mirror of
https://gitlab.kitware.com/vtk/vtk-m
synced 2024-09-08 13:23:51 +00:00
125 lines
3.5 KiB
C++
125 lines
3.5 KiB
C++
//============================================================================
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// Copyright (c) Kitware, Inc.
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// All rights reserved.
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// See LICENSE.txt for details.
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//
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// This software is distributed WITHOUT ANY WARRANTY; without even
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// the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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// PURPOSE. See the above copyright notice for more information.
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//============================================================================
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#include <cmath>
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#include <iostream>
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#include <vector>
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#include <vtkm/cont/DataSetBuilderUniform.h>
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#include <vtkm/io/ImageWriterPNG.h>
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#include <vtkm/worklet/WorkletMapField.h>
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// The logistic map is xᵢ₊₁ = rxᵢ(1-xᵢ).
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// If we start this iteration out at (say) x₀ = 0.5, the map has "transients",
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// which we must iterate away to produce the final image.
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template <typename T>
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class LogisticBurnIn : public vtkm::worklet::WorkletMapField
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{
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public:
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LogisticBurnIn(T rmin, vtkm::Id width)
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: rmin_(rmin)
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, width_(width)
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{
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}
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using ControlSignature = void(FieldOut);
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using ExecutionSignature = _1(WorkIndex);
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VTKM_EXEC T operator()(vtkm::Id workIndex) const
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{
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T r = rmin_ + (4.0 - rmin_) * workIndex / (width_ - 1);
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T x = 0.5;
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// 2048 should be enough iterations to get rid of the transients:
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int n = 0;
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while (n++ < 2048)
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{
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x = r * x * (1 - x);
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}
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return x;
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}
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private:
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T rmin_;
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vtkm::Id width_;
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};
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// After burn-in, the iteration is periodic but in general not convergent,
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// i.e., for large enough i, there exists an integer p > 0 such that
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// xᵢ₊ₚ = xᵢ for all i.
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// So color the pixels corresponding to xᵢ, xᵢ₊₁, .. xᵢ₊ₚ.
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template <typename T>
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class LogisticLimitPoints : public vtkm::worklet::WorkletMapField
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{
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public:
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LogisticLimitPoints(T rmin, vtkm::Id width, vtkm::Id height)
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: rmin_(rmin)
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, width_(width)
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, height_(height)
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{
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orange_ = vtkm::Vec4f(1.0, 0.5, 0.0, 0.0);
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}
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using ControlSignature = void(FieldIn, WholeArrayOut);
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using ExecutionSignature = void(_1, _2, WorkIndex);
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template <typename OutputArrayPortalType>
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VTKM_EXEC void operator()(T x, OutputArrayPortalType& outputArrayPortal, vtkm::Id workIndex) const
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{
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T r = rmin_ + (4.0 - rmin_) * workIndex / (width_ - 1);
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// We can't display need more limit points than pixels of height:
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vtkm::Id limit_points = 0;
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while (limit_points++ < height_)
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{
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vtkm::Id j = vtkm::Round(x * (height_ - 1));
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outputArrayPortal.Set(j * width_ + workIndex, orange_);
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x = r * x * (1 - x);
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}
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}
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private:
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T rmin_;
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vtkm::Id width_;
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vtkm::Id height_;
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vtkm::Vec4f orange_;
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};
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int main()
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{
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vtkm::Id height = 1800;
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vtkm::Id width = height * 1.618;
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vtkm::cont::DataSetBuilderUniform dsb;
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vtkm::cont::DataSet ds = dsb.Create(vtkm::Id2(width, height));
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vtkm::cont::ArrayHandle<double> x;
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x.Allocate(width);
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vtkm::cont::Invoker invoke;
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double rmin = 2.9;
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auto burnIn = LogisticBurnIn<double>(rmin, width);
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invoke(burnIn, x);
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vtkm::cont::ArrayHandle<vtkm::Vec4f> pixels;
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pixels.Allocate(width * height);
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auto wp = pixels.WritePortal();
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for (vtkm::Id i = 0; i < pixels.GetNumberOfValues(); ++i)
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{
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wp.Set(i, vtkm::Vec4f(0, 0, 0, 0));
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}
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auto limitPoints = LogisticLimitPoints<double>(rmin, width, height);
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invoke(limitPoints, x, pixels);
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std::string colorFieldName = "pixels";
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ds.AddPointField(colorFieldName, pixels);
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std::string filename = "logistic.png";
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vtkm::io::ImageWriterPNG writer(filename);
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writer.WriteDataSet(ds, colorFieldName);
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std::cout << "Now open " << filename << "\n";
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}
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