framework's demo2 game is cool and had not something wrong with demo2. but when I implement my own explosion effect(copy the demo2's code to my project), and I found my game had something strange when displayed the explosion's smoke, and I fixed it.

the code(Explosion.cpp line:29 ):
<br />float alpha = 1 - (Boy::Environment::instance()->getTime() - mStartTime) / mDuration;<br />g->setAlpha(alpha);<br />g->setDrawMode(Boy::Graphics::DRAWMODE_ADDITIVE);<br />for (int i=0 ; i<NUM_PARTICLES ; i++)<br />{<br />    g->pushTransform();<br />    g->translate(<br />        mParticlePositions[i].x,<br />        mParticlePositions[i].y);<br />    g->drawImage(mImage);<br />    g->popTransform();<br />}<br />g->setColorizationEnabled(false);<br />g->setDrawMode(Boy::Graphics::DRAWMODE_NORMAL);<br />

should be modified to
<br />float alpha = 1 - (Boy::Environment::instance()->getTime() - mStartTime) / mDuration;<br />if ( alpha < 0 )       //changed here.............<br />    alpha = 0;<br />g->setAlpha(alpha);<br />g->setDrawMode(Boy::Graphics::DRAWMODE_ADDITIVE);<br />for (int i=0 ; i<NUM_PARTICLES ; i++)<br />{<br />    g->pushTransform();<br />    g->translate(<br />        mParticlePositions[i].x,<br /> mParticlePositions[i].y);<br />    g->drawImage(mImage);<br />    g->popTransform();<br />}<br />g->setAlpha(1);                // and here........<br />g->setColorizationEnabled(false);<br />g->setDrawMode(Boy::Graphics::DRAWMODE_NORMAL);<br />

hope it helpful. :)
and sorry for my bad English.