Updated tutorial_fixed_materials (markdown)

tutorial_fixed_materials.md

@@ -12,4 +12,32 @@ Here is the list of all the options available for fixed materials:
 
 From this point, every option will be explained in detail:
 
+### Fixed Flags
+
+These are a set of flags that control general aspects of the material.
+
+#### Use Alpha
+
+This flag needs to be active for transparent materials to blend with what is behind, otherwise display will always be opaque. Do not enable this flag unless the material really needs it, because it can severely affect performance and quality. Materials with transparency will also not cast shadows (unless they contain opaque areas and the "opaque pre-pass" hint is turned on, see the [Materials](tutorial_materials) tutorial for more information).
+
+<p align="center"><img src="images/fixed_material_alpha.png"></p>
+
+#### Use Vertex Colors
+
+Vertex color painting is a very common technique to add detail to geometry. 3D DCCs all support this, and many even support baking occlusion to it. Godot allows this information to be used in the fixed material by modulating the diffuse color when enabled.
+
+<p align="center"><img src="images/fixed_material_vcols.png"></p>
+
+#### Point Size
+
+Point size is used to set the point size (in pixels) for when rendering points. This feature is mostly used in tools and HUDs
+
+#### Discard Alpha
+
+When alpha is enabled (see above) the invisible pixels are blended with what is behind them. In some combinations (of using alpha to render depth) it may be possible that invisible pixels cover other objects. 
+If this is the case, enable this option for the material. This option is often used in combination with "opaque pre-pass" hint (see the [Materials](tutorial_materials) tutorial for more information).
+
+### Parameters
+
+