add EXT_primitive_voxels #48
There are no files selected for viewing
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change | ||||
|---|---|---|---|---|---|---|
| @@ -0,0 +1,73 @@ | ||||||
| # EXT_primitive_voxels | ||||||
|
|
||||||
| ## Contributors | ||||||
| - Daniel Krupka, Cesium | ||||||
| - Ian Lilley, Cesium | ||||||
| - Sean Lilley, Cesium | ||||||
|
|
||||||
| ## Status | ||||||
| Draft | ||||||
|
|
||||||
| ## Dependencies | ||||||
| Written against the glTF 2.0 specification. | ||||||
|
|
||||||
| ## Overview | ||||||
|
|
||||||
| This extension allows primitives to use their attribute data to represent volumetric (voxel) data. | ||||||
|
|
||||||
| ``` | ||||||
| { | ||||||
| "meshes": [ | ||||||
| { | ||||||
| "primitives": [ | ||||||
| { | ||||||
| "attributes": { | ||||||
| "_TEMPERATURE": 1 | ||||||
| }, | ||||||
| "mode": 2147483648, | ||||||
| "extensions": { | ||||||
| "EXT_primitive_voxels": { | ||||||
| "dimensions": [8, 8, 8], | ||||||
| "neighboringEdges": { | ||||||
| "leftCount": [1, 1, 1], | ||||||
| "rightCount": [1, 1, 1] | ||||||
IanLilleyT marked this conversation as resolved.
Show resolved
Hide resolved
|
||||||
| } | ||||||
| } | ||||||
| } | ||||||
| } | ||||||
| ] | ||||||
| } | ||||||
| ] | ||||||
| } | ||||||
| ``` | ||||||
|
|
||||||
| The extension adds three new primitive modes, corresponding to voxel grid geometries: | ||||||
| - `0x80000000` (`2147483648`) - A Cartesian box. The grid is a Cartesian grid of equally-sized boxes. | ||||||
| - `0x80000001` (`2147483649`) - A cylinder. The grid is a stack of concentric rings, evenly divided around the circumference. | ||||||
| - `0x80000002` (`2147483650`) - An ellipsoid. The grid is a set of concentric ellipsoids, divided evenly in latitude and longitude. | ||||||
|
|
||||||
|  | ||||||
|  | ||||||
|  | ||||||
|
There was a problem hiding this comment. The blender UI and wireframe is distracting. I'm starting to think these diagrams should be rendered as voxels with the native coordinate systems labelled in addition to the cartesian coordinate system. The images take up too much space and are not aligned. Try using a markdown table with equally sized images. |
||||||
|
|
||||||
| These grids all define "unit" objects centered at the origin, contained in the bounding box between `(-1, -1, -1)` and `(1, 1, 1)`. Node transforms | ||||||
| should be used to position, orient, and scale the voxel grid as needed. The `POSITION` attribute is _not_ required or used by this extension - all positioning | ||||||
| is through node transforms. | ||||||
|
|
||||||
| The `dimensions` property of the extension specifies the voxel grid dimensions: | ||||||
|
There was a problem hiding this comment. There should be a short explanation of how these coordinates map to the memory layout There was a problem hiding this comment. Totally agree, you've described this to me as a "reinterpret cast", but it would be good to describe this in more detail in the spec. There was a problem hiding this comment. Diagrams and pictures could be helpful here, like showing how the same voxel grid maps to these different shapes. |
||||||
| - x/y/z for boxes | ||||||
| - r/z/theta for cylinders | ||||||
|
There was a problem hiding this comment. In glTF, y is up -- is the cylinder z coordinate pointing in the y direction or the z direction? this should be made clear (perhaps with a diagram) There was a problem hiding this comment. I changed the cylinder coordinate names from 👍 to a diagram. |
||||||
| - lon/lat/height for ellipsoids | ||||||
|
There was a problem hiding this comment.
Suggested change
|
||||||
|
|
||||||
| Dimensions must be nonzero. | ||||||
|
|
||||||
| The `neighboringEdges` property specifies how many rows of attribute data in each dimension come from | ||||||
| neighboring grids. This is useful in situations where the primitive represents a single tile in a larger grid, and | ||||||
| data from neighboring tiles is needed for non-local effects e.g. blurring, antialiasing. `neighboringEdges.leftCount` and `neighboringEdges.rightCount` specify | ||||||
| the count for neighbors before and after the grid in each dimension, e.g. a `leftCount` of 1 and a `rightCount` of 2 in the `y` dimension mean that each | ||||||
| series of values in a given `y`-slice is preceded by one value and followed by two. | ||||||
|
|
||||||
| The neighbor data must be supplied with the rest of the voxel data - this means if `d1`, `d2`, `d3` are the grid dimensions and `n` is `neighborEdgeCount`, the attribute must supply `(d1 + n)*(d2 + n)*(d3 + n)` elements. | ||||||
|
There was a problem hiding this comment. This equation should be reworked now that |
||||||
|
|
||||||
| ## Optional vs. Required | ||||||
| This extension is required, meaning it should be placed in both the `extensionsUsed` list and `extensionsRequired` list. | ||||||
Loading
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
Loading
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
Loading
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,54 @@ | ||
| { | ||
| "$schema": "https://json-schema.org/draft/2020-12/schema", | ||
| "$id": "mesh.primitive.EXT_primitive_voxels.schema.json", | ||
| "title": "EXT_primitive_voxels glTF Mesh Primitive extension", | ||
| "type": "object", | ||
| "description": "`EXT_primitive_voxels` extension for a primitive in a glTF model, to specify voxel grid geomtetry for volumetric data", | ||
| "allOf": [ | ||
| { | ||
| "$ref": "glTFProperty.schema.json" | ||
| } | ||
| ], | ||
| "properties": { | ||
| "dimensions": { | ||
| "type": "array", | ||
| "description": "Dimensions of the voxel grid. x/y/z for a box, r/theta/z for a cylinder, lat/lon/height for an ellipsoid.", | ||
| "items": { | ||
| "type": "integer", | ||
| "minimum": 1 | ||
| }, | ||
| "minItems": 3, | ||
| "maxItems": 3 | ||
| }, | ||
| "neighboringEdges": { | ||
| "type": { | ||
| "properties": { | ||
| "leftCount": { | ||
| "type": "array", | ||
| "description": "Number of neighboring data values left of the grid.", | ||
| "items": { | ||
| "type": "integer", | ||
| "minimum": 0, | ||
| "default": 0 | ||
| }, | ||
| "minItems": 3, | ||
| "maxItems": 3 | ||
| }, | ||
| "rightCount": { | ||
| "type": "array", | ||
| "description": "Number of neighboring data values right of the grid.", | ||
| "items": { | ||
| "type": "integer", | ||
| "minimum": 0, | ||
| "default": 0 | ||
| }, | ||
| "minItems": 3, | ||
| "maxItems": 3 | ||
| } | ||
| } | ||
| }, | ||
| "description": "The number of rows of neighboring tiles' voxel data." | ||
| } | ||
| }, | ||
| "required": ["dimensions"] | ||
| } |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
The spec doesn't say much about the attributes used here. Some questions:
POSITION,NORMAL,TEXCOORD_n, etc.) have well-defined behavior in a voxel context? or are they treated the same as custom attributes like_TEMPERATUREhere?