Preview
@RequiresApi(value = 21)
public final class Preview extends UseCase
A use case that provides a camera preview stream for displaying on-screen.
The preview stream is connected to the Surface provided via SurfaceProvider. The application decides how the Surface is shown, and is responsible for managing the Surface lifecycle after providing it.
To display the preview with the correct orientation, app needs to take different actions based on the source of the Surface. If the Surface is backed by a SurfaceView, it will always be in the device's display orientation. If the Surface is backed by ImageReader, MediaCodec or other objects, it's the application's responsibility to calculate the rotation. If the Surface is backed by a SurfaceTexture, getTransformMatrix can be used to transform the preview to natural orientation. The value is available after a frame is pushed to the SurfaceTexture and its onFrameAvailable has been called. TextureView handles this automatically and always puts the preview in the natural orientation. To further transform the TextureView to display orientation, the app needs to apply the current display rotation. Example:
switch (getWindowManager().getDefaultDisplay().getRotation()) {
case Surface.ROTATION_0:
displayRotation = 0;
break;
case Surface.ROTATION_90:
displayRotation = 90;
break;
case Surface.ROTATION_180:
displayRotation = 180;
break;
case Surface.ROTATION_270:
displayRotation = 270;
break;
default:
throw new UnsupportedOperationException(
"Unsupported display rotation: " + displayRotation);
}
matrix.postRotate(-displayRotation, centerX, centerY);
textureView.setTransform(matrix);
Summary
Nested types |
|---|
public final class Preview.Builder implements ExtendableBuilderBuilder for a |
public interface Preview.SurfaceProviderA interface implemented by the application to provide a |
Public methods |
|
|---|---|
@Nullable ResolutionInfo |
Gets selected resolution information of the |
int |
Returns the rotation that the intended target resolution is expressed in. |
void |
@UiThreadSets a |
void |
@UiThreadSets a |
void |
setTargetRotation(int targetRotation)Sets the target rotation. |
@NonNull String |
toString() |
Public methods
getResolutionInfo
public @Nullable ResolutionInfo getResolutionInfo()
Gets selected resolution information of the Preview.
The returned ResolutionInfo will be expressed in the coordinates of the camera sensor. It will be the same as the resolution inside a SurfaceRequest to request a surface for Preview.
The resolution information might change if the use case is unbound and then rebound or setTargetRotation is called to change the target rotation setting. The application needs to call getResolutionInfo again to get the latest ResolutionInfo for the changes.
| Returns | |
|---|---|
@Nullable ResolutionInfo |
the resolution information if the use case has been bound by the |
getTargetRotation
public int getTargetRotation()
Returns the rotation that the intended target resolution is expressed in.
The rotation is set when constructing an Preview instance using setTargetRotation. If not set, the target rotation defaults to the value of getRotation of the default display at the time the use case is created. The use case is fully created once it has been attached to a camera.
| Returns | |
|---|---|
int |
The rotation of the intended target. |
setSurfaceProvider
@UiThread
public void setSurfaceProvider(@Nullable Preview.SurfaceProvider surfaceProvider)
Sets a SurfaceProvider to provide a Surface for Preview.
Setting the provider will signal to the camera that the use case is ready to receive data. The provider will be triggered on main thread. If the provider is removed by calling this again with a null SurfaceProvider then the camera will stop producing data for this Preview instance.
| Parameters | |
|---|---|
@Nullable Preview.SurfaceProvider surfaceProvider |
SurfaceProvider that provides a |
setSurfaceProvider
@UiThread
public void setSurfaceProvider(
@NonNull Executor executor,
@Nullable Preview.SurfaceProvider surfaceProvider
)
Sets a SurfaceProvider to provide a Surface for Preview.
Setting the provider will signal to the camera that the use case is ready to receive data. If the provider is removed by calling this again with a null SurfaceProvider then the camera will stop producing data for this Preview instance.
| Parameters | |
|---|---|
@NonNull Executor executor |
on which the surfaceProvider will be invoked. |
@Nullable Preview.SurfaceProvider surfaceProvider |
SurfaceProvider that provides a |
setTargetRotation
public void setTargetRotation(int targetRotation)
Sets the target rotation.
This adjust the getTargetRotation, which once applied will update the output to match target rotation specified here.
While rotation can also be set via setTargetRotation , using setTargetRotation allows the target rotation to be set without rebinding new use cases. When this function is called, value set by setTargetResolution will be updated automatically to make sure the suitable resolution can be selected when the use case is bound.
If not set here or by configuration, the target rotation will default to the value of getRotation of the default display at the time the use case is created. The use case is fully created once it has been attached to a camera.
| Parameters | |
|---|---|
int targetRotation |
Target rotation of the output image, expressed as one of |
| See also | |
|---|---|
setTargetRotation |