Blanket Slider using Symmetry technique
Though there are some trend to break the frame of blankets, still blanket is one of the fundamental mapping technique being used by several mappers. Since the principle of the P slider (3 point slider) is "the portion of a circle which goes through 3 control points", making a blanket slider has been simple enough.
However as the image above, a blanket using one's intuition has chances to fail blanketing the note perfectly, and could contain some error. True that we could complete the blanket by moving the control point here and there, but this thread is purposing to construct a mathematically perfect blanket slider.
As mentioned above since the slider path always go through 3 control points, we can found the certain pixel where the slider path should certainly pass assuming the note we are intending to blanket is in the center of the screen (256,192). Representatively, horizontally, vertically, or 90 degree flipped pixel of the head of slider (2) would be the ones.
As a result, a slider like above is made, but this is longer than our intended rhythm 1/1.
In this case, we can shorten the length by using Beat Snap Divisor. Since the length of this slider is 3/2, adjusting the Beat Snap Divisor to 1/1 and touching the control point of the slider will shorten the length to 1/1 while having the same format.
With using this simple method, several variations are possible. Whenever you want a blanket pattern, you could refer this technique.