Rotation And Scaling Features; Figure 32 - Referencing Rotated Background Data - Nintendo GAME BOY ADVANCE Programming Manual

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6.1.7 BG Rotation and Scaling Features
Rotation and scaling of the BG as a whole can be performed in a rotation/scaling BG screen.
With rotation, BG data is referenced as shown in the following figure.

Figure 32 - Referencing Rotated Background Data

Origin
( , 0 ) 0
Rotation center
coordinate
( ,
x y
0
y-axis
AGB-06-0001-002-B13
Released: May 27, 2005
Game Boy Advance Programming Manual
Coordinate
before rotation
( , )
x y
1 1
Coordinate after
rotation
( , )
x y
2 2
q
)
0
dx
q
dy
d y
µ
q
d x
µ
BG display screen
Horizontal line before
rotation
*
B G
d a
t a
r e
f e r
e n
c e
a r
e a
H o
(distance moved in direction x, same line) = (1 / a )
dx
dy (distance moved in direction y, same line) = - (1 / b )
(distance moved in direction x, next line) = ( 1 / a )
d x
µ
(distance moved in direction y, next line) = ( 1 / b )
d y
µ
a: Magnification along x-axis
b: Magnification along y-axis
May 25, 2005
x-axis
r i z
o n
t a l
r o t l i n
a t i e a
o n
f t e
r
cos q
sin q
sin q
cos q
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