unidepth/layers/positional_encoding.py

"""
Author: Luigi Piccinelli
Licensed under the CC-BY NC 4.0 license (http://creativecommons.org/licenses/by-nc/4.0/)
"""

from math import pi
from typing import Optional

import torch
import torch.nn as nn
from einops import rearrange, repeat


class PositionEmbeddingSine(nn.Module):
    def __init__(
        self, num_pos_feats=64, temperature=10000, normalize=False, scale=None
    ):
        super().__init__()
        self.num_pos_feats = num_pos_feats
        self.temperature = temperature
        self.normalize = normalize
        if scale is not None and normalize is False:
            raise ValueError("normalize should be True if scale is passed")
        if scale is None:
            scale = 2 * pi
        self.scale = scale

    def forward(
        self, x: torch.Tensor, mask: Optional[torch.Tensor] = None
    ) -> torch.Tensor:
        if mask is None:
            mask = torch.zeros(
                (x.size(0), x.size(2), x.size(3)), device=x.device, dtype=torch.bool
            )
        not_mask = ~mask
        y_embed = not_mask.cumsum(1, dtype=torch.float32)
        x_embed = not_mask.cumsum(2, dtype=torch.float32)
        if self.normalize:
            eps = 1e-6
            y_embed = y_embed / (y_embed[:, -1:, :] + eps) * self.scale
            x_embed = x_embed / (x_embed[:, :, -1:] + eps) * self.scale

        dim_t = torch.arange(self.num_pos_feats, dtype=torch.float32, device=x.device)
        dim_t = self.temperature ** (
            2 * torch.div(dim_t, 2, rounding_mode="floor") / self.num_pos_feats
        )

        pos_x = x_embed[:, :, :, None] / dim_t
        pos_y = y_embed[:, :, :, None] / dim_t
        pos_x = torch.stack(
            (pos_x[:, :, :, 0::2].sin(), pos_x[:, :, :, 1::2].cos()), dim=4
        ).flatten(3)
        pos_y = torch.stack(
            (pos_y[:, :, :, 0::2].sin(), pos_y[:, :, :, 1::2].cos()), dim=4
        ).flatten(3)
        pos = torch.cat((pos_y, pos_x), dim=3).permute(0, 3, 1, 2)
        return pos

    def __repr__(self, _repr_indent=4):
        head = "Positional encoding " + self.__class__.__name__
        body = [
            "num_pos_feats: {}".format(self.num_pos_feats),
            "temperature: {}".format(self.temperature),
            "normalize: {}".format(self.normalize),
            "scale: {}".format(self.scale),
        ]
        # _repr_indent = 4
        lines = [head] + [" " * _repr_indent + line for line in body]
        return "\n".join(lines)


class LearnedSinusoidalPosEmb(nn.Module):
    def __init__(self, dim):
        super().__init__()
        assert (dim % 2) == 0
        half_dim = dim // 2
        self.weights = nn.Parameter(torch.randn(half_dim))

    def forward(self, x):
        x = rearrange(x, "b -> b 1")
        freqs = x * rearrange(self.weights, "d -> 1 d") * 2 * pi
        fouriered = torch.cat((freqs.sin(), freqs.cos()), dim=-1)
        fouriered = torch.cat((x, fouriered), dim=-1)
        return fouriered


def generate_fourier_features(x, max_freq=64, num_bands=16):
    x = x.unsqueeze(-1)
    device, dtype, orig_x = x.device, x.dtype, x

    scales = torch.linspace(
        -max_freq / 2, max_freq / 2, num_bands, device=device, dtype=dtype
    )
    scales = scales[(*((None,) * (len(x.shape) - 1)), Ellipsis)]

    x = x * scales * pi
    x = torch.cat([x.sin(), x.cos()], dim=-1)
    x = torch.cat((x, orig_x), dim=-1)
    return x.flatten(-2)


def broadcat(tensors, dim=-1):
    num_tensors = len(tensors)
    shape_lens = set(list(map(lambda t: len(t.shape), tensors)))
    assert len(shape_lens) == 1, "tensors must all have the same number of dimensions"
    shape_len = list(shape_lens)[0]
    dim = (dim + shape_len) if dim < 0 else dim
    dims = list(zip(*map(lambda t: list(t.shape), tensors)))
    expandable_dims = [(i, val) for i, val in enumerate(dims) if i != dim]
    assert all(
        [*map(lambda t: len(set(t[1])) <= 2, expandable_dims)]
    ), "invalid dimensions for broadcastable concatentation"
    max_dims = list(map(lambda t: (t[0], max(t[1])), expandable_dims))
    expanded_dims = list(map(lambda t: (t[0], (t[1],) * num_tensors), max_dims))
    expanded_dims.insert(dim, (dim, dims[dim]))
    expandable_shapes = list(zip(*map(lambda t: t[1], expanded_dims)))
    tensors = list(map(lambda t: t[0].expand(*t[1]), zip(tensors, expandable_shapes)))
    return torch.cat(tensors, dim=dim)


