(´・ω・｀)cosθを求めるか
D3DXVECTOR2 vecPos[ 2 ];
float a = 0, b = 0;
float dot = 0;
float cosin = 0;
float degree = 0;
float acosin = 0;
vecPos[ 0 ] = D3DXVECTOR2( 2.0f, 1.0f );
vecPos[ 1 ] = D3DXVECTOR2( 1.0f, 3.0f );
a = D3DXVec2Length( &vecPos[ 0 ] );
b = D3DXVec2Length( &vecPos[ 1 ] );
dot = D3DXVec2Dot( &vecPos[ 0 ], &vecPos[ 1 ] );
if( dot != 0 ){
cosin = dot / ( a * b ) ;
}else{
}
if( cosin > 1.0 ){
cosin = 1.0f;
}
if( cosin < -1.0 ){
cosin = -1.0f;
}
acosin = acos( cosin );
degree = D3DXToDegree( acosin );