Pixel Buffer (pixbuf) Module¶

Since	Origin / Contributor	Maintainer	Source
2020-??	nwf	nwf	pixbuf.c

The pixbuf library offers C-array byte objects and convenient utility functions for maintaining small frame buffers, usually for use with LED arrays, as supported by, e.g., ws2812.

pixbuf.newBuffer()¶

Allocate a new memory buffer to store LED values.

Syntax¶

pixbuf.newBuffer(numberOfLeds, numberOfChannels)

Parameters¶

numberOfLeds length of the LED strip (in pixels)
numberOfChannels the channel count (bytes per pixel)

Returns¶

pixbuf.buffer object

pixbuf.buffer:get()¶

Return the value at the given position, in native strip color order.

Syntax¶

buffer:get(index)

Parameters¶

index position in the buffer (1 for first LED)

Returns¶

(color)

Example¶

buffer = pixbuf.newBuffer(32, 4)
print(buffer:get(1))
0   0   0   0

pixbuf.buffer:set()¶

Set the value at the given position, in native strip color order.

Syntax¶

buffer:set(index, color)

Parameters¶

index position in the buffer (1 for the first LED)
color payload of the color

Payload could be: - number, number, ..., passing as many colors as required by the array type - table should contain one value per color required by the array type - string with a natural multiple of the colors required by the array type

string inputs may be used to set multiple consecutive pixels!

Returns¶

The buffer

Example¶

buffer = pixbuf.newBuffer(32, 3)
buffer:set(1, 255, 0, 0) -- set the first LED green for a GRB strip

buffer = pixbuf.newBuffer(32, 4)
buffer:set(1, {255, 0, 0, 255}) -- set the first LED white and red for a RGBW strip

-- set the first LED green for a RGB strip and exploit the return value
buffer = pixbuf.newBuffer(32, 3):set(1, string.char(0, 255, 0))

pixbuf.buffer:size()¶

Return the size of the buffer in number of LEDs.

Syntax¶

buffer:size()

Parameters¶

none

Returns¶

int

pixbuf.buffer:channels()¶

Return the buffer's channel count.

Syntax¶

buffer:channels()

Parameters¶

none

Returns¶

int

pixbuf.buffer:fill()¶

Fill the buffer with the given color. The number of given bytes must match the channel count of the buffer.

Syntax¶

buffer:fill(color)

Parameters¶

color bytes for each channel

Returns¶

The buffer

Example¶

buffer:fill(0, 0, 0) -- fill the buffer with black for a RGB strip

pixbuf.buffer:dump()¶

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().

Syntax¶

buffer:dump()

Returns¶

A string containing the pixel values.

Example¶

local s = buffer:dump()

pixbuf.buffer:replace()¶

Inserts a string (or a pixbuf) into another buffer with an offset. The buffer must be of the same type or an error will be thrown.

Syntax¶

buffer:replace(source[, offset])

Parameters¶

source the pixel values to be set into the buffer. This is either a string or a pixbuf.
offset the offset where the source is to be placed in the buffer. Default is 1. Negative values can be used.

Returns¶

nil

Example¶

buffer:replace(anotherbuffer:dump()) -- copy one buffer into another via a string
buffer:replace(anotherbuffer) -- copy one buffer into another
newbuffer = buffer.sub(1)     -- make a copy of a buffer into a new buffer

pixbuf.buffer:mix()¶

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, more usefully, do a cross fade. The pixel values are computed as integers and then range limited to [0, 255]. This means that negative factors work as expected, and that the order of combining buffers does not matter.

Syntax¶

buffer:mix(factor1, buffer1, ...)

Parameters¶

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.
buffer1 This is the source buffer. It must be of the same shape as the destination buffer.

There can be any number of factor/buffer pairs.

Returns¶

The output buffer.

Example¶

-- loads buffer with a crossfade between buffer1 and buffer2
buffer:mix(256 - crossmix, buffer1, crossmix, buffer2)

-- multiplies all values in buffer by 0.75
-- This can be used in place of buffer:fade
buffer:mix(192, buffer)

pixbuf.buffer:mix4I5()¶

Like pixbuf.buffer:mix() but treats the first channel as a scaling, 5-bit intensity value. The buffers must all have four channels. This is mostly useful for APA102 LEDs.

pixbuf.buffer:power()¶

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 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 pulse width modulation will cause the average current to scale linearly with pixel value.

