added image_demo demo

Signed-off-by: soblin <hilo.soblin@gmail.com>

README.md

@@ -68,7 +68,7 @@ gives
 
 ![minimal example](./gallery/images/hello_world.png)
 
-### example1 - subplots
+### subplots
 
 From [gallery/subplots_axes_and_figures/align_labels_demo.cpp](https://github.com/soblin/matplotlibcpp17/blob/master/gallery/subplots_axes_and_figures/align_labels_demo.cpp).
 
@@ -91,7 +91,7 @@ From [gallery/subplots_axes_and_figures/align_labels_demo.cpp](https://github.co
 
 ![subplots_axes_and_figures](./gallery/images/align_labels_demo.png)
 
-### example2 - bar plot
+### bar plot
 
 From [gallery/lines_bars_and_markers/bar_label_demo.cpp](https://github.com/soblin/matplotlibcpp17/blob/master/gallery/lines_bars_and_markers/bar_label_demo.cpp). Here `subplots()` returns `tuple<Figure, Axes>`.
 
@@ -120,7 +120,26 @@ From [gallery/lines_bars_and_markers/bar_label_demo.cpp](https://github.com/sobl
 
 ![bar_label_demo1](./gallery/images/bar_label_demo1.png)
 
-### example3 - fill
+### image
+
+2D-style pybind11 array can be plotted as an image using `imshow()` function.
+
+From [images_contours_and_fields/image_demo](https://github.com/soblin/matplotlibcpp17/blob/master/gallery/images_contours_and_fields/image_demo.cpp)
+
+- [original python code](https://matplotlib.org/stable/gallery/images_contours_and_fields/image_demo.html)
+
+```cpp
+  vector<vector<double>> Z2D{...};
+  auto Zpy = py::array(py::cast(std::move(Z2D)));
+  ax.imshow(Args(Zpy), Kwargs("interpolation"_a = "bilinear",
+                              "cmap"_a = "RdYlGn", "origin"_a = "lower",
+                              "extent"_a = py::make_tuple(-3, 3, -3, 3),
+                              "vmax"_a = vmax, "vmin"_a = vmin));
+```
+
+![image_demo](./gallery/images/image_demo.png)
+
+### fill
 
 Fucntions like `subplots`, `TBD`s are overloaded because they return different types depending on the arguments. Here `subplots()` returns `tuple<Figure, vector<Axes>>`.
 
@@ -138,7 +157,7 @@ From [gallery/lines_bars_and_markers](https://github.com/soblin/matplotlibcpp17/
 
 ![fill](./gallery/images/fill.png)
 
-### example4 - quiver
+### quiver
 
 Use `.unwrap()` method to pass wrapper class of matplotlibcpp17 to plotting functions.
 
@@ -161,7 +180,7 @@ From [gallery/images_contours_and_fields/quiver_demo.cpp](https://github.com/sob
 
 ![quiver_demo3](./gallery/images/quiver_demo_3.png)
 
-### example5 - gif
+### gif
 
 Currently only `ArtistAnimation` is supported. `FuncAnimation` interface maybe implemented in the future.
 

gallery/images_contours_and_fields/CMakeLists.txt

 add_demo(quiver_demo quiver_demo.cpp)
 add_demo(contourf_log contourf_log)
+add_demo(image_demo image_demo)
 
 add_custom_target(
   images_contours_and_fields
-  DEPENDS quiver_demo contourf_log
+  DEPENDS quiver_demo contourf_log image_demo
   COMMAND quiver_demo
   COMMAND contourf_log
+  COMMAND image_demo
   COMMENT "running images_contours_and_fields"
   WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../images")

