Lining up Inner and Outer Ticks

[bigjoeystud]

I've got a problem and I realize it is a long shot at being able to fix without seeing code, but here's the deal:

I have inner ticks (QwtPlotScaleItem) and outer ticks plotting together, but when I first render my plot, the inner/outer scales are not lined up. The instant I resize my plot, they shift and line up correctly.

I am using my own versions of QwtScaleDraw's, but I am using the standard QwtScaleWidget's though. I have setScaleDivFromAxis (true) and have plotLayout ()->setAlignCanvasToScales (true) also set. I'm not even sure if that's relevant.

I also have all axes enabled, but in some cases I disable the labels and ticks. In every case where they are not lined up, it is when the major tick is not at the beginning of the axis. I also always use setAttribute (QwtScaleEngine::Floating, true) on the scale engine which I set for every axis. I only use linear and log scales.

I feel like it might be an order of operations thing that I am not getting, but I really have no idea of where to look at trying to debug this.

Anyway, like I said, this may be a long shot, but if you have any ideas, I'd love to hear them!

Thanks,
Joey

[Uwe]

I'm aware of a bug that can be responsible for 1 pixel difference between an inner and outer scale - but your situation looks more like an update problem.
Hard to say something useful without having a demo application.

Uwe

[bigjoeystud]

Ok! I think I made an example program by merging the timescale example in playground with my program.

When you start it up, the scales on the left are a little off. You resize the plot and they are fine.

Joey

Here's my diff:

Index: mainwindow.cpp
===================================================================
--- mainwindow.cpp      (revision 1453)
+++ mainwindow.cpp      (working copy)
@@ -9,7 +9,7 @@
     QMainWindow( parent )
 {
     Settings settings;
-    settings.startDateTime = QDateTime( QDate( 2012, 3, 10 ), QTime( 0, 5, 0 ) );
+    settings.startDateTime = QDateTime( QDate( 2011, 1, 17 ), QTime( 0, 5, 0 ) );
     settings.endDateTime = QDateTime( QDate( 2012, 3, 10 ), QTime( 0, 6, 0, 5 ) );
     settings.maxMajorSteps = 10;
     settings.maxMinorSteps = 8;
Index: plot.cpp
===================================================================
--- plot.cpp    (revision 1453)
+++ plot.cpp    (working copy)
@@ -5,6 +5,7 @@
 #include "timescaledraw.h"
 #include <qwt_plot_panner.h>
 #include <qwt_plot_magnifier.h>
+#include <qwt_plot_scaleitem.h>
 
 Plot::Plot( QWidget *parent ):
     QwtPlot( parent )
@@ -25,9 +26,53 @@
         const bool on = ( i == axis );
         panner->setAxisEnabled( i, on );
         magnifier->setAxisEnabled( i, on );
+        _innerTicks [i] = NULL;
     }
+    InnerTicks (QwtPlot::yLeft, true, true);
+    InnerTicks (QwtPlot::xBottom, true, true);
 }
 
+void
+Plot::InnerTicks (int axisId, bool showMajor, bool showMinor)
+{
+    QwtScaleDraw::Alignment align;
+    if (showMajor || showMinor) {
+        if (_innerTicks [axisId] == NULL) {
+            _innerTicks [axisId] = new QwtPlotScaleItem ();
+            switch (axisId) {
+                case QwtPlot::yLeft : align = QwtScaleDraw::RightScale;
+                                      _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yLeft);
+                                      break;
+                case QwtPlot::yRight : align = QwtScaleDraw::LeftScale;
+                                       _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yRight);
+                                       break;
+                case QwtPlot::xBottom : align = QwtScaleDraw::TopScale;
+                                        _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yLeft);
+                                        break;
+                case QwtPlot::xTop : align = QwtScaleDraw::BottomScale;
+                                     if (axisScaleDraw (axisId)->hasComponent (QwtAbstractScaleDraw::Labels))
+                                         _innerTicks [axisId]->setAxes (QwtPlot::xTop, QwtPlot::yLeft);
+                                     else _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yLeft);
+                                     break;
+            }
+            _innerTicks [axisId]->setAlignment (align);
+            _innerTicks [axisId]->setBorderDistance (0); // attach to border
+            _innerTicks [axisId]->scaleDraw ()->enableComponent (QwtAbstractScaleDraw::Labels, false);
+        }
+        if (showMajor) _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MajorTick, 8);
+            else _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MajorTick, 0);
+        if (showMinor) _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MinorTick, 4);
+            else _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MinorTick, 0);
+
+        _innerTicks [axisId]->setScaleDivFromAxis (true);
+        _innerTicks [axisId]->attach (this);
+    } else {
+        if (_innerTicks [axisId] != NULL) {
+            _innerTicks [axisId]->detach ();
+        }
+    }
+}
+
 void Plot::applySettings( const Settings &settings )
 {
     const int axis = QwtPlot::yLeft;
Index: plot.h
===================================================================
--- plot.h      (revision 1453)
+++ plot.h      (working copy)
@@ -4,6 +4,7 @@
 #include <qwt_plot.h>
 
 class Settings;
+class QwtPlotScaleItem;
 
 class Plot: public QwtPlot
 {
@@ -14,6 +15,11 @@
 
 public Q_SLOTS:
     void applySettings( const Settings & );
+
+private:
+
+    void InnerTicks(int, bool, bool);
+    QwtPlotScaleItem *_innerTicks [4];
 };
 
