Reintroduce pointcloud render without Float_V message (backport #755)

[mergify]

🦟 Bug fix

This bug

Summary

Re-introduce point cloud rendering without the Float_V message.

I tested it with the following program:

#include <iostream>
#include <cmath>
#include <thread>
#include <chrono>
#include <gz/msgs/pointcloud_packed.pb.h>
#include <gz/msgs/PointCloudPackedUtils.hh>
#include <gz/transport/Node.hh>

int main(int argc, char** argv)
{
  // Create a transport node.
  gz::transport::Node node;

  // Define the topic to publish on.
  std::string topic = "/sphere_points";

  // Create a publisher for PointCloudPacked messages.
  auto pub = node.Advertise<gz::msgs::PointCloudPacked>(topic);

  if (!pub)
  {
    std::cerr << "Error advertising topic [" << topic << "]" << std::endl;
    return -1;
  }

  // Sphere parameters
  double radius = 1.0;
  int num_theta = 20;
  int num_phi = 40;

  // Prepare the message
  gz::msgs::PointCloudPacked msg;
  // Initialize header
  msg.mutable_header()->mutable_stamp()->set_sec(0);
  msg.mutable_header()->mutable_stamp()->set_nsec(0);

  // Initialize PointCloudPacked
  gz::msgs::InitPointCloudPacked(msg, "frame_id", false,
      {{"xyz", gz::msgs::PointCloudPacked::Field::FLOAT32}});

  int num_points = (num_theta + 1) * num_phi;
  msg.set_width(num_points);
  msg.set_height(1);
  msg.set_is_dense(true);
  msg.mutable_data()->resize(num_points * msg.point_step());

  gz::msgs::PointCloudPackedIterator<float> iterX(msg, "x");
  gz::msgs::PointCloudPackedIterator<float> iterY(msg, "y");
  gz::msgs::PointCloudPackedIterator<float> iterZ(msg, "z");

  const double PI = std::acos(-1.0);

  for (int i = 0; i <= num_theta; ++i)
  {
    double theta = PI * i / num_theta;
    for (int j = 0; j < num_phi; ++j)
    {
      double phi = 2.0 * PI * j / num_phi;

      double x = radius * std::sin(theta) * std::cos(phi);
      double y = radius * std::sin(theta) * std::sin(phi);
      double z = radius * std::cos(theta);

      *iterX = static_cast<float>(x);
      *iterY = static_cast<float>(y);
      *iterZ = static_cast<float>(z);
      ++iterX;
      ++iterY;
      ++iterZ;
    }
  }

  std::cout << "Publishing a sphere with " << num_points
            << " points on topic [" << topic << "]" << std::endl;

  // Publish the message in a loop
  while (true)
  {
    if (!pub.Publish(msg))
    {
        std::cerr << "Failed to publish message" << std::endl;
    }
    std::this_thread::sleep_for(std::chrono::milliseconds(1000));
  }

  return 0;
}

TODO: Color support: I think we should not implement the color rendering support here, rather perhaps we should have some PointCloud representation in gz-math. For now there is rudimentary support for colors in this PR.

Checklist

• Signed all commits for DCO
• Added a screen capture or video to the PR description that demonstrates the fix (as needed)
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• Updated Bazel files (if adding new files). Created an issue otherwise.
• While waiting for a review on your PR, please help review another open pull request to support the maintainers
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---

This is an automatic backport of pull request #755 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of d8b6a54 has failed:

On branch mergify/bp/ign-gui6/pr-755
Your branch is up to date with 'origin/ign-gui6'.

You are currently cherry-picking commit d8b6a54.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   src/plugins/point_cloud/PointCloud.cc

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally