mql5-indicator-patterns

MQL5 indicators use a dual-buffer architecture: visible buffers for chart display and hidden buffers to track recalculation state. Assign buffers with SetIndexBuffer(), set PLOT_DRAW_TYPE and PLOT_COLOR, manage array indexing carefully, and maintain proper buffer synchronization during OnCalculate() to prevent data drift and ensure accurate visual output.

Common OnCalculate() failures stem from incorrect buffer indexing, missing warmup calculations, improper new-bar detection, or stale static state. Debug by validating array bounds, confirming rates_total and prev_calculated logic, ensuring buffers are initialized before plotting, and testing on both real-time and backtest data to catch timing issues.

Implement new-bar detection by comparing the current bar time with a static variable storing the previous bar's timestamp. Process new bars only once per timeframe, reset rolling-window calculations, and use this pattern to prevent duplicate processing that causes indicator values to drift or recalculate unexpectedly.

Yes. Multi-timeframe MQL5 indicators fetch data from higher timeframes using iClose(), iHigh(), and related functions, then aggregate or combine that data within your OnCalculate() logic. Implement separate buffers for each timeframe, handle asynchronous data loading, and apply warmup calculations to ensure stability across both real-time and backtest scenarios.

Discrepancies occur when warmup calculations are skipped, new-bar detection fails, or static state persists incorrectly between sessions. Ensure prev_calculated resets appropriately, apply enough historical bars for indicator stabilization, and test forward indexing logic to confirm consistent behavior under both backtesting and live market conditions.

Explicitly set display scale using SetIndexDrawBegin() and PLOT_DRAW_BEGIN, configure visible buffers with SetIndexBuffer(..., true) and hidden buffers with false, apply PLOT_SCALE_TYPE for normalization, and validate that chart-scaling settings don't override your indicator's intended visual range.