102 lines
4.5 KiB
Text
102 lines
4.5 KiB
Text
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.. _doc_using_multimesh:
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Optimization using MultiMeshes
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==============================
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For large amount of instances (in the thousands), that need to be constantly processed
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(and certain amount of control needs to be retained),
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:ref:`using servers directly <doc_using_servers>` is the recommended optimization.
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When the amount of objects reach the hundreds of thousands or millions,
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none of these approaches are efficient anymore. Still, depending on the requirements, there
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is one more optimization possible.
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MultiMeshes
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-----------
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A :ref:`MultiMesh<class_MultiMesh>` is a single draw primitive that can draw up to millions
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of objects in one go. It's extremely efficient because it uses the GPU hardware to do this
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(in OpenGL ES 2.0, it's less efficient because there is no hardware support for it, though).
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The only drawback is that there is no *screen* or *frustum* culling possible for individual instances.
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This means, that millions of objects will be *always* or *never* drawn, depending on the visibility
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of the whole MultiMesh. It is possible to provide a custom visibility rect for them, but it will always
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be *all-or-none* visibility.
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If the objects are simple enough (just a couple of vertices), this is generally not much of a problem
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as most modern GPUs are optimized for this use case. A workaround is to create several MultiMeshes
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for different areas of the world.
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It is also possible to execute some logic inside the vertex shader (using the ``INSTANCE_ID`` or
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``INSTANCE_CUSTOM`` built-in constants). For an example of animating thousands of objects in a MultiMesh,
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see the :ref:`Animating thousands of fish <doc_animating_thousands_of_fish>` tutorial. Information
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to the shader can be provided via textures (there are floating-point :ref:`Image<class_Image>` formats
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which are ideal for this).
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Another alternative is to use GDNative and C++, which should be extremely efficient (it's possible
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to set the entire state for all objects using linear memory via the
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:ref:`VisualServer.multimesh_set_as_bulk_array() <class_VisualServer_method_multimesh_set_as_bulk_array>`
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function). This way, the array can be created with multiple threads, then set in one call, providing
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high cache efficiency.
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Finally, it's not required to have all MultiMesh instances visible. The amount of visible ones can be
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controlled with the :ref:`MultiMesh.visible_instance_count <class_MultiMesh_property_visible_instance_count>`
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property. The typical workflow is to allocate the maximum amount of instances that will be used,
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then change the amount visible depending on how many are currently needed.
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Multimesh example
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-----------------
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Here is an example of using a MultiMesh from code. Languages other than GDScript may be more
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efficient for millions of objects, but for a few thousands, GDScript should be fine.
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.. tabs::
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.. code-tab:: gdscript GDScript
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extends MultiMeshInstance
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func _ready():
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# Create the multimesh.
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multimesh = MultiMesh.new()
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# Set the format first.
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multimesh.transform_format = MultiMesh.TRANSFORM_3D
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multimesh.color_format = MultiMesh.COLOR_NONE
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multimesh.custom_data_format = MultiMesh.CUSTOM_DATA_NONE
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# Then resize (otherwise, changing the format is not allowed).
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multimesh.instance_count = 10000
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# Maybe not all of them should be visible at first.
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multimesh.visible_instance_count = 1000
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# Set the transform of the instances.
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for i in multimesh.visible_instance_count:
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multimesh.set_instance_transform(i, Transform(Basis(), Vector3(i * 20, 0, 0)))
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.. code-tab:: csharp C#
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using Godot;
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using System;
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public class YourClassName : MultiMeshInstance
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{
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public override void _Ready()
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{
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// Create the multimesh.
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Multimesh = new MultiMesh();
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// Set the format first.
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Multimesh.TransformFormat = MultiMesh.TransformFormatEnum.Transform3d;
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Multimesh.ColorFormat = MultiMesh.ColorFormatEnum.None;
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Multimesh.CustomDataFormat = MultiMesh.CustomDataFormatEnum.None;
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// Then resize (otherwise, changing the format is not allowed)
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Multimesh.InstanceCount = 1000;
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// Maybe not all of them should be visible at first.
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Multimesh.VisibleInstanceCount = 1000;
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// Set the transform of the instances.
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for (int i = 0; i < Multimesh.VisibleInstanceCount; i++)
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{
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Multimesh.SetInstanceTransform(i, new Transform(Basis.Identity, new Vector3(i * 20, 0, 0)));
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}
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}
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}
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