vtkScatterPlotBug

Introduction

This repository contains an example program that reproduces a bug in the VTK library related to 2D plotting.

The version used (v8.2.0) is the lastest available in the official VTK repository.

The issue was found by modifying the scatter plot test shown in the VTK repository.

This repository refers to the VTK issue: https://gitlab.kitware.com/vtk/vtk/issues/17686.

Description

When adding a vtkPlot to a vtkChartXY object, its content is not rendered correctly if:

1. vtkRenderWindowInteractor is not being used and the view is rendered directly by the user (situation common in off-screen rendering usage).
2. The x data values are ~100 times the x data range (more details in the Example section).

The provided example shows this behavior both for vtkChart::LINE and vtkChart::POINTS plots.

Y-axis range is fixed between 0.0 to 3.0 to better show the issue effect. Range is fixed in such a way that the plots are well between its boundaries.

Once compiled the example program can be used with:

Use: ./Plot [X DATA SHIFT] [ENABLE WORKAROUND]
Where:
[X DATA SHIFT]: floating point constant that will be added to all X coordinates.
[ENABLE WORKAROUND]: integer(0,1) enables or disables the workaround.

Examples

The example in this repository shows how it's possible to reproduce the issue for a fixed data range of:

x_range = x_max - m_min = 4

$ ./Plot 0.0 0
Using: vtk version 8.2.0
x_data = {1, 2, 3, 4, 5} 
y_data_point_plot = {1, 1, 1, 1, 1} 
y_data_line_plot = {2, 2, 2, 2, 2}

A chart is correctly shown as seen in the picture:

By shifting the ordinates of 400 = x_range * 100:

$ ./Plot 400 0
Using: vtk version 8.2.0
x_data = {401, 402, 403, 404, 405} 
y_data_point_plot = {1, 1, 1, 1, 1} 
y_data_line_plot = {2, 2, 2, 2, 2}}

The chart is not correctly displayed, as seen in the picture:

While the scale of the axis is correct the two vtkPlot are not shown.

Workaround

In the previous examples the view was rendered only once. An empirical workaround to this issue consists in marking the view as Modified() and re-render it a second time. The code snippet is the following:

  view->Render();

  if (WORKAROUNT_ENABLED)
  {
    view->Modified();
    view->Render();
  }

By running the second example with the workaround activated the results are:

Using: vtk version 8.2.0
WORKAROUND ENABLED!
x_data = {401, 402, 403, 404, 405} 
y_data_point_plot = {1, 1, 1, 1, 1} 
y_data_line_plot = {2, 2, 2, 2, 2} 

The plot is correctly rendered as seen in the picture: