343 lines
10 KiB
Markdown
343 lines
10 KiB
Markdown
# Pixel Buffer (pixbuf) Module
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| Since | Origin / Contributor | Maintainer | Source |
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| :----- | :-------------------- | :---------- | :------ |
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| 2020-?? | [nwf](https://github.com/nwf) | nwf | [pixbuf.c](../../app/modules/pixbuf.c) |
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The pixbuf library offers C-array byte objects and convenient utility functions
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for maintaining small frame buffers, usually for use with LED arrays, as
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supported by, e.g., ws2812.
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## pixbuf.newBuffer()
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Allocate a new memory buffer to store LED values.
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#### Syntax
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`pixbuf.newBuffer(numberOfLeds, numberOfChannels)`
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#### Parameters
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- `numberOfLeds` length of the LED strip (in pixels)
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- `numberOfChannels` the channel count (bytes per pixel)
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#### Returns
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`pixbuf.buffer` object
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## pixbuf.buffer:get()
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Return the value at the given position, in native strip color order
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#### Syntax
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`buffer:get(index)`
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#### Parameters
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- `index` position in the buffer (1 for first LED)
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#### Returns
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`(color)`
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#### Example
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```lua
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buffer = pixbuf.newBuffer(32, 4)
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print(buffer:get(1))
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0 0 0 0
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```
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## pixbuf.buffer:set()
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Set the value at the given position, in native strip color order
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#### Syntax
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`buffer:set(index, color)`
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#### Parameters
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- `index` position in the buffer (1 for the first LED)
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- `color` payload of the color
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Payload could be:
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- `number, number, ...`, passing as many colors as required by the array type
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- `table` should contain one value per color required by the array type
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- `string` with a natural multiple of the colors required by the array type
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`string` inputs may be used to set multiple consecutive pixels!
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#### Returns
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The buffer
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#### Example
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```lua
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buffer = pixbuf.newBuffer(32, 3)
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buffer:set(1, 255, 0, 0) -- set the first LED green for a GRB strip
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```
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```lua
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buffer = pixbuf.newBuffer(32, 4)
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buffer:set(1, {255, 0, 0, 255}) -- set the first LED white and red for a RGBW strip
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```
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```lua
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-- set the first LED green for a RGB strip and exploit the return value
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buffer = pixbuf.newBuffer(32, 3):set(1, string.char(0, 255, 0))
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```
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## pixbuf.buffer:size()
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Return the size of the buffer in number of LEDs
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#### Syntax
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`buffer:size()`
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#### Parameters
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none
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#### Returns
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`int`
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## pixbuf.buffer:channels()
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Return the buffer's channel count
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#### Syntax
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`buffer:channels()`
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#### Parameters
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none
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#### Returns
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`int`
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## pixbuf.buffer:fill()
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Fill the buffer with the given color.
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The number of given bytes must match the channel count of the buffer.
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#### Syntax
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`buffer:fill(color)`
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#### Parameters
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- `color` bytes for each channel
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#### Returns
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The buffer
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#### Example
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```lua
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buffer:fill(0, 0, 0) -- fill the buffer with black for a RGB strip
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```
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## pixbuf.buffer:dump()
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Returns the contents of the buffer (the pixel values) as a string. This can then be saved to a file or sent over a network and may be fed back to [`pixbuf.buffer:set()`](#pixbufbufferset).
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#### Syntax
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`buffer:dump()`
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#### Returns
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A string containing the pixel values.
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#### Example
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```lua
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local s = buffer:dump()
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```
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## pixbuf.buffer:replace()
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Inserts a string (or a pixbuf) into another buffer with an offset.
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The buffer must be of the same type or an error will be thrown.
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#### Syntax
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`buffer:replace(source[, offset])`
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#### Parameters
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- `source` the pixel values to be set into the buffer. This is either a string or a pixbuf.
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- `offset` the offset where the source is to be placed in the buffer. Default is 1. Negative values can be used.
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#### Returns
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`nil`
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#### Example
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```lua
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buffer:replace(anotherbuffer:dump()) -- copy one buffer into another via a string
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buffer:replace(anotherbuffer) -- copy one buffer into another
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newbuffer = buffer.sub(1) -- make a copy of a buffer into a new buffer
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```
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## pixbuf.buffer:mix()
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This is a general method that loads data into a buffer that is a linear combination of data from other buffers. It can be used to copy a buffer or,
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more usefully, do a cross fade. The pixel values are computed as integers and then range limited to [0, 255]. This means that negative
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factors work as expected, and that the order of combining buffers does not matter.
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#### Syntax
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`buffer:mix(factor1, buffer1, ...)`
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#### Parameters
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- `factor1` This is the factor that the contents of `buffer1` are multiplied by. This factor is scaled by a factor of 256. Thus `factor1` value of 256 is a factor of 1.0.
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- `buffer1` This is the source buffer. It must be of the same shape as the destination buffer.
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There can be any number of factor/buffer pairs.
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#### Returns
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The output buffer.
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#### Example
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```lua
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-- loads buffer with a crossfade between buffer1 and buffer2
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buffer:mix(256 - crossmix, buffer1, crossmix, buffer2)
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-- multiplies all values in buffer by 0.75
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-- This can be used in place of buffer:fade
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buffer:mix(192, buffer)
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```
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## pixbuf.buffer:mix4I5()
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Like [`pixbuf.buffer:mix()`](#pixbufbuffermix) but treats the first channel as
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a scaling, 5-bit intensity value. The buffers must all have four channels.
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This is mostly useful for APA102 LEDs.
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## pixbuf.buffer:power()
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Computes the total energy requirement for the buffer. This is merely the total sum of all the pixel values (which assumes that each color in each
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pixel consumes the same amount of power). A real WS2812 (or WS2811) has three constant current drivers of 20mA -- one for each of R, G and B. The
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pulse width modulation will cause the *average* current to scale linearly with pixel value.