def rotate_half(x):
    x = rearrange(x, "... (d r) -> ... d r", r=2)
    x1, x2 = x.unbind(dim=-1)
    x = torch.stack((-x2, x1), dim=-1)
    return rearrange(x, "... d r -> ... (d r)")


class VisionRotaryEmbedding(nn.Module):
    def __init__(
        self,
        dim,
        pt_seq_len,
        ft_seq_len=None,
        custom_freqs=None,
        freqs_for="lang",
        theta=10000,
        max_freq=10,
        num_freqs=1,
    ):
        super().__init__()
        if custom_freqs:
            freqs = custom_freqs
        elif freqs_for == "lang":
            freqs = 1.0 / (
                theta ** (torch.arange(0, dim, 2)[: (dim // 2)].float() / dim)
            )
        elif freqs_for == "pixel":
            freqs = torch.linspace(1.0, max_freq / 2, dim // 2) * pi
        elif freqs_for == "constant":
            freqs = torch.ones(num_freqs).float()
        else:
            raise ValueError(f"unknown modality {freqs_for}")

        if ft_seq_len is None:
            ft_seq_len = pt_seq_len
        t = torch.arange(ft_seq_len) / ft_seq_len * pt_seq_len

        freqs_h = torch.einsum("..., f -> ... f", t, freqs)
        freqs_h = repeat(freqs_h, "... n -> ... (n r)", r=2)

        freqs_w = torch.einsum("..., f -> ... f", t, freqs)
        freqs_w = repeat(freqs_w, "... n -> ... (n r)", r=2)

        freqs = broadcat((freqs_h[:, None, :], freqs_w[None, :, :]), dim=-1)

        self.register_buffer("freqs_cos", freqs.cos())
        self.register_buffer("freqs_sin", freqs.sin())

        print("======== shape of rope freq", self.freqs_cos.shape, "========")

    def forward(self, t, start_index=0):
        rot_dim = self.freqs_cos.shape[-1]
        end_index = start_index + rot_dim
        assert (
            rot_dim <= t.shape[-1]
        ), f"feature dimension {t.shape[-1]} is not of sufficient size to rotate in all the positions {rot_dim}"
        t_left, t, t_right = (
            t[..., :start_index],
            t[..., start_index:end_index],
            t[..., end_index:],
        )
        t = (t * self.freqs_cos) + (rotate_half(t) * self.freqs_sin)
        return torch.cat((t_left, t, t_right), dim=-1)


class VisionRotaryEmbeddingFast(nn.Module):
    def __init__(
        self,
        dim,
        pt_seq_len,
        ft_seq_len=None,
        custom_freqs=None,
        freqs_for="lang",
        theta=10000,
        max_freq=10,
        num_freqs=1,
    ):
        super().__init__()
        if custom_freqs:
            freqs = custom_freqs
        elif freqs_for == "lang":
            freqs = 1.0 / (
                theta ** (torch.arange(0, dim, 2)[: (dim // 2)].float() / dim)
            )
        elif freqs_for == "pixel":
            freqs = torch.linspace(1.0, max_freq / 2, dim // 2) * pi
        elif freqs_for == "constant":
            freqs = torch.ones(num_freqs).float()
        else:
            raise ValueError(f"unknown modality {freqs_for}")

        if ft_seq_len is None:
            ft_seq_len = pt_seq_len
        t = torch.arange(ft_seq_len) / ft_seq_len * pt_seq_len

        freqs = torch.einsum("..., f -> ... f", t, freqs)
        freqs = repeat(freqs, "... n -> ... (n r)", r=2)
        freqs = broadcat((freqs[:, None, :], freqs[None, :, :]), dim=-1)

        freqs_cos = freqs.cos().view(-1, freqs.shape[-1])
        freqs_sin = freqs.sin().view(-1, freqs.shape[-1])

        self.register_buffer("freqs_cos", freqs_cos)
        self.register_buffer("freqs_sin", freqs_sin)

    def forward(self, t):
        return t * self.freqs_cos + rotate_half(t) * self.freqs_sin