Special auto-synced parameters and definitions

Lightworks provides the following variables, automatically updated by the CPU, for use in effects (GPU). To use these variables, they must be declared outside and above all shaders and functions. Then these variables are globally available with the automatic values for the entire effect.

//--------------------------------------------------------------//
// Definitions and declarations
//--------------------------------------------------------------//

float _Progress;  
float _OutputAspectRatio;  
float _OutputHeight;  
float _OutputWidth;  

float _Length;
float _LengthFrames;
float _OutputFPS;

float _FgWidthNormalised;    // "Fg" stands as an example for the name of the input (replace if different). 
float _FgHeightNormalised;   // Replace "Fg" if different.
float _FgWidth;              // Replace "Fg" if different.
float _FgHeight;             // Replace "Fg" if different.
float _FgXScale;             // Replace "Fg" if different.
float _FgYScale;             // Replace "Fg" if different.

Descriptions:

Basic variables:

float _Progress; // Relative position in effect progress 0 to 1. Please note some peculiarities: Details
float _OutputAspectRatio; // The aspect-ratio of the current output format
float _OutputHeight; // Please note some peculiarities: Details
float _OutputWidth; // The width of the current output format in pixels

Starting with Lightworks 14.5 is also available:

float _Length; // Length of the effect in sec. Please note some peculiarities: Details
float _LengthFrames; // Length of the effect in frames. Please note some peculiarities: Details
float _OutputFPS; // eg. 24.0, 25.0, 29.97, etc

Starting with Lightworks 2021.1 is also available:

In the following, “Fg” was only used in the code to represent the name of the respective input (replace if different).

Great White reported

If you have an input called ‘Fg’, then Lightworks will attempt to supply:

Absolute input dimensions:
float _FgWidth; // width of image of the “Fg” input in pixels
float _FgHeight; // height of image of the “Fg” input in pixels
Important: For inputs with other names, replace “Fg” with the name of the input.

Automatic aspect ratio scaling parameters:
float _FgXScale; // scaling factor of the “Fg” input
float _FgYScale; // scaling factor of the “Fg” input
Important: For inputs with other names, replace “Fg” with the name of the input.
These variables have something to do with different aspect ratios of the input texture compared to the aspect ratio of the shader output texture. This applies to effect nodes of the type CanSize = true which have more than one input. Such effects extend the output texture (and internal Reder texture) to the sequence aspect ratio (or export) with transparent black or another background. Otherwise the values are 1 (as with effects with only one input).
The absolute texture dimensions are irrelevant for these variables.
For effects with more than one input, these scale parameters are influenced by:

Project settings wide / narrow
Sequence aspect ratio or export aspect ratio
The aspect ratio of the input relevant for the parameter.

Automatic scaling parameters:
float _FgWidthNormalised; // width of image of the “Fg” input divided by width of node output format
float _FgHeightNormalised; // height of image of the “Fg” input divided by width of node output format
Important: For inputs with other names, replace “Fg” with the name of the input.
This applies to effect nodes of the type CanSize = true which have more than one input. Such effects extend the output shader texture to the sequence aspect ratio with transparent black or other background. If there is a texture with larger dimensions at another input, the shader output texture is expanded accordingly under certain conditions.
For effects with more than one input, these scale parameters are influenced by:

Sequence dimensions (if sequence dimensions are greater than input dimensions). Or export dimensions
Sequence aspect ratio or export aspect ratio
The Dimensions of the input relevant for the parameter (without Project settings wide / narrow because this works differently).
Dimensions at other inputs because this can extend the output dimensions.

Preprocessor, predefined (starting with Lightworks 14.5):

To avoid unexpected results when using older versions of Lightworks,
the availability of variables can now be checked (LW 14.5).
Each definition shares the same name as its associated parameter, but is in upper case:

_PROGRESS
_OUTPUTASPECTRATIO
_OUTPUTHEIGHT
_OUTPUTWIDTH

_LENGTH
_LENGTHFRAMES
_OUTPUTFPS

For example, if _LENGTH is not defined, then only the basic variables are available.

#ifdef _LENGTH
   // Insert code
#else
   // Insert code
#endif

Check on which operating system the effect is used:

WINDOWS
OSX
LINUX

These are already defined outside of the effect, but not on Lightworks versions before LW14.5
Example of a platform analysis:

#ifdef WINDOWS
   // Insert code
#else
   // Insert code
#endif

Example Code

More ideas and Discussions:
www.lwks.com start from page 8 below of this thread and continue on the following pages.

Code_for_developing_Lightworks_effects

Here we collect code to create Lightworks.fx effects.