GPencil: Fading based on distance to reference object in Opacity and Thickness modifiers

This patch allows you to dynamically control stroke's opacity and thickness using an object for distance reference in the modifier. Fading range is adjustable, and it is compatible with current curve/vertex group selection.

Reviewed By: #grease_pencil, antoniov, mendio

Maniphest Tasks: T82177, T80194

Differential Revision: https://developer.blender.org/D9091

4 files changed, 147 insertions, 2 deletions

diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.c b/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.c
index a156fca5b7b..0d2e7e93d52 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.c
@@ -203,6 +203,21 @@ void gpencil_modifier_curve_panel_draw(const bContext *UNUSED(C), Panel *panel)
   uiTemplateCurveMapping(layout, ptr, "curve", 0, false, false, false, false);
 }
 
+void gpencil_modifier_fading_draw(const bContext *UNUSED(C), Panel *panel)
+{
+  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, NULL);
+
+  uiLayout *layout = panel->layout;
+  uiLayoutSetPropSep(layout, true);
+
+  bool fading_enabled = RNA_boolean_get(ptr, "use_fading");
+  uiItemR(layout, ptr, "object", 0, NULL, ICON_CUBE);
+  uiLayout *sub = uiLayoutColumn(layout, true);
+  uiItemR(sub, ptr, "fading_start", 0, NULL, ICON_NONE);
+  uiItemR(sub, ptr, "fading_end", 0, IFACE_("End"), ICON_NONE);
+  uiItemR(layout, ptr, "fading_end_factor", 0, NULL, ICON_NONE);
+}
+
 /**
  * Draw modifier error message.
  */
diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.h b/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.h
index 782b36d47ed..75907aaa781 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.h
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.h
@@ -37,6 +37,8 @@ void gpencil_modifier_masking_panel_draw(Panel *panel, bool use_material, bool u
 void gpencil_modifier_curve_header_draw(const bContext *C, Panel *panel);
 void gpencil_modifier_curve_panel_draw(const bContext *C, Panel *panel);
 
+void gpencil_modifier_fading_draw(const bContext *UNUSED(C), Panel *panel);
+
 void gpencil_modifier_panel_end(struct uiLayout *layout, PointerRNA *ptr);
 
 struct PointerRNA *gpencil_modifier_panel_get_property_pointers(struct Panel *panel,
diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c b/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c
index c193fc49362..838e073115e 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c
@@ -47,6 +47,8 @@
 #include "BKE_screen.h"
 
 #include "DEG_depsgraph.h"
+#include "DEG_depsgraph_build.h"
+#include "DEG_depsgraph_query.h"
 
 #include "UI_interface.h"
 #include "UI_resources.h"
@@ -84,6 +86,39 @@ static void copyData(const GpencilModifierData *md, GpencilModifierData *target)
   tgmd->curve_intensity = BKE_curvemapping_copy(gmd->curve_intensity);
 }
 
+static float give_opacity_fading_factor(OpacityGpencilModifierData *mmd,
+                                        Object *ob_this,
+                                        float *pos,
+                                        bool apply_obmat)
+{
+  float factor_depth = 1;
+
+  if (((mmd->flag & GP_OPACITY_FADING) == 0) || ((mmd->object) == NULL)) {
+    return factor_depth;
+  }
+
+  float gvert[3];
+  if (apply_obmat) {
+    mul_v3_m4v3(gvert, ob_this->obmat, pos);
+  }
+  float dist = len_v3v3(mmd->object->obmat[3], gvert);
+  float fading_max = MAX2(mmd->fading_start, mmd->fading_end);
+  float fading_min = MIN2(mmd->fading_start, mmd->fading_end);
+
+  /* Better with ratiof() function from line art. */
+  if (dist > fading_max) {
+    factor_depth = 0;
+  }
+  else if (dist <= fading_max && dist > fading_min) {
+    factor_depth = (fading_max - dist) / (fading_max - fading_min);
+  }
+  else {
+    factor_depth = 1;
+  }
+
+  return factor_depth;
+}
+
 /* opacity strokes */
 static void deformStroke(GpencilModifierData *md,
                          Depsgraph *UNUSED(depsgraph),
@@ -138,6 +173,9 @@ static void deformStroke(GpencilModifierData *md,
         factor_curve *= BKE_curvemapping_evaluateF(mmd->curve_intensity, 0, value);
       }
 
