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This page shows the designs available in Backdrop, along with an explanation
of the parameters. Animated images are shown in a video on the about page.
When setting parameters, please consider the following general guidelines.
1. X and Y
X increases from left to right. Y increases from top to bottom. (X=0, Y=0)
refers to the top left of the screen. Occasionally, values of YMin and YMax may
be set. YMin will be nearer the top of the screen, and YMin will be nearer the
bottom.
2. Max and Min
When Max and Min values are shown, actual values are set randomly between
these two limits.
3. Probabilities
All probabilities are between 0.0 (never happens) and 1.0 (happens every
frame).
4. Colours
Colours can be selected by name, e.g. HotPink, or specified by their rgb
values in the format 23,130,255. The red, green and blue numbers are within the
limits 0-255. All colour change speeds are the change in r,g and b values per
frame, so a colour speed change of 1 will take the red value from 0 to 255 in
255 frames. At 25 frames per second, this will take just over 10 seconds.
5. Values
In some cases, values can be set which may appear to be beyond any reasonable
use. This is not an error yet to be fixed. I do not know what people want to
create as artists, so have left the values as wide as possible.
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A blended background is a slowly changing blend of colours. The colour range is
limited by setting
upper and lower limits for red, green and blue colour values.
The number of blended colours is set by the grid size, which by default is set
to 3. In the image on the left, the three colours across the top are cyan, lime, cyan.
The speed of change can also be set.
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Circles shows popping circles on a blended background. In this
case, the two background colours are set to blue, so no blend is seen.
The following parameters can be set
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| BackgroundColour1 | The background colour at the top |
| BackgroundColour2 | The background colour at the bottom |
| ForegroundColour | The colour of the circles |
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| Border | The border width and height within which no circles are placed |
| Diameter | The maximum diameter of a circle before it pops |
| NumberOfCircles | The number of circles |
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| Speed | The speed of growth of the circles |
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Points of light drift around the screen like snow or flying insects,
moving randomly from one direction to the next.
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| BackgroundColour1 | The background colour at the top |
| BackgroundColour2 | The background colour at the bottom |
| ForegroundColour1 | The colour of 1/4 of the points |
| ForegroundColour2 | The colour of 1/4 of the points |
| ForegroundColour3 | The colour of 1/4 of the points |
| ForegroundColour4 | The colour of 1/4 of the points |
| IntensityMax | The maximum intensity of any point |
| IntensityMin | The minimum intensity of any point. When the points are generated,
all intensities are set randomly between the min and max limits |
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| Border | The border width and height within which no circles are placed |
| NumberOfFloaters | The number of drifting points |
| SizeMax | The maximum diameter of a point |
| SizeMin | The minimum diameter of a point |
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| DriftX | The speed, in pixels per frame, of drift in the x direction |
| DriftY | The speed of drift in the Y direction. Both
DriftX and DriftY can be positive or negative. |
| SpeedMax | The maximum speed of movement in any direction of a point |
| SpeedMin | The minimum speed |
| TurnMax | The maximum turn angle in degrees |
| TurnProbability | The probability, in each frame, of a turn taking place. If this is set to 0.04 (or 1/25), and the frame rate is 25 frames per second (fps),
then on average 1 turn will occur every second. The angle of the turn will be somewhere
between 0 and TurnMax degrees. |
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Configuring fire is straightforward enough. Four seed colours provide
the blended colours of the flames, and the average flame width and flame
trigger probabilities can be altered. |
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| Colour1 | The cloud colour |
| Colour2 | The other cloud colour. Colours are rotated between these two extremes. |
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| Roughness | The roughness used to generate the clouds - defaults to 70 |
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| Speed | The colour change speed. See the colour note at the top of this page |
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| LimitLower | A value between 0 and 1 creates a lower cut-off layer in the cloud |
| LimitUpper | Upper cut-off. It should be higher than the lower limit |
| Smoothing | Pixel smoothing radius. If 1 is specified, the pixel colour
will be averaged to the average of the pixel and its 8 neighbours. |
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The glowing panel provides a framed background and a panel whose glow
moves around, occasionally accompanied by a flash around the border as
shown here.
