Migrate SubmapTexture and SubmapSlice logics from cartographer_ros (#782)

Towards [RFC06](https://github.com/googlecartographer/rfcs/blob/master/text/0006-serve-ros-map-from-pbstream.md).

Migrates
* `FillSubmapSlice` from `pbstream_to_rosmap_main.cc` 
* `SubmapTexture` logics from cartographer_ros

cartographer/io/submap_painter.cc

@@ -61,10 +61,9 @@ PaintSubmapSlicesResult PaintSubmapSlices(
     const double resolution) {
   Eigen::AlignedBox2f bounding_box;
   {
-    auto surface = ::cartographer::io::MakeUniqueCairoSurfacePtr(
-        cairo_image_surface_create(::cartographer::io::kCairoFormat, 1, 1));
-    auto cr =
-        ::cartographer::io::MakeUniqueCairoPtr(cairo_create(surface.get()));
+    auto surface = MakeUniqueCairoSurfacePtr(
+        cairo_image_surface_create(kCairoFormat, 1, 1));
+    auto cr = MakeUniqueCairoPtr(cairo_create(surface.get()));
     const auto update_bounding_box = [&bounding_box, &cr](double x, double y) {
       cairo_user_to_device(cr.get(), &x, &y);
       bounding_box.extend(Eigen::Vector2f(x, y));
@@ -87,12 +86,10 @@ PaintSubmapSlicesResult PaintSubmapSlices(
   const Eigen::Array2f origin(-bounding_box.min().x() + kPaddingPixel,
                               -bounding_box.min().y() + kPaddingPixel);
 
-  auto surface =
-      ::cartographer::io::MakeUniqueCairoSurfacePtr(cairo_image_surface_create(
-          ::cartographer::io::kCairoFormat, size.x(), size.y()));
+  auto surface = MakeUniqueCairoSurfacePtr(
+      cairo_image_surface_create(kCairoFormat, size.x(), size.y()));
   {
-    auto cr =
-        ::cartographer::io::MakeUniqueCairoPtr(cairo_create(surface.get()));
+    auto cr = MakeUniqueCairoPtr(cairo_create(surface.get()));
     cairo_set_source_rgba(cr.get(), 0.5, 0.0, 0.0, 1.);
     cairo_paint(cr.get());
     cairo_translate(cr.get(), origin.x(), origin.y());
@@ -107,5 +104,82 @@ PaintSubmapSlicesResult PaintSubmapSlices(
   return PaintSubmapSlicesResult(std::move(surface), origin);
 }
 
