src/ui/lib/escher/mesh/tessellation.cc

// Copyright 2016 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/ui/lib/escher/mesh/tessellation.h"

#include <lib/syslog/cpp/macros.h>
#include <math.h>

#include <algorithm>

#include "src/ui/lib/escher/shape/mesh_builder.h"
#include "src/ui/lib/escher/shape/mesh_builder_factory.h"

namespace escher {

struct VertexAttributePointers {
  vec2* pos2 = nullptr;
  vec3* pos3 = nullptr;
  vec2* uv = nullptr;
  vec2* pos_offset = nullptr;
  float* perim = nullptr;
};

// Get pointers to each of the supported vertex attributes within the
// memory pointed to by |vertex|. This is based on the attributes' offsets
// (looked up in the MeshBuilder).
// If the |MeshSpec| does not include an attribute, its corresponding pointer
// will be null.
VertexAttributePointers GetVertexAttributePointers(uint8_t* vertex, size_t vertex_size,
                                                   const MeshSpec& spec, MeshBuilderPtr builder) {
  FX_CHECK(builder->vertex_stride() <= vertex_size);
  FX_DCHECK(spec.IsValidOneBufferMesh());

  VertexAttributePointers attribute_pointers{};

  // Compute the offset of each vertex attribute.
  if (spec.has_attribute(0, MeshAttribute::kPosition2D)) {
    attribute_pointers.pos2 =
        reinterpret_cast<vec2*>(vertex + spec.attribute_offset(0, MeshAttribute::kPosition2D));
  }
  if (spec.has_attribute(0, MeshAttribute::kPosition3D)) {
    attribute_pointers.pos3 =
        reinterpret_cast<vec3*>(vertex + spec.attribute_offset(0, MeshAttribute::kPosition3D));
  }
  if (spec.has_attribute(0, MeshAttribute::kUV)) {
    attribute_pointers.uv =
        reinterpret_cast<vec2*>(vertex + spec.attribute_offset(0, MeshAttribute::kUV));
  }
  if (spec.has_attribute(0, MeshAttribute::kPositionOffset)) {
    attribute_pointers.pos_offset =
        reinterpret_cast<vec2*>(vertex + spec.attribute_offset(0, MeshAttribute::kPositionOffset));
  }
  if (spec.has_attribute(0, MeshAttribute::kPerimeterPos)) {
    attribute_pointers.perim =
        reinterpret_cast<float*>(vertex + spec.attribute_offset(0, MeshAttribute::kPerimeterPos));
  }
  return attribute_pointers;
}

IndexedTriangleMesh2d<vec2> NewCircleIndexedTriangleMesh(const MeshSpec& spec,
                                                         uint32_t subdivisions, vec2 center,
                                                         float radius) {
  FX_DCHECK((spec == MeshSpec{.attributes = {MeshAttribute::kPosition2D, MeshAttribute::kUV}}));
  IndexedTriangleMesh2d<vec2> mesh;

  // Compute the number of vertices in the tessellated circle.
  uint32_t outer_vertex_count = 4;
  while (subdivisions-- > 0) {
    outer_vertex_count *= 2;
  }

  const uint32_t vertex_count = outer_vertex_count + 1;  // Add 1 for center.
  const uint32_t index_count = outer_vertex_count * 3;

  mesh.resize_indices(index_count);
  mesh.resize_vertices(vertex_count);

  // Generate vertex positions.
  vec2* pos = mesh.positions.data();
  vec2* uv = mesh.attributes1.data();

  // Build center vertex.
  pos[0] = center;
  uv[0] = vec2(0.5, 0.5);
  pos += 1;
  uv += 1;

  // Outer vertices.
  const float radian_step = static_cast<float>(2 * M_PI / outer_vertex_count);
  for (uint32_t i = 0; i < outer_vertex_count; ++i) {
    // Direction of the current vertex from the center of the circle.
    float radians = static_cast<float>(i) * radian_step;
    vec2 dir(sin(radians), cos(radians));

    pos[i] = dir * radius + center;
    uv[i] = 0.5f * (dir + vec2(1.f, 1.f));
  }

  // Generate triangle indices.
  auto* current_tri = mesh.indices.data();
  const uint32_t triangle_count = index_count / 3;
  current_tri[0] = 0;
  current_tri[1] = 1;
  current_tri[2] = triangle_count;
  current_tri += 3;
  for (uint32_t i = 1; i < triangle_count; ++i) {
    current_tri[0] = 0;
    current_tri[1] = i + 1;
    current_tri[2] = i;
    current_tri += 3;
  }

