GPencil: New Percentage parameter in Build modifier

Add a factor to determine the percentage affected.

This parameter is used to hide part of the stroke and to have a full control of how the points are displayed and not linked to current scene frame.

{F8526502}

{F8526511}

Reviewed By: mendio, pepeland

Differential Revision: https://developer.blender.org/D7682

4 files changed, 28 insertions, 1 deletions

diff --git a/release/scripts/startup/bl_ui/properties_data_modifier.py b/release/scripts/startup/bl_ui/properties_data_modifier.py
index 1552e10cdf7..29fcb06ac67 100644
--- a/release/scripts/startup/bl_ui/properties_data_modifier.py
+++ b/release/scripts/startup/bl_ui/properties_data_modifier.py
@@ -2182,6 +2182,11 @@ class DATA_PT_gpencil_modifiers(ModifierButtonsPanel, Panel):
         sub.prop(md, "frame_start", text="Start")
         sub.prop(md, "frame_end", text="End")
 
+        col.prop(md, "use_percentage")
+        sub = col.column(align=True)
+        sub.active = md.use_percentage
+        sub.prop(md, "percentage_factor")
+
         layout.label(text="Influence Filters:")
 
         split = layout.split(factor=0.25)
diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencilbuild.c b/source/blender/gpencil_modifiers/intern/MOD_gpencilbuild.c
index c31f73df25d..71a051629d8 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencilbuild.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencilbuild.c
@@ -406,6 +406,7 @@ static void generate_geometry(GpencilModifierData *md,
 {
   BuildGpencilModifierData *mmd = (BuildGpencilModifierData *)md;
   const bool reverse = (mmd->transition != GP_BUILD_TRANSITION_GROW);
+  const bool is_percentage = (mmd->flag & GP_BUILD_PERCENTAGE);
 
   const float ctime = DEG_get_ctime(depsgraph);
 
@@ -500,7 +501,8 @@ static void generate_geometry(GpencilModifierData *md,
   }
 
   /* Determine how far along we are between the keyframes */
-  float fac = (ctime - start_frame) / (end_frame - start_frame);
+  float fac = is_percentage ? mmd->percentage_fac :
+                              (ctime - start_frame) / (end_frame - start_frame);
 
   /* Time management mode */
   switch (mmd->mode) {
diff --git a/source/blender/makesdna/DNA_gpencil_modifier_types.h b/source/blender/makesdna/DNA_gpencil_modifier_types.h
index deb955f5551..dc4b0997b00 100644
--- a/source/blender/makesdna/DNA_gpencil_modifier_types.h
+++ b/source/blender/makesdna/DNA_gpencil_modifier_types.h
@@ -370,6 +370,9 @@ typedef struct BuildGpencilModifierData {
    * For the "Concurrent" mode, when should "shorter" strips start/end.
    */
   short time_alignment;
+  /** Factor of the stroke (used instead of frame evaluation. */
+  float percentage_fac;
+  char _pad[4];
 } BuildGpencilModifierData;
 
 typedef enum eBuildGpencil_Mode {
@@ -405,6 +408,9 @@ typedef enum eBuildGpencil_Flag {
   /* Restrict modifier to only operating between the nominated frames */
   GP_BUILD_RESTRICT_TIME = (1 << 2),
   GP_BUILD_INVERT_LAYERPASS = (1 << 3),
+
+  /* Use a percentage instead of frame number to evaluate strokes. */
+  GP_BUILD_PERCENTAGE = (1 << 4),
 } eBuildGpencil_Flag;
 
 typedef struct LatticeGpencilModifierData {
diff --git a/source/blender/makesrna/intern/rna_gpencil_modifier.c b/source/blender/makesrna/intern/rna_gpencil_modifier.c
index 1906c663c54..e6cc14da667 100644
--- a/source/blender/makesrna/intern/rna_gpencil_modifier.c
+++ b/source/blender/makesrna/intern/rna_gpencil_modifier.c
@@ -1671,6 +1671,20 @@ static void rna_def_modifier_gpencilbuild(BlenderRNA *brna)
       prop, "Restrict Frame Range", "Only modify strokes during the specified frame range");
   RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
 
+  /* Use percentage */
+  prop = RNA_def_property(srna, "use_percentage", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", GP_BUILD_PERCENTAGE);
+  RNA_def_property_ui_text(
+      prop, "Restrict Visible Points", "Use a percentage factor to determine the visible points");
+  RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
+
+  /* Percentage factor. */
+  prop = RNA_def_property(srna, "percentage_factor", PROP_FLOAT, PROP_FACTOR);
+  RNA_def_property_float_sdna(prop, NULL, "percentage_fac");
+  RNA_def_property_ui_text(prop, "Factor", "Defines how much of the stroke is visible");
+  RNA_def_property_range(prop, 0.0f, 1.0f);
+  RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
+
   prop = RNA_def_property(srna, "frame_start", PROP_FLOAT, PROP_NONE);
   RNA_def_property_float_sdna(prop, NULL, "start_frame");
   RNA_def_property_ui_text(