android: camera_device: Register MAX_DIGITAL_ZOOM

Register the ANDROID_SCALER_AVAILABLE_MAX_DIGITAL_ZOOM static metadata
inspecting the ScalerCrop control's limits.

Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/android/camera_device.cpp

@@ -1018,9 +1018,26 @@ const camera_metadata_t *CameraDevice::getStaticMetadata()
 	}
 
 	/* Scaler static metadata. */
-	float maxDigitalZoom = 1;
+	{
-	staticMetadata_->addEntry(ANDROID_SCALER_AVAILABLE_MAX_DIGITAL_ZOOM,
+		/*
-				  &maxDigitalZoom, 1);
+		 * \todo The digital zoom factor is a property that depends
+		 * on the desired output configuration and the sensor frame size
+		 * input to the ISP. This information is not available to the
+		 * Android HAL, not at initialization time at least.
+		 *
+		 * As a workaround rely on pipeline handlers initializing the
+		 * ScalerCrop control with the camera default configuration and
+		 * use the maximum and minimum crop rectangles to calculate the
+		 * digital zoom factor.
+		 */
+		const auto info = controlsInfo.find(&controls::ScalerCrop);
+		Rectangle min = info->second.min().get<Rectangle>();
+		Rectangle max = info->second.max().get<Rectangle>();
+		float maxZoom = std::min(1.0f * max.width / min.width,
+					 1.0f * max.height / min.height);
+		staticMetadata_->addEntry(ANDROID_SCALER_AVAILABLE_MAX_DIGITAL_ZOOM,
+					  &maxZoom, 1);
+	}
 
 	std::vector<uint32_t> availableStreamConfigurations;
 	availableStreamConfigurations.reserve(streamConfigurations_.size() * 4);