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173 lines
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ReStructuredText
173 lines
7.3 KiB
ReStructuredText
.. _doc_custom_postprocessing:
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Custom post-processing
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======================
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Introduction
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------------
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Godot provides many post-processing effects out of the box, including Bloom, DOF, and SSAO. Sometimes you
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want to write your own custom effect. Here's how you can do so.
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Post-processing effects are shaders applied to a frame after Godot rendered it. You first want to render
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your scene into a :ref:`Viewport <class_Viewport>`, then render the ``Viewport``
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inside a :ref:`ViewportTexture <class_ViewportTexture>` and show it on the screen.
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The easiest way to implement a custom post-processing shader is to use Godot's built-in ability to read from
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the screen texture. If you're not familiar with this, you should read the :ref:`Screen Reading Shaders
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Tutorial <doc_screen-reading_shaders>` first.
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.. note::
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As of the time of writing, Godot does not support rendering to multiple buffers at the same time. Your
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post-processing shader will not have access to normals or other render passes. You only have
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access to the rendered frame.
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Single pass post-processing
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---------------------------
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You will need a ``Viewport`` to render your scene to, and a scene to render your
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``Viewport`` on the screen. You can use a :ref:`ViewportContainer
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<class_ViewportContainer>` to display your ``Viewport`` on the entire screen or inside
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another :ref:`Control <class_Control>` node.
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.. note::
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Rendering using a ``Viewport`` gives you control over
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how the scene render, including the framerate, and you can use the
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``ViewportContainer`` to render 3D objects in a 2D scene.
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For this demo, we will use a :ref:`Node2D <class_Node2D>` with a ``ViewportContainer`` and finally a
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``Viewport``. Your **Scene** tab should look like this:
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.. image:: img/post_hierarchy1.png
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Inside the ``Viewport``, you can have whatever you want. This will contain
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your main scene. For this tutorial, we will use a field of random boxes:
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.. image:: img/post_boxes.png
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Add a new :ref:`ShaderMaterial <class_ShaderMaterial>` to the ``ViewportContainer``, and assign a new
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shader resource to it. You can access your rendered ``Viewport`` with the built-in ``TEXTURE`` uniform.
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.. note::
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You can choose not to use a ``ViewportContainer``, but if you do so, you will
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need to create your own uniform in the shader and pass the ``Viewport`` texture in
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manually, like so:
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.. code-block:: glsl
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// Inside the Shader.
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uniform sampler2D ViewportTexture;
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And you can pass the texture into the shader from GDScript like so:
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::
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# In GDScript.
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func _ready():
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$Sprite.material.set_shader_param("ViewportTexture", $Viewport.get_texture())
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Copy the following code to your shader. The above code is a single pass edge detection filter, a
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`Sobel filter <https://en.wikipedia.org/wiki/Sobel_operator>`_.
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.. code-block:: glsl
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shader_type canvas_item;
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void fragment() {
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vec3 col = -8.0 * texture(TEXTURE, UV).xyz;
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col += texture(TEXTURE, UV + vec2(0.0, SCREEN_PIXEL_SIZE.y)).xyz;
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col += texture(TEXTURE, UV + vec2(0.0, -SCREEN_PIXEL_SIZE.y)).xyz;
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col += texture(TEXTURE, UV + vec2(SCREEN_PIXEL_SIZE.x, 0.0)).xyz;
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col += texture(TEXTURE, UV + vec2(-SCREEN_PIXEL_SIZE.x, 0.0)).xyz;
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col += texture(TEXTURE, UV + SCREEN_PIXEL_SIZE.xy).xyz;
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col += texture(TEXTURE, UV - SCREEN_PIXEL_SIZE.xy).xyz;
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col += texture(TEXTURE, UV + vec2(-SCREEN_PIXEL_SIZE.x, SCREEN_PIXEL_SIZE.y)).xyz;
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col += texture(TEXTURE, UV + vec2(SCREEN_PIXEL_SIZE.x, -SCREEN_PIXEL_SIZE.y)).xyz;
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COLOR.xyz = col;
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}
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.. note::
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The Sobel filter reads pixels in a 9x9 grid around the current pixel and adds them together, using weight.
