Wave filter

Format

filter(type="wave", ...)

Args

• x: Horiztonal direction and period of wave
• y: Vertical direction and period of wave
• size: Maximum distortion in pixels (defaults to 1)
• offset: Phase of wave, in periods (e.g., 0 to 1)
• flags: Defaults to 0; see below for other flags

Applies a wave distortion effect to this image.

The x and y parameters specify both the direction and period of the wave; the period is sqrt(x*x + y*y).

This filter is meant to be animated, from whatever offset you want to offset+1, and then repeating. With multiple waves, you can produce a very convincing water effect.

Example

#define WAVE_COUNT 7
atom/proc/WaterEffect()
    var/start = filters.len
    var/X,Y,rsq,i,f
    for(i=1, i<=WAVE_COUNT, ++i)
        // choose a wave with a random direction and a period between 10 and 30 pixels
        do
            X = 60*rand() - 30
            Y = 60*rand() - 30
            rsq = X*X + Y*Y
        while(rsq<100 || rsq>900)   // keep trying if we don't like the numbers
        // keep distortion (size) small, from 0.5 to 3 pixels
        // choose a random phase (offset)
        filters += filter(type="wave", x=X, y=Y, size=rand()*2.5+0.5, offset=rand())
    for(i=1, i<=WAVE_COUNT, ++i)
        // animate phase of each wave from its original phase to phase-1 and then reset;
        // this moves the wave forward in the X,Y direction
        f = filters[start+i]
        animate(f, offset=f:offset, time=0, loop=-1, flags=ANIMATION_PARALLEL)
        animate(offset=f:offset-1, time=rand()*20+10)

The equation governing the wave distortion is size × sin(2π(d - offset)), where d is the number of wave periods’ distance from the center along the x, y direction.

The WAVE_SIDEWAYS flag will cause the distortion to be transverse (perpendicular) to the wave instead of in the same direction as the wave. The WAVE_BOUNDED flag limits the distortion to the confines of this image, instead of lettings its pixels spill out a little further from the distortion (and likewise, transparent pixels spill inward).

Up to 10 waves can be stacked together in a single pass of the filter, as long as they have the same WAVE_BOUNDED flags.

See also