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

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)