Module: Tea::Clipping

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

Overview

The Clipping mixin enables anything with an SDL-like buffer can get, set and use a clipping rectangle to restrict where drawing takes place.

To use the Clipping mixin, include it, and provide a clipping_buffer method that returns the buffer to be clipped.

include Tea::Clipping
def clipping_buffer
  @sdl_buffer
end

Instance Method Summary collapse

Instance Method Details

#clip(x = nil, y = nil, w = nil, h = nil) ⇒ Object

Get, set or run a block with a clipping rectangle that restricts where drawing can take place.

Getting the current clipping rectangle:

x, y, width, height = clippable_object.clip

Setting a new clipping rectangle:

old_x, old_y, old_w, old_h = clippable_object.clip(new_x, new_y, new_w, new_h)

Running a block with a clipping rectangle temporarily set:

clippable_object.clip(clip_x, clip_y, clip_w, clip_h) do
  # Draw onto clippable_object within clip rect here.
end



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# File 'lib/tea/mix_clipping.rb', line 37

def clip(x=nil, y=nil, w=nil, h=nil)
  buffer = clipping_buffer

  # rubysdl's SDL::Surface#get_clip_rect doesn't return anything useful.
  # Seems to be a bug, or at least compilation quirk.
  @clipping_rect = [0, 0, buffer.w, buffer.h] unless @clipping_rect
  old_clipping_rect = @clipping_rect

  case
  when !(x || y || w || h)                  # Get clip rect.
    # Do nothing.
  when x && y && w && h && !block_given?    # Set clip rect.
    @clipping_rect = [x, y, w, h]
    buffer.set_clip_rect *@clipping_rect
  when x && y && w && h &&  block_given?    # Run block with clip rect.
    @clipping_rect = [x, y, w, h]
    buffer.set_clip_rect *@clipping_rect
    begin
      yield
    ensure
      @clipping_rect = old_clipping_rect
      buffer.set_clip_rect *old_clipping_rect
    end
  else
    arg_count = 0
    [x, y, w, h].each { |arg| arg_count += 1 if arg == nil }
    raise ArgumentError, "wrong number of arguments (#{arg_count} for 0 or 4)", caller
  end

  old_clipping_rect
end