  return mesh;
}

IndexedTriangleMesh2d<vec2> NewFlatRectangleMesh(vec2 origin, vec2 extent, vec2 top_left_uv,
                                                 vec2 bottom_right_uv) {
  MeshSpec spec{MeshAttribute::kPosition2D | MeshAttribute::kUV};
  IndexedTriangleMesh2d<vec2> mesh;

  const size_t vertex_count = 4;
  const size_t index_count = 6;

  mesh.resize_indices(index_count);
  mesh.resize_vertices(vertex_count);

  vec2* pos = mesh.positions.data();
  vec2* uv = mesh.attributes1.data();
  auto* indices = mesh.indices.data();

  // Positions. Start from the bottom left-hand corner
  // and wind counterclockwise.
  pos[0] = vec2(origin.x, origin.y + extent.y);
  pos[1] = origin + extent;
  pos[2] = vec2(origin.x + extent.x, origin.y);
  pos[3] = origin;

  uv[0] = vec2(top_left_uv.x, bottom_right_uv.y);
  uv[1] = bottom_right_uv;
  uv[2] = vec2(bottom_right_uv.x, top_left_uv.y);
  uv[3] = top_left_uv;

  indices[0] = 0;
  indices[1] = 1;
  indices[2] = 2;
  indices[3] = 0;
  indices[4] = 2;
  indices[5] = 3;

  return mesh;
}

// Constructs an axis-aligned unit cube mesh.
IndexedTriangleMesh3d<vec2> NewCubeIndexedTriangleMesh(const MeshSpec& spec) {
  FX_DCHECK((spec == MeshSpec{.attributes = {MeshAttribute::kPosition3D, MeshAttribute::kUV}}));
  IndexedTriangleMesh3d<vec2> mesh;

  const size_t vertex_count = 8;  // Four in front, four in back.
  const size_t index_count = 36;  // 6 faces * 2 triangles * 3 verts.

  mesh.resize_indices(index_count);
  mesh.resize_vertices(vertex_count);

  vec3* pos = mesh.positions.data();
  vec2* uv = mesh.attributes1.data();
  auto* indices = mesh.indices.data();

  // Front four verts.
  pos[0] = vec3(0, 0, 0);
  pos[1] = vec3(1, 0, 0);
  pos[2] = vec3(1, 1, 0);
  pos[3] = vec3(0, 1, 0);

  // Back four verts.
  pos[4] = vec3(0, 1, 1);
  pos[5] = vec3(1, 1, 1);
  pos[6] = vec3(1, 0, 1);
  pos[7] = vec3(0, 0, 1);

  // TODO(fxbug.dev/7307): Add separate box mesh type with split verts and proper uv coords. Since
  // this box is currently only being used for wireframe rendering, it doesn't need texcoords.
  for (size_t t = 0; t < vertex_count; t++) {
    uv[t] = vec2(0.f, 0.f);
  }

  size_t index = 0;
  auto AddIndex = [&index, &indices](uint32_t val) {
    indices[index] = val;
    index++;
  };

  auto AddTriangle = [&AddIndex](uint32_t val1, uint32_t val2, uint32_t val3) {
    AddIndex(val1);
    AddIndex(val2);
    AddIndex(val3);
  };

  // Front face.
  AddTriangle(0, 1, 2);
  AddTriangle(0, 2, 3);

  // Top face.
  AddTriangle(2, 4, 3);
  AddTriangle(2, 5, 4);

  // Right face.
  AddTriangle(1, 5, 2);
  AddTriangle(1, 5, 6);

  // Left face.
  AddTriangle(0, 4, 7);
  AddTriangle(0, 3, 4);

  // Back face.
  AddTriangle(5, 7, 4);
  AddTriangle(5, 6, 7);

  // Bottom face.
  AddTriangle(0, 7, 6);
  AddTriangle(0, 6, 1);

  return mesh;
}

MeshPtr NewCircleMesh(MeshBuilderFactory* factory, BatchGpuUploader* gpu_uploader,
                      const MeshSpec& spec, int subdivisions, vec2 center, float radius,
                      float offset_magnitude) {
  // Compute the number of vertices in the tessellated circle.
  FX_DCHECK(subdivisions >= 0);
  FX_DCHECK(spec.IsValidOneBufferMesh());
  uint32_t outer_vertex_count = 4;
  while (subdivisions-- > 0) {
    outer_vertex_count *= 2;
  }

  uint32_t vertex_count = outer_vertex_count + 1;  // Add 1 for center vertex.
  uint32_t index_count = outer_vertex_count * 3;

  auto builder = factory->NewMeshBuilder(gpu_uploader, spec, vertex_count, index_count);

