# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
from torch.nn import functional as F

from fsdet.structures import Instances


def detector_postprocess(results, output_height, output_width):
    """
    Resize the output instances.
    The input images are often resized when entering an object detector.
    As a result, we often need the outputs of the detector in a different
    resolution from its inputs.

    This function will resize the raw outputs of an R-CNN detector
    to produce outputs according to the desired output resolution.

    Args:
        results (Instances): the raw outputs from the detector.
            `results.image_size` contains the input image resolution the detector sees.
            This object might be modified in-place.
        output_height, output_width: the desired output resolution.

    Returns:
        Instances: the resized output from the model, based on the output resolution
    """
    scale_x, scale_y = (output_width / results.image_size[1], output_height / results.image_size[0])
    results = Instances((output_height, output_width), **results.get_fields())

    if results.has("pred_boxes"):
        output_boxes = results.pred_boxes
    elif results.has("proposal_boxes"):
        output_boxes = results.proposal_boxes

    output_boxes.scale(scale_x, scale_y)
    output_boxes.clip(results.image_size)

    results = results[output_boxes.nonempty()]

    return results
