Module: Tea::Grabbing

Included in:
Bitmap, Screen
Defined in:
lib/tea/mix_grabbing.rb

Overview

This module gives bitmap-like objects a grab method that takes a ‘snapshot’ of some part of it and returns it as a new Bitmap.

To use this mixin, include it and define a grabbing_buffer method:

include Grabbing
def grabbing_buffer
  @my_sdl_buffer
end

Instance Method Summary collapse

Instance Method Details

#grab(*box) ⇒ Object

Grab some part of the bitmap-like object, and return it as a new Tea::Bitmap object.

This can be called in two ways:

  • ()

    create a deep-copy of the whole bitmap-like object.

  • (x, y, w, h)

    copy the pixels within the box at (x, y) of size w * h.

May raise Tea::Error if the box given (if any) is outside the bitmap.



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# File 'lib/tea/mix_grabbing.rb', line 33

def grab(*box)
  buffer = grabbing_buffer

  case box.length
  when 0
    x = 0
    y = 0
    w = buffer.w
    h = buffer.h
  when 4
    if clipped_box = grabbing_clip(*box, 0, 0, buffer.w, buffer.h)
      x, y, w, h = clipped_box
    else
      raise Tea::Error, "cannot grab (#{x}, #{y}, #{w}, #{h}), not within (#{buffer.x}, #{buffer.y}, #{buffer.w}, #{buffer.h})", caller
    end
  else
    raise ArgumentError, "wrong number of arguments (#{box.length} for 0 or 4)", caller
  end

  bitmap = Bitmap.new(w, h, Tea::Color::CLEAR)

  for buf_y in y...(y + h)
    for buf_x in x...(x + w)
      bitmap[buf_x - x, buf_y - y] = Color.mix(*buffer.get_rgba(buffer[buf_x, buf_y]))
    end
  end

  bitmap
end

#grabbing_clip(x, y, w, h, bound_x, bound_y, bound_w, bound_h) ⇒ Object

Keep the rect (x, y, w, h) within the rect (bound_x, bound_y, bound_w, bound_h).

Returns [in_x, in_y, in_w, in_h], defining a rect like (x, y, w, h), but within the bounding rect. Returns nil if the rect given is not within the bounding rect at all, i.e. w or h would be less than 1.



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# File 'lib/tea/mix_grabbing.rb', line 68

def grabbing_clip(x, y, w, h, bound_x, bound_y, bound_w, bound_h)
  return nil if x + w <= bound_x || x >= bound_x + bound_w || y + h <= bound_y || y >= bound_y + bound_h

  in_x = (x >= bound_x) ? x : bound_x
  in_y = (y >= bound_y) ? y : bound_y

  x2 = x + w
  y2 = y + h
  in_x2 = (x2 <= bound_x + bound_w) ? x2 : bound_x + bound_w
  in_y2 = (y2 <= bound_y + bound_h) ? y2 : bound_y + bound_h
  in_w = in_x2 - in_x
  in_h = in_y2 - in_y

  [in_x, in_y, in_w, in_h]
end