2D Graphics - Game Programming Algorithms and Techniques - page 31

frameTime * animFPS
frameNum += frameTime * animFPS
// Check if we've advanced past the last
frame, and must wrap.
if frameNum >= animData.frameInfo [ anim-
Num ]. numFrames
// The modulus (%) makes sure we wrap
correctly.
// (Eg. If numFrames == 10 and frameNum
== 11, frameNum would
// wrap to 11 % 10 = 1).
frameNum = frameNum % anim-
Data.frameInfo [ animNum ]. numFrames
end
// Update the active image.
// (startFrame is relative to all the im-
ages, while frameNum is
// relative to the first frame of this par-
ticular animation).
int imageNum = animData.frameInfo [ anim-
Num ]. startFrame + frameNum
image = animData.images [ imageNum ]
// We use fmod (floating point modulus) for
the same reason
// as the % above.
frameTime = fmod( frameTime , 1 / animFPS )
end
end
Althoughthisimplementationof AnimatedSprite willworkforloopinganim-
ations, it has no support for transitions between animations. If such functionality is
required, it's advisable to create an animation state machine. Chapter 9 , “ Artificial
Intelligence , ” discusses the state design pattern in the context of AI, but said state
pattern could just as easily apply to an animation state machine.