piano/js/components/Key/Key.js

/*globals React, App */

(function () {
    'use strict';

    /**
     * Displays a key on keyboard
     *
     * @prop {note: int}            MIDI note identifier
     * @prop {canPlay: function}    Whether the note can be manually played
     */
    App.components.create('Key', {
        displayName: 'Key',
        mixins: [React.addons.PureRenderMixin],
        
        propTypes: {
            note: React.PropTypes.number.isRequired
        },
        
        getInitialState: function () {
            return {
                channels: []
            };
        },

        getDefaultProps: function () {
            return {
                note: 0,
                canPlay: function () {}
            };
        },
        
        /**
         * Start playing note on given channel with given velocity
         *
         * @param {channel: number}     Channel ID
         * @param {velocity: number}    Note velocity
         */
        on: function (channel, velocity) {
            if (this.state.channels.indexOf(channel) > -1) {
                return;
            }
            
            App.MIDI.output.noteOn(
                (channel === -1) ? 0 : channel,
                this.props.note,
                velocity,
                0
            );
            
            this.setState({
                channels: this.state.channels.concat([
                    channel
                ])
            });
        },
        
        /**
         * Stop playing note on previous channel
         *
         * @param {channel: number} Channel ID
         * @param {channel: Array}  Channels IDs (default: all current)
         */
        off: function (channels) {
            var i, length, channel, current,
                index;
            
            current = this.state.channels.slice(0);
            
            if (channels === undefined) {
                channels = this.state.channels;
            } else if (!Array.isArray(channels)) {
                channels = [channels];
            }
            
            length = channels.length;
            
            for (i = 0; i < length; i += 1) {
                channel = channels[i];
                
                App.MIDI.output.noteOff(
                    (channel === -1) ? 0 : channel,
                    this.props.note,
                    0
                );
                
                index = current.indexOf(channel);
                
                // remove channels from current playing
                if (index > -1) {
                    current.splice(index, 1);
                }
            }
            
            this.setState({
                channels: current
            });
        },
        
        /**
         * Start playing note on mouse over
         */
        mouseOver: function () {
            if (!this.props.canPlay()) {
                return;
            }
            
            this.mouseDown();
        },
        
        /**
         * Play on mouse down
         */
        mouseDown: function (e) {
            if (e && e.button !== 0) {
                return;
            }
            
            this.on(-1, 127);
        },

        /**
         * Render key
         */
        render: function () {
            var black = App.components.Note.Board.black, offset,
                pianoNote = this.props.note, style, channels, channel,
                isBlack = (black.indexOf(this.props.note) > -1);
            
            offset = pianoNote - black.filter(function (el) {
                return el < pianoNote;
            }).length - App.MIDI.keyOffset;
            
            // if it is a black key, we position it absolutely;
            // otherwise we just play on its width to avoid rounding
            // errors causing display glitches
            if (isBlack) {
                style = {
                    left: 'calc(100% / 52 * ' + offset + ')',
                    zIndex: App.MIDI.keyOffset + 88
                };
            } else {
                style = {
                    width: 'calc(100% / 52 * ' + (offset + 1) + ')',
                    zIndex: App.MIDI.keyOffset + 88 - pianoNote
                };
            }
            
            // get channel ID
            channels = this.state.channels;
            
            if (channels.length > 0) {
                channel = channels[channels.length - 1];
            } else {
                channel = false;
            }
            
            return React.DOM.span({
                className: 'key',
                
                onMouseDown: this.mouseDown,
                onMouseOver: this.mouseOver,
                onMouseUp: this.off.bind(this, -1),
                onMouseOut: this.off.bind(this, -1),
                
                style: style,
                'data-channel': channel,
                'data-black': isBlack
            });
        }
    });
}());