Procedural Texture

Using the filter

The filter has several key components that must be understood in order to use it effectively:

• Equation lines
  • The equation line entries are where you type the expressions and functions to achieve the desired result. Multiple line entries are typically used to target separate channels—if you are targeting all channels simultaneously then you would only need one entry.
• Channel targets
  • When you create a new expression line, just the channel red (R) is targeted by default, meaning only the red channel data is affected by the outcome of the expression. You can click on the R, G, B and A channel labels to add or remove them from the expression. Channel targeting is an important part of achieving the desired result from the expression.
  • To target all colour data cumulatively, enable R, G and B but not A.
  • To target just the alpha channel data, disable R, G and B and enable A.
• Variables
  • Function results can be assigned to variables in order to streamline the overall expression and aid readability. The syntax follows the convention of var varname=function();
  • You can define as many variables as required—simply separate them with a semicolon (;).
  • e.g. var v=vec2(rx, ry); var clr=vec3(R,G,B);
  • The above creates two variables: one a vector from relative X and Y canvas positions (v), and the other a vector from the RGB colour data (clr). The variables v and clr can then be used in a following function or set of functions.
• Functions
  • Functions bring everything together and are used to achieve the final result.
  • See the extensive table below for a full list of available functions: they range from mathematical calculations to vector creation, interpolators, oscillators and noise generators.
  • The syntax follows the typical convention of function(input, parameter) (multiple inputs and parameters where applicable).
  • e.g. scurveinterp(T a, T b, T t) could be used as scurveinterp(R, B, 0.5). This would interpolate between red and blue channel data with a balance/mix of 50% (since the balance can be a value between 0 and 1).
• Parentheses
  • Parentheses are used for groupings exactly as they would be in traditional mathematics.
  • For example, take this equation line: R/(a*2)
  • By putting a*2 in parentheses, it will be evaluated first before being divided into R.
  • Here is a more complex example: var v2=vec2(rx/w/2, ry/h/(b*2)); dir(v2*(a*2))*(c*2) (the parantheses are highlighted in bold)
  • In this example, the variable b is multiplied by 2, but this is evaluated first before becoming part of the final ry/h/(b*2) calculation. If this expression was not in parentheses, the outcome would be different.
• Custom Inputs
  • Custom inputs can improve the accessibility of the expressions and allow parameters to be altered quickly.
  • There are several input buttons depending on the type of custom input required (see the Custom Inputs list above).
  • Custom inputs are assigned to variables for use in the expressions. Simplified variable names are provided by default when you add a new custom input, e.g. a, b, c.
  • You can name these input variables whatever you wish so long as they do not clash with established function names and persistent variables (e.g. w for width, R for red channel, vec2 for a vector creation function). If you have clashing variables, they will simply be unable to be referenced.
  • To use them, reference them in a function, e.g. perlin(rx, ry, a, b)—where a controls octaves and b controls persistence.