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Merge pull request #4969 from Calinou/screen-reading-shaders-backbuffercopy

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Clarify when to use BackBufferCopy in Screen-reading shaders
This commit is contained in:
Max Hilbrunner
2021-07-06 08:32:53 +02:00
committed by GitHub
parent 0e68dcff89 ed27f6fc3d
commit 982615c9c5
1 changed files with 14 additions and 7 deletions
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21
tutorials/shaders/screen-reading_shaders.rst
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@@ -6,7 +6,7 @@ Screen-reading shaders
Introduction
~~~~~~~~~~~~
Very often, it is desired to make a shader that reads from the same
It is often desired to make a shader that reads from the same
screen to which it's writing. 3D APIs, such as OpenGL or DirectX, make this very
difficult because of internal hardware limitations. GPUs are extremely
parallel, so reading and writing causes all sorts of cache and coherency
@@ -15,7 +15,7 @@ properly.
The workaround is to make a copy of the screen, or a part of the screen,
to a back-buffer and then read from it while drawing. Godot provides a
few tools that make this process easy!
few tools that make this process easy.
SCREEN_TEXTURE built-in texture
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -42,7 +42,7 @@ of blur at no cost.
.. note::
Mipmaps are not generated in GLES2 due to poor performance and compatibility with older
devices.
devices.
SCREEN_TEXTURE example
~~~~~~~~~~~~~~~~~~~~~~
@@ -101,13 +101,20 @@ With correct back-buffer copying, the two spheres blend correctly:
.. image:: img/texscreen_demo2.png
In 3D, there is less flexibility to solve this particular issue because the
``SCREEN_TEXTURE`` is only captured once. Be careful when using
.. warning:
Materials that use ``SCREEN_TEXTURE`` are considered transparent themselves and
will not appear in the resulting ``SCREEN_TEXTURE`` of other materials.
If you plan to instance a scene that uses a material with ``SCREEN_TEXTURE``,
you will need to use a BackBufferCopy node.
In 3D, there is less flexibility to solve this particular issue because the
``SCREEN_TEXTURE`` is only captured once. Be careful when using
``SCREEN_TEXTURE`` in 3D as it won't capture transparent objects and may capture
some opaque objects that are in front of the object.
You can reproduce the back-buffer logic in 3D by creating a :ref:`Viewport <class_Viewport>`
with a camera in the same position as your object, and then use the
with a camera in the same position as your object, and then use the
:ref:`Viewport's <class_Viewport>` texture instead of ``SCREEN_TEXTURE``.
Back-buffer logic
@@ -136,7 +143,7 @@ Godot:
DEPTH_TEXTURE
~~~~~~~~~~~~~
For 3D Shaders, it's also possible to access the screen depth buffer. For this,
For 3D shaders, it's also possible to access the screen depth buffer. For this,
the ``DEPTH_TEXTURE`` built-in is used. This texture is not linear; it must be
converted via the inverse projection matrix.