This is done by adding a new element "customFieldTypes" to the extension info structure. Ex:
```
customFieldTypes: {
angleField: {
implementation: { fromJson: options => new AngleField(options) },
output: 'number',
outputShape: 2,
}
}
```
Field types are defined by an implementation that has to match what is expected by ScratchBlocks.Field.register and its output and shape.
src/engine/runtime.js has been updated to handle the new "customFieldTypes"-field:
- Existing (global) field types cannot be overridden
- New fields are "namespaced" to the extension in the same way as opcodes are.
Once the custom field type has been picked up by scratch-vm a "EXTENSION_FIELD_ADDED" event is emitted.
It is then up to the hosting app to call ScratchBlocks.Field.register to register the field type with ScratchBlocks. Ex:
```
vm.addListener('EXTENSION_FIELD_ADDED', fieldInfo => {
this.ScratchBlocks.Field.register(fieldInfo.name, fieldInfo.implementation);
});
```
Erik Mejer Hansen
ceaa3c7857