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79 lines
4.3 KiB
Markdown
79 lines
4.3 KiB
Markdown
# BufferTransform
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`BufferTransform` is an internal helper class for `Transform`, responsible for managing resources and state required for reading from and/or writing to `Buffer` objects. It auto creates `feedbackBufferes` when requested, creates `TransformFeedback` objects. Maintains all buffer bindings, when swapping is eanbled, two binding objects are created for easy switching of all WebGL resource binginds.
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NOTE: In following sections 'buffer transform' is used to refer to 'reading from and/or writing to `Buffer` objects'.
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## Constructor
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### Transform(gl : WebGL2RenderingContext, props: Object)
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* `gl` (`WebGLRenderingContext`) gl - context
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* `props` (`Object`, Optional) - contains following data.
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* `sourceBuffers` (`Object`, Optional) - key and value pairs, where key is the name of vertex shader attribute and value is the corresponding `Attribute`, `Buffer` or attribute descriptor object.
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* `feedbackBuffers` (`Object`, Optional) - key and value pairs, where key is the name of vertex shader varying and value is the corresponding `Buffer` object or buffer params object. If a buffer params object is specified, it will contain following fields, these can be used to capture data into the buffer at particular offset and size.
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* `buffer`=(Buffer) - Buffer object to be bound.
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* `byteOffset`=(Number, default: 0) - Byte offset that is used to start recording the data in the buffer.
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* `byteSize`=(Number, default: remaining buffer size) - Size in bytes that is used for recording the data.
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* `varyings` (`Array`, Optional) - Array of vertex shader varyings names. When not provided this can be deduced from `feedbackBuffers`.
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NOTE: If only reading from `Buffer` objects, above optional props doesn't have to be supplied during construction, but can be supplied using `update` method. If writing to `Buffer` objects, either `varyings` or `feedbackBuffers` must be supplied.
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## Methods (Model props)
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### getDrawOptions(opts: Object) : Object
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Returns resources required when performing `Model.draw()` options.
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* `opts` (`Object`) - Any existing `opts.attributes` will be merged with new attributes.
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Returns an Object : {attributes, transformFeedback}.
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### updateModelProps(props: Object) : Object
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Updates input `props` object with data required for buffer transform.
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* `opts` (`Object`) - If writing to `Buffer` objects, `opts.varying` will be updated.
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Returns updated object.
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## Methods (Resource management)
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### setupResources(opts: Object)
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Sets up internal resources needed writing to buffers.
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* `opts` (`Object`) - contains following data.
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* `model` (`Model`, Optional) - `Model` object that is used to perform draw operations.
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### swap()
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If `feedbackMap` is provided during construction, performs source and feedback buffers swap as per the `feedbackMap`.
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### update(props: Object)
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Updates buffer bindings for one or more source or feedback buffers.
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* `props` (`Object`) - contains following data.
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* `sourceBuffers` (`Object`, Optional) - key and value pairs, where key is the name of vertex shader attribute and value is the corresponding `Attribute`, `Buffer` or attribute descriptor object.
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* `feedbackBuffers` (`Object`, Optional) - key and value pairs, where key is the name of vertex shader varying and value is the corresponding `Buffer` object or buffer params object. If a buffer params object is specified, it will contain following fields, these can be used to capture data into the buffer at particular offset and size.
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* `buffer`=(Buffer) - Buffer object to be bound.
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* `byteOffset`=(Number, default: 0) - Byte offset that is used to start recording the data in the buffer.
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* `byteSize`=(Number, default: remaining buffer size) - Size in bytes that is used for recording the data.
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## Methods (Accessors)
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### getBuffer(varyingName : String) : Buffer
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Returns current feedback buffer corresponding to given varying name.
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* `varyingName` (`String`) - varying name.
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### getData([options : Object]) : ArrayBufferView
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Reads and returns data from current feedback buffer corresponding to the given varying name.
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* `options.varyingName` (`String`, Optional) - when specified, first checks if there is a corresponding feedback buffer, if so reads data from this buffer and returns. When not specified, there must be target texture and data is read from this texture and returned.
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