  // Generate vertex positions.
  constexpr size_t kMaxVertexSize = 100;
  uint8_t vertex[kMaxVertexSize];
  auto vertex_p = GetVertexAttributePointers(vertex, kMaxVertexSize, spec, builder);

  // Build center vertex.
  FX_CHECK(vertex_p.pos2);
  (*vertex_p.pos2) = center;
  if (vertex_p.uv)
    (*vertex_p.uv) = vec2(0.5f, 0.5f);
  if (vertex_p.pos_offset)
    (*vertex_p.pos_offset) = vec2(0.f, 0.f);
  // TODO: This is an undesirable singularity.  Perhaps it would be better to
  // treat circles as a ring with inner radius of zero?
  if (vertex_p.perim)
    (*vertex_p.perim) = 0.f;
  builder->AddVertexData(vertex, builder->vertex_stride());

  // Outer vertices.
  const float outer_vertex_count_reciprocal = static_cast<float>(1. / outer_vertex_count);
  const float radian_step = static_cast<float>(2. * M_PI / outer_vertex_count);
  for (uint32_t i = 0; i < outer_vertex_count; ++i) {
    float radians = static_cast<float>(i) * radian_step;

    // Direction of the current vertex from the center of the circle.
    vec2 dir(sin(radians), cos(radians));

    (*vertex_p.pos2) = dir * radius + center;
    if (vertex_p.uv)
      (*vertex_p.uv) = 0.5f * (dir + vec2(1.f, 1.f));
    if (vertex_p.pos_offset)
      (*vertex_p.pos_offset) = dir * offset_magnitude;
    if (vertex_p.perim)
      (*vertex_p.perim) = static_cast<float>(i) * outer_vertex_count_reciprocal;

    builder->AddVertexData(vertex, builder->vertex_stride());
  }

  // Vertex indices.
  for (uint32_t i = 1; i < outer_vertex_count; ++i) {
    builder->AddIndex(0);
    builder->AddIndex(i + 1);
    builder->AddIndex(i);
  }
  builder->AddIndex(0);
  builder->AddIndex(1);
  builder->AddIndex(outer_vertex_count);

  auto mesh = builder->Build();
  FX_DCHECK(mesh->num_indices() == index_count);
  FX_DCHECK(mesh->bounding_box() == BoundingBox(vec3(center.x - radius, center.y - radius, 0),
                                                vec3(center.x + radius, center.y + radius, 0)));
  return mesh;
}

MeshPtr NewRingMesh(MeshBuilderFactory* factory, BatchGpuUploader* gpu_uploader,
                    const MeshSpec& spec, int subdivisions, vec2 center, float outer_radius,
                    float inner_radius, float outer_offset_magnitude,
                    float inner_offset_magnitude) {
  // Compute the number of vertices in the tessellated circle.
  FX_DCHECK(subdivisions >= 0);
  FX_DCHECK(spec.IsValidOneBufferMesh());
  uint32_t outer_vertex_count = 4;
  while (subdivisions-- > 0) {
    outer_vertex_count *= 2;
  }

  uint32_t vertex_count = outer_vertex_count * 2;
  uint32_t index_count = outer_vertex_count * 6;

  auto builder = factory->NewMeshBuilder(gpu_uploader, spec, vertex_count, index_count);

  // Generate vertex positions.
  constexpr size_t kMaxVertexSize = 100;
  uint8_t vertex[kMaxVertexSize];
  auto vertex_p = GetVertexAttributePointers(vertex, kMaxVertexSize, spec, builder);
  FX_CHECK(vertex_p.pos2);

  const float outer_vertex_count_reciprocal = static_cast<float>(1. / outer_vertex_count);
  const float radian_step = static_cast<float>(2. * M_PI / outer_vertex_count);
  for (uint32_t i = 0; i < outer_vertex_count; ++i) {
    float radians = static_cast<float>(i) * radian_step;

    // Direction of the current vertex from the center of the circle.
    vec2 dir(sin(radians), cos(radians));