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| BackgroundColour1 | The background colour at the top |
| BackgroundColour2 | The background colour at the bottom |
| EdgeGlowColour | The colour of the edge glow |
| GlowColour | The colour of the glow on the panel |
| PanelColour | The colour of the panel |
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| Delay | The number of frames before the edge glow starts
or restarts |
| EdgeGlowAllSides | If false, the edge glow moves along the
top and down the right hand side. If true, this is mirrored down the
left and along the bottom. |
| EdgeGlowLength | The length of the glow in pixels |
| Rebound | When the glow reaches the bottom right it can
rebound (true) or disappear (false) |
| Speed | The number of pixels the edge glow advances each
frame |
| Thickness | The thickness of the edge glow (2 pixels on
the left) |
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| Height | The height of the panel |
| Left | The left coordinate of the panel |
| Top | The top, or Y coordinate of the panel |
| Width | The width of the panel |
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| GlowHeight | The height of the glowing area |
| GlowSpeed | the speed at which the glow moves around. Once
the glow reaches the edge of the panel, it rebounds the same as in
Pong, or electronic tennis. |
| GlowWidth | The width of the glowing area |
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Gritty plasma provides an oscillating wave-like pattern.
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| Colour1 | One colour |
| Colour2 | The other colour |
| LimitToSelectedColours | If true, the pattern oscillates between the two colours.
If false, it can wrap around the full spectrum and create some more interesting patterns |
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| NumberOfWaves | The plasma pattern is generated by either a single wave,
or two or three intersecting waves. The more waves, the more the pattern varies, and the slower the calculation time. |
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| Speed | The colour change speed. See the colour note at the top of this page |
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| Smoothing | A nearest neighbour smoothing function to blend out the grittiness |
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| Colour 1 to 11 | One of 11 colours |
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| NumberOfLines | The number of lines or horizonatal bars |
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| HeightMin | The minimum height a bar reaches before it starts trying to grow |
| SpeedMax | The maximum speed at which the border between two bars can move up or down |
| SpeedMin | The minimum speed. Actual speeds are randomized between the max and min |
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Life is reputedly the most copied algorithm in computing. Some knowledge of Conway's algorithm may help
to better understand this pattern. There is a wikipedia article here.
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| BackgroundColour1 | The background colour at the top |
| BackgroundColour2 | The background colour at the bottom |
| ForegroundColour 1 to 4 | When a colour is selected, a blended mix of the four colours
is created. This blend represents the ages 0 to 255. |
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| AgeMax | The maximum age a cell (in this case a pixel)
reaches before it dies |
| CanDieOfOldAge | If false, then AgeMax is not used in
calculations |
| OvercrowdingLimit | If the number of alive neighbours
(adjacent and immediately diagonal pixels - total 8) reaches this
value, then the cell dies |
| SeedProbability | The probability of a pixel coming back
to life after is has died |
| SuddenDeathProbability | The probability of a pixel
suddenly dying |
| UndercrowdingLimit | If the number of alive neighbours
(adjacent and immediately diagonal pixels - total 8) does not equal
this value, then the cell dies. This is only useful for creating
patterns which shrink away from the corners |
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| DrawBackground | A cell which is dead or of zero age will
be drawn in ForegroundColour1. To draw all zero aged cells as a
blended background, set this to true. |
| Smoothing | Smoothing in this case does not apply to
colour smoothing, but to age smoothing. A number greater than 0 will
produce a less grainy and more uniform pattern. |
| Wrap | If true, then calculations are wrapped around from right to left and top to bottom.
This will avoid edge effects |
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Moving shapes provides shapes moving from left to right, with depth, so
nearer shapes move faster than far shapes, producing a star field type
appearance. The parameters are similar to floating shapes, with the
exceptions of:
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| Shape | Circle, disk or squares are available |
| Show depth | the depth function is optional |
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A grid of panels of varying intensity fade in and out against a blended background. To avoid varying intensities,
set IntensityMax and IntensityMin to the same value. Most of the parameters
require no explanation. Here are the exceptions:
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| PanelsNotDrawn | A list of panels not drawn beginning with 1 top left, 2 the next right and so on.
If there are 2 panels across, then the panel below 1 will be three. To avoid drawing these three panels,
enter 1,2,3 in this field |
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| FadeInSpeedMax | A value of 1 means the panel will fade in immediately, or appear fully on in 1 frame.
A value of 0.04 at a frame rate of 25fps will mean fade in takes 1 second to full intensity |
| FadeInSpeedMin | With FadeInSpeedMax, provides a measure of variance so all
panels do not fade in at the same speed |
| FadeOutSpeedMax | As above |
| FadeOutSpeedMin | As above |
| ProbabilityOfFadeIn | When a panel has faded out, this is the likelihood of it fading back in.
