Method perform

src/core/task.ts:139–243

* @param step Specified step. * @param skip Skip customer perform call. * @param modBy Sampling window size. * @param modDataCount Sampling count. * @return whether unfinished.

(performArgs?: PerformArgs)

     * @return whether unfinished.
     */
    perform(performArgs?: PerformArgs): boolean {
        const upTask = this._upstream;
        const skip = performArgs && performArgs.skip;

        // TODO some refactor.
        // Pull data. Must pull data each time, because context.data
        // may be updated by Series.setData.
        if (this._dirty && upTask) {
            const context = this.context;
            context.data = context.outputData = upTask.context.outputData;
        }

        if (this.__pipeline) {
            this.__pipeline.currentTask = this;
        }

        let planResult;
        if (this._plan && !skip) {
            planResult = this._plan(this.context);
        }

        // Support sharding by mod, which changes the render sequence and makes the rendered graphic
        // elements uniformed distributed when progress, especially when moving or zooming.
        const lastModBy = normalizeModBy(this._modBy);
        const lastModDataCount = this._modDataCount || 0;
        const modBy = normalizeModBy(performArgs && performArgs.modBy);
        const modDataCount = performArgs && performArgs.modDataCount || 0;
        if (lastModBy !== modBy || lastModDataCount !== modDataCount) {
            planResult = 'reset';
        }

        function normalizeModBy(val: number) {
            !(val >= 1) && (val = 1); // jshint ignore:line
            return val;
        }

        let forceFirstProgress;
        if (this._dirty || planResult === 'reset') {
            this._dirty = false;
            forceFirstProgress = this._doReset(skip);
        }

        this._modBy = modBy;
        this._modDataCount = modDataCount;

        const step = performArgs && performArgs.step;

        if (upTask) {
            if (__DEV__) {
                assert(upTask._outputDueEnd != null);
            }
            this._dueEnd = upTask._outputDueEnd;
        }
        // DataTask or overallTask
        else {
            if (__DEV__) {
                assert(!this._progress || this._count);
            }