215 lines
11 KiB
ReStructuredText
215 lines
11 KiB
ReStructuredText
.. _doc_gles2_gles3_differences:
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Differences between GLES2 and GLES3
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===================================
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This page documents the differences between GLES2 and GLES3 that are by design and are not the result
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of bugs. There may be differences that are unintentional, but they should be reported as bugs.
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.. note:: "GLES2" and "GLES3" are the names used in Godot for the two OpenGL-based rendering backends.
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In terms of graphics APIs, the GLES2 backend maps to OpenGL 2.1 on desktop, OpenGL ES 2.0 on
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mobile and WebGL 1.0 on the web. The GLES3 backend maps to OpenGL 3.3 on desktop, OpenGL ES
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3.0 on mobile and WebGL 2.0 on the web.
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Particles
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---------
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GLES2 cannot use the :ref:`Particles <class_Particles>` or :ref:`Particles2D <class_Particles2D>` nodes
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as they require advanced GPU features. Instead, use :ref:`CPUParticles <class_CPUParticles>` or
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:ref:`CPUParticles2D <class_CPUParticles2D>`, which provides a similar interface to a
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:ref:`ParticlesMaterial <class_ParticlesMaterial>`.
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.. tip:: Particles and Particles2D can be converted to their CPU equivalent node with the "Convert to
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CPUParticles" option in the editor.
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``SCREEN_TEXTURE`` mip-maps
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---------------------------
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In GLES2, ``SCREEN_TEXTURE`` (accessed via a :ref:`ShaderMaterial <class_ShaderMaterial>`) does not have
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computed mip-maps. So when accessing at a different LOD, the texture will not appear blurry.
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``DEPTH_TEXTURE``
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-----------------
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While GLES2 supports ``DEPTH_TEXTURE`` in shaders, it may not work on some old hardware (especially mobile).
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Color space
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-----------
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GLES2 and GLES3 are in different color spaces. This means that colors will appear slightly
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different between them especially when lighting is used.
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If your game is going to use both GLES2 and GLES3, you can use an ``if``
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statement check and see if the output is in sRGB, using ``OUTPUT_IS_SRGB``. ``OUTPUT_IS_SRGB`` is
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``true`` in GLES2 and ``false`` in GLES3.
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HDR
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---
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GLES2 is not capable of using High Dynamic Range (HDR) rendering features. If HDR is set for your
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project, or for a given viewport, Godot will still use Low Dynamic Range (LDR) which limits
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viewport values to the ``0-1`` range.
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The Viewport **Debanding** property and associated project setting will also have
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no effect when HDR is disabled. This means debanding can't be used in GLES2.
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SpatialMaterial features
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------------------------
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In GLES2, the following advanced rendering features in the :ref:`SpatialMaterial <class_SpatialMaterial>` are missing:
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- Refraction
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- Subsurface scattering
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- Anisotropy
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- Clearcoat
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- Depth mapping
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When using SpatialMaterials they will not even appear in the editor.
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In custom :ref:`ShaderMaterials <class_ShaderMaterial>`, you can set values for these features but they
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will be non-functional. For example, you will still be able to set the ``SSS`` built-in (which normally adds
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subsurface scattering) in your shader, but nothing will happen.
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Environment features
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--------------------
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In GLES2, the following features in the :ref:`Environment <class_Environment>` are missing:
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- Auto exposure
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- Tonemapping
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- Screen space reflections
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- Screen space ambient occlusion
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That means that in GLES2 environments you can only set:
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- Sky (including procedural sky)
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- Ambient light
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- Fog
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- Depth of field
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- Glow (also known as bloom)
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- Adjustment
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GIProbes
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--------
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:ref:`GIProbes <class_GIProbe>` do not work in GLES2. Instead use :ref:`Baked Lightmaps <class_BakedLightmap>`.
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For a description of how baked lightmaps work see the :ref:`Baked Lightmaps tutorial <doc_baked_lightmaps>`.
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Contact shadows
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---------------
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The ``shadow_contact`` property of :ref:`Lights <class_Light>` is not supported in GLES2 and so does nothing.
