screenspace_general
screenspace_general is a Vertex shader available in all
Source games since
Source 2007.[confirm] It is most commonly used to draw generic screenspace effects.
Unlike other shaders using screenspaceeffect as its vertex shader, screenspace_general allows developers to easily access and modify its pixel shader, 4 texture samplers and 4 shader register constants.[Clarify]
This can be useful for quickly iterating and testing screen effects, without having to reload all shaders, or recompile stdshaders to define/modify parameters.
Notable usage
dev/halo_add_to_screen
Used by the TF2 Glow Effect (2013 SDK) to help create an outline around models using stencils.
It uses the haloaddoutline_ps20 pixel shader to apply cheap blur. $C0_X controls the glow fade value (restricted to 1.0f in code.)
$C0_X actually does what it says it is supposed to do.Parameters
screenspace_general.cppTools
An SDK to easily create custom pixel shaders for any Source game is available here: ficool2/sdk_screenspace_shaders.