add some comments

yt_idv/shader_objects.py

@@ -239,6 +239,11 @@ class Shader(traitlets.HasTraits):
         This can either be a string containing a full source of a shader,
         an absolute path to a source file or a filename of a shader
         residing in the ./shaders/ directory.
+    allow_null : bool
+        If True (default) then shader compilation errors will be caught and
+        printed without raising exception (convenient for general use and for
+        developing new shaders). If False, any compilation errors will raise
+        a RunTimeError (useful for CI testing).
 
     """
 

yt_idv/tests/test_yt_idv.py

@@ -163,6 +163,8 @@ def test_curves(osmesa_fake_amr, image_store):
 
 @pytest.fixture()
 def set_very_bad_shader():
+    # this temporarily points the default vertex shader source file to a
+    # bad shader that will raise compilation errors.
     known_shaders = shader_objects.known_shaders
     good_shader = known_shaders["vertex"]["default"]["source"]
     known_shaders["vertex"]["default"]["source"] = "bad_shader.vert.glsl"
@@ -171,6 +173,8 @@ def set_very_bad_shader():
 
 
 def test_bad_shader(osmesa_empty, set_very_bad_shader):
+    # this test is meant to check that a bad shader would indeed be caught
+    # by the subsequent test_shader_programs test.
     shader_name = "box_outline"
     program = shader_objects.component_shaders[shader_name]["default"]