267 lines
12 KiB
Text
267 lines
12 KiB
Text
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.. _doc_lights_and_shadows:
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3D lights and shadows
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=====================
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Introduction
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------------
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Light sources emit light that mixes with the materials and produces a visible
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result. Light can come from several types of sources in a scene:
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- From the Material itself in the form of the emission color (though
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it does not affect nearby objects unless baked).
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- Light Nodes: Directional, Omni and Spot.
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- Ambient Light in the
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:ref:`Environment <class_Environment>`.
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- Baked Light (read :ref:`doc_baked_lightmaps`).
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The emission color is a material property. You can read more about it
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in the :ref:`doc_spatial_material` tutorial.
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Light nodes
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-----------
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There are three types of light nodes: `Directional light`_,
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`Omni light`_ and `Spot light`_. Let's take a look at the common
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parameters for lights:
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.. image:: img/light_params.png
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Each one has a specific function:
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- **Color**: Base color for emitted light.
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- **Energy**: Energy multiplier. This is useful for saturating lights or working with :ref:`doc_high_dynamic_range`.
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- **Indirect Energy**: Secondary multiplier used with indirect light (light bounces). This works in baked light or GIProbe.
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- **Negative**: Light becomes subtractive instead of additive. It's sometimes useful to manually compensate some dark corners.
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- **Specular**: Affects the intensity of the specular blob in objects affected by this light. At zero, this light becomes a pure diffuse light.
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- **Bake Mode**: Sets the bake mode for the light. For more information see :ref:`doc_baked_lightmaps`
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- **Cull Mask**: Objects that are in the selected layers below will be affected by this light.
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Note that objects disabled via this cull mask will still cast shadows.
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If you don't want disabled objects to cast shadows, adjust the ``cast_shadow`` property on the
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GeometryInstance to the desired value.
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Shadow mapping
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^^^^^^^^^^^^^^
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Lights can optionally cast shadows. This gives them greater realism (light does
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not reach occluded areas), but it can incur a bigger performance cost.
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There is a list of generic shadow parameters, each also has a specific function:
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- **Enabled**: Check to enable shadow mapping in this light.
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- **Color**: Areas occluded are multiplied by this color. It is black by default, but it can be changed to tint shadows.
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- **Bias**: When this parameter is too small, self shadowing occurs. When too large, shadows separate from the casters. Tweak to what works best for you.
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- **Contact**: Performs a short screen-space raycast to reduce the gap generated by the bias. Contact shadows are only available when using the GLES3 backend.
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- **Reverse Cull Face**: Some scenes work better when shadow mapping is rendered with face-culling inverted.
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Below is an image of what tweaking bias looks like. Default values work for most
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cases, but in general it depends on the size and complexity of geometry.
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.. image:: img/shadow_bias.png
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Finally, if gaps can't be solved, the **Contact** option can help (at a performance cost):
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.. image:: img/shadow_contact.png
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Any sort of bias issues can always be fixed by increasing the shadow map resolution,
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although that may lead to decreased performance.
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.. tip::
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If shadow biasing is a problem in your scene, the following settings are a good starting point:
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- Enable **Reverse Cull Face**. This reduces shadow peter-panning significantly
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and prevents lights from exhibiting shadow acne at grazing angles.
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The main downside is that it may cause lighting to leak in some corners.
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The other downside is that materials that have their cull mode set to
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**Disabled** or MeshInstances with Cast Shadow set to **Double-Sided**
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may exhibit shadow acne.
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- Set **Bias** to ``-0.01``. The bias should be a negative value when
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**Reverse Cull Face** is enabled, but it should be a positive value when it's disabled.
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- For DirectionalLight, set the directional shadow **Normal Bias** to ``0.0``
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and **Bias Split Scale** to ``0.0``. Depending on your scene, you may also
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want to further decrease **Bias** to a value between ``-0.05`` and ``-0.1``.
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Following the above tips should make it possible to avoid gaps in shadows without
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resorting to contact shadows (which have many issues of their own).
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If shadow acne is still visible after performing the above tweaks,
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try subdividing your meshes further in your 3D modeling software.
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Directional light
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~~~~~~~~~~~~~~~~~
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This is the most common type of light and represents a light source
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very far away (such as the sun). It is also the cheapest light to compute and should be used whenever possible
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(although it's not the cheapest shadow-map to compute, but more on that later).
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Directional light models an infinite number of parallel light rays
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covering the whole scene. The directional light node is represented by a big arrow which
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indicates the direction of the light rays. However, the position of the node
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does not affect the lighting at all and can be anywhere.
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.. image:: img/light_directional.png
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Every face whose front-side is hit by the light rays is lit, while the others stay dark. Most light types
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have specific parameters, but directional lights are pretty simple in nature, so they don't.
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Directional shadow mapping
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^^^^^^^^^^^^^^^^^^^^^^^^^^
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To compute shadow maps, the scene is rendered (only depth) from an orthogonal point of view that covers
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the whole scene (or up to the max distance). There is, however, a problem with this approach because objects
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closer to the camera receive blocky shadows.
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.. image:: img/shadow_blocky.png
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To fix this, a technique named "Parallel Split Shadow Maps" (or PSSM) is used. This splits the view frustum in 2 or 4 areas. Each
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area gets its own shadow map. This allows small areas close to the viewer to have the same shadow resolution as a huge, far-away area.
