ARKit基础（四）——HitTest点击测试

这个view主要展示在ARKit中点击2d界面如何映射到3d空间。

ar空间中有一杯咖啡，点击屏幕如果点中咖啡杯，咖啡杯会变色，如果点中现实中的桌子，咖啡杯会移动到桌子上，如果点击的地方不是杯子又没有桌子这样的平面，杯子会漂浮在前方0.7米的空中。

我们将使用下面三个方法：

SCNSceneRenderer
 - (NSArray<SCNHitTestResult *> *)hitTest:(CGPoint)point options:(NSDictionary<SCNHitTestOption, id> *)options;
 //从屏幕中一点，视线方向发出一条射线，返回射线击中的所有3D对象

ARSCNView
- (NSArray<ARHitTestResult *> *)hitTest:(CGPoint)point types:(ARHitTestResultType)types;
//从屏幕中一点，视线方向发出一条射线，返回射线击中的AR锚

SCNSceneRenderer
- (SCNVector3)unprojectPoint:(SCNVector3)point;
//屏幕中一点在3D空间的映射

首先我们把咖啡杯加入场景并给这个节点起个名字

SCNScene *scene = [SCNScene sceneNamed:@"art.scnassets/cup/cup.scn"];
cupNode=scene.rootNode.childNodes[0];
cupNode.position = SCNVector3Make(0, -0.3,-0.5);
cupNode.name=@"cup";
[sceneView.scene.rootNode addChildNode:cupNode];

当点击屏幕的时候，我们首先检测是否点中咖啡杯。

UITouch *touch=[touches anyObject];
CGPoint point = [touch locationInView:[touch view]];
NSArray *arr=[sceneView hitTest:point options:nil];
if (arr.count>0) {
    SCNHitTestResult *node=[arr objectAtIndex:0];
    if ([node.node.name isEqualToString:@"cup"]) {
         //点中咖啡执行变色
         [self changeColor];
         return;
    } 
}

我们通过加一个环境光的方式让咖啡杯变色

-(void)changeColor{
    if (lightNode==nil) {
        SCNLight *light=[SCNLight light];
        light.type=SCNLightTypeOmni;
        light.color=[UIColor blueColor];
        
        lightNode=[SCNNode node];
        lightNode.position=SCNVector3Make(0, 0, 100);
        lightNode.light=light;
    }
    
    if (lightNode.parentNode==nil) {
        [sceneView.scene.rootNode addChildNode:lightNode];
    }else{
        [lightNode removeFromParentNode];
    }
}

如果没有击中咖啡杯，我们检测是否击中检测到的平面，比如桌面、地面等等。

NSArray *arr1=[sceneView hitTest:point types:ARHitTestResultTypeExistingPlane];
if (arr1.count>0) {
     //击中一个平面，找到平面上击中点的坐标
     ARHitTestResult *plane=[arr1 objectAtIndex:0];
     SCNVector3 planePos=SCNVector3Make(plane.worldTransform.columns[3].x, plane.worldTransform.columns[3].y, plane.worldTransform.columns[3].z);
     //让咖啡杯移动到那一点
     [self cupMoveTo:planePos];
}

茶杯移动

-(void)cupMoveTo:(SCNVector3) position{
    CABasicAnimation *animation=[CABasicAnimation animationWithKeyPath:@"transform.translation"];
    animation.toValue=[NSValue valueWithSCNVector3:position];
    animation.removedOnCompletion=NO;
    animation.duration=2;
    animation.fillMode=kCAFillModeForwards;
    [cupNode addAnimation:animation forKey:@"move"];
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        cupNode.position= position;
    });
}

如果没有击中咖啡杯，也没有击中检测到的平面，我们让咖啡移动到，点击处前方0.7米的空中。

-(SCNVector3)worldPositionFromScreenPosition:(CGPoint)position{
    ARFrame *frame = sceneView.session.currentFrame;
    SCNVector3 cameraPos=SCNVector3Make(frame.camera.transform.columns[3].x, frame.camera.transform.columns[3].y, frame.camera.transform.columns[3].z);
    SCNVector3 positionVec = SCNVector3Make(position.x, position.y,1.0);
    SCNVector3 screenPosOnFarClippingPlane = [sceneView unprojectPoint:positionVec];
    //rayDirection 为射线的方向向量
    SCNVector3 rayDirection=SCNVector3Make(screenPosOnFarClippingPlane.x-cameraPos.x,screenPosOnFarClippingPlane.y-cameraPos.y,screenPosOnFarClippingPlane.z-cameraPos.z);
    float leng=sqrtf(rayDirection.x * rayDirection.x + rayDirection.y * rayDirection.y + rayDirection.z * rayDirection.z);
    rayDirection=SCNVector3Make(rayDirection.x/leng,rayDirection.y/leng,rayDirection.z/leng);
    //返回 rayDirection方向上，相机前方0.7米处坐标
    return [self getNewPointLinePoint:cameraPos lineVector:rayDirection distance:0.7];
}

getNewPointLinePoint 返回已知直线L过点m（m1，m2，m3），且方向向量为VL（v1，v2，v3）求与m距离d的点n的坐标

-(SCNVector3)getNewPointLinePoint:(SCNVector3)linePoint
                          lineVector:(SCNVector3)lineVector
                            distance:(float)distance{
    float vpt=(lineVector.x*lineVector.x+lineVector.y*lineVector.y+lineVector.z*lineVector.z);
    if (vpt==0) {
        return {FLT_MAX,FLT_MAX,FLT_MAX};
    }
    
    float t=pow(distance*distance/vpt,0.5);
    float x=linePoint.x+lineVector.x*t;
    float y=linePoint.y+lineVector.y*t;
    float z=linePoint.z+lineVector.z*t;
    
    return SCNVector3Make(x,y,z);
}

完整代码

#import "ARHitTestResultViewController.h"

