The env_render entity allows you to change the rendering properties of most of the visible entities in the game (monsters, func_walls etc.), while the map is running. The four render properties of the env_render will be copied to its target. Exactly how different entities are affected by different render properties varies, so only general information about them will be provided below. If you require more specific information, check the entity guide page for the entity you want to alter.
Render FX (renderfx) - Gives the entity certain visual effects depending on Render Mode.
Normal (0) - No visual effects.
Slow Pulse (1) - Entity slowly pulses with transparency. Faint.
Fast Pulse (2) - Entity quickly pulses with transparency. Faint.
Fast Wide Pulse (4) - Entity quickly pulses with transparency. Strong.
Slow Fade Away (5) - Seemingly unused.
Fast Fade Away (6) - Seemingly unused.
Slow Become Solid (7) - Seemingly unused.
Fast Become Solid (8) - Seemingly unused.
Slow Strobe (9) - A very slow strobe effect between visible and invisible.
Fast Strobe (10) - A medium strobe effect between visible and invisible.
Faster Strobe (11) - A very fast strobe effect between visible and invisible.
Slow Flicker (13) - Entity flickers in and out of visibility.
Fast Flicker (13) - Entity quickly flickers in and out of visibility.
Constant Glow (14) - Seemingly unused.
Distort (15) - Entity has a slight fast pulsing of transparency.
Hologram (Distort + fade) (16) - Entity has a slight fast pulsing of transparency. Fades out with distance.
Render Mode (rendermode) - Allows special rendering modes to be applied to the given entity. Varies greatly with different types of entities.
Normal (0) - Standard rendering. Render FX and FX Amount will generally have no effect.
Color (1) - Usually applies a the colour specified in FX Color to the entity.
Texture (2) - Usually allows the entity to become transparent.
Glow (3) - Usually allows the entity to become transparent. Intended for sprites, and has further effects with them.
Solid (4) - Usually allows the entity to become transparent.
Additive (5) - Usually gives the entity an additive effect.
FX Amount (1 - 255) (renderamt) - In all but "Normal" Render Mode, usually alters how transparent the entity is. Scales from 0 (invisible) to 255 (solid, normal).
FX Color (R G B) (rendercolour) - Usually sets the colour applied to the entity when using the Color Render Mode.
Target (target) - Defines the name of the entity the rendering properties will be copied to.
Name (targetname) - Name is a general attribute used to identify entities.
No Renderfx (1) - If enabled, the Render FX attribute will not be copied to the target entity.
No Renderamt (2) - If enabled, the FX Amount attribute will not be copied to the target entity.
No Rendermode (4) - If enabled, the Render Mode attribute will not be copied to the target entity.
No Rendercolor (8) - If enabled, the FX Color attribute will not be copied to the target entity.
This entity can be used to alter render properties on the fly. Among other uses, this can allow you to create the illusion of complex-moving objects that would be impossible to create with a single entity. By rendering visually identical entities visible/invisible at the same time, you could, for example, have a func_rotating door handle rotate downwards as though to open a door, then switch its visibility with another identical door handle already in the same position that can then rotate with the door.
From the VERC Archive
The simplest example involves creating a crate that you make disappear -
Create a crate (func_wall) and give it a Name (targetname) of crate1.
Place an env_render in your level, near the crate. Give it a Name of crate1_render. Set its target to crate1. Set its render mode to 'texture' (2), and its fx amount to '0'.
Create a func_button and set its target to crate1_render.
When the button gets pressed, the crate disappears. Note that you could use a multi_manager and a string of env_render entities to make the crate gradually fade out of existence rather than disappear suddenly.
This effect is useful for creating the illusion of entities that are bound together in some impossible way (at least for the engine). For example, if you wanted a tank to drive onto a field then start firing, that would seem to imply a func_train (for the movement) and a func_tank (for the firing) being bound together. Instead, the func_tank was always sitting on the field, but it started invisible. When the func_train drove out to the func_tank position, two things happen - the func_train is triggered invisible (as the above crate example), and the func_tank is triggered to be visible.
*Note*: in the above example with the tanks, its important to restrict the player from interacting with the "invisible tank" as this would ruin any sense of illusion that has been created.