GPencil: New Strength mode for Opacity modifier

This new option applies the opacity using the strength of the stroke instead to use the alpha channel of the material.

Tested in greasepencil-object branch

{F7712796}

The vertex group filter has been removed because this filter is not logic in Material mode and must be valid only in Strength mode.

{F7713147}

Reviewers: pepeland, mendio

Reviewed By: mendio

Differential Revision: https://developer.blender.org/D5650

4 files changed, 75 insertions, 29 deletions

diff --git a/release/scripts/startup/bl_ui/properties_data_modifier.py b/release/scripts/startup/bl_ui/properties_data_modifier.py
index 47c911821fc..dcdb1e22bde 100644
--- a/release/scripts/startup/bl_ui/properties_data_modifier.py
+++ b/release/scripts/startup/bl_ui/properties_data_modifier.py
@@ -2012,15 +2012,19 @@ class DATA_PT_gpencil_modifiers(ModifierButtonsPanel, Panel):
         col.prop(md, "factor")
 
         row = layout.row()
-        row.prop(md, "create_materials")
-        row.prop(md, "modify_color")
+        row.prop(md, "opacity_mode", text="Mode")
 
-        col = layout.column()
-        col.separator()
-        col.label(text="Vertex Group:")
-        row = col.row(align=True)
-        row.prop_search(md, "vertex_group", ob, "vertex_groups", text="")
-        row.prop(md, "invert_vertex", text="", icon='ARROW_LEFTRIGHT')
+        if md.opacity_mode == 'MATERIAL':
+            row = layout.row()
+            row.prop(md, "create_materials")
+            row.prop(md, "modify_color", text="Change")
+        else:
+            col = layout.column()
+            col.separator()
+            col.label(text="Vertex Group:")
+            row = col.row(align=True)
+            row.prop_search(md, "vertex_group", ob, "vertex_groups", text="")
+            row.prop(md, "invert_vertex", text="", icon='ARROW_LEFTRIGHT')
 
         col = layout.column()
         col.separator()
diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c b/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c
index c2ab672b68b..22610771045 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencilopacity.c
@@ -89,38 +89,56 @@ static void deformStroke(GpencilModifierData *md,
     return;
   }
 
-  if (mmd->modify_color != GP_MODIFY_COLOR_FILL) {
-    gps->runtime.tmp_stroke_rgba[3] *= mmd->factor;
-    /* if factor is > 1, then force opacity */
-    if (mmd->factor > 1.0f) {
-      gps->runtime.tmp_stroke_rgba[3] += mmd->factor - 1.0f;
+  if (mmd->opacity_mode == GP_OPACITY_MODE_MATERIAL) {
+    if (mmd->modify_color != GP_MODIFY_COLOR_FILL) {
+      gps->runtime.tmp_stroke_rgba[3] *= mmd->factor;
+      /* if factor is > 1, then force opacity */
+      if (mmd->factor > 1.0f) {
+        gps->runtime.tmp_stroke_rgba[3] += mmd->factor - 1.0f;
+      }
+      CLAMP(gps->runtime.tmp_stroke_rgba[3], 0.0f, 1.0f);
     }
-    CLAMP(gps->runtime.tmp_stroke_rgba[3], 0.0f, 1.0f);
-  }
 
-  if (mmd->modify_color != GP_MODIFY_COLOR_STROKE) {
-    gps->runtime.tmp_fill_rgba[3] *= mmd->factor;
-    /* if factor is > 1, then force opacity */
-    if (mmd->factor > 1.0f && gps->runtime.tmp_fill_rgba[3] > 1e-5) {
-      gps->runtime.tmp_fill_rgba[3] += mmd->factor - 1.0f;
+    if (mmd->modify_color != GP_MODIFY_COLOR_STROKE) {
+      gps->runtime.tmp_fill_rgba[3] *= mmd->factor;
+      /* if factor is > 1, then force opacity */
+      if (mmd->factor > 1.0f && gps->runtime.tmp_fill_rgba[3] > 1e-5) {
+        gps->runtime.tmp_fill_rgba[3] += mmd->factor - 1.0f;
+      }
+      CLAMP(gps->runtime.tmp_fill_rgba[3], 0.0f, 1.0f);
     }
-    CLAMP(gps->runtime.tmp_fill_rgba[3], 0.0f, 1.0f);
-  }
 
-  /* if opacity > 1.0, affect the strength of the stroke */
-  if (mmd->factor > 1.0f) {
+    /* if opacity > 1.0, affect the strength of the stroke */
+    if (mmd->factor > 1.0f) {
+      for (int i = 0; i < gps->totpoints; i++) {
+        bGPDspoint *pt = &gps->points[i];
+        pt->strength += mmd->factor - 1.0f;
+        CLAMP(pt->strength, 0.0f, 1.0f);
+      }
+    }
+  }
+  /* Apply opacity by strength */
+  else {
     for (int i = 0; i < gps->totpoints; i++) {
       bGPDspoint *pt = &gps->points[i];
       MDeformVert *dvert = gps->dvert != NULL ? &gps->dvert[i] : NULL;
 
