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Image:mapPixel

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Transforms pixels in the Image using a function.

The callback function passed to this function will be called once for each pixel. For each pixel, the function will be called with its x and y coordinate and the red, green, blue, and alpha components of its color. Whatever the function returns will be used as the new color for the pixel.

The callback function will potentially be called thousands of times, so it's best to keep the amount of code in there small and fast.

Image:mapPixel(callback, x, y, w, h)

Arguments

NameTypeDefaultDescription
callbackfunction The function that will be called for each pixel.
xnumber0 The x coordinate of the upper-left corner of the area of the Image to affect.
ynumber0 The y coordinate of the upper-left corner of the area of the Image to affect.
wnumberimage:getWidth() The width of the area to affect.
hnumberimage:getHeight() The height of the area to affect.

Returns

Nothing

Notes

The following texture formats are supported: r8, rg8, rgba8, r16, rg16, rgba16, r32f, rg32f, rgba32f.

Examples

Convert an Image to grayscale.

image:mapPixel(function(x, y, r, g, b, a)
  local brightness = .21 * r + .72 * g + .07 * b
  return brightness, brightness, brightness, a
end)

Efficient Image updates using FFI. Due to the low-level nature, this will be a lot faster, but it's specialized to the rgba8 image format and risks crashing if used improperly.

local ffi = require 'ffi'

function lovr.load()
  local w, h = 256, 256

  image = lovr.data.newImage(w, h)

  local pointer = ffi.cast('uint8_t*', image:getPointer())

  for y = 0, h - 1 do
    for x = 0, w - 1 do
      pointer[(y * w + x) * 4 + 0] = (x / w) * 255
      pointer[(y * w + x) * 4 + 1] = (y / h) * 255
      pointer[(y * w + x) * 4 + 2] = 255
      pointer[(y * w + x) * 4 + 3] = 255
    end
  end

  texture = lovr.graphics.newTexture(image)
end

function lovr.draw(pass)
  pass:fill(texture)
end

See also