class ChunkyPNG::Canvas

The ChunkyPNG::Canvas class represents a raster image as a matrix of pixels.

This class supports loading a Canvas from a PNG datastream, and creating a {ChunkyPNG::Datastream PNG datastream} based on this matrix. ChunkyPNG only supports 8-bit color depth, otherwise all of the PNG format's variations are supported for both reading and writing.

This class offers per-pixel access to the matrix by using x,y coordinates. It uses a palette (see {ChunkyPNG::Palette}) to keep track of the different colors used in this matrix.

The pixels in the canvas are stored as 4-byte fixnum, representing 32-bit RGBA colors (8 bit per channel). The module {ChunkyPNG::Color} is provided to work more easily with these number as color values.

The module {ChunkyPNG::Canvas::Operations} is imported for operations on the whole canvas, like cropping and alpha compositing. Simple drawing functions are imported from the {ChunkyPNG::Canvas::Drawing} module.

Attributes

height[R]

@return [Integer] The number of rows in this canvas

pixels[R]

@return [Array<ChunkyPNG::Color>] The list of pixels in this canvas.

This array always should have +width * height+ elements.
width[R]

@return [Integer] The number of columns in this canvas

Public Class Methods

from_canvas(canvas) click to toggle source

Creates a new canvas instance by duplicating another instance. @param [ChunkyPNG::Canvas] canvas The canvas to duplicate @return [ChunkyPNG::Canvas] The newly constructed canvas instance.

    # File lib/chunky_png/canvas.rb
103 def self.from_canvas(canvas)
104   new(canvas.width, canvas.height, canvas.pixels.dup)
105 end
new(width, height, initial = ChunkyPNG::Color::TRANSPARENT) click to toggle source

Initializes a new Canvas instance.

@overload initialize(width, height, background_color)

@param [Integer] width The width in pixels of this canvas
@param [Integer] height The height in pixels of this canvas
@param [Integer, ...] background_color The initial background color of
  this canvas. This can be a color value or any value that
  {ChunkyPNG::Color.parse} can handle.

@overload initialize(width, height, initial)

@param [Integer] width The width in pixels of this canvas
@param [Integer] height The height in pixels of this canvas
@param [Array<Integer>] initial The initial pizel values. Must be an
  array with <tt>width * height</tt> elements.
   # File lib/chunky_png/canvas.rb
78 def initialize(width, height, initial = ChunkyPNG::Color::TRANSPARENT)
79   @width, @height = width, height
80 
81   if initial.kind_of?(Array)
82     unless initial.length == width * height
83       raise ArgumentError, "The initial array should have #{width}x#{height} = #{width*height} elements!"
84     end
85     @pixels = initial
86   else
87     @pixels = Array.new(width * height, ChunkyPNG::Color.parse(initial))
88   end
89 end

Public Instance Methods

==(other)
Alias for: eql?
[](x, y) click to toggle source

Returns a single pixel's color value from this canvas. @param [Integer] x The x-coordinate of the pixel (column) @param [Integer] y The y-coordinate of the pixel (row) @return [Integer] The current color value at the provided coordinates. @raise [ChunkyPNG::OutOfBounds] when the coordinates are outside of the

image's dimensions.

@see get_pixel

    # File lib/chunky_png/canvas.rb
173 def [](x, y)
174   assert_xy!(x, y)
175   @pixels[y * width + x]
176 end
[]=(x, y, color) click to toggle source

Replaces a single pixel in this canvas. @param [Integer] x The x-coordinate of the pixel (column) @param [Integer] y The y-coordinate of the pixel (row) @param [Integer] color The new color for the provided coordinates. @return [Integer] The new color value for this pixel, i.e.

<tt>color</tt>.

@raise [ChunkyPNG::OutOfBounds] when the coordinates are outside of the

image's dimensions.

@see set_pixel

    # File lib/chunky_png/canvas.rb
134 def []=(x, y, color)
135   assert_xy!(x, y)
136   @pixels[y * width + x] = ChunkyPNG::Color.parse(color)
137 end
area() click to toggle source

Returns the area of this canvas in number of pixels. @return [Integer] The number of pixels in this canvas

    # File lib/chunky_png/canvas.rb
121 def area
122   pixels.length
123 end
column(x) click to toggle source

Returns an extracted column as vector of pixels. @param [Integer] x The 0-based column index. @return [Array<Integer>] The vector of pixels in the requested column.