@interface ARHitTestResultViewController ()<ARSCNViewDelegate>{
    IBOutlet ARSCNView *sceneView;
    SCNNode *lightNode;
    SCNNode *cupNode;
    BOOL isMoving;
}
@end

@implementation ARHitTestResultViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    sceneView.delegate = self;

    SCNScene *scene = [SCNScene sceneNamed:@"art.scnassets/candle/candle.scn"];
    cupNode=scene.rootNode.childNodes[0];
    cupNode.position = SCNVector3Make(0, -0.3,-0.5);
    cupNode.name=@"cup";
    // Set the scene to the view
    [sceneView.scene.rootNode addChildNode:cupNode];
    
    isMoving = false;
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    // Create a session configuration
    ARWorldTrackingConfiguration *configuration = [ARWorldTrackingConfiguration new];
    configuration.planeDetection = ARPlaneDetectionHorizontal;
    // Run the view's session
    [sceneView.session runWithConfiguration:configuration];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    // Pause the view's session
    [sceneView.session pause];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    // NSLog(@"touch the screen");
    
    UITouch *touch=[touches anyObject];
    CGPoint point = [touch locationInView:[touch view]];
    
    NSArray *arr=[sceneView hitTest:point options:nil];
    if (arr.count>0) {
        SCNHitTestResult *node=[arr objectAtIndex:0];
        NSLog(@"nodename %@",node.node.name);
        if ([node.node.name isEqualToString:@"cup"]) {
            [self changeColor];
            return;
        }
    }
    
    NSArray *arr1=[sceneView hitTest:point types:ARHitTestResultTypeExistingPlane];
    if (arr1.count>0) {
        NSLog(@"hit plane right");
        ARHitTestResult *plane=[arr1 objectAtIndex:0];
        SCNVector3 planePos=SCNVector3Make(plane.worldTransform.columns[3].x, plane.worldTransform.columns[3].y, plane.worldTransform.columns[3].z);
        [self cupMoveTo:planePos];
        return;
    }
    
    SCNVector3 planePos=[self worldPositionFromScreenPosition:point];
    [self cupMoveTo:planePos];
}

-(void)changeColor{
    if (lightNode==nil) {
        SCNLight *light=[SCNLight light];
        light.type=SCNLightTypeOmni;
        light.color=[UIColor blueColor];
        
        lightNode=[SCNNode node];
        lightNode.position=SCNVector3Make(0, 0, 100);
        lightNode.light=light;
    }
    
    if (lightNode.parentNode==nil) {
        [sceneView.scene.rootNode addChildNode:lightNode];
    }else{
        [lightNode removeFromParentNode];
    }
}
    
-(void)cupMoveTo:(SCNVector3) position{
    if (isMoving){
        return;
    }
    isMoving = true;

    CABasicAnimation *animation=[CABasicAnimation animationWithKeyPath:@"transform.translation"];
    animation.toValue=[NSValue valueWithSCNVector3:position];
    animation.removedOnCompletion=NO;
    animation.duration=2;
    animation.fillMode=kCAFillModeForwards;
    
    [cupNode addAnimation:animation forKey:@"move"];
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        cupNode.position= position;
        isMoving=false;
    });
}

-(SCNVector3)worldPositionFromScreenPosition:(CGPoint)position{
    ARFrame *frame = sceneView.session.currentFrame;
    SCNVector3 cameraPos=SCNVector3Make(frame.camera.transform.columns[3].x, frame.camera.transform.columns[3].y, frame.camera.transform.columns[3].z);
    SCNVector3 positionVec = SCNVector3Make(position.x, position.y,1.0);
    SCNVector3 screenPosOnFarClippingPlane = [sceneView unprojectPoint:positionVec];
    
    SCNVector3 rayDirection=SCNVector3Make(screenPosOnFarClippingPlane.x-cameraPos.x,screenPosOnFarClippingPlane.y-cameraPos.y,screenPosOnFarClippingPlane.z-cameraPos.z);
    float leng=sqrtf(rayDirection.x * rayDirection.x + rayDirection.y * rayDirection.y + rayDirection.z * rayDirection.z);
    rayDirection=SCNVector3Make(rayDirection.x/leng,rayDirection.y/leng,rayDirection.z/leng);
    
    return [self getNewPointLinePoint:cameraPos lineVector:rayDirection distance:0.7];
}

//已知直线L过点m（m1，m2，m3），且方向向量为VL（v1，v2，v3）
//求与m距离d的点n
-(SCNVector3)getNewPointLinePoint:(SCNVector3)linePoint
                          lineVector:(SCNVector3)lineVector
                            distance:(float)distance{
    float vpt=(lineVector.x*lineVector.x+lineVector.y*lineVector.y+lineVector.z*lineVector.z);
    if (vpt==0) {
        return {FLT_MAX,FLT_MAX,FLT_MAX};
    }
    
    float t=pow(distance*distance/vpt,0.5);
    float x=linePoint.x+lineVector.x*t;
    float y=linePoint.y+lineVector.y*t;
    float z=linePoint.z+lineVector.z*t;
    
    return SCNVector3Make(x,y,z);
}

@end