gallery_star.cpp

This gallery example demonstrates creating custom geometric shapes using Plotly.cpp by generating coordinate points programmatically. It showcases the creation of a five-pointed star through mathematical coordinate calculation and path-based visualization.

Features demonstrated:

• Custom geometric shape generation using mathematical calculations
• Polar coordinate conversion to Cartesian coordinates
• Path closure for complete shape formation
• Scatter plot with both lines and markers for shape definition
• Equal axis scaling to maintain shape proportions
• Custom styling with color differentiation for lines and markers
• Helper function design for reusable shape generation

Mathematical concepts:

• Star geometry with alternating outer and inner radii
• Angular positioning using multiples of (36-degree increments)
• Polar-to-Cartesian coordinate transformation: ,
• Path completion by connecting back to the starting point

The star shape is created with outer radius 1.0, inner radius 0.4, and centered at the origin, demonstrating precise geometric control through programmatic coordinate generation.

Five-Pointed Star Geometric Shape

 
#include "plotly/plotly.hpp"
#include "utils/arg_parser.hpp"
#include <cmath>
#include <utility>
#include <vector>

auto createStarShape(double cx, double cy, double rOuter, double rInner)
    -> std::pair<std::vector<double>, std::vector<double>> {
  std::vector<double> x;
  std::vector<double> y;
  const double angle = M_PI / 5.0; // 36 degrees
 
  for (int i = 0; i < 10; i++) {
    double r = (i % 2 == 0) ? rOuter : rInner;
    double theta = (i * angle) + M_PI / 2.0; // start from top
    double xPoint = cx + (r * std::cos(theta));
    double yPoint = cy + (r * std::sin(theta));
    x.push_back(xPoint);
    y.push_back(yPoint);
  }
 
  // Close the path by adding the first point again
  x.push_back(x[0]);
  y.push_back(y[0]);
 
  return std::make_pair(x, y);
}
 
auto main(int argc, char *argv[]) -> int {
  // Parse command line arguments
  auto args = parseGalleryArgs(argc, argv);
 
  plotly::Figure fig;
  fig.openBrowser(args.headless);
 
  // Create star shape with center at (0,0), outer radius 1, inner radius 0.4
  auto [x, y] = createStarShape(0.0, 0.0, 1.0, 0.4);
 
  fig.newPlot({{{"x", x},
                {"y", y},
                {"type", "scatter"},
                {"mode", "lines+markers"},
                {"line", {{"shape", "linear"}, {"color", "gold"}}},
                {"marker", {{"color", "red"}, {"size", 8}}}}},
              {{"title", {{"text", "Star Shape Plot"}}},
               {"xaxis", {{"scaleanchor", "y"}, {"range", {-1.5, 1.5}}}},
               {"yaxis", {{"range", {-1.5, 1.5}}}},
               {"showlegend", false}});
 
  if (!args.headless) {
    fig.waitClose();
  } else {
    // Save image instead of opening browser
    plotly::Object imageOpts = {{"format", "png"},
                                {"width", 800},
                                {"height", 600},
                                {"filename", "star"}};
    fig.downloadImage(imageOpts);
  }
 
  return 0;
}