从 iOS 4 开始,我使用以下方法来设置焦点:
- (void) focusAtPoint:(CGPoint)point
{
AVCaptureDevice *device = [[self captureInput] device];
NSError *error;
if ([device isFocusModeSupported:AVCaptureFocusModeAutoFocus] &&
[device isFocusPointOfInterestSupported])
{
if ([device lockForConfiguration:&error]) {
[device setFocusPointOfInterest:point];
[device setFocusMode:AVCaptureFocusModeAutoFocus];
[device unlockForConfiguration];
} else {
NSLog(@"Error: %@", error);
}
}
}
在 iOS 4 设备上,这可以正常工作。但在 iOS 5 上,实时摄像头画面冻结,几秒钟后就完全变黑了。没有抛出异常或错误。
如果我注释掉 setFocusPointOfInterest 或 setFocusMode ,则不会发生该错误。所以它们两者的结合就会导致这种行为。
您给出的 setFocusPointOfInterest: 函数的观点不正确。这就是它崩溃的原因。
将此方法添加到您的程序中并使用此函数返回的值
- (CGPoint)convertToPointOfInterestFromViewCoordinates:(CGPoint)viewCoordinates
{
CGPoint pointOfInterest = CGPointMake(.5f, .5f);
CGSize frameSize = [[self videoPreviewView] frame].size;
AVCaptureVideoPreviewLayer *videoPreviewLayer = [self prevLayer];
if ([[self prevLayer] isMirrored]) {
viewCoordinates.x = frameSize.width - viewCoordinates.x;
}
if ( [[videoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResize] ) {
pointOfInterest = CGPointMake(viewCoordinates.y / frameSize.height, 1.f - (viewCoordinates.x / frameSize.width));
} else {
CGRect cleanAperture;
for (AVCaptureInputPort *port in [[[[self captureSession] inputs] lastObject] ports]) {
if ([port mediaType] == AVMediaTypeVideo) {
cleanAperture = CMVideoFormatDescriptionGetCleanAperture([port formatDescription], YES);
CGSize apertureSize = cleanAperture.size;
CGPoint point = viewCoordinates;
CGFloat apertureRatio = apertureSize.height / apertureSize.width;
CGFloat viewRatio = frameSize.width / frameSize.height;
CGFloat xc = .5f;
CGFloat yc = .5f;
if ( [[videoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResizeAspect] ) {
if (viewRatio > apertureRatio) {
CGFloat y2 = frameSize.height;
CGFloat x2 = frameSize.height * apertureRatio;
CGFloat x1 = frameSize.width;
CGFloat blackBar = (x1 - x2) / 2;
if (point.x >= blackBar && point.x <= blackBar + x2) {
xc = point.y / y2;
yc = 1.f - ((point.x - blackBar) / x2);
}
} else {
CGFloat y2 = frameSize.width / apertureRatio;
CGFloat y1 = frameSize.height;
CGFloat x2 = frameSize.width;
CGFloat blackBar = (y1 - y2) / 2;
if (point.y >= blackBar && point.y <= blackBar + y2) {
xc = ((point.y - blackBar) / y2);
yc = 1.f - (point.x / x2);
}
}
} else if ([[videoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResizeAspectFill]) {
if (viewRatio > apertureRatio) {
CGFloat y2 = apertureSize.width * (frameSize.width / apertureSize.height);
xc = (point.y + ((y2 - frameSize.height) / 2.f)) / y2;
yc = (frameSize.width - point.x) / frameSize.width;
} else {
CGFloat x2 = apertureSize.height * (frameSize.height / apertureSize.width);
yc = 1.f - ((point.x + ((x2 - frameSize.width) / 2)) / x2);
xc = point.y / frameSize.height;
}
}
pointOfInterest = CGPointMake(xc, yc);
break;
}
}
}
return pointOfInterest;
}
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