getVars( shaderStage ) {

		let snippet = '';

		const vars = this.vars[ shaderStage ];

		if ( vars !== undefined ) {

			for ( const variable of vars ) {

				snippet += `${ this.getVar( variable.type, variable.name ) }; `;

			}

		}

		return snippet;

	}
Returns the variable definitions as a shader string for the given shader stage.

@param {('vertex'|'fragment'|'compute'|'any')} shaderStage - The shader stage.
@return {string} The variable code section.