Syntax¶

buffer:power()

Returns¶

An integer which is the sum of all the pixel values.

Example¶

-- Dim the buffer to no more than the PSU can provide
local psu_current_ma = 1000
local led_current_ma = 20
local led_sum = psu_current_ma * 255 / led_current_ma

local p = buffer:power()
if p > led_sum then
  buffer:mix(256 * led_sum / p, buffer) -- power is now limited
end

pixbuf.buffer:powerI()¶

Like pixbuf.buffer:power() but treats the first channel as a scaling intensity value.

pixbuf.buffer:fade()¶

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.

Syntax¶

buffer:fade(value [, direction])

Parameters¶

value value by which to divide or multiply each byte
direction pixbuf.FADE_IN or pixbuf.FADE_OUT. Defaults to pixbuf.FADE_OUT

Returns¶

nil

Example¶

buffer:fade(2)
buffer:fade(2, pixbuf.FADE_IN)

pixbuf.buffer:fadeI()¶

Like pixbuf.buffer:fade() but treats the first channel as a scaling intensity value. This is mostly useful for APA102 LEDs.

pixbuf.buffer:shift()¶

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 standard start and end offset Lua notation. Negative values count backwards from the end of the buffer.

Syntax¶

buffer:shift(value [, mode[, i[, j]]])

Parameters¶

value number of pixels by which to rotate the buffer. Positive values rotate forwards, negative values backwards.
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.
i is the first offset in the buffer to be affected. Negative values are permitted and count backwards from the end. Default is 1.
j is the last offset in the buffer to be affected. Negative values are permitted and count backwards from the end. Default is -1.

Returns¶

nil

Example¶

buffer:shift(3)

pixbuf.buffer:sub()¶

This implements the extraction function like string.sub. The indexes are in leds and all the same rules apply.

Syntax¶

buffer1:sub(i[, j])

Parameters¶

i This is the start of the extracted data. Negative values can be used.
j this is the end of the extracted data. Negative values can be used. The default is -1.

Returns¶

A buffer containing the extracted piece.

Example¶

b = buffer:sub(1,10)

pixbuf.buffer:__concat()¶

This implements the .. operator to concatenate two buffers. They must have the same number of colors per led.

Syntax¶

buffer1 .. buffer2

Parameters¶

buffer1 this is the start of the resulting buffer
buffer2 this is the end of the resulting buffer

Returns¶

The concatenated buffer.

Example¶

ws2812.write(buffer1 .. buffer2)

pixbuf.buffer:map()¶

Map a function across each pixel of one, or zip a function along two, pixbuf(s), storing into the buffer on which it is called.

Syntax¶

buffer0:map(f, [buffer1], [start1], [end1], [buffer2, [start2]])

Parameters¶

f This is the mapping function; it is applied for each pixel to all channels of buffer1 and all channels of buffer2, if given. It must return a value for each channel of the output buffer, buffer0.
buffer1 The first source buffer. Defaults to buffer0.
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.
end1 this is the end of the mapped range. Negative values can be used. The default is -1 (i.e., the end of buffer1).
buffer2 is a second buffer, for zip operations
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.

buffer0 must have sufficient room to recieve all pixels from start1 to end1 (which is true of the defaults, when buffer1 is buffer0 and start1 is 1 and end1 is -1). buffer2, if given, must have sufficient pixels after start2.

Returns¶

buffer0

Examples¶

Change channel order within a single buffer:

buffer:map(function(r,g,b) return g,r,b end)

Change channel order for a subset of pixels:

buffer:map(function(r,g,b) return g,r,b end, nil, 2, 5)

Extract one channel for a subset of pixels:

outbuf = pixbuf.create(11, 1)
outbuf:map(function(r,g,b) return b end, inbuf, 10, 20)

Concatenate channels per pixel, possibly with different offsets in buffers:

outbuf:map(function(...) return ... end, inbuf1, inbuf2)
outbuf:map(function(...) return ... end, inbuf1, 5, 10, inbuf2, 3)