cop vex context
Define a custom COP operator with a program that sets RGBA or Cr,Cg,Cb,C4 values in an image.
The COP evaluation works by setting either the R, G, B, A or the Cr,Cg, Cb,C4 variables. The variables are initialized to the color of the first input (or zero for R, G, B and 1 for A if there is no input). It then calls the COP function. If any of the variables are modified, then they will be used to determine the new color for the current pixel.
The RGBA variables are for programmer convenience; they read and write directly to the Color and Alpha planes. Reading from RGB and A will give you the value of the first input’s color plane and alpha plane. If one or both of these planes do not exist, 0 will be returned. If you are writing to R, G, B or A and either Color and/or Alpha doesn’t exist, the planes will be created for you. If you only write to R, a full Color plane will be created, but with the G and B channels set to 0.
The channel variables, Cr to C4, are more flexible. They allow you to write to any plane’s channels. If a channel of a plane does not exist and you write to it, nothing happens. For example, when cooking the Alpha plane (with only 1 channel), if Cg, Cb or C4 is written to, the data is lost; only Cr is valid. However, no error occurs, since it is possible to have planes with different sizes in the same sequence. You can read from a channel variable in exactly the same way as reading from the R,G,B and A variables. The channel variable will be filled with the pixel values from the plane in the first input corresponding to the one being cooked. You should not mix writing to R,G,B,A and Cr,Cg,Cb,C4 in the same VEX function. While it will not harm anything, it can lead to confusing results if you are writing different things to R and Cr and the function is cooking the Color plane.
Globals
| PS (read-only) | Size of the current plane being cooked (the number of channels). |
| IX (read-only) | Horizontal position of the pixel currently being shaded. This will be in the range of (0, XRES-1). |
| PXSC (read-only) | The pixel scale that is currently being used in the cook. At 50% resolution, this global will have a value of 0.5. This is useful for scaling any kernels, pixel translations and lengths so that proxy images look similar to the full resolution result. |
| AS (read-only) | Array size of the current plane. |
| EF (read-only) | End frame of the current sequence. |
| SF (read-only) | Starting frame of the current sequence. |
| H (read-only) | Hue of the current pixel, a floating point number from 0 to 1. HSV is calculated based on the Color plane (C), not the current plane. |
| Cb | Value of plane component 3. Unlike B, this represents the current plane’s values. |
| FR (read-only) | Frame rate of the current sequence. |
| C4 | Value of plane component 4. Unlike A, this represents the current plane’s values. |
| G | Green value of the current pixel, a floating point number between 0 and 1. If the COP does not have a color plane (C), one will be created. |
| V (read-only) | Value (or intensity) of the current pixel, a floating point number from 0 to 1. |
| I (read-only) | Index number of the current image, starting at 0. |
| NP (read-only) | Number of planes in the image (for example, for an RGBA image this would be 2 since the COP contains 2 planes, Color and Alpha). |
| A | Alpha value of the current pixel, a floating point number between 0 and 1. If the COP does not have an alpha plane (A), one will be created. |
| F (read-only) | Frame number of the current image. |
| PNAME (read-only) | Name of the current plane being cooked. |
| X (read-only) | Horizontal location of the center of the current pixel being shaded in the range 0 to 1. Zero being the left hand side of the image, and 1 being the right hand side. |
| Cr | Value of plane component 1. Unlike R, this represents the current plane’s values. |
| S (read-only) | Saturation of the current pixel, a floating point number from 0 to 1. |
| TIME (read-only) | Time of the current image. |
| R | Red value of the current pixel, a floating point number between 0 and 1. If the COP does not have a color plane (C), one will be created. |
| YRES (read-only) | Vertical resolution (in pixels) of the image being processed. |
| IY (read-only) | Vertical position of the pixel currently being shaded. This will be in the range of (0, YRES-1). |
| XRES (read-only) | Horizontal resolution (in pixels) of the image being processed. |
| AI (read-only) | Array index of the current plane that is being cooked (from 0 to AS-1). |
| Cg | Value of plane component 2. Unlike G, this represents the current plane’s values. |
| B | Blue value of the current pixel, a floating point number between 0 and 1. If the COP does not have a color plane (C), one will be created. |
| AR (read-only) | Aspect ratio of the image being processed. |
| PL (read-only) | Index of the current plane being cooked. |
| Y (read-only) | Vertical location of the center of the current pixel being shaded in the range 0 to 1. Zero being the bottom of the image, and 1 being the top. |
| NI (read-only) | Number of images in the sequence. |
| TINC (read-only) | Time increment between frames at the global frame rate. |