    // Build outer-ring vertex.
    (*vertex_p.pos2) = dir * outer_radius + center;
    if (vertex_p.uv) {
      // Munge the texcoords slightly to avoid wrapping artifacts.  This matters
      // when both:
      //   - the vk::SamplerAddressMode is eRepeat
      //   - the vk::Filter is eLinear
      (*vertex_p.uv) = 0.49f * (dir + vec2(1.f, 1.02f));
      // TODO(fxbug.dev/7199): once we can specify a SamplerAddressMode of eClampToEdge,
      // remove the hack above and replace it with the code below:
      // (*vertex_p.uv) = 0.5f * (dir + vec2(1.f, 1.f));
    }
    if (vertex_p.pos_offset)
      (*vertex_p.pos_offset) = dir * outer_offset_magnitude;
    if (vertex_p.perim)
      (*vertex_p.perim) = static_cast<float>(i) * outer_vertex_count_reciprocal;
    builder->AddVertexData(vertex, builder->vertex_stride());

    // Build inner-ring vertex.  Only the position and offset may differ from
    // the corresponding outer-ring vertex.
    (*vertex_p.pos2) = dir * inner_radius + center;
    if (vertex_p.pos_offset) {
      // Positive offsets point inward, toward the center of the circle.
      (*vertex_p.pos_offset) = dir * -inner_offset_magnitude;
    }
    builder->AddVertexData(vertex, builder->vertex_stride());
  }

  // Generate vertex indices.
  for (uint32_t i = 2; i < vertex_count; i += 2) {
    builder->AddIndex(i - 2);
    builder->AddIndex(i - 1);
    builder->AddIndex(i);
    builder->AddIndex(i);
    builder->AddIndex(i - 1);
    builder->AddIndex(i + 1);
  }
  builder->AddIndex(vertex_count - 2);
  builder->AddIndex(vertex_count - 1);
  builder->AddIndex(0);
  builder->AddIndex(0);
  builder->AddIndex(vertex_count - 1);
  builder->AddIndex(1);

  auto mesh = builder->Build();
  FX_DCHECK(mesh->num_indices() == index_count);
  FX_DCHECK(mesh->bounding_box() ==
            BoundingBox(vec3(center.x - outer_radius, center.y - outer_radius, 0),
                        vec3(center.x + outer_radius, center.y + outer_radius, 0)));
  return mesh;
}

MeshPtr NewRectangleMesh(MeshBuilderFactory* factory, BatchGpuUploader* gpu_uploader,
                         const MeshSpec& spec, int subdivisions, vec2 extent, vec2 top_left,
                         float top_offset_magnitude, float bottom_offset_magnitude) {
  // Compute the number of vertices in the tessellated circle.
  FX_DCHECK(subdivisions >= 0);
  uint32_t vertices_per_side = 2;
  while (subdivisions-- > 0) {
    vertices_per_side *= 2;
  }

  uint32_t vertex_count = vertices_per_side * 2;
  uint32_t index_count = (vertices_per_side - 1) * 6;

  auto builder = factory->NewMeshBuilder(gpu_uploader, spec, vertex_count, index_count);

  // Generate vertex positions.
  constexpr size_t kMaxVertexSize = 100;
  uint8_t vertex[kMaxVertexSize];
  auto vertex_p = GetVertexAttributePointers(vertex, kMaxVertexSize, spec, builder);
  FX_CHECK(vertex_p.pos2);

  const float vertices_per_side_reciprocal = 1.f / static_cast<float>(vertices_per_side - 1);
  for (uint32_t i = 0; i < vertices_per_side; ++i) {
    // Build bottom vertex.
    (*vertex_p.pos2) =
        top_left + vec2(extent.x * static_cast<float>(i) * vertices_per_side_reciprocal, extent.y);
    if (vertex_p.uv)
      (*vertex_p.uv) = vec2(static_cast<float>(i) * vertices_per_side_reciprocal, 1.f);
    if (vertex_p.pos_offset)
      (*vertex_p.pos_offset) = vec2(0, 1.f * bottom_offset_magnitude);
    if (vertex_p.perim)
      (*vertex_p.perim) = static_cast<float>(i) * vertices_per_side_reciprocal;
    builder->AddVertexData(vertex, builder->vertex_stride());

