MQL5 Visual Indicator Patterns

Battle-tested patterns for creating custom MQL5 indicators with proper display, buffer management, and real-time updates.

Self-Evolving Skill: This skill improves through use. If instructions are wrong, parameters drifted, or a workaround was needed — fix this file immediately, don't defer. Only update for real, reproducible issues.

When to Use This Skill

Use this skill when:

• Creating custom MQL5 indicators for MetaTrader 5

• Debugging indicator display or buffer issues

• Setting up OnCalculate with proper warmup handling

• Implementing new bar detection patterns

Quick Reference

Essential Patterns

Display Scale (for small values < 1.0):

IndicatorSetDouble(INDICATOR_MINIMUM, 0.0);

IndicatorSetDouble(INDICATOR_MAXIMUM, 0.1);

Buffer Setup (visible + hidden):

SetIndexBuffer(0, BufVisible, INDICATOR_DATA);        // Visible

SetIndexBuffer(1, BufHidden, INDICATOR_CALCULATIONS); // Hidden

New Bar Detection (prevents drift):

static int last_processed_bar = -1;

bool is_new_bar = (i > last_processed_bar);

Warmup Calculation:

int StartCalcPosition = underlying_warmup + own_warmup;

PlotIndexSetInteger(0, PLOT_DRAW_BEGIN, StartCalcPosition);

Common Pitfalls

Blank Display: Set explicit scale (see Display Scale reference)

Rolling Window Drift: Use new bar detection with hidden buffer (see Recalculation reference)

Misaligned Plots: Calculate correct PLOT_DRAW_BEGIN (see Complete Template reference)

Forward-Indexed Arrays: Always set ArraySetAsSeries(buffer, false)

Key Patterns

For production MQL5 indicators:

• Explicit scale for small values (< 1.0 range)

• Hidden buffers for recalculation tracking

• New bar detection prevents rolling window drift

• Static variables maintain state efficiently

• Proper warmup calculation prevents misalignment

• Forward indexing for code clarity

These patterns solve the most common indicator development issues encountered in real-world MT5 development.

Troubleshooting

Issue

Cause

Solution

Blank indicator window

Scale not set for small values

Set INDICATOR_MINIMUM/MAXIMUM explicitly

Values drifting over time

Rolling window not reset

Use new bar detection with hidden buffer

Misaligned plot start

Wrong PLOT_DRAW_BEGIN

Calculate: underlying_warmup + own_warmup

Reversed array indexing

Series mode enabled

Call ArraySetAsSeries(buffer, false)

Buffer values incorrect

Wrong INDICATOR_DATA type

Use INDICATOR_CALCULATIONS for hidden buffers

Compile error on buffer

Buffer count mismatch

Match #property indicator_buffers with SetIndexBuffer

Indicator not updating

OnCalculate return wrong

Return rates_total to signal successful calculation

Performance issues

Recalculating all bars

Only recalculate from prev_calculated onwards

Reference Documentation

For detailed information, see:

• Display Scale - Fix blank indicator windows for small values

• Buffer Patterns - Visible and hidden buffer architecture

• Recalculation - Bar detection and rolling window state management

• Complete Template - Full working example with all patterns

• Debugging - Checklist for troubleshooting display issues

Post-Execution Reflection

After this skill completes, check before closing:

• Did the command succeed? — If not, fix the instruction or error table that caused the failure.

• Did parameters or output change? — If the underlying tool's interface drifted, update Usage examples and Parameters table to match.

• Was a workaround needed? — If you had to improvise (different flags, extra steps), update this SKILL.md so the next invocation doesn't need the same workaround.

Only update if the issue is real and reproducible — not speculative.