terrylica 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.