Obj Rotation/Scaling Feature; Figure 49 - Obj Character Data Referenced With Rotation - Nintendo GAME BOY ADVANCE Programming Manual

May 25, 2005
6.3.4

OBJ Rotation/Scaling Feature

The rotation and scaling feature for OBJ is essentially the same as that for BG.

Figure 49 - OBJ Character Data Referenced with Rotation

OBJ Character Data
y-axis d
µ
q
d x
µ
When an OBJ is displayed, the OBJ character data are referenced horizontally, beginning from the left-
uppermost position. Rotation display can be achieved by adding an angle to the reference direction. The
center of rotation is fixed at the center of the OBJ field. If a reference point surpasses the specified OBJ
size, it becomes transparent.
6.3.4.1 Operations Used in OBJ Rotation/Scaling Processing
1. Specify the rotation/scaling parameter number to be applied in OBJ Attribute 1 of the OAM.
2. The image-processing circuit sums the increases in the x direction (dx, dy) in relation to the center of
rotation (OBJ field center), which serves as reference point, to calculate the x-direction coordinates.
3. When the line is advanced, the increases in the y-direction (d
are summed to calculate the coordinate of the starting point for rendering the next line. The processing
in step 2) above, is then performed.
6.3.4.2 Rotation/Scaling Parameters
Specifies the direction of character data reference in OBJ rotation/scaling processing.
© 1999-2005 NINTENDO
OBJ (Object)
*
(distance moved in x direction, same line) = ( 1 /
dx
(distance moved in y direction, same line) = - ( 1 /
dx dy
(distance moved in x direction, next line) = ( 1 /
q d x
µ
dy
(distance moved in y direction, next line) = ( 1 /
d y
µ
y
D o
u b
l e -
S i z
e O
b j e
c t
F i e
l d
*
*
O b
j e c
t F
i e l
d
OBJ Center
H o
r i z
B e
o n
f o r
t a l
e R
o t a
a: Magnification along x-axis
b: Magnification along y-axis
x, d y) in relation to the reference point,
µ µ
57
x-axis
L i n
e
t i o
n
a
)
cos q
b
)
sin q
a
)
sin q
b
)
cos q
AGB-06-0001-002-B13
Released: May 27, 2005