       /* verify vertex group */
-      const float weight = get_modifier_point_weight(
+      float weight = get_modifier_point_weight(
           dvert, (mmd->flag & GP_OPACITY_INVERT_VGROUP) != 0, def_nr);
       if (weight < 0.0f) {
+        continue;
+      }
+      if (def_nr < 0) {
         pt->strength += mmd->factor - 1.0f;
       }
       else {
-        pt->strength += (mmd->factor - 1.0f) * weight;
+        /* High factor values, change weight too. */
+        if ((mmd->factor > 1.0f) && (weight < 1.0f)) {
+          weight += mmd->factor - 1.0f;
+          CLAMP(weight, 0.0f, 1.0f);
+        }
+        pt->strength += (mmd->factor - 1) * weight;
       }
       CLAMP(pt->strength, 0.0f, 1.0f);
     }
@@ -152,8 +170,10 @@ static void bakeModifier(Main *bmain, Depsgraph *depsgraph, GpencilModifierData
 
         deformStroke(md, depsgraph, ob, gpl, gpf, gps);
 
-        gpencil_apply_modifier_material(
-            bmain, ob, mat, gh_color, gps, (bool)(mmd->flag & GP_OPACITY_CREATE_COLORS));
+        if (mmd->opacity_mode == GP_OPACITY_MODE_MATERIAL) {
+          gpencil_apply_modifier_material(
+              bmain, ob, mat, gh_color, gps, (bool)(mmd->flag & GP_OPACITY_CREATE_COLORS));
+        }
       }
     }
   }
diff --git a/source/blender/makesdna/DNA_gpencil_modifier_types.h b/source/blender/makesdna/DNA_gpencil_modifier_types.h
index f094d630fc8..7d407dc85bc 100644
--- a/source/blender/makesdna/DNA_gpencil_modifier_types.h
+++ b/source/blender/makesdna/DNA_gpencil_modifier_types.h
@@ -200,6 +200,11 @@ typedef enum eModifyColorGpencil_Flag {
   GP_MODIFY_COLOR_FILL = 2,
 } eModifyColorGpencil_Flag;
 
+typedef enum eOpacityModesGpencil_Flag {
+  GP_OPACITY_MODE_MATERIAL = 0,
+  GP_OPACITY_MODE_STRENGTH = 1,
+} eOpacityModesGpencil_Flag;
+
 typedef struct TintGpencilModifierData {
   GpencilModifierData modifier;
   /** Layer name. */
@@ -274,7 +279,9 @@ typedef struct OpacityGpencilModifierData {
   float factor;
   /** Modify stroke, fill or both. */
   char modify_color;
-  char _pad[3];
+  /** Mode of opacity, colors or strength */
+  char opacity_mode;
+  char _pad[2];
   /** Custom index for passes. */
   int layer_pass;
   char _pad1[4];
diff --git a/source/blender/makesrna/intern/rna_gpencil_modifier.c b/source/blender/makesrna/intern/rna_gpencil_modifier.c
index 0b40cc9f7f9..f4458a49768 100644
--- a/source/blender/makesrna/intern/rna_gpencil_modifier.c
+++ b/source/blender/makesrna/intern/rna_gpencil_modifier.c
@@ -133,6 +133,16 @@ static const EnumPropertyItem modifier_modify_color_items[] = {
     {0, NULL, 0, NULL, NULL},
 };
 
+static const EnumPropertyItem modifier_opacity_mode_items[] = {
+    {GP_OPACITY_MODE_MATERIAL,
+     "MATERIAL",
+     0,
+     "Material",
+     "Modify opacity using alpha channel of material"},
+    {GP_OPACITY_MODE_STRENGTH, "STRENGTH", 0, "Strength", "Modify opacity using point strength"},
+    {0, NULL, 0, NULL, NULL},
+};
+
 static const EnumPropertyItem modifier_gphook_falloff_items[] = {
     {eGPHook_Falloff_None, "NONE", 0, "No Falloff", ""},
     {eGPHook_Falloff_Curve, "CURVE", 0, "Curve", ""},
@@ -1164,6 +1174,11 @@ static void rna_def_modifier_gpencilopacity(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Mode", "Set what colors of the stroke are affected");
   RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
 
+  prop = RNA_def_property(srna, "opacity_mode", PROP_ENUM, PROP_NONE);
+  RNA_def_property_enum_items(prop, modifier_opacity_mode_items);
+  RNA_def_property_ui_text(prop, "Opacity Mode", "Set what mode used to define opacity");
+  RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
+
   prop = RNA_def_property(srna, "layer", PROP_STRING, PROP_NONE);
   RNA_def_property_string_sdna(prop, NULL, "layername");
   RNA_def_property_ui_text(prop, "Layer", "Layer name");