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	blind-spiral-gradient.1 - blind - suckless command-line video editing utility
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	blind-spiral-gradient.1 (3903B)
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	1 .TH BLIND-SPIRAL-GRADIENT 1 blind
	2 .SH NAME
	3 blind-spiral-gradient - Generate a video with a spiral gradient
	4 .SH SYNOPSIS
	5 .B blind-spiral-gradient
	6 [-s
	7 .I spirals
	8 \| -t]
	9 [-al]
	10 -w
	11 .I width
	12 -h
	13 .I height
	14 .SH DESCRIPTION
	15 .B blind-spiral-gradient
	16 prints a video with a spiral gradient to stdout,
	17 parameters for each from is read from each frame
	18 in stdin. The gradient is stored in all channels
	19 of the video.
	20 .P
	21 The video in stdin must contain 2 to 5 pixels per
	22 frame (inclusively). The first pixel shall point
	23 to the beginning of the gradient (where the value
	24 is 0) and the second pixel shall point to the end
	25 of the gradient (where the value is 1). In these
	26 pixels, the value of the first channel specifies
	27 the X-position and the value of the second
	28 channel specifies Y-position, the other channels
	29 are ignored. The angle of the vector between these
	30 two pixels determine the angle of the spiral.
	31 .P
	32 If there are four or five pixel in each frame in
	33 stdin, the third and fourth pixels are used to
	34 modify the shape of the spiral so that it is
	35 based on a superellipse instead of a circle.
	36 The first and second channel of third pixel creates
	37 a vector that is normalised. This vector and its
	38 normal creates the basis of an imaginary coordinate
	39 system with its origo at the beginning of the spiral.
	40 The superellipse defined by the equation
	41 .RI \| x \|^ a +\| y / m \|^ b =1,
	42 where
	43 .I x
	44 is the distance from origo along the vector,
	45 .I y
	46 is the distance from origo along the vector's normal,
	47 .IR a ,
	48 .IR b ,
	49 and
	50 .I m
	51 are the values of the first, second, and third
	52 channels, respectively, in the fourth pixel. and has
	53 the distance 1 from origo at all points on it. If
	54 .IR a ,
	55 .IR b ,
	56 and
	57 .I m
	58 have the values 2, 2, and 1, respectively, these
	59 pixels have no effect on the spiral's shape.
	60 The third and fourth channels in the third pixel
	61 and the fourth channel in the fourth pixel are
	62 ignored.
	63 .P
	64 If there are three or five pixels, the channels,
	65 in order, in the last pixel, specifies the value
	66 .IR a ,
	67 .IR e ,
	68 .IR p ,
	69 and
	70 .IR k ,
	71 whose default values are 0, 1, 1, and 1, respectively.
	72 .I k
	73 is ignored unless
	74 .B -l
	75 is used. If
	76 .B -l
	77 is not used, the spiral is defined by the equation
	78 .IR r = a +( b /( 2\fBpi\fP )^ e ) v ^( ep ).
	79 If
	80 .B -l
	81 is used, the spiral is defined by the equation
	82 .RI log( r / k )= a +(log( b )/( 2\fBpi\fP )^ e ) v ^( ep ).
	83 .I r
	84 is defined as the distance from the center of the
	85 spiral,
	86 .I b
	87 is defined as the distance between the points
	88 specified in the first and second pixel from stdin,
	89 and
	90 .I v
	91 is defined as the angle.
	92 .SH NOTES
	93 Pixels after the end of the gradient have values
	94 larger than 1.
	95 .BR blind-*-wave (1)
	96 commands can be used to put all values between
	97 0 and 1.
	98 .SH OPTIONS
	99 .TP
	100 .B -a
	101 Create a spiral that gones anticlockwise.
	102 .TP
	103 .B -l
	104 Create a logarithmic spiral.
	105 .TP
	106 .BR -s " "\fIspirals\fP
	107 Draw
	108 .I spirals
	109 spirals
	110 going out the specified centre instead of
	111 just one spiral. The spirals are uniformly
	112 distributed.
	113 .I spirals
	114 can be any non-zero real number.
	115 .TP
	116 .B -t
	117 Base the resulting values only on the angle
	118 in the spiral formula rather than then both
	119 the angle and radius. This is useful for
	120 creating transitions with spiral effects.
	121 .TP
	122 .BR -w " "\fIwidth\fP
	123 The width of the video, in pixels.
	124 .TP
	125 .BR -h " "\fIheight\fP
	126 The height of the video, in pixels.
	127 .SH NOTES
	128 Because
	129 .B -s
	130 has no affect when
	131 .B -t
	132 is applied,
	133 .B -s
	134 and
	135 .B -t
	136 cannot be combined unless
	137 .I spirals
	138 is 1. This will change in the future
	139 if a way to meaningfully combined the
	140 two flags is found.
	141 .SH SEE ALSO
	142 .BR blind (7),
	143 .BR blind-from-text (7),
	144 .BR blind-cone-gradient (1),
	145 .BR blind-linear-gradient (1),
	146 .BR blind-radial-gradient (1),
	147 .BR blind-square-gradient (1),
	148 .BR blind-double-sine-wave (1),
	149 .BR blind-round-wave (1),
	150 .BR blind-sawtooth-wave (1),
	151 .BR blind-sinc-wave (1),
	152 .BR blind-sine-wave (1),
	153 .BR blind-triangular-wave (1),
	154 .BR blind-spectrum (1)
	155 .SH AUTHORS
	156 Mattias Andrée
	157 .RI < [email protected] >