Clarify features that are only available in GLES3

This complements the "Differences between GLES2 and GLES3" page
by incorporating some of its information in individual pages.

tutorials/3d/environment_and_post_processing.rst

@@ -136,6 +136,8 @@ In practice, it makes light stand out more across the fog.
 Tonemap
 ^^^^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 Selects the tone-mapping curve that will be applied to the scene, from a short
 list of standard curves used in the film and game industry. Tone mapping can make
 light and dark areas more homogeneous, even though the result is not that strong.
@@ -148,6 +150,8 @@ Tone mapping options are:
 Auto Exposure (HDR)
 ^^^^^^^^^^^^^^^^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 Even though, in most cases, lighting and texturing are heavily artist controlled,
 Godot supports a simple high dynamic range implementation with the auto exposure
 mechanism. This is generally used for the sake of realism when combining
@@ -188,6 +192,8 @@ in the Environment.
 Screen-Space Reflections (SSR)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 While Godot supports three sources of reflection data (Sky, ReflectionProbe, and
 GIProbe), they may not provide enough detail for all situations. Scenarios
 where Screen Space Reflections make the most sense are when objects are in
@@ -212,6 +218,8 @@ Keep in mind that screen-space-reflections only work for reflecting opaque geome
 Screen-Space Ambient Occlusion (SSAO)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 As mentioned in the **Ambient** section, areas where light from light nodes
 does not reach (either because it's outside the radius or shadowed) are lit
 with ambient light. Godot can simulate this using GIProbe, ReflectionProbe,
@@ -255,6 +263,8 @@ Tweaking SSAO is possible with several parameters:
 Depth of Field / Far Blur
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 This effect simulates focal distance on high end cameras. It blurs objects behind
 a given range. It has an initial **Distance** with a **Transition** region
 (in world units):
@@ -267,6 +277,8 @@ the **Quality** may be needed in order to avoid artifacts.
 Depth of Field / Near Blur
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 This effect simulates focal distance on high end cameras. It blurs objects close
 to the camera (acts in the opposite direction as far blur).
 It has an initial **Distance** with a **Transition** region (in world units):
@@ -284,6 +296,8 @@ given object:
 Glow
 ^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 In photography and film, when light amount exceeds the maximum supported by the
 media (be it analog or digital), it generally bleeds outwards to darker regions
 of the image. This is simulated in Godot with the **Glow** effect.
@@ -335,6 +349,8 @@ gets rids of it, at a minimal performance cost.
 Adjustments
 ^^^^^^^^^^^
 
+*This feature is only available when using the GLES3 backend.*
+
 At the end of processing, Godot offers the possibility to do some standard
 image adjustments.
 

tutorials/3d/gi_probes.rst

@@ -6,6 +6,10 @@ GI Probes
 Introduction
 ------------
 
+.. note:: This feature is only available when using the GLES3 backend.
+          :ref:`doc_baked_lightmaps` can be used as an alternative
+          when using the GLES2 renderer.
+
 Just like with :ref:`doc_reflection_probes`, and as stated in
 the :ref:`doc_spatial_material`, objects can show reflected or diffuse light.
 GI Probes are similar to Reflection Probes, but they use a different and more

tutorials/3d/lights_and_shadows.rst

@@ -23,7 +23,7 @@ Light nodes
 -----------
 
 There are three types of light nodes: `Directional light`_,
-`Omni light`_ and `Spot light`_. Let's take a look at the common 
+`Omni light`_ and `Spot light`_. Let's take a look at the common
 parameters for lights:
 
 .. image:: img/light_params.png
@@ -47,7 +47,7 @@ There is a list of generic shadow parameters, each also has a specific function:
 -  **Enabled**: Check to enable shadow mapping in this light.
 -  **Color**: Areas occluded are multiplied by this color. It is black by default, but it can be changed to tint shadows.
 -  **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.
--  **Contact**: Performs a short screen-space raycast to reduce the gap generated by the bias.
+-  **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.
 -  **Reverse Cull Faces**: Some scenes work better when shadow mapping is rendered with face-culling inverted.
 
 Below is an image of what tweaking bias looks like. Default values work for most

tutorials/3d/spatial_material.rst

@@ -354,6 +354,8 @@ intermediate values generally works best.
 Clearcoat
 ~~~~~~~~~
 
+*This feature is only available when using the GLES3 backend.*
+
 The *Clearcoat* parameter is used to add a secondary pass of transparent coat
 to the material. This is common in car paint and toys. In practice, it's a
 smaller specular blob added on top of the existing material.
@@ -361,6 +363,8 @@ smaller specular blob added on top of the existing material.
 Anisotropy
 ~~~~~~~~~~
 
+*This feature is only available when using the GLES3 backend.*
+
 This changes the shape of the specular blob and aligns it to tangent space.
 Anisotropy is commonly used with hair, or to make materials such as brushed
 aluminum more realistic. It works especially well when combined with flowmaps.
@@ -381,6 +385,8 @@ AO map. It is recommended to bake ambient occlusion whenever possible.
 Depth
 ~~~~~
 
+*This feature is only available when using the GLES3 backend.*
+
 Setting a depth map on a material produces a ray-marched search to emulate the
 proper displacement of cavities along the view direction. This is not real
 added geometry, but an illusion of depth. It may not work for complex objects,
@@ -392,6 +398,8 @@ but it produces a realistic depth effect for textures. For best results,
 Subsurface Scattering
 ~~~~~~~~~~~~~~~~~~~~~
 
+*This feature is only available when using the GLES3 backend.*
+
 This effect emulates light that penetrates an object's surface, is scattered,
 and then comes out. It is useful to create realistic skin, marble, colored
 liquids, etc.
@@ -410,6 +418,8 @@ such as plant leaves, grass, human ears, etc.
 Refraction
 ~~~~~~~~~~~
 
+*This feature is only available when using the GLES3 backend.*
+
 When refraction is enabled, it supersedes alpha blending, and Godot attempts to
 fetch information from behind the object being rendered instead. This allows
 distorting the transparency in a way similar to refraction in real life.