A value of 0.04 at a frame rate of 25fps will mean that on average, 1 second elapses before a panel fades in. |
| ProbabilityOfFadeOut | As above |
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| BackgroundColour1 | The background colour at the top |
| BackgroundColour2 | The background colour at the bottom |
| ForegroundColour1 | The colour of 1/4 of the rectangles |
| ForegroundColour2 | The colour of 1/4 of the rectangles |
| ForegroundColour3 | The colour of 1/4 of the rectangles |
| ForegroundColour4 | The colour of 1/4 of the rectangles |
| IntensityMax | The maximum intensity of any rectangle |
| IntensityMin | The minimum intensity of any rectangle. When the
rectangles are generated,
all intensities are set randomly between the min and max limits |
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| HeightMin | The minimum height of any rectangle |
| NumberOfRectangles | The number of rectangles |
| RotatedHeightMax | If RotateHorizontals is set to true,
this value will limit the maximum height to a value less than
WidthMax if required. Otherwise, too many rectangles stretch off the
top and bottom of a rectangular window. |
| RotateHorizontals | Set to true, will rotate the
rectangles that move from left to right or right to left. |
| WidthMax | The maximum width of any rectangle |
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| SpeedMax | The maximum speed of movement in any direction of a point |
| SpeedMin | The minimum speed |
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It may help to think of this as a reflective stage with a curtain in the
background. This is how I explain it below.
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| TopCentreColour | Reflections takes a single colour, which
is the colour in the middle at the top of the screen. Cunning
transforms are then applied to this single colour to generate the
background |
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| AngleMax | Beams to the left of centre lean to the left,
and to the right of centre lean to the right at this angle. |
| BeamColour | The colour of the beams |
| Beam profile | The beams are drawn fading in towards the
centre. The profile of the fade can be set to Bell (a bell curve),
Linear (straight up and down), Square 1, a square law, and Square 2,
an alternative square law. |
| IntensityMax | The maximum beam intensity |
| IntensityMin | The minimum beam intensity |
| NumberOfBeams | The number of beams |
| WidthMax | The maximum width of a beam |
| WidthMin | The minimum width of a beam |
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| SpeedMax | The maximum speed of movement to left or right
of a beam |
| SpeedMin | The minimum speed |
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| PerspectiveIntensity | The fading intensity from back to
front of stage caused by the perspective |
| PerspectiveSpread | The spread of the reflections on the
stage from back to front. Negative numbers will show as convergence
rather than spreading |
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Ribbons is a complex algorithm. It may be best to twiddle rather than to
try and understand it.
The change limits are defined as DSomething or
DSomething2, this refers to first and second order differentials as in
dy/dx or d2y/d2x.
The switch probabilities refer to an increasing
colour or other value switching from increasing to decreasing or vice
versa.
The ribbons are generated from left to right, so many of the min/max
pairs are used only to define starting conditions at the left.
Limits try to contain the ribbons, but are guidelines rather than
absolute values.
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| DColourMax | The maximum change in colour. As colour is
held in a 256 part blended array, a value of 1 will mean a
transition from the beginning to the end of the array in 256 pixels
along the x axis. As this is a max value, this is weighted by a
random number, so the actual transition will take somewhere between
256 and infinity. |
| DColourMin | The minimum change in colour. Specifying
DColourMin as 1 and DColourMax as 2 will mean an average transition
of 384 pixels. |
| DIntensityMax | The maximum change intensity. As the
intensity range is 0.0 to 1.0, this should be a small number. |
| DIntensityMin | The minimum change in intensity (between
0.0 and 1.0). When the minimum value is reached as a ribbon
progresses from left to right, the intensity starts increasing.
