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Inward-Facing Ticks Usage Guide

QwtPlot::TickDirection is a tick direction control feature provided by Qwt, allowing axis tick marks to be displayed inside the plot area instead of the default outside display. This is very useful in scenarios requiring compact layouts or special visual effects.

Main Features

Features

  • ✅ Tick direction control: Supports both outward (default) and inward tick display modes
  • ✅ Independent axis control: Each axis (XBottom, XTop, YLeft, YRight) can be set independently
  • ✅ Style synchronization: Inward ticks share the same style settings as outward ticks (length, color, line width)
  • ✅ Dynamic switching: Tick direction can be switched at any time without resetting tick styles

Basic Concepts

Tick Direction Description

In traditional plots, axis tick marks extend outward from the axis line (outward display). The inward tick feature makes tick marks extend inward from the canvas edge, achieving different visual effects.

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Outward ticks (default):
    ────┼────┼────┼────┼───→ Main axis (axis line)
       │    │    │    │    Tick marks (extending outward)
      0    2    4    6    8  Labels

Inward ticks:
    ────┼────┼────┼────┼───→ Main axis (axis line)
       │    │    │    │    Tick marks (extending inward)
      0    2    4    6    8  Labels (still outside)
    ┌──────────────────────┐
    │  ← Ticks extend into canvas    │  Canvas area
    └──────────────────────┘

TickDirection Enum

Enum Value Description
QwtPlot::TickOutside Outward ticks (default behavior)
QwtPlot::TickInside Inward ticks, extending inward from canvas edge

Usage

An example of inward tick display is located at: examples/2D/ticks_inside. Screenshot:

ticks_inside

1. Basic Usage

Setting the tick direction for a single axis:

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#include <QwtPlot>

QwtPlot* plot = new QwtPlot();

// Set YLeft axis ticks to face inward
plot->setAxisTickDirection(QwtAxis::YLeft, QwtPlot::TickInside);

// Set XBottom axis ticks to face inward
plot->setAxisTickDirection(QwtAxis::XBottom, QwtPlot::TickInside);

// Refresh display
plot->replot();

// Effect: Tick marks on YLeft and XBottom axes display inward from canvas edge,
//         main axis and labels remain outside canvas, consistent with outward tick style

2. Querying Current Settings

Getting the current tick direction of an axis:

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// Query YLeft axis tick direction
QwtPlot::TickDirection dir = plot->axisTickDirection(QwtAxis::YLeft);

if (dir == QwtPlot::TickInside) {
    // Ticks currently face inward
} else {
    // Ticks currently face outward (default)
}

3. Restoring Default Settings

Restoring tick direction to the default outward display:

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// Restore YLeft axis ticks to face outward
plot->setAxisTickDirection(QwtAxis::YLeft, QwtPlot::TickOutside);

plot->replot();

// Effect: YLeft axis ticks restored to traditional outward display

4. Batch Setting All Axes

Setting tick direction for multiple axes simultaneously:

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// Set all axes to inward ticks
plot->setAxisTickDirection(QwtAxis::YLeft, QwtPlot::TickInside);
plot->setAxisTickDirection(QwtAxis::YRight, QwtPlot::TickInside);
plot->setAxisTickDirection(QwtAxis::XBottom, QwtPlot::TickInside);
plot->setAxisTickDirection(QwtAxis::XTop, QwtPlot::TickInside);

plot->replot();

Core Methods

Method Parameters Description
setAxisTickDirection(axisId, direction) QwtAxisId, TickDirection Set tick direction for specified axis
axisTickDirection(axisId) QwtAxisId Get tick direction for specified axis

Notes

Style Inheritance

Inward tick marks automatically inherit the style settings of outward ticks, including:
- Tick length (set via QwtScaleDraw::setTickLength())
- Line width (set via QwtScaleDraw::setPenWidthF())
- Color (set via QwtScaleWidget::setScaleColor())

Refresh Timing

Calling setAxisTickDirection() automatically triggers autoRefresh(). When autoReplot is enabled, it will refresh automatically. To refresh immediately, call replot().

Use with Parasite Axes

The inward tick feature can be used with parasite plots (Parasite Plot). Each parasite plot can independently set its tick direction.

Differences from QwtPlotScaleItem

Feature TickDirection QwtPlotScaleItem
Purpose Control main axis tick direction Add additional axes inside canvas
Tick Style Inherits main axis style Can set style independently
Display Position Replaces/changes main axis ticks Overlays as independent layer
Use Cases Compact layout or special effects needed Reference scales needed inside canvas

Example Code

Complete example located at: examples/2D/ticks_inside/

This example demonstrates:
- Independent control of four axes
- Real-time tick direction switching
- Batch setting functionality

References