Logistic map as an example of how to use the ImageWriter.

examples/CMakeLists.txt

@@ -24,6 +24,7 @@ if(VTKm_ENABLE_EXAMPLES)
   add_subdirectory(histogram)
   add_subdirectory(ising)
   add_subdirectory(lagrangian)
+  add_subdirectory(logistic_map)
   add_subdirectory(mesh_quality)
   add_subdirectory(multi_backend)
   add_subdirectory(oscillator)

examples/logistic_map/CMakeLists.txt

@@ -0,0 +1,16 @@
+##============================================================================
+##  Copyright (c) Kitware, Inc.
+##  All rights reserved.
+##  See LICENSE.txt for details.
+##
+##  This software is distributed WITHOUT ANY WARRANTY; without even
+##  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+##  PURPOSE.  See the above copyright notice for more information.
+##============================================================================
+cmake_minimum_required(VERSION 3.12...3.19 FATAL_ERROR)
+project(LogisticMap CXX)
+
+find_package(VTKm REQUIRED QUIET)
+
+add_executable(LogisticMap LogisticMap.cxx)
+target_link_libraries(LogisticMap PRIVATE vtkm_io)

examples/logistic_map/LogisticMap.cxx

@@ -0,0 +1,62 @@
+//============================================================================
+//  Copyright (c) Kitware, Inc.
+//  All rights reserved.
+//  See LICENSE.txt for details.
+//
+//  This software is distributed WITHOUT ANY WARRANTY; without even
+//  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+//  PURPOSE.  See the above copyright notice for more information.
+//============================================================================
+
+#include <iostream>
+#include <vtkm/cont/DataSetBuilderUniform.h>
+#include <vtkm/io/ImageWriterPNG.h>
+
+
+int main()
+{
+  size_t height = 1800;
+  size_t width = height * 1.618;
+  vtkm::cont::DataSetBuilderUniform dsb;
+  vtkm::cont::DataSet ds = dsb.Create(vtkm::Id2(width, height));
+
+  std::vector<double> x(width, 0.5);
+
+  double rmin = 2.9;
+  for (size_t i = 0; i < width; ++i)
+  {
+    double r = rmin + (4.0 - rmin) * i / (width - 1);
+    int n = 0;
+    // 2048 should be enough iterations to be "converged";
+    // though of course the iterations actually don't all converge but cycle or are chaotic.
+    while (n++ < 2048)
+    {
+      x[i] = r * x[i] * (1 - x[i]);
+    }
+  }
+
+
+  vtkm::Vec4f v(1.0, 0.5, 0.0, 0.0);
+  std::vector<vtkm::Vec4f> pixelValues(width * height, vtkm::Vec4f(0, 0, 0, 0));
+  int iterates = 0;
+  // We don't need more iterates than pixels of height,
+  // by the pigeonhole principle.
+  while (iterates++ < height)
+  {
+    for (size_t i = 0; i < width; ++i)
+    {
+      double r = rmin + (4.0 - rmin) * i / (width - 1);
+      double y = x[i];
+      assert(y >= 0 && y <= 1);
+      size_t j = std::round(y * (height - 1));
+      pixelValues[j * width + i] = v;
+      x[i] = r * x[i] * (1 - x[i]);
+    }
+  }
+
+  ds.AddPointField("pixels", pixelValues);
+  std::string filename = "logistic.png";
+  vtkm::io::ImageWriterPNG writer(filename);
+  writer.WriteDataSet(ds);
+  std::cout << "Now open " << filename << "\n";
+}