我必须确定用户是进行顺时针旋转手势还是逆时针旋转手势。我已经启动了Vector位置以及当前和之前的触摸。虽然我认为起始矢量不是很有用,因为如果用户也可以在两者之间改变旋转。也就是说他可以改变从顺时针到逆时针的旋转。就像旋转x-box的d-pad一样。 对于想法的现场演示,就像Dead Trigger 2开发者所做的那样,没有屏幕按钮只是使用手势在屏幕上旋转。 我如何识别它?
答案 0 :(得分:2)
要确定2D输入是顺时针还是逆时针旋转,请从旋转原点找到两个矢量的叉积,看它是负还是正。一个向量来自前一个输入,另一个向量来自当前输入。
在伪代码中。
centerX = screenCenterX; // point user is rotating around
centerY = screenCenterY;
inputX = getUserX(); // gets X and Y input coords
inputY = getUserY(); //
lastVecX = inputX - centerX; // the previous user input vector x,y
lastVecY = inputY - centerY; //
while(true){ // loop
inputX = getUserX(); // gets X and Y input coords
inputY = getUserY(); //
vecInX = inputX - centerX; // get the vector from center to input
vecInY = inputY - centerY; //
// now get the cross product
cross = lastVecX * vecInY - lastVecY * vecInX;
if(cross > 0) then rotation is clockwise
if(cross < 0) then rotation is anticlockwise
if(cross == 0) then there is no rotation
lastVecX = vecInX; // save the current input vector
lastVecY = vecInY; //
} // Loop until the cows come home.
为了得到你需要的角度来规范化矢量,然后交叉积是角度变化的罪。
在伪代码中
vecInX = inputX - centerX; // get the vector from center to input
vecInY = inputY - centerY; //
// normalized input Vector by getting its length
length = sqrt(vecInX * vecInX + vecInY * vecInY);
// divide the vector by its length
vecInX /= length;
vecInY /= length;
// input vector is now normalised. IE it has a unit length
// now get the cross product
cross = lastVecX * vecInY - lastVecY * vecInX;
// Because the vectors are normalised the cross product will be in a range
// of -1 to 1 with < 0 anticlockwise and > 0 clockwise
changeInAngle = asin(cross); // get the change in angle since last input
absoluteAngle += changeInAngle; // track the absolute angle
lastVecX = vecInX; // save the current normalised input vector
lastVecY = vecInY; //
// loop