    # File lib/chunky_png/canvas.rb
199 def column(x)
200   assert_x!(x)
201   (0...height).inject([]) { |pixels, y| pixels << get_pixel(x, y) }
202 end
dimension() click to toggle source

Returns the dimension (width x height) for this canvas. @return [ChunkyPNG::Dimension] A dimension instance with the width and

height set for this canvas.
    # File lib/chunky_png/canvas.rb
115 def dimension
116   ChunkyPNG::Dimension.new(width, height)
117 end
eql?(other) click to toggle source

Equality check to compare this canvas with other matrices. @param other The object to compare this Matrix to. @return [true, false] True if the size and pixel values of the other

canvas are exactly the same as this canvas's size and pixel values.
    # File lib/chunky_png/canvas.rb
276 def eql?(other)
277   other.kind_of?(self.class) && other.pixels == self.pixels &&
278         other.width == self.width && other.height == self.height
279 end
Also aliased as: ==
get_pixel(x, y) click to toggle source

Returns a single pixel from this canvas, without checking bounds. The return value for this method is undefined if the coordinates are out of bounds.

@param (see []) @return [Integer] The current pixel at the provided coordinates.

    # File lib/chunky_png/canvas.rb
184 def get_pixel(x, y)
185   @pixels[y * width + x]
186 end
include?(*point_like)
Alias for: include_point?
include_point?(*point_like) click to toggle source

Checks whether the given coordinates are in the range of the canvas @param [ChunkyPNG::Point, Array, Hash, String] point_like The point to

check.

@return [true, false] True if the x and y coordinates of the point are

within the limits of this canvas.

@see ChunkyPNG.Point

    # File lib/chunky_png/canvas.rb
232 def include_point?(*point_like)
233   dimension.include?(ChunkyPNG::Point(*point_like))
234 end
Also aliased as: include?
include_x?(x) click to toggle source

Checks whether the given x-coordinate is in the range of the canvas @param [Integer] x The y-coordinate of the pixel (column) @return [true, false] True if the x-coordinate is in the range of this

canvas.
    # File lib/chunky_png/canvas.rb
261 def include_x?(x)
262   x >= 0 && x < width
263 end
include_xy?(x, y) click to toggle source

Checks whether the given x- and y-coordinate are in the range of the canvas

@param [Integer] x The x-coordinate of the pixel (column) @param [Integer] y The y-coordinate of the pixel (row) @return [true, false] True if the x- and y-coordinate is in the range of

this canvas.
    # File lib/chunky_png/canvas.rb
245 def include_xy?(x, y)
246   y >= 0 && y < height && x >= 0 && x < width
247 end
include_y?(y) click to toggle source

Checks whether the given y-coordinate is in the range of the canvas @param [Integer] y The y-coordinate of the pixel (row) @return [true, false] True if the y-coordinate is in the range of this

canvas.
    # File lib/chunky_png/canvas.rb
253 def include_y?(y)
254   y >= 0 && y < height
255 end
initialize_copy(other) click to toggle source

Initializes a new Canvas instances when being cloned. @param [ChunkyPNG::Canvas] other The canvas to duplicate @return [void] @private

   # File lib/chunky_png/canvas.rb
95 def initialize_copy(other)
96   @width, @height = other.width, other.height
97   @pixels = other.pixels.dup
98 end
inspect() click to toggle source

Alternative implementation of the inspect method. @return [String] A nicely formatted string representation of this canvas. @private

    # File lib/chunky_png/canvas.rb
296 def inspect
297   inspected = "<#{self.class.name} #{width}x#{height} ["
298   for y in 0...height
299     inspected << "\n\t[" << row(y).map { |p| ChunkyPNG::Color.to_hex(p) }.join(' ') << ']'
300   end
301   inspected << "\n]>"
302 end
palette() click to toggle source

Returns the palette used for this canvas. @return [ChunkyPNG::Palette] A palette which contains all the colors that

are being used for this image.
    # File lib/chunky_png/canvas.rb
268 def palette
269   ChunkyPNG::Palette.from_canvas(self)
270 end
replace_column!(x, vector) click to toggle source

Replaces a column of pixels on this canvas. @param [Integer] x The 0-based column index. @param [Array<Integer>] vector The vector of pixels to replace the column

with.

@return [void]

    # File lib/chunky_png/canvas.rb
219 def replace_column!(x, vector)
220   assert_x!(x) && assert_height!(vector.length)
221   for y in 0...height do
222     set_pixel(x, y, vector[y])
223   end
224 end
replace_row!(y, vector) click to toggle source

Replaces a row of pixels on this canvas. @param [Integer] y The 0-based row index. @param [Array<Integer>] vector The vector of pixels to replace the row

with.