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What makes it interesting is that it assigns weights to each pixel; +1 for each of the eight around the
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center and -8 for the center pixel. The choice of weights is called a "kernel". You can use different
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kernels to create edge detection filters, outlines, and all sorts of effects.
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.. image:: img/post_outline.png
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Multi-pass post-processing
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--------------------------
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Some post-processing effects like blur are resource intensive. If you break them down in multiple passes
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however, you can make them run a lot faster. In a multipass material, each pass takes the result from the
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previous pass as an input and processes it.
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To make a multi-pass post-processing shader, you stack ``Viewport`` nodes. In the example above, you
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rendered the content of one ``Viewport`` object into the root ``Viewport``, through a ``ViewportContainer``
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node. You can do the same thing for a multi-pass shader by rendering the content of one ``Viewport`` into
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another and then rendering the last ``Viewport`` into the root ``Viewport``.
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Your scene hierarchy will look something like this:
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.. image:: img/post_hierarchy2.png
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Godot will render the bottom ``Viewport`` node first. So if the order of the passes matters for your
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shaders, make sure that you assign the shader you want to apply first to the lowest ``ViewportContainer`` in
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the tree.
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.. note::
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You can also render your Viewports separately without nesting them like this. You just
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need to use two Viewports and to render them one after the other.
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Apart from the node structure, the steps are the same as with the single-pass post-processing shader.
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As an example, you could write a full screen Gaussian blur effect by attaching the following pieces of code
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to each of the :ref:`ViewportContainers <class_ViewportContainer>`. The order in which you apply the shaders
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does not matter:
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.. code-block:: glsl
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shader_type canvas_item;
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// Blurs the screen in the X-direction.
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void fragment() {
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vec3 col = texture(TEXTURE, UV).xyz * 0.16;
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col += texture(TEXTURE, UV + vec2(SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.15;
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col += texture(TEXTURE, UV + vec2(-SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.15;
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col += texture(TEXTURE, UV + vec2(2.0 * SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.12;
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col += texture(TEXTURE, UV + vec2(2.0 * -SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.12;
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col += texture(TEXTURE, UV + vec2(3.0 * SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.09;
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col += texture(TEXTURE, UV + vec2(3.0 * -SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.09;
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col += texture(TEXTURE, UV + vec2(4.0 * SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.05;
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col += texture(TEXTURE, UV + vec2(4.0 * -SCREEN_PIXEL_SIZE.x, 0.0)).xyz * 0.05;
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COLOR.xyz = col;
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}
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.. code-block:: glsl
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shader_type canvas_item;
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// Blurs the screen in the Y-direction.
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void fragment() {
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vec3 col = texture(TEXTURE, UV).xyz * 0.16;
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col += texture(TEXTURE, UV + vec2(0.0, SCREEN_PIXEL_SIZE.y)).xyz * 0.15;
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col += texture(TEXTURE, UV + vec2(0.0, -SCREEN_PIXEL_SIZE.y)).xyz * 0.15;
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col += texture(TEXTURE, UV + vec2(0.0, 2.0 * SCREEN_PIXEL_SIZE.y)).xyz * 0.12;
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col += texture(TEXTURE, UV + vec2(0.0, 2.0 * -SCREEN_PIXEL_SIZE.y)).xyz * 0.12;
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col += texture(TEXTURE, UV + vec2(0.0, 3.0 * SCREEN_PIXEL_SIZE.y)).xyz * 0.09;
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col += texture(TEXTURE, UV + vec2(0.0, 3.0 * -SCREEN_PIXEL_SIZE.y)).xyz * 0.09;
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col += texture(TEXTURE, UV + vec2(0.0, 4.0 * SCREEN_PIXEL_SIZE.y)).xyz * 0.05;
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col += texture(TEXTURE, UV + vec2(0.0, 4.0 * -SCREEN_PIXEL_SIZE.y)).xyz * 0.05;
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COLOR.xyz = col;
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}
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Using the above code, you should end up with a full screen blur effect like below.
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.. image:: img/post_blur.png
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For more information on how ``Viewport`` nodes work, see the :ref:`Viewports Tutorial <doc_viewports>`.
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