+      float factor_depth = give_opacity_fading_factor(mmd, ob, &pt->x, true);
+      factor_curve = interpf(factor_curve, mmd->fading_end_factor, factor_depth);
+
       if (def_nr < 0) {
         if (mmd->flag & GP_OPACITY_NORMALIZE) {
           pt->strength = factor_curve;
@@ -167,6 +205,10 @@ static void deformStroke(GpencilModifierData *md,
   /* Fill using opacity factor. */
   if (mmd->modify_color != GP_MODIFY_COLOR_STROKE) {
     gps->fill_opacity_fac = mmd->factor;
+
+    float factor_depth = give_opacity_fading_factor(mmd, ob, ob->obmat[3], true);
+    gps->fill_opacity_fac = interpf(mmd->factor, mmd->fading_end_factor, factor_depth);
+
     CLAMP(gps->fill_opacity_fac, 0.0f, 1.0f);
   }
 }
@@ -201,6 +243,18 @@ static void foreachIDLink(GpencilModifierData *md, Object *ob, IDWalkFunc walk,
   OpacityGpencilModifierData *mmd = (OpacityGpencilModifierData *)md;
 
   walk(userData, ob, (ID **)&mmd->material, IDWALK_CB_USER);
+  walk(userData, ob, (ID **)&mmd->object, IDWALK_CB_NOP);
+}
+
+static void updateDepsgraph(GpencilModifierData *md,
+                            const ModifierUpdateDepsgraphContext *ctx,
+                            const int UNUSED(mode))
+{
+  OpacityGpencilModifierData *mmd = (OpacityGpencilModifierData *)md;
+  if (mmd->object != NULL) {
+    DEG_add_object_relation(ctx->node, mmd->object, DEG_OB_COMP_TRANSFORM, "Opacity Modifier");
+  }
+  DEG_add_object_relation(ctx->node, ctx->object, DEG_OB_COMP_TRANSFORM, "Opacity Modifier");
 }
 
 static void panel_draw(const bContext *UNUSED(C), Panel *panel)
@@ -228,6 +282,20 @@ static void panel_draw(const bContext *UNUSED(C), Panel *panel)
   gpencil_modifier_panel_end(layout, ptr);
 }
 
+static void fading_header_draw(const bContext *UNUSED(C), Panel *panel)
+{
+  uiLayout *layout = panel->layout;
+
+  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, NULL);
+
+  uiItemR(layout, ptr, "use_fading", 0, NULL, ICON_NONE);
+}
+
+static void fading_panel_draw(const bContext *C, Panel *panel)
+{
+  gpencil_modifier_fading_draw(C, panel);
+}
+
 static void mask_panel_draw(const bContext *UNUSED(C), Panel *panel)
 {
   PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, NULL);
@@ -266,6 +334,9 @@ static void panelRegister(ARegionType *region_type)
 {
   PanelType *panel_type = gpencil_modifier_panel_register(
       region_type, eGpencilModifierType_Opacity, panel_draw);
+
+  gpencil_modifier_subpanel_register(
+      region_type, "fading", "", fading_header_draw, fading_panel_draw, panel_type);
   PanelType *mask_panel_type = gpencil_modifier_subpanel_register(
       region_type, "mask", "Influence", NULL, mask_panel_draw, panel_type);
   gpencil_modifier_subpanel_register(
@@ -289,7 +360,7 @@ GpencilModifierTypeInfo modifierType_Gpencil_Opacity = {
     /* initData */ initData,
     /* freeData */ freeData,
     /* isDisabled */ NULL,
-    /* updateDepsgraph */ NULL,
+    /* updateDepsgraph */ updateDepsgraph,
     /* dependsOnTime */ NULL,
     /* foreachIDLink */ foreachIDLink,
     /* foreachTexLink */ NULL,
diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencilthick.c b/source/blender/gpencil_modifiers/intern/MOD_gpencilthick.c
index a13f8d64755..ee53fe2f168 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencilthick.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencilthick.c
@@ -43,6 +43,8 @@
 #include "BKE_screen.h"
 
 #include "DEG_depsgraph.h"
+#include "DEG_depsgraph_build.h"
+#include "DEG_depsgraph_query.h"
 
