@Override
protected void processOnMove(float currentX, float currentY, float offsetX, float offsetY) {
if (currentY < mDownY) {
super.processOnMove(currentX, currentY, offsetX, offsetY);
return;
}
// distance from top
final float scrollTop = (currentY - mDownY) * DRAG_RATE + mDownPos;
final float currentDragPercent = scrollTop / mOneHeight;
if (currentDragPercent < 0) {
setOffset(offsetX, 0);
return;
}
mCurrentDragPercent = currentDragPercent;
// 0 ~ 1
float boundedDragPercent = Math.min(1f, Math.abs(currentDragPercent));
float extraOS = scrollTop - mOneHeight;
// 0 ~ 2
// if extraOS lower than 0, which means scrollTop lower than onHeight, tensionSlingshotPercent
// will be 0.
float tensionSlingshotPercent = Math.max(0, Math.min(extraOS, mOneHeight * 2) / mOneHeight);
float tensionPercent =
(float) ((tensionSlingshotPercent / 4) - Math.pow((tensionSlingshotPercent / 4), 2)) * 2f;
float extraMove = (mOneHeight) * tensionPercent / 2;
int targetY = (int) ((mOneHeight * boundedDragPercent) + extraMove);
int change = targetY - getCurrentPosY();
setOffset(currentX, change);
}
@Override
public void onRelease() {
super.onRelease();
mReleasePos = getCurrentPosY();
mReleasePercent = mCurrentDragPercent;
}
@Override
public void setHeaderHeight(int height) {
super.setHeaderHeight(height);
mOneHeight = height * 4f / 5;
}
@Override
public void onPressDown(float x, float y) {
super.onPressDown(x, y);
mDownY = y;
mDownPos = getCurrentPosY();
}