Similarly, when the maximum is reached, the intensity starts
decreasing. |
| DThicknessMax | The maximum change in thickness |
| DThicknessMin | The minimum change in thickness. These
numbers are used only to define the starting conditions of each
ribbon at the left |
| Dy2Max | The maximum 2nd order differential of y with
respect to x |
| Dy2Min | The maximum 2nd order differential of y with
respect to x. These numbers are used only to define starting
conditions |
| DyMax | The maximum change in y from one pixel to the next
along the x axis. |
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| ColourSwitchProbability | The likelihood of an increasing
colour value switching to a decreasing colour value, or a decreasing
one switching to an increasing one |
| IntensitySwitchProbability | The likelihood of an
increasing intensity value switching to a decreasing intensity
value, and vice versa |
| ThicknessSwitchProbability | The likelihood of an
increasing thickness value switching to a decreasing thickness
value, and vice versa |
| ySwitchProbability | The likelihood of an increasing y
value switching to a decreasing y value, and vice versa |
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| BackgroundColour1 | The background colour at the top |
| BackgroundColour2 | The background colour at the bottom |
| ForegroundColour1 | The colour of 1/4 of the rectangles |
| ForegroundColour2 | The colour of 1/4 of the rectangles |
| ForegroundColour3 | The colour of 1/4 of the rectangles |
| ForegroundColour4 | The colour of 1/4 of the rectangles |
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| NumberOfRibbons | The number of ribbons |
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| MovementSmoothing | A next neighbour averaging width
applied to the movement of the ribbons. A low value will look more
jerky than a high one |
| Steps | When moving , the first ribbon moves to the
location of the second ribbon then the third and so on in sequence
until is returns to its original starting position. Steps is the
number of steps taken to move from the first position to the
position of the next ribbon. The less steps, the faster the ribbons
will appear to move |
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| IntensityMax | The maximum intensity reached before
increasing intensity is switched to decreasing intensity |
| IntensityMin | The minimum intensity reached before
decreasing intensity is switched to increasing intensity |
| ThicknessMax | The maximum thickness reached before
increasing thickness is switched to decreasing thickness |
| ThicknessMin | The maximum thickness reached before
increasing thickness is switched to decreasing thickness. |
| ThicknessStartMax | Allows ribbons to begin wider or
narrower than they are further right |
| yLeftMin, yLeftMax, yRightMin, yRightMax | An attempt to
box the ribbon generator into specified bounds. In reality, with
movement smoothing and random position generation, it may or may not
occur. |
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| ThicknessSmoothing | A next neighbour averaging of ribbon
thickness. A higher number creates a more curved appearance to the
ribbon, a low value a more angular appearance |
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Spangles are randomly generated flashes of light or darkness against a
blended background. There are no challenges in the setting of
parameters. |
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An animated sunset or sunrise is generated
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| HighColour | The colour of the sky at the top of the frame
when the sun is high |
| HighColourL | The colour of the sky at the top of the
frame when the sun is low |
| LowColour | The colour of the sky at the horizon when the
sun is high |
| LowColourL | The colour of the sky at the horizon when the
sun is high |
| SeaColourFar | The colour of the sea or ground at the
horizon when the sun is high |
| SeaColourFarL | The colour of the sea or ground at the
horizon when the sun is low |
| SeaColourNear | The colour of the sea or ground at the
bottom of the frame when the sun is high |
| SeaColourNearL | The colour of the sea or ground at the
bottom of the frame when the sun is high |
| StarColour | The colour of the stars |
| SunColour | The colour of the sun |
| SunIntensity | The intensity of the sun (0.0 to 1.0) |
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| Border | The width and height of the border around the edge
in which no stars are positioned |
| NumberOfSparkles | As the sun rises or descends, and the
sea, in its restless turmoil endeavours ever onward, its surface
catches sparkles. The number of the sparkles visible in each frame
can be set here. |
| NumberOfStars | The number of stars in the sky. As the sun
sets, they fade into view, as it rises, they fade out of view. |
| SkyToSeaRatio | A number between 0.0 and 1.0. A value of
0.5 will produce equal sky and sea/ground areas. |
| StarSizeMax | The maximum size of any star |
| SunDiameter | The diameter of the sun |
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| Delay | The number of frames before the rising or setting
begins |
| FadeStars | When set to true, the stars fade in for
sunsets, and fade out for sunrises. Use this set to false, and click
the randomize button to get a pleasing distribution of stars, then
set it to true before playing or recording |
| SparkleSpeedMax | The maximum speed at which sparkles fade in and fade out |
| Speed | The speed of the movement of the sun |
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| Direction | Sunrise or sunset |
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| Colour1 | The colour of the crest of a wave |
| Colour2 | The colour at the trough |
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| NumberOfWaves | More complex wave patterns are generated
with more waves. Limited to a maximum of 3 |
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| Speed | The speed of change, which is the phase change per
frame in radians |
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| AmplitudeMax | Set a ceiling on the wave height |
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Most of the grunge work of drawing antialiased shapes comes from Computer
Graphics Principles and Practice by Foley, van Dam, Feiner and Hughes
The fire routine is ported from code posted on CodeProject by David Swigger
Horizontals was inspired by a greetings card published by WH Smiths
Ribbons was inspired by a Samsung advert for Vista, but came out little like
the initial intention.
The original Life algorithm was created by John Conway.
http://en.wikipedia.org/wiki/Conway's_Game_of_Life
The Reflections default colour scheme is similar to the one on the startup
window in Vista
The fractal cloud generation is ported from code on GarageGames by Josef Jahn
Thanks to Corinna John for her work on reading and writing AVI files
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