Merge pull request #4093 from Calinou/glow-bicubic-upscale-gles2

Clarify the GLES2 Environment glow limitations

tutorials/3d/environment_and_post_processing.rst

@@ -337,12 +337,22 @@ interesting glow patterns:
 .. image:: img/environment_glow_layers2.png
 
 Finally, as the highest layers are created by stretching small blurred images,
-it is possible that some blockiness may be visible. Enabling **Bicubic Upscaling**
+The effect may appear blocky. Enabling **Bicubic Upscale**
 gets rids of it, at a minimal performance cost.
-*Note that this is effective only when using the GLES3 backend.*
 
 .. image:: img/environment_glow_bicubic.png
 
+.. note::
+
+    When using the GLES2 backend, bicubic upscale is only supported on
+    graphics cards that provide the ``GL_EXT_gpu_shader4`` extension. Nearly all
+    desktop and laptop graphics cards provide this extension, but not all mobile
+    GPUs do.
+
+    Also, note that GLES2 does not support High Dynamic Range (HDR) rendering. As a
+    result, you will need different glow settings compared to GLES3 to get a
+    good-looking glow.
+
 Adjustments
 ^^^^^^^^^^^
 

tutorials/misc/gles2_gles3_differences.rst

@@ -86,6 +86,8 @@ That means that in GLES2 environments you can only set:
 - Glow (also known as bloom)
 - Adjustment
 
+See :ref:`doc_environment_and_post_processing` for more information.
+
 GIProbes
 --------