Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Adds 3DTILES_binary_buffers extension #415

Closed
wants to merge 7 commits into from
Closed

Adds 3DTILES_binary_buffers extension #415

Changes from all commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
60bcc55
Adds preliminary design for 3DTILES_binary_buffers
Jun 6, 2020
8031e2a
Adds example
Jun 6, 2020
a937cf1
Adds property reference
sanjeetsuhag Jun 8, 2020
578f57b
Fixes property description for element type and component type to cor…
sanjeetsuhag Jun 8, 2020
d2e143f
Minor fixes
Jun 9, 2020
a7a0f3f
Adds byte boundary note for BIT component type
Jun 9, 2020
f1f27f7
Adds data alignment section, adds NONUNIFORM element type for storage…
sanjeetsuhag Jun 10, 2020
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
194 changes: 194 additions & 0 deletions extensions/3DTILES_binary_buffers/README.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,194 @@
# 3DTILES_binary_buffers

## Overview

This extension to 3D Tiles enables storage of binary data in external buffers.

## Data Alignment

The byte offset of a buffer view into a buffer must be a multiple of the size of the buffer view's component type. For a buffer view that uses the `BIT` element type, the data must be padded with `0`s to meet the nearest byte boundary.

Buffer views of matrix type have data stored in column-major order; start of each column must be aligned to 4-byte boundaries. To achieve this, three `elementType`/`componentType` combinations require special layout:

**MAT2, 1-byte components**
```
| 00| 01| 02| 03| 04| 05| 06| 07|
|===|===|===|===|===|===|===|===|
|m00|m10|---|---|m01|m11|---|---|
```

**MAT3, 1-byte components**
```
| 00| 01| 02| 03| 04| 05| 06| 07| 08| 09| 0A| 0B|
|===|===|===|===|===|===|===|===|===|===|===|===|
|m00|m10|m20|---|m01|m11|m21|---|m02|m12|m22|---|
```

**MAT3, 2-byte components**
```
| 00| 01| 02| 03| 04| 05| 06| 07| 08| 09| 0A| 0B| 0C| 0D| 0E| 0F| 10| 11| 12| 13| 14| 15| 16| 17|
|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|===|
|m00|m00|m10|m10|m20|m20|---|---|m01|m01|m11|m11|m21|m21|---|---|m02|m02|m12|m12|m22|m22|---|---|
```

Alignment requirements apply only to start of each column, so trailing bytes could be omitted if there's no further data.

## Properties Reference

---------------------------------------
### 3DTILES_binary_buffers.bufferViews

`bufferViews` provide a typed view into a `buffer`.

**Properties**

| |Type|Description|Required|
|---|----|-----------|--------|
|**buffer**|`integer`|The index of the buffer.|☑️ Yes|
|**byteOffset**|`integer`|The offset relative to the start of the buffer in bytes.|☑️ Yes|
|**byteLength**|`integer`|The length of the bufferView in bytes.| ☑️ Yes|
|**elementCount**|`integer`|The number of elements in the buffer view.| ☑️ Yes|
|**elementByteOffsetsBufferView**|`integer`|The index of the bufferView containing byte offsets for each element. Must be defined for the STRING and NONUNIFORM element types.|No|
|**elementType**|`string`|Specifies if the attribute is a scalar, vector, matrix or string.|No, default is `SCALAR`.|
|**componentType**|`string`|The datatype of components in the attribute. Must be defined for every other element type, except STRING and NONUNIFORM (in which case it will be ignored).|No|


#### Element Types

| Element Type | No. of components |
|:------------:|:-----------------:|
| SCALAR | 1 |
| STRING | 1 |
| NONUNIFORM | 1 |
| VEC2 | 2 |
| VEC3 | 3 |
| VEC4 | 4 |
| MAT2 | 4 |
| MAT3 | 9 |
| MAT4 | 16 |

*Note: The `STRING` element type only stores UTF-8 encoded strings.*

#### Component Types

| Component | Size (bits) |
|:---------:|:------------:|
| BIT | 1 |
| BYTE | 8 |
| UNSIGNED_BYTE | 8 |
| SHORT | 16 |
| UNSIGNED_SHORT | 16 |
| HALF_FLOAT | 16 |
| INT | 32 |
| UNSIGNED_INT | 32 |
| FLOAT | 32 |
| DOUBLE | 64 |


---------------------------------------
### 3DTILES_binary_buffers.buffers
A buffer points to a blob data.

**Properties**

| |Type|Description|Required|
|---|----|-----------|--------|
|**uri**|`string`|The uri of the buffer.| ☑️ Yes|
|**byteLength**|`integer`|The total byte length of the buffer.| ☑️ Yes|

## Examples

### 3DTILES_implicit_tiling and 3DTILES_tile_metadata

```json
{
"asset": {
"version": "1.0"
},
"extensions": {
"3DTILES_implicit_tiling": {
"tilingScheme": "quadtree",
"subdivision": {
"completeLevels": 2,
"bufferView": 0
},
"content": {
"levelOffset": 2,
"levelOffsetFill": 0,
"bufferView": 1
},
"metadata": {
"levelOffset": 2,
"levelOffsetFill": 0,
"bufferView": 1
}
},
"3DTILES_tile_metadata": {
"properties": {
"surfaceArea": {
"semantic": "_SURFACE_AREA",
"bufferView": 2
},
"tileId": {
"semantic": "_TILE_ID",
"bufferView": 3
}
}
},
"3DTILES_binary_buffers": {
"bufferViews": [
{
"elementType": "VEC2",
"componentType": "BIT",
"byteOffset": 0,
"byteLength": 2,
"buffer": 0
},
{
"elementType": "SCALAR",
"componentType": "BIT",
"byteOffset": 2,
"byteLength": 4,
"buffer": 0
},
{
"elementType": "SCALAR",
"componentType": "FLOAT",
"byteOffset": 0,
"byteLength": 32,
"buffer": 1
},
{
"elementType": "STRING",
"byteOffset": 32,
"byteLength": 64,
"elementByteOffsetsBufferView": 4,
"buffer": 2
},
{
"elementType": "SCALAR",
"componentType": "UNSIGNED_INT",
"byteOffset": 0,
"byteLength": 32,
"buffer": 2
}
],
"buffers": [
{
"uri": "implicit.bin",
"byteLength": 6
},
{
"uri": "metadata_surface_area.bin",
"byteLength": 32
},
{
"uri": "metadata_tile_id.bin",
"byteLength": 96
}
]
}
}
}

```