    // Build top vertex.
    (*vertex_p.pos2) =
        top_left + vec2(extent.x * static_cast<float>(i) * vertices_per_side_reciprocal, 0);
    if (vertex_p.uv)
      (*vertex_p.uv) = vec2(static_cast<float>(i) * vertices_per_side_reciprocal, 0);
    if (vertex_p.pos_offset)
      (*vertex_p.pos_offset) = vec2(0, -1.f * top_offset_magnitude);
    if (vertex_p.perim)
      (*vertex_p.perim) = static_cast<float>(i) * vertices_per_side_reciprocal;
    builder->AddVertexData(vertex, builder->vertex_stride());
  }

  // Generate vertex indices.
  for (uint32_t i = 2; i < vertex_count; i += 2) {
    builder->AddIndex(i - 2);
    builder->AddIndex(i - 1);
    builder->AddIndex(i);
    builder->AddIndex(i);
    builder->AddIndex(i - 1);
    builder->AddIndex(i + 1);
  }

  auto mesh = builder->Build();
  FX_DCHECK(mesh->num_indices() == index_count);
  return mesh;
}

MeshPtr NewFullScreenMesh(MeshBuilderFactory* factory, BatchGpuUploader* gpu_uploader) {
  MeshSpec spec{MeshAttribute::kPosition2D | MeshAttribute::kUV};

  // Some internet lore has it that it is better to use a single triangle rather
  // than a rectangle composed of a pair of triangles, so that is what we do.
  // The triangle extends beyond the bounds of the screen, and is clipped so
  // that each fragment has the same position and UV coordinates as would a
  // two-triangle quad. In each vertex, the first two coordinates are position,
  // and the second two are UV coords.
  return factory->NewMeshBuilder(gpu_uploader, spec, 3, 3)
      ->AddVertex(vec4(-1.f, -1.f, 0.f, 0.f))
      .AddVertex(vec4(3.f, -1.f, 2.f, 0.f))
      .AddVertex(vec4(-1.f, 3.f, 0.f, 2.f))
      .AddIndex(0)
      .AddIndex(1)
      .AddIndex(2)
      .Build();
}

MeshPtr NewSphereMesh(MeshBuilderFactory* factory, BatchGpuUploader* gpu_uploader,
                      const MeshSpec& spec, int subdivisions, vec3 center, float radius) {
  FX_DCHECK(subdivisions >= 0);
  FX_DCHECK(spec.IsValidOneBufferMesh());
  size_t vertex_count = 9;
  size_t triangle_count = 8;
  for (int i = 0; i < subdivisions; ++i) {
    // At each level of subdivision, an additional vertex is added for each
    // triangle, and each triangle is split into three.
    vertex_count += triangle_count;
    triangle_count *= 3;
  }

  // Populate initial octahedron.
  auto builder = factory->NewMeshBuilder(gpu_uploader, spec, vertex_count, triangle_count * 3);
  constexpr size_t kMaxVertexSize = 100;
  uint8_t vertex[kMaxVertexSize];
  auto vertex_p = GetVertexAttributePointers(vertex, kMaxVertexSize, spec, builder);
  FX_CHECK(vertex_p.pos3);

  // Positions and UV-coordinates for the initial octahedron.  The vertex with
  // position (-radius, 0, 0) is replicated 4 times, with different UV-coords
  // each time.  This is a consequence of surface parameterization that is
  // described in the header file.
  const vec3 positions[] = {
      vec3(radius, 0.f, 0.f),  vec3(0.f, 0.f, radius),  vec3(0.f, -radius, 0.f),
      vec3(0.f, 0.f, -radius), vec3(0.f, radius, 0.f),  vec3(-radius, 0.f, 0.f),
      vec3(-radius, 0.f, 0.f), vec3(-radius, 0.f, 0.f), vec3(-radius, 0.f, 0.f)};
  const vec2 uv_coords[] = {vec2(.5f, .5f), vec2(1.f, .5f), vec2(.5f, 0.f),
                            vec2(0.f, .5f), vec2(.5f, 1.f), vec2(0.f, 0.f),
                            vec2(1.f, 0.f), vec2(1.f, 1.f), vec2(0.f, 1.f)};

  for (int i = 0; i < 9; ++i) {
    (*vertex_p.pos3) = positions[i] + center;
    if (vertex_p.uv) {
      (*vertex_p.uv) = uv_coords[i];
    }
    builder->AddVertexData(vertex, builder->vertex_stride());
  }
  builder->AddTriangle(0, 1, 2)
      .AddTriangle(0, 2, 3)
      .AddTriangle(0, 3, 4)
      .AddTriangle(0, 4, 1)
      .AddTriangle(5, 2, 1)
      .AddTriangle(6, 3, 2)
      .AddTriangle(7, 4, 3)
      .AddTriangle(8, 1, 4);

