Recently I've been experimenting with expression node on nuke and apparently it is capable of doing some mathematical equation and since I'm still in the beginning of learning, I want to make some simple line using this mathematical equation, which is:
x = y or can be written as x - y = z
This equation will create a 45 degree line (1st photo) since if x = 1 and y = 1 then the value of z will be 0 and it means that if the x is equal with the y then the value of z will be 0 else the value will be either -y if the value of x is less than the value of y or x if the value of x is more than the value of y.
The nuke itself will display the value on the viewer and if the value is 0 or under it will appear black and if the value is more than 1 than it will appear white. You can also look for the coordinate by hovering the mouse on the pixel over the viewer.
So, it seems that we succeed in creating a basic line, but the line that i want is the line that we can move or rotate. So first lets start to make the line move which is actually quite easy. We just need to define the center where the line start.
We need to make the center first by adding 2d position knob on nuke (2nd Photo). To do that you can make it by :
You can access the value of the knob by using knobname.value in this case since knob name is Center you can use Center.x or Center.y
By default x - y is equal with (x - 0) - (y - 0) where the center is on (0,0) so this time we need to make the center changeable.
After that here come the equation to move the line.
(x-Center.x) - (y-Center.y)
It will set the center of the line to the coordinate of Center that we provide. If we move the Center Coordinate the line will follow.
Next we want to rotate the line by certain degree. We will need additional knob where we can change the degree as we want. It can be done by adding Floating Point Slider Knob and set the maximum value to 360 since it is means the whole circle.
We will need to change the degree of rotation to radians by using:
Ok next the equation to rotate a point mathematicaly is:
x' = x * cos (theta) - y * sin (theta)
y' = x * sin (theta) + y * cos (theta)
Since we already got the x or y then to rotate it we will just need one of the equation either x' or y' (CMIIW):
# Vertical Line
(x-Center.x) * cos (theta) - (y-Center.y) * sin (theta)
# Horizontal Line
(x-Center.x) * sin (theta) + (y-Center.y) * cos (theta)
Tada!! You have successfully create a rotateable line!!
now we will need to clamp the value so it won't be less than 0 or more than 1, by using:
clamp((x-Center.x) * sin (theta) + (y-Center.y) * cos (theta))
Thanks for reading!
Happy Experimenting :)
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