 #endif

Index: mainwindow.cpp
===================================================================
--- mainwindow.cpp      (revision 1453)
+++ mainwindow.cpp      (working copy)
@@ -9,7 +9,7 @@
     QMainWindow( parent )
 {
     Settings settings;
-    settings.startDateTime = QDateTime( QDate( 2012, 3, 10 ), QTime( 0, 5, 0 ) );
+    settings.startDateTime = QDateTime( QDate( 2011, 1, 17 ), QTime( 0, 5, 0 ) );
     settings.endDateTime = QDateTime( QDate( 2012, 3, 10 ), QTime( 0, 6, 0, 5 ) );
     settings.maxMajorSteps = 10;
     settings.maxMinorSteps = 8;
Index: plot.cpp
===================================================================
--- plot.cpp    (revision 1453)
+++ plot.cpp    (working copy)
@@ -5,6 +5,7 @@
 #include "timescaledraw.h"
 #include <qwt_plot_panner.h>
 #include <qwt_plot_magnifier.h>
+#include <qwt_plot_scaleitem.h>
 
 Plot::Plot( QWidget *parent ):
     QwtPlot( parent )
@@ -25,9 +26,53 @@
         const bool on = ( i == axis );
         panner->setAxisEnabled( i, on );
         magnifier->setAxisEnabled( i, on );
+        _innerTicks [i] = NULL;
     }
+    InnerTicks (QwtPlot::yLeft, true, true);
+    InnerTicks (QwtPlot::xBottom, true, true);
 }
 
+void
+Plot::InnerTicks (int axisId, bool showMajor, bool showMinor)
+{
+    QwtScaleDraw::Alignment align;
+    if (showMajor || showMinor) {
+        if (_innerTicks [axisId] == NULL) {
+            _innerTicks [axisId] = new QwtPlotScaleItem ();
+            switch (axisId) {
+                case QwtPlot::yLeft : align = QwtScaleDraw::RightScale;
+                                      _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yLeft);
+                                      break;
+                case QwtPlot::yRight : align = QwtScaleDraw::LeftScale;
+                                       _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yRight);
+                                       break;
+                case QwtPlot::xBottom : align = QwtScaleDraw::TopScale;
+                                        _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yLeft);
+                                        break;
+                case QwtPlot::xTop : align = QwtScaleDraw::BottomScale;
+                                     if (axisScaleDraw (axisId)->hasComponent (QwtAbstractScaleDraw::Labels))
+                                         _innerTicks [axisId]->setAxes (QwtPlot::xTop, QwtPlot::yLeft);
+                                     else _innerTicks [axisId]->setAxes (QwtPlot::xBottom, QwtPlot::yLeft);
+                                     break;
+            }
+            _innerTicks [axisId]->setAlignment (align);
+            _innerTicks [axisId]->setBorderDistance (0); // attach to border
+            _innerTicks [axisId]->scaleDraw ()->enableComponent (QwtAbstractScaleDraw::Labels, false);
+        }
+        if (showMajor) _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MajorTick, 8);
+            else _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MajorTick, 0);
+        if (showMinor) _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MinorTick, 4);
+            else _innerTicks [axisId]->scaleDraw ()->setTickLength (QwtScaleDiv::MinorTick, 0);
+
+        _innerTicks [axisId]->setScaleDivFromAxis (true);
+        _innerTicks [axisId]->attach (this);
+    } else {
+        if (_innerTicks [axisId] != NULL) {
+            _innerTicks [axisId]->detach ();
+        }
+    }
+}
+
 void Plot::applySettings( const Settings &settings )
 {
     const int axis = QwtPlot::yLeft;
Index: plot.h
===================================================================
--- plot.h      (revision 1453)
+++ plot.h      (working copy)
@@ -4,6 +4,7 @@
 #include <qwt_plot.h>
 
 class Settings;
+class QwtPlotScaleItem;
 
 class Plot: public QwtPlot
 {
@@ -14,6 +15,11 @@
 
 public Q_SLOTS:
     void applySettings( const Settings & );
+
+private:
+
+    void InnerTicks(int, bool, bool);
+    QwtPlotScaleItem *_innerTicks [4];
 };
 
 #endif

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[Uwe]

An issue with an internal cache of the scale item: fixed in SVN ( trunk + 6.0 branch )

Uwe