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#### Syntax
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`buffer:power()`
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#### Returns
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An integer which is the sum of all the pixel values.
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#### Example
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```lua
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-- Dim the buffer to no more than the PSU can provide
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local psu_current_ma = 1000
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local led_current_ma = 20
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local led_sum = psu_current_ma * 255 / led_current_ma
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local p = buffer:power()
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if p > led_sum then
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buffer:mix(256 * led_sum / p, buffer) -- power is now limited
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end
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```
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## pixbuf.buffer:powerI()
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Like [`pixbuf.buffer:power()`](#pixbufbufferpower) but treats the first channel as
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a scaling intensity value.
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## pixbuf.buffer:fade()
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Fade in or out. Defaults to out. Multiply or divide each byte of each led with/by the given value. Useful for a fading effect.
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#### Syntax
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`buffer:fade(value [, direction])`
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#### Parameters
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- `value` value by which to divide or multiply each byte
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- `direction` pixbuf.FADE\_IN or pixbuf.FADE\_OUT. Defaults to pixbuf.FADE\_OUT
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#### Returns
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`nil`
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#### Example
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```lua
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buffer:fade(2)
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buffer:fade(2, pixbuf.FADE_IN)
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```
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## pixbuf.buffer:fadeI()
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Like [`pixbuf.buffer:fade()`](#pixbufbufferfade) but treats the first channel as
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a scaling intensity value. This is mostly useful for APA102 LEDs.
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## pixbuf.buffer:shift()
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Shift the content of (a piece of) the buffer in positive or negative direction. This allows simple animation effects. A slice of the buffer can be specified by using the
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standard start and end offset Lua notation. Negative values count backwards from the end of the buffer.
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#### Syntax
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`buffer:shift(value [, mode[, i[, j]]])`
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#### Parameters
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- `value` number of pixels by which to rotate the buffer. Positive values rotate forwards, negative values backwards.
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- `mode` is the shift mode to use. Can be one of `pixbuf.SHIFT_LOGICAL` or `pixbuf.SHIFT_CIRCULAR`. In case of SHIFT\_LOGICAL, the freed pixels are set to 0 (off). In case of SHIFT\_CIRCULAR, the buffer is treated like a ring buffer, inserting the pixels falling out on one end again on the other end. Defaults to SHIFT\_LOGICAL.
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- `i` is the first offset in the buffer to be affected. Negative values are permitted and count backwards from the end. Default is 1.
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- `j` is the last offset in the buffer to be affected. Negative values are permitted and count backwards from the end. Default is -1.
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#### Returns
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`nil`
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#### Example
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```lua
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buffer:shift(3)
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```
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## pixbuf.buffer:sub()
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This implements the extraction function like `string.sub`. The indexes are in leds and all the same rules apply.
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#### Syntax
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`buffer1:sub(i[, j])`
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#### Parameters
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- `i` This is the start of the extracted data. Negative values can be used.
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- `j` this is the end of the extracted data. Negative values can be used. The default is -1.
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#### Returns
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A buffer containing the extracted piece.
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#### Example
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```
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b = buffer:sub(1,10)
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```
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## pixbuf.buffer:__concat()
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This implements the `..` operator to concatenate two buffers. They must have the same number of colors per led.
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#### Syntax
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`buffer1 .. buffer2`
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#### Parameters
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- `buffer1` this is the start of the resulting buffer
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- `buffer2` this is the end of the resulting buffer
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#### Returns
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The concatenated buffer.
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#### Example
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```
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ws2812.write(buffer1 .. buffer2)
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```
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## pixbuf.buffer:map()
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Map a function across each pixel of one, or zip a function along two,
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pixbuf(s), storing into the buffer on which it is called.
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#### Syntax
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`buffer0:map(f, [buffer1], [start1], [end1], [buffer2, [start2]])`
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#### Parameters
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- `f` This is the mapping function; it is applied for each pixel to all channels of `buffer1` and
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all channels of `buffer2`, if given. It must return a value for each channel of the output
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buffer, `buffer0`.
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- `buffer1` The first source buffer. Defaults to `buffer0`.
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- `start1` This is the start of the mapped range of `buffer1`. Negative values can be used and will be interpreted as before the end of `buffer1`. The default is 1.
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- `end1` this is the end of the mapped range. Negative values can be used. The default is -1 (i.e., the end of `buffer1`).
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- `buffer2` is a second buffer, for zip operations
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- `start2` This is the start of the mapped range within `buffer2`. Negative values can be used and will be interpreted as before the end of `buffer2`. The default is 1.
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`buffer0` must have sufficient room to recieve all pixels from `start1` to
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`end1` (which is true of the defaults, when `buffer1` is `buffer0` and `start1`
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is 1 and `end1` is -1). `buffer2`, if given, must have sufficient pixels after
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`start2`.
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#### Returns
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`buffer0`
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#### Examples
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Change channel order within a single buffer:
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```Lua
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buffer:map(function(r,g,b) return g,r,b end)
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```
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Change channel order for a subset of pixels:
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```Lua
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buffer:map(function(r,g,b) return g,r,b end, nil, 2, 5)
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```
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Extract one channel for a subset of pixels:
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```Lua
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outbuf = pixbuf.create(11, 1)
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outbuf:map(function(r,g,b) return b end, inbuf, 10, 20)
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```
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Concatenate channels per pixel, possibly with different offsets in buffers:
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```Lua
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outbuf:map(function(...) return ... end, inbuf1, inbuf2)
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outbuf:map(function(...) return ... end, inbuf1, 5, 10, inbuf2, 3)
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```
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