frame ->sdl_test_event: type=name,
fields=sheetFor testing only. Build an SDL event of type for this frame
and process it as if SDL reported it. This allows testing input that is
not available on the test machine, such as pen and touch input.
type is one of mouse_motion, mouse_button_down,
mouse_button_up, mouse_wheel, pen_proximity_in,
pen_proximity_out, pen_down, pen_up, pen_motion,
pen_button_down, pen_button_up, pen_axis, finger_down,
finger_up, finger_motion, finger_canceled, pinch_begin,
pinch_update, pinch_end, key_down, key_up
and text_input. The attributes of fields are
named after the fields of the SDL event structure (e.g., x, y, which, button, pressure);
missing fields are 0. Positions are relative to the frame, except for
the finger events, whose x and y are
normalised to 0..1 as in SDL. The wheel event takes dx, dy
(precise) and integer_x,
integer_y (whole notches). The key events take key
(the SDL keycode), scancode, mod and repeat,
and text_input takes
char, the code point of the text.
