# swap_udc_1
# written by John Dannenhoffer

# two Bodys on top of Stack
BOX       0  0  0  1  1  1
CYLINDER  0  0  0  1  0  0  1
SPHERE    0  0  0  1
UDPRIM    $$/swap

SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   4  # cylinder
STORE     .
SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   2  # sphere
STORE     .
SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   6  # box
STORE     .

# Mark Body on top of Stack
BOX       0  0  0  1  1  1
MARK
CYLINDER  0  0  0  1  0  0  1
UDPRIM    $$/swap

ASSERT    @stack[@stack.size] 0  #mark
STORE     .
SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   4  # cylinder
STORE     .
SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   6  # box
STORE     .

# Body Mark on top of Stack
BOX       0  0  0  1  1  1
CYLINDER  0  0  0  1  0  0  1
MARK
UDPRIM    $$/swap

SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   4  # cylinder
STORE     .
ASSERT    @stack[@stack.size] 0  #mark
STORE     .
SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   6  # box
STORE     .

# two Marks on top of Stack
BOX       0  0  0  1  1  1
MARK
MARK
UDPRIM    $$/swap

ASSERT    @stack[@stack.size] 0  #mark
STORE     .
ASSERT    @stack[@stack.size] 0  #mark
STORE     .
SELECT    BODY     @stack[@stack.size]
ASSERT    @nface   6  # box
STORE     .

# not enough entries on Stack (throws error)
SET       okay  1
BOX       0  0  0  1  1  1
UDPRIM    $$/swap
CATBEG    999
   SET    okay  0
CATEND
ASSERT    okay  0

END