1// Copyright 2024-2025 Google LLC
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//      http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15// Proto definitions for delta-coded storage of Ink strokes.
16
17syntax = "proto2";
18
19package androidx.ink.storage.proto;
20
21// Efficiently encodes a sequence of numbers, compressed lossily using delta
22// coding (but sequences of integers can be represented exactly).  The first
23// value in the represented sequence is equal to `offset + scale * deltas[0]`,
24// and each successive Nth value is equal to `value[N-1] + scale * deltas[N]`.
25//
26// When representing a sequence of integers, the `scale` and `offset` fields
27// must be integral (or omitted, and their default values used).  Otherwise,
28// this can represent a sequence of floating point numbers at whatever level of
29// precision yields a good tradeoff between accuracy and gzip-compressibility of
30// the delta sequence.
31message CodedNumericRun {
32  repeated sint32 deltas = 1 [packed = true];
33  optional float scale = 2 [default = 1];
34  optional float offset = 3;
35}
36