIL_check_seconds_timer_i() & UINT_MAX);
-    rng_seed ^= POINTER_AS_UINT(mmd);
-    mmd_eval->rng = BLI_rng_new(rng_seed);
-    mmd->rng = mmd_eval->rng;
-    /* Get lower frame number */
-    mmd_eval->scene_frame = get_lower_frame(gpd);
-    mmd->scene_frame = mmd_eval->scene_frame;
-  }
-
   if (!is_stroke_affected_by_modifier(ob,
                                       mmd->layername,
                                       mmd->pass_index,
@@ -200,22 +155,14 @@ static void deformStroke(
     normalize_v3(vec2);
     /* Use random noise */
     if (mmd->flag & GP_NOISE_USE_RANDOM) {
-      sc_diff = abs(sc_frame - mmd->scene_frame) % mmd->step;
-      /* Only recalc if the gp frame change or is a step. */
-      if ((mmd->gp_frame != sc_frame) && (sc_diff == 0)) {
-        vran = mmd->vrand1 = BLI_rng_get_float(mmd->rng);
-        vdir = mmd->vrand2 = BLI_rng_get_float(mmd->rng);
-        mmd->gp_frame = sc_frame;
+      stroke_seed = BLI_hash_int_2d((sc_frame / mmd->step) + gps->totpoints, mmd->seed + 1);
+      vran = BLI_hash_frand(stroke_seed);
+      if (mmd->flag & GP_NOISE_FULL_STROKE) {
+        vdir = BLI_hash_frand(stroke_seed + 3);
       }
       else {
-        vran = mmd->vrand1;
-        if (mmd->flag & GP_NOISE_FULL_STROKE) {
-          vdir = mmd->vrand2;
-        }
-        else {
-          int f = (mmd->vrand2 * 10.0f) + i;
-          vdir = f % 2;
-        }
+        int f = (BLI_hash_frand(stroke_seed + 3) * 10.0f) + i;
+        vdir = f % 2;
       }
     }
     else {
@@ -226,7 +173,6 @@ static void deformStroke(
       else {
         vdir = i % 2;
       }
-      mmd->gp_frame = -999999;
     }
 
     /* if vec2 is zero, set to something */
@@ -314,7 +260,7 @@ GpencilModifierTypeInfo modifierType_Gpencil_Noise = {
     /* remapTime */ NULL,
 
     /* initData */ initData,
-    /* freeData */ freeData,
+    /* freeData */ NULL,
     /* isDisabled */ NULL,
     /* updateDepsgraph */ NULL,
     /* dependsOnTime */ dependsOnTime,

source/blender/makesdna/DNA_gpencil_modifier_types.h

@@ -90,16 +90,10 @@ typedef struct NoiseGpencilModifierData {
   float factor;
   /** How many frames before recalculate randoms. */
   int step;
-  /** Last gp frame used. */
-  int gp_frame;
-  /** First scene frame used. */
-  int scene_frame;
-  /** Random values. */
-  float vrand1, vrand2;
-  struct RNG *rng;
   /** Custom index for passes. */
   int layer_pass;
-  char _pad[4];
+  /** Random seed */
+  int seed;
 } NoiseGpencilModifierData;
 
 typedef enum eNoiseGpencil_Flag {

source/blender/makesrna/intern/rna_gpencil_modifier.c

@@ -377,6 +377,10 @@ static void rna_def_modifier_gpencilnoise(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Random", "Use random values");
   RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
 
+  prop = RNA_def_property(srna, "seed", PROP_INT, PROP_UNSIGNED);
+  RNA_def_property_ui_text(prop, "Seed", "Random seed");
+  RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
+
   prop = RNA_def_property(srna, "use_edit_position", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "flag", GP_NOISE_MOD_LOCATION);
   RNA_def_property_ui_text(