blind-spiral-gradient.1 (3903B)

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 AndrĂ©e 157 .RI < maandree@kth.se >