  // TODO(fxbug.dev/7329): this is a hack to ease implementation.  We don't currently
  // need any tessellated spheres; this is just a way to verify that 3D meshes
  // are working properly.
  FX_DCHECK(spec.attributes[0] == (MeshAttribute::kPosition3D | MeshAttribute::kUV))
      << "Tessellated sphere must have UV-coordinates.";
  size_t position_offset = reinterpret_cast<uint8_t*>(vertex_p.pos3) - vertex;
  size_t uv_offset = reinterpret_cast<uint8_t*>(vertex_p.uv) - vertex;
  while (subdivisions-- > 0) {
    // For each level of subdivision, iterate over all existing triangles and
    // split them into three.
    // TODO(fxbug.dev/7329): see comment in header file... this approach is broken, but
    // sufficient for our current purpose.
    const size_t subdiv_triangle_count = builder->index_count() / 3;
    FX_DCHECK(subdiv_triangle_count * 3 == builder->index_count());

    for (size_t tri_ind = 0; tri_ind < subdiv_triangle_count; ++tri_ind) {
      // Obtain indices for the current triangle, and the position/UV coords for
      // the corresponding vertices.
      uint32_t* tri = builder->GetIndex(tri_ind * 3);
      uint32_t ind0 = tri[0];
      uint32_t ind1 = tri[1];
      uint32_t ind2 = tri[2];
      uint8_t* vert0 = builder->GetVertex(ind0);
      uint8_t* vert1 = builder->GetVertex(ind1);
      uint8_t* vert2 = builder->GetVertex(ind2);
      vec3 pos0 = *reinterpret_cast<vec3*>(vert0 + position_offset);
      vec3 pos1 = *reinterpret_cast<vec3*>(vert1 + position_offset);
      vec3 pos2 = *reinterpret_cast<vec3*>(vert2 + position_offset);
      vec2 uv0 = *reinterpret_cast<vec2*>(vert0 + uv_offset);
      vec2 uv1 = *reinterpret_cast<vec2*>(vert1 + uv_offset);
      vec2 uv2 = *reinterpret_cast<vec2*>(vert2 + uv_offset);

      // Create a new vertex by averaging the existing vertex attributes.
      (*vertex_p.pos3) = center + radius * glm::normalize((pos0 + pos1 + pos2) / 3.f - center);
      (*vertex_p.uv) = (uv0 + uv1 + uv2) / 3.f;
      builder->AddVertexData(vertex, builder->vertex_stride());

      // Replace the current triangle in-place with a new triangle that refers
      // to the new vertex.  Then, add two new triangles that also refer to the
      // new vertex.
      uint32_t new_ind = static_cast<uint32_t>(builder->vertex_count()) - 1;
      tri[2] = new_ind;
      builder->AddTriangle(ind1, ind2, new_ind).AddTriangle(ind2, ind0, new_ind);
    }
  }
  return builder->Build();
}

// Helper function that returns a standard mesh used for testing.  It looks like
// like this in the standard Vulkan coordinate system (positive y down).
//     (-1,-1) _______ (1,-1)
//           /\      /\                        3    4
//         /   \   /   \         indices:
//       /______\/______\                   0    1    2
//  (-2,1)    (0,1)     (2,1)
IndexedTriangleMesh2d<vec2> GetStandardTestMesh2d() {
  return IndexedTriangleMesh2d<vec2>{
      .indices = {0, 1, 3, 3, 1, 4, 4, 1, 2},
      .positions = {vec2(-2, 1), vec2(0, 1), vec2(2, 1), vec2(-1, -1), vec2(1, -1)},
      .attributes1 = {vec2(0, 1), vec2(0.5f, 1), vec2(1, 1), vec2(0, 0), vec2(1, 0)}};
}

IndexedTriangleMesh3d<vec2> GetStandardTestMesh3d() {
  auto mesh2d = GetStandardTestMesh2d();

  IndexedTriangleMesh3d<vec2> mesh3d;
  mesh3d.indices = mesh2d.indices;
  mesh3d.attributes1 = mesh2d.attributes1;
  for (const vec2& pos : mesh2d.positions) {
    mesh3d.positions.push_back(vec3(pos, 11));
  }
  return mesh3d;
}

}  // namespace escher