+void FillSubmapSlice(
+    const ::cartographer::transform::Rigid3d& global_submap_pose,
+    const ::cartographer::mapping::proto::Submap& proto,
+    SubmapSlice* const submap_slice) {
+  ::cartographer::mapping::proto::SubmapQuery::Response response;
+  ::cartographer::transform::Rigid3d local_pose;
+  if (proto.has_submap_3d()) {
+    ::cartographer::mapping_3d::Submap submap(proto.submap_3d());
+    local_pose = submap.local_pose();
+    submap.ToResponseProto(global_submap_pose, &response);
+  } else {
+    ::cartographer::mapping_2d::Submap submap(proto.submap_2d());
+    local_pose = submap.local_pose();
+    submap.ToResponseProto(global_submap_pose, &response);
+  }
+  submap_slice->pose = global_submap_pose;
+
+  auto& texture_proto = response.textures(0);
+  const SubmapTexture::Pixels pixels = UnpackTextureData(
+      texture_proto.cells(), texture_proto.width(), texture_proto.height());
+  submap_slice->width = texture_proto.width();
+  submap_slice->height = texture_proto.height();
+  submap_slice->resolution = texture_proto.resolution();
+  submap_slice->slice_pose =
+      ::cartographer::transform::ToRigid3(texture_proto.slice_pose());
+  submap_slice->surface =
+      DrawTexture(pixels.intensity, pixels.alpha, texture_proto.width(),
+                  texture_proto.height(), &submap_slice->cairo_data);
+}
+
+SubmapTexture::Pixels UnpackTextureData(const std::string& compressed_cells,
+                                        const int width, const int height) {
+  SubmapTexture::Pixels pixels;
+  std::string cells;
+  ::cartographer::common::FastGunzipString(compressed_cells, &cells);
+  const int num_pixels = width * height;
+  CHECK_EQ(cells.size(), 2 * num_pixels);
+  pixels.intensity.reserve(num_pixels);
+  pixels.alpha.reserve(num_pixels);
+  for (int i = 0; i < height; ++i) {
+    for (int j = 0; j < width; ++j) {
+      pixels.intensity.push_back(cells[(i * width + j) * 2]);
+      pixels.alpha.push_back(cells[(i * width + j) * 2 + 1]);
+    }
+  }
+  return pixels;
+}
+
+UniqueCairoSurfacePtr DrawTexture(const std::vector<char>& intensity,
+                                  const std::vector<char>& alpha,
+                                  const int width, const int height,
+                                  std::vector<uint32_t>* const cairo_data) {
+  CHECK(cairo_data->empty());
+
+  // Properly dealing with a non-common stride would make this code much more
+  // complicated. Let's check that it is not needed.
+  const int expected_stride = 4 * width;
+  CHECK_EQ(expected_stride, cairo_format_stride_for_width(kCairoFormat, width));
+  for (size_t i = 0; i < intensity.size(); ++i) {
+    // We use the red channel to track intensity information. The green
+    // channel we use to track if a cell was ever observed.
+    const uint8_t intensity_value = intensity.at(i);
+    const uint8_t alpha_value = alpha.at(i);
+    const uint8_t observed =
+        (intensity_value == 0 && alpha_value == 0) ? 0 : 255;
+    cairo_data->push_back((alpha_value << 24) | (intensity_value << 16) |
+                          (observed << 8) | 0);
+  }
+
+  auto surface = MakeUniqueCairoSurfacePtr(cairo_image_surface_create_for_data(
+      reinterpret_cast<unsigned char*>(cairo_data->data()), kCairoFormat, width,
+      height, expected_stride));
+  CHECK_EQ(cairo_surface_status(surface.get()), CAIRO_STATUS_SUCCESS)
+      << cairo_status_to_string(cairo_surface_status(surface.get()));
+  return surface;
+}
+
 }  // namespace io
 }  // namespace cartographer

cartographer/io/submap_painter.h

@@ -21,6 +21,9 @@
 #include "cairo/cairo.h"
 #include "cartographer/io/image.h"
 #include "cartographer/mapping/id.h"
+#include "cartographer/mapping/proto/submap.pb.h"
+#include "cartographer/mapping_2d/submaps.h"
+#include "cartographer/mapping_3d/submaps.h"
 #include "cartographer/transform/rigid_transform.h"
 
 namespace cartographer {
@@ -55,10 +58,43 @@ struct SubmapSlice {
   int metadata_version = -1;
 };
 
+struct SubmapTexture {
+  struct Pixels {
+    std::vector<char> intensity;
+    std::vector<char> alpha;
+  };
+  Pixels pixels;
+  int width;
+  int height;
+  double resolution;
+  ::cartographer::transform::Rigid3d slice_pose;
+};
+
+struct SubmapTextures {
+  int version;
+  std::vector<SubmapTexture> textures;
+};
+
 PaintSubmapSlicesResult PaintSubmapSlices(
     const std::map<::cartographer::mapping::SubmapId, SubmapSlice>& submaps,
     double resolution);
 
+void FillSubmapSlice(
+    const ::cartographer::transform::Rigid3d& global_submap_pose,
+    const ::cartographer::mapping::proto::Submap& proto,
+    SubmapSlice* const submap_slice);
+
+// Unpacks cell data as provided by the backend into 'intensity' and 'alpha'.
+SubmapTexture::Pixels UnpackTextureData(const std::string& compressed_cells,
+                                        int width, int height);
+
+// Draw a texture into a cairo surface. 'cairo_data' will store the pixel data
+// for the surface and must therefore outlive the use of the surface.
+UniqueCairoSurfacePtr DrawTexture(const std::vector<char>& intensity,
+                                  const std::vector<char>& alpha, int width,
+                                  int height,
+                                  std::vector<uint32_t>* cairo_data);
+
 }  // namespace io
 }  // namespace cartographer