@return [void]

    # File lib/chunky_png/canvas.rb
209 def replace_row!(y, vector)
210   assert_y!(y) && assert_width!(vector.length)
211   pixels[y * width, width] = vector
212 end
row(y) click to toggle source

Returns an extracted row as vector of pixels @param [Integer] y The 0-based row index @return [Array<Integer>] The vector of pixels in the requested row

    # File lib/chunky_png/canvas.rb
191 def row(y)
192   assert_y!(y)
193   pixels.slice(y * width, width)
194 end
set_pixel(x, y, color) click to toggle source

Replaces a single pixel in this canvas, without bounds checking.

This method return value and effects are undefined for coordinates out of bounds of the canvas.

@param [Integer] x The x-coordinate of the pixel (column) @param [Integer] y The y-coordinate of the pixel (row) @param [Integer] pixel The new color for the provided coordinates. @return [Integer] The new color value for this pixel, i.e.

<tt>color</tt>.
    # File lib/chunky_png/canvas.rb
149 def set_pixel(x, y, color)
150   @pixels[y * width + x] = color
151 end
set_pixel_if_within_bounds(x, y, color) click to toggle source

Replaces a single pixel in this canvas, with bounds checking. It will do noting if the provided coordinates are out of bounds.

@param [Integer] x The x-coordinate of the pixel (column) @param [Integer] y The y-coordinate of the pixel (row) @param [Integer] pixel The new color value for the provided coordinates. @return [Integer] The new color value for this pixel, i.e.

<tt>color</tt>, or <tt>nil</tt> if the coordinates are out of bounds.
    # File lib/chunky_png/canvas.rb
161 def set_pixel_if_within_bounds(x, y, color)
162   return unless include_xy?(x, y)
163   @pixels[y * width + x] = color
164 end
to_image() click to toggle source

Creates an ChunkyPNG::Image object from this canvas. @return [ChunkyPNG::Image] This canvas wrapped in an Image instance.

    # File lib/chunky_png/canvas.rb
289 def to_image
290   ChunkyPNG::Image.from_canvas(self)
291 end

Protected Instance Methods

assert_height!(vector_length) click to toggle source

Throws an exception if the vector_length does not match this canvas' height.

    # File lib/chunky_png/canvas.rb
341 def assert_height!(vector_length)
342   if height != vector_length
343     raise ChunkyPNG::ExpectationFailed,
344       "The length of the vector (#{vector_length}) does not match the canvas height (#{height})!"
345   end
346   true
347 end
assert_size!(matrix_width, matrix_height) click to toggle source

Throws an exception if the matrix width and height does not match this canvas' dimensions.

    # File lib/chunky_png/canvas.rb
360 def assert_size!(matrix_width, matrix_height)
361   if width  != matrix_width
362     raise ChunkyPNG::ExpectationFailed,
363       'The width of the matrix does not match the canvas width!'
364   end
365   if height != matrix_height
366     raise ChunkyPNG::ExpectationFailed,
367       'The height of the matrix does not match the canvas height!'
368   end
369   true
370 end
assert_width!(vector_length) click to toggle source

Throws an exception if the vector_length does not match this canvas' width.

    # File lib/chunky_png/canvas.rb
351 def assert_width!(vector_length)
352   if width != vector_length
353     raise ChunkyPNG::ExpectationFailed,
354       "The length of the vector (#{vector_length}) does not match the canvas width (#{width})!"
355   end
356   true
357 end
assert_x!(x) click to toggle source

Throws an exception if the x-coordinate is out of bounds.

    # File lib/chunky_png/canvas.rb
316 def assert_x!(x)
317   unless include_x?(x)
318     raise ChunkyPNG::OutOfBounds, "Column index #{x} out of bounds!"
319   end
320   true
321 end
assert_xy!(x, y) click to toggle source

Throws an exception if the x- or y-coordinate is out of bounds.

    # File lib/chunky_png/canvas.rb
332 def assert_xy!(x, y)
333   unless include_xy?(x, y)
334     raise ChunkyPNG::OutOfBounds, "Coordinates (#{x},#{y}) out of bounds!"
335   end
336   true
337 end
assert_y!(y) click to toggle source

Throws an exception if the y-coordinate is out of bounds.

    # File lib/chunky_png/canvas.rb
324 def assert_y!(y)
325   unless include_y?(y)
326     raise ChunkyPNG::OutOfBounds, "Row index #{y} out of bounds!"
327   end
328   true
329 end
replace_canvas!(new_width, new_height, new_pixels) click to toggle source

Replaces the image, given a new width, new height, and a new pixel array.

    # File lib/chunky_png/canvas.rb
307 def replace_canvas!(new_width, new_height, new_pixels)
308   unless new_pixels.length == new_width * new_height
309     raise ArgumentError, "The provided pixel array should have #{new_width * new_height} items"
310   end
311   @width, @height, @pixels = new_width, new_height, new_pixels
312   self
313 end