gallery/images_contours_and_fields/image_demo.cpp

+// example from
+// https://matplotlib.org/stable/gallery/images_contours_and_fields/image_demo.html
+
+#include <matplotlibcpp17/pyplot.h>
+
+#include <xtensor/xbuilder.hpp>
+#include <xtensor/xview.hpp>
+
+#include <vector>
+#include <string>
+#include <algorithm>
+
+using namespace std;
+using namespace matplotlibcpp17;
+
+using mesh2D = vector<vector<double>>;
+
+int main() {
+  const double delta = 0.025;
+  const auto x = xt::arange<double>(-3.0, 3.0, delta);
+  auto [X_, Y_] = xt::meshgrid(x, x);
+  auto Z1_ = xt::exp(-xt::pow(X_, 2) - xt::pow(Y_, 2));
+  auto Z2_ = xt::exp(-xt::pow(X_ - 1, 2) - xt::pow(Y_ - 1, 2));
+  auto Z_ = (Z1_ - Z2_) * 2.0;
+
+  // to vector
+  vector<double> X(X_.begin(), X_.end()), Y(Y_.begin(), Y_.end()),
+      Z1(Z1_.begin(), Z1_.end()), Z2(Z2_.begin(), Z2_.end());
+  // to vector<vector>
+  const int xsz = x.shape()[0], ysz = x.shape()[0];
+  mesh2D Z2D(xsz);
+  for (int i = 0; i < xsz; ++i) {
+    Z2D[i].resize(ysz);
+    for (int j = 0; j < ysz; ++j) {
+      Z2D[i][j] = Z_(i, j);
+    }
+  }
+
+  py::scoped_interpreter guard{};
+  auto plt = matplotlibcpp17::pyplot::import();
+  auto [fig, ax] = plt.subplots();
+  const double vmax = *max_element(Z_.begin(), Z_.end()),
+               vmin = *min_element(Z_.begin(), Z_.end());
+  auto Zpy = py::array(py::cast(std::move(Z2D)));
+  ax.imshow(Args(Zpy), Kwargs("interpolation"_a = "bilinear",
+                              "cmap"_a = "RdYlGn", "origin"_a = "lower",
+                              "extent"_a = py::make_tuple(-3, 3, -3, 3),
+                              "vmax"_a = vmax, "vmin"_a = vmin));
+#if USE_GUI
+  plt.show();
+#else
+  plt.savefig(Args("image_demo.png"));
+#endif
+  return 0;
+}

include/matplotlibcpp17/axes.h

@@ -118,6 +118,10 @@ public:
   pybind11::object hist2d(const pybind11::tuple &args = pybind11::tuple(),
                           const pybind11::dict &kwargs = pybind11::dict());
 
+  // imshow
+  pybind11::object imshow(const pybind11::tuple &args = pybind11::tuple(),
+                          const pybind11::dict &kwargs = pybind11::dict());
+
   // invert_yaxis
   pybind11::object
   invert_yaxis(const pybind11::tuple &args = pybind11::tuple(),
@@ -260,10 +264,12 @@ private:
     LOAD_FUNC_ATTR(hist, self);
     LOAD_FUNC_ATTR(hist2d, self);
     LOAD_FUNC_ATTR(invert_yaxis, self);
+    LOAD_FUNC_ATTR(imshow, self);
     LOAD_FUNC_ATTR(legend, self);
     LOAD_FUNC_ATTR(pcolormesh, self);
     LOAD_FUNC_ATTR(plot, self);
-    // NOTE: only when called with projection='3d', `plot_surface`, `plot_wireframe`, `set_zlabel` prop exists.
+    // NOTE: only when called with projection='3d', `plot_surface`,
+    // `plot_wireframe`, `set_zlabel` prop exists.
     try {
       LOAD_FUNC_ATTR(plot_surface, self);
       LOAD_FUNC_ATTR(plot_wireframe, self);
@@ -315,6 +321,7 @@ private:
   pybind11::object hist_attr;
   pybind11::object hist2d_attr;
   pybind11::object invert_yaxis_attr;
+  pybind11::object imshow_attr;
   pybind11::object legend_attr;
   pybind11::object pcolormesh_attr;
   pybind11::object plot_attr;
@@ -522,6 +529,13 @@ pybind11::object Axes::invert_yaxis(const pybind11::tuple &args,
   return ret;
 }
 
+// imshow
+pybind11::object Axes::imshow(const pybind11::tuple &args,
+                              const pybind11::dict &kwargs) {
+  pybind11::object ret = imshow_attr(*args, **kwargs);
+  return ret;
+}
+
 // legend
 legend::Legend Axes::legend(const pybind11::tuple &args,
                             const pybind11::dict &kwargs) {