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.. image:: img/pssm_explained.png
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With this, shadows become more detailed:
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.. image:: img/shadow_pssm.png
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To control PSSM, a number of parameters are exposed:
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.. image:: img/directional_shadow_params.png
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Each split distance is controlled relative to the camera far (or shadow
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**Max Distance** if greater than zero), so *0.0* is the eye position and *1.0*
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is where the shadow ends at a distance. Splits are in-between. Default values
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generally work well, but tweaking the first split a bit is common to give more
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detail to close objects (like a character in a third person game).
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Always make sure to set a shadow *Max Distance* according to what the scene needs.
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A lower maximum distance will result in better-looking shadows.
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Sometimes, the transition between a split and the next can look bad. To fix this,
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the **"Blend Splits"** option can be turned on, which sacrifices detail in exchange
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for smoother transitions:
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.. image:: img/blend_splits.png
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The **"Normal Bias"** parameter can be used to fix special cases of self shadowing
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when objects are perpendicular to the light. The only downside is that it makes
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the shadow a bit thinner.
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.. image:: img/normal_bias.png
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The **"Bias Split Scale"** parameter can control extra bias for the splits that
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are far away. If self shadowing occurs only on the splits far away, this value can fix them.
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Finally, the **"Depth Range"** has two settings:
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- **Stable**: Keeps the shadow stable while the camera moves, and the blocks that appear in the outline when close to the shadow edges remain in-place. This is the default and generally desired, but it reduces the effective shadow resolution.
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- **Optimized**: Tries to achieve the maximum resolution available at any given time. This may result in a "moving saw" effect on shadow edges, but at the same time the shadow looks more detailed (so this effect may be subtle enough to be forgiven).
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Just experiment which setting works better for your scene.
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Shadowmap size for directional lights can be changed in Project Settings -> Rendering -> Quality:
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.. image:: img/project_setting_shadow.png
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Increasing it can solve bias problems, but decrease performance. Shadow mapping is an art of tweaking.
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Omni light
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~~~~~~~~~~
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Omni light is a point source that emits light spherically in all directions up to a given
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radius.
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.. image:: img/light_omni.png
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In real life, light attenuation is an inverse function, which means omni lights don't have a radius.
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This is a problem because it means computing several omni lights would become demanding.
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To solve this, a *Range* is introduced together with an attenuation function.
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.. image:: img/light_omni_params.png
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These two parameters allow tweaking how this works visually in order to find aesthetically pleasing results.
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.. image:: img/light_attenuation.png
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Omni shadow mapping
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^^^^^^^^^^^^^^^^^^^
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Omni light shadow mapping is relatively straightforward. The main issue that needs to be
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considered is the algorithm used to render it.
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Omni Shadows can be rendered as either **"Dual Paraboloid" or "Cube Mapped"**.
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The former renders quickly, but can cause deformations,
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while the later is more correct, but costlier.
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.. image:: img/shadow_omni_dp_cm.png
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If the objects being rendered are mostly irregular, Dual Paraboloid is usually
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enough. In any case, as these shadows are cached in a shadow atlas (more on that at the end), it
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may not make a difference in performance for most scenes.
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Spot light
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~~~~~~~~~~
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Spot lights are similar to omni lights, except they emit light only into a cone
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(or "cutoff"). They are useful to simulate flashlights,
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car lights, reflectors, spots, etc. This type of light is also attenuated towards the
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opposite direction it points to.
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.. image:: img/light_spot.png
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Spot lights share the same **Range** and **Attenuation** as **OmniLight**, and add two extra parameters:
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- **Angle**: The aperture angle of the light
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- **Angle Attenuation**: The cone attenuation, which helps soften the cone borders.
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Spot shadow mapping
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^^^^^^^^^^^^^^^^^^^
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Spots don't need any parameters for shadow mapping. Keep in mind that, at more than 89 degrees of aperture, shadows
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stop functioning for spots, and you should consider using an Omni light instead.
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Shadow atlas
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~~~~~~~~~~~~
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Unlike Directional lights, which have their own shadow texture, Omni and Spot lights are assigned to slots of a shadow atlas.
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This atlas can be configured in Project Settings -> Rendering -> Quality -> Shadow Atlas.
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.. image:: img/shadow_atlas.png
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The resolution applies to the whole Shadow Atlas. This atlas is divided into four quadrants:
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.. image:: img/shadow_quadrants.png
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Each quadrant can be subdivided to allocate any number of shadow maps; the following is the default subdivision:
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.. image:: img/shadow_quadrants2.png
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The allocation logic is simple. The biggest shadow map size (when no subdivision is used)
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represents a light the size of the screen (or bigger).
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Subdivisions (smaller maps) represent shadows for lights that are further away
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from view and proportionally smaller.
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Every frame, the following procedure is performed for all lights:
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1. Check if the light is on a slot of the right size. If not, re-render it and move it to a larger/smaller slot.
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2. Check if any object affecting the shadow map has changed. If it did, re-render the light.
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3. If neither of the above has happened, nothing is done, and the shadow is left untouched.
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If the slots in a quadrant are full, lights are pushed back to smaller slots, depending on size and distance.
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This allocation strategy works for most games, but you may want to use a separate one in some cases (for example, a top-down game where
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all lights are around the same size and quadrants may all have the same subdivision).
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Shadow filter quality
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~~~~~~~~~~~~~~~~~~~~~
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The filter quality of shadows can be tweaked. This can be found in
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Project Settings -> Rendering -> Quality -> Shadows.
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Godot supports no filter, PCF5 and PCF13.
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.. image:: img/shadow_pcf1.png
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It affects the blockyness of the shadow outline:
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.. image:: img/shadow_pcf2.png
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