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80 lines
3.2 KiB
Markdown
80 lines
3.2 KiB
Markdown
# Geometry
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The Geometry class holds a collection of vertex array attributes representing a geometric primitive.
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A geometry is considered a "primitive" when it can be rendered with a single GPU draw call. Multiple geometry primitives can be composed into a composite geometry using the `Mesh` and `Model` classes.
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To learn more about attributes refer to the `Accessor` class that holds metadata for each attributes.
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## Usage
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Create a pyramid geometry (used in lesson 4 of learning WebGL examples).
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```typescript
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const pyramidGeometry= new Geometry({
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attributes: {
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positions: new Float32Array([ ... ]),
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colors: {
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size: 4,
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value: new Float32Array([ ... ])
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}
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}
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});
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```
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## Properties
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### `id: string`
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An id for the model. If not provided, a random unique identifier will be created.
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### topology
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The draw mode, or primitive type.
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Some options are `triangle-list` (default), `triangle-strip`, `point-list`, `line-list`.
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### `attributes`
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An object with buffer/attribute names and buffer/attribute descriptors to be set before rendering the model.
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### `indices`
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An optional `Accessor` instance that contains the indices (aka elements) for this geometry. Can be `null` or `undefined` if this primitive doesn't use indices. Note that indices can also be stored inside `attributes`.
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## Methods
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### constructor(props : Object)
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The constructor for the `Geometry` class. Use this to create a new `Geometry`.
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```typescript
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const geometry = new Geometry(props);
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```
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### setProps(props : Object)
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Update properties
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## Types and Enumerations
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### topology
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Follows glTF/OpenGL/WebGL conventions:
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### Typical Attributes
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| Attribute | Description |
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| --------------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
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| `indices` | (_array_, optional) An array of numbers describing the vertex indices for each face. |
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| `positions` | (_array_, optional) An array of floats that describe the vertices of the model. |
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| `normals` | (_array_, optional) An array of floats that describe the normals of the model. |
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| `texCoords` | (_mixed_, optional) Can be an array of floats indicating the texture coordinates for the texture to be used or an object that has texture ids as | keys and an array of floats as values. |
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| `colors` | (_array_, optional) An array of colors in RGBA. If just one color is specified that color will be used for all faces. |
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| `pickingColors` | (_array_, optional) A custom set of colors to render the object to texture when performing the color picking algorithm. |
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## Remarks
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- The Geometry class does not take a `WebGLRenderingContext` and is intentionally
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- The `Geometry` class holds the [glTF2 "primitive" specification](https://github.com/KhronosGroup/glTF/tree/master/specification/2.0), although morph `targets` are not yet supported.
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