png_canvas

A pure Ruby reimplementation of Rui Carmo's pngcanvas Python library, featuring text writing and few renames.

Just add it in your Gemfile:

gem 'png_canvas'

and require it when needed:

require 'png_canvas'

You can render the reference image with:

png = PngCanvas.new(512, 512)
png.rectangle(0, 0, 512 - 1, 512 - 1)

png.vertical_gradient(1, 1, 512 - 2, 512 - 2, [0xff, 0, 0, 0xff], [0x20, 0, 0xff, 0x80])

png.color = [0, 0, 0, 0xff]
png.line(0, 0, 512 - 1, 512 - 1)
png.line(0, 0, 512 / 2, 512 - 1)
png.line(0, 0, 512 - 1, 512 / 2)

png.copy_rectangle(1, 1, 512 / 2 - 1, 512 / 2 - 1, 1, 512 / 2, png)

png.blend_rectangle(1, 1, 512 / 2 - 1, 512 / 2 - 1, 512 / 2, 0, png)
png.save 'reference.png'

• Constructor parameters: width, height, bgcolor: default bgcolor, color: default fgcolor

Colors are specified as 4 element arrays, each representing red, green, blue and alpha values ranging from 0 to 255.

Default background color is white: [0xff, 0xff, 0xff, 0xff]

Default foreground color is black: [0x00, 0x00, 0x00, 0xff]

• color(color): sets the default foreground color for the following points and lines
• point(x, y, color = nil): draws a point at x, y using the specified color (if any) or default
• text(x0, y0, string, color = nil): writes the string of text at x0, y0
• line(x0, y0, x1, y1): draws a single line using default color
• polyline(point_array): draws lines using default color
• vertical_gradient(x0, y0, x1, y1, from_color, to_color): draws a rectangular color gradient from from_color to to_color
• rectangle(x0, y0, x1, y1): draws a rectangle with default color
• filled_rectangle(x0, y0, x1, y1): draws a filled rectangle with default color
• copy_rectangle(x0, y0, x1, y1, dx, dy, destination_png): copies rectangle from destination_png to current canvas with dx, dy offset
• blend_rectangle(x0, y0, x1, y1, dx, dy, destination_png, alpha = 0xff): copies rectangle from destination_png to current canvas using alpha transparency
• save(file_path): saves the canvas to the file_path
• load(file_path): loads the PNG file from the file_path for manipulation
• dump: returns the contents of the canvas as binary

• Fork it
• Write your feature with a test
• Issue a pull request
• …
• Profit!