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Light performance
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-----------------
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In GLES2, performance scales poorly with several lights, as each light is processed in a separate render
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pass (in opposition to GLES3 which is all done in a single pass). Try to limit scenes to as few lights as
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possible in order to achieve greatest performance.
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Texture compression
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-------------------
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On mobile, GLES2 requires ETC texture compression, while GLES3 requires ETC2. ETC2 is enabled by default,
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so if exporting to mobile using GLES2 make sure to set the project setting
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``rendering/vram_compression/import_etc`` and then reimport textures.
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.. warning::
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Since ETC doesn't support transparency, you must reimport textures that contain
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an alpha channel to use the Uncompressed, Lossy or Lossless compression mode
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(instead of Video RAM). This can be done in the Import dock after selecting
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them in the FileSystem dock.
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Blend shapes
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------------
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In GLES2, blend shapes are implemented on the CPU instead of the GPU.
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Accordingly, they may not perform as well as blend shapes in GLES3. To avoid
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performance issues when using blend shapes in GLES2, try to minimize the number
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of blend shapes that are updated each frame.
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Shading language
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----------------
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GLES3 provides many built-in functions that GLES2 does not. Below is a list of functions
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that are not available or are have limited support in GLES2.
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For a complete list of built-in GLSL functions see the :ref:`Shading Language doc <doc_shading_language>`.
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| Function | |
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+=============================================================================================+==================================================+
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| vec_type **modf** ( vec_type x, out vec_type i ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec_int_type **floatBitsToInt** ( vec_type x ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec_uint_type **floatBitsToUint** ( vec_type x ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec_type **intBitsToFloat** ( vec_int_type x ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec_type **uintBitsToFloat** ( vec_uint_type x ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| ivec2 **textureSize** ( sampler2D_type s, int lod ) | See workaround below |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| ivec2 **textureSize** ( samplerCube s, int lod ) | See workaround below |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec4_type **texture** ( sampler_type s, vec_type uv [, float bias] ) | **bias** not available in vertex shader |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec4_type **textureProj** ( sampler_type s, vec_type uv [, float bias] ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec4_type **textureLod** ( sampler_type s, vec_type uv, float lod ) | Only available in vertex shader on some hardware |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec4_type **textureProjLod** ( sampler_type s, vec_type uv, float lod ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec4_type **textureGrad** ( sampler_type s, vec_type uv, vec_type dPdx, vec_type dPdy ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec_type **dFdx** ( vec_type p ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec_type **dFdy** ( vec_type p ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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| vec_type **fwidth** ( vec_type p ) | |
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+---------------------------------------------------------------------------------------------+--------------------------------------------------+
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.. note:: Functions not in GLES2's GLSL were added with Godots own shader standard library. These functions may perform worse in GLES2 compared to GLES3.
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``textureSize()`` workaround
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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GLES2 does not support ``textureSize()``. You can get the size of a texture the old fashioned way by passing in a
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uniform with the texture size yourself.
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.. code-block:: glsl
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// In the shader:
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uniform sampler2D textureName;
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uniform vec2 textureName_size;
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::
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# In GDScript:
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material_name.set_shader_param("textureName", my_texture)
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material_name.set_shader_param("textureName_size", my_texture_size)
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Built in variables and render modes
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-----------------------------------
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Godot also provides many built-in variables and render modes. Some cannot be supported in GLES2. Below is a list of
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built-in variables and render modes that, when written to, will have no effect or could even cause issues when using
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the GLES2 backend.
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+----------------------------+
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| Variable / Render Mode |
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+============================+
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| ``ensure_correct_normals`` |
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+----------------------------+
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| ``INSTANCE_ID`` |
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+----------------------------+
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| ``DEPTH`` |
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+----------------------------+
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| ``ANISOTROPY`` |
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+----------------------------+
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| ``ANISOTROPY_FLOW`` |
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+----------------------------+
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| ``SSS_STRENGTH`` |
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+----------------------------+
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