user: How do I use GreasePencilBuildModifier(Modifier) in Blender? Include parameters, examples, warnings and best practices.

assistant: # GreasePencilBuildModifier(Modifier)

base classes — [`bpy_struct`](bpy.types.bpy_struct.html#bpy.types.bpy_struct "bpy.types.bpy_struct"), [`Modifier`](bpy.types.Modifier.html#bpy.types.Modifier "bpy.types.Modifier")

*class* bpy.types.GreasePencilBuildModifier(*Modifier*)
:   Animate strokes appearing and disappearing

    concurrent_time_alignment
    :   How should strokes start to appear/disappear

        - `START`
          Align Start – All strokes start at same time (i.e. short strokes finish earlier).
        - `END`
          Align End – All strokes end at same time (i.e. short strokes start later).

        Type:
        :   enum in [`'START'`, `'END'`], default `'START'`

    fade_factor
    :   Defines how much of the stroke is fading in/out

        Type:
        :   float in [0, 1], default 0.0

    fade_opacity_strength
    :   How much strength fading applies on top of stroke opacity

        Type:
        :   float in [0, 1], default 0.0

    fade_thickness_strength
    :   How much strength fading applies on top of stroke thickness

        Type:
        :   float in [0, 1], default 0.0

    frame_end
    :   End Frame (when Restrict Frame Range is enabled)

        Type:
        :   float in [-1.04857e+06, 1.04857e+06], default 125.0

    frame_start
    :   Start Frame (when Restrict Frame Range is enabled)

        Type:
        :   float in [-1.04857e+06, 1.04857e+06], default 1.0

    invert_layer_filter
    :   Invert layer filter

        Type:
        :   boolean, default False

    invert_layer_pass_filter
    :   Invert layer pass filter

        Type:
        :   boolean, default False

    invert_material_filter
    :   Invert material filter

        Type:
        :   boolean, default False

    invert_material_pass_filter
    :   Invert material pass filter

        Type:
        :   boolean, default False

    layer_pass_filter
    :   Layer pass filter

        Type:
        :   int in [0, 100], default 0

    length
    :   Maximum number of frames that the build effect can run for (unless another GP keyframe occurs before this time has elapsed)

        Type:
        :   float in [1, 1.04857e+06], default 100.0

    material_filter
    :   Material used for filtering

        Type:
        :   [`Material`](bpy.types.Material.html#bpy.types.Material "bpy.types.Material")

    material_pass_filter
    :   Material pass

        Type:
        :   int in [0, 100], default 0

    mode
    :   How strokes are being built

        - `SEQUENTIAL`
          Sequential – Strokes appear/disappear one after the other, but only a single one changes at a time.
        - `CONCURRENT`
          Concurrent – Multiple strokes appear/disappear at once.
        - `ADDITIVE`
          Additive – Builds only new strokes (assuming ‘additive’ drawing).

        Type:
        :   enum in [`'SEQUENTIAL'`, `'CONCURRENT'`, `'ADDITIVE'`], default `'SEQUENTIAL'`

    object
    :   Object used as build starting position

        Type:
        :   [`Object`](bpy.types.Object.html#bpy.types.Object "bpy.types.Object")

    open_fading_panel
    :   Type:
        :   boolean, default False

    open_frame_range_panel
    :   Type:
        :   boolean, default False

    open_influence_panel
    :   Type:
        :   boolean, default False

    percentage_factor
    :   Defines how much of the stroke is visible

        Type:
        :   float in [0, 1], default 0.0

    speed_factor
    :   Multiply recorded drawing speed by a factor

        Type:
        :   float in [0, 100], default 1.2

    speed_maxgap
    :   The maximum gap between strokes in seconds

        Type:
        :   float in [0, 100], default 0.5

    start_delay
    :   Number of frames after each GP keyframe before the modifier has any effect

        Type:
        :   float in [0, 1.04857e+06], default 0.0

    target_vertex_group
    :   Output Vertex group

        Type:
        :   string, default “”, (never None)

    time_mode
    :   Use drawing speed, a number of frames, or a manual factor to build strokes

        - `DRAWSPEED`
          Natural Drawing Speed – Use recorded speed multiplied by a factor.
        - `FRAMES`
          Number of Frames – Set a fixed number of frames for all build animations.
        - `PERCENTAGE`
          Percentage Factor – Set a manual percentage to build.

        Type:
        :   enum in [`'DRAWSPEED'`, `'FRAMES'`, `'PERCENTAGE'`], default `'FRAMES'`

    transition
    :   How are strokes animated (i.e. are they appearing or disappearing)

        - `GROW`
          Grow – Show points in the order they occur in each stroke (e.g. for animating lines being drawn).
        - `SHRINK`
          Shrink – Hide points from the end of each stroke to the start (e.g. for animating lines being erased).
        - `FADE`
          Vanish – Hide points in the order they occur in each stroke (e.g. for animating ink fading or vanishing after getting drawn).

        Type:
        :   enum in [`'GROW'`, `'SHRINK'`, `'FADE'`], default `'GROW'`

    tree_node_filter
    :   Layer name

        Type:
        :   string, default “”, (never None)

    use_fading
    :   Fade out strokes instead of directly cutting off

        Type:
        :   boolean, default False

    use_layer_group_filter
    :   Filter by layer group name

        Type:
        :   boolean, default False

    use_layer_pass_filter
    :   Use layer pass filter

        Type:
        :   boolean, default False

    use_material_pass_filter
    :   Use material pass filter

        Type:
        :   boolean, default False

    use_percentage
    :   Use a percentage factor to determine the visible points

        Type:
        :   boolean, default False

    use_restrict_frame_range
    :   Only modify strokes during the specified frame range

        Type:
        :   boolean, default False

    *classmethod* bl_rna_get_subclass(*id*, *default=None*, */*)
    :   Parameters:
        :   **id** (*str*) – The RNA type identifier.

        Returns:
        :   The RNA type or default when not found.

        Return type:
        :   [`bpy.types.Struct`](bpy.types.Struct.html#bpy.types.Struct "bpy.types.Struct") subclass

    *classmethod* bl_rna_get_subclass_py(*id*, *default=None*, */*)
    :   Parameters:
        :   **id** (*str*) – The RNA type identifier.

        Returns:
        :   The class or default when not found.

        Return type:
        :   type