 #include "UI_interface.h"
 #include "UI_resources.h"
@@ -128,6 +130,30 @@ static void deformStroke(GpencilModifierData *md,
     }
 
     float curvef = 1.0f;
+
+    float factor_depth = 1;
+
+    if (mmd->flag & GP_THICK_FADING) {
+      if (mmd->object) {
+        float gvert[3];
+        mul_v3_m4v3(gvert, ob->obmat, &pt->x);
+        float dist = len_v3v3(mmd->object->obmat[3], gvert);
+        float fading_max = MAX2(mmd->fading_start, mmd->fading_end);
+        float fading_min = MIN2(mmd->fading_start, mmd->fading_end);
+
+        /* Better with ratiof() function from line art. */
+        if (dist > fading_max) {
+          factor_depth = 0;
+        }
+        else if (dist <= fading_max && dist > fading_min) {
+          factor_depth = (fading_max - dist) / (fading_max - fading_min);
+        }
+        else {
+          factor_depth = 1;
+        }
+      }
+    }
+
     if ((mmd->flag & GP_THICK_CUSTOM_CURVE) && (mmd->curve_thickness)) {
       /* Normalize value to evaluate curve. */
       float value = (float)i / (gps->totpoints - 1);
@@ -144,6 +170,9 @@ static void deformStroke(GpencilModifierData *md,
       weight *= curvef;
     }
 
+    float fac_begin = mmd->flag & GP_THICK_NORMALIZE ? 1 : mmd->thickness_fac;
+    target *= interpf(fac_begin, mmd->fading_end_factor, factor_depth);
+
     pt->pressure = interpf(target, pt->pressure, weight);
 
     CLAMP_MIN(pt->pressure, 0.0f);
@@ -171,6 +200,32 @@ static void foreachIDLink(GpencilModifierData *md, Object *ob, IDWalkFunc walk,
   ThickGpencilModifierData *mmd = (ThickGpencilModifierData *)md;
 
   walk(userData, ob, (ID **)&mmd->material, IDWALK_CB_USER);
+  walk(userData, ob, (ID **)&mmd->object, IDWALK_CB_NOP);
+}
+
+static void updateDepsgraph(GpencilModifierData *md,
+                            const ModifierUpdateDepsgraphContext *ctx,
+                            const int UNUSED(mode))
+{
+  ThickGpencilModifierData *mmd = (ThickGpencilModifierData *)md;
+  if (mmd->object != NULL) {
+    DEG_add_object_relation(ctx->node, mmd->object, DEG_OB_COMP_TRANSFORM, "Thickness Modifier");
+  }
+  DEG_add_object_relation(ctx->node, ctx->object, DEG_OB_COMP_TRANSFORM, "Thickness Modifier");
+}
+
+static void fading_header_draw(const bContext *UNUSED(C), Panel *panel)
+{
+  uiLayout *layout = panel->layout;
+
+  PointerRNA *ptr = gpencil_modifier_panel_get_property_pointers(panel, NULL);
+
+  uiItemR(layout, ptr, "use_fading", 0, NULL, ICON_NONE);
+}
+
+static void fading_panel_draw(const bContext *C, Panel *panel)
+{
+  gpencil_modifier_fading_draw(C, panel);
 }
 
 static void panel_draw(const bContext *UNUSED(C), Panel *panel)
@@ -202,6 +257,8 @@ static void panelRegister(ARegionType *region_type)
 {
   PanelType *panel_type = gpencil_modifier_panel_register(
       region_type, eGpencilModifierType_Thick, panel_draw);
+  gpencil_modifier_subpanel_register(
+      region_type, "fading", "", fading_header_draw, fading_panel_draw, panel_type);
   PanelType *mask_panel_type = gpencil_modifier_subpanel_register(
       region_type, "mask", "Influence", NULL, mask_panel_draw, panel_type);
   gpencil_modifier_subpanel_register(region_type,
@@ -229,7 +286,7 @@ GpencilModifierTypeInfo modifierType_Gpencil_Thick = {
     /* initData */ initData,
     /* freeData */ freeData,
     /* isDisabled */ NULL,
-    /* updateDepsgraph */ NULL,
+    /* updateDepsgraph */ updateDepsgraph,
     /* dependsOnTime */ NULL,
     /* foreachIDLink */ foreachIDLink,
     /* foreachTexLink */ NULL,