MinusculeRender/src/minus_renderer.cc

// Copyright 2024 Bytedance Inc. All Rights Reserved.
// Author: tianlei.richard@qq.com (tianlei.richard)

#include <cmath>

#include "minus_renderer.h"
#include "rasterizer.h"

#include "spdlog/spdlog.h"

MinusRenderer::MinusRenderer(float near, float far, float fov,
                             float aspect_ratio,
                             std::vector<Triangle> &&primitives)
    : near_(near), far_(far), fov_(fov), aspect_ratio_(aspect_ratio),
      height_(calculate_height(fov, near)),
      width_(calculate_width(height_, aspect_ratio)), primitives_(primitives) {
  spdlog::info("fov: {}, aspect ratio: {}, width: {}, height: {}", fov_,
               aspect_ratio_, width_, height_);
}

float MinusRenderer::calculate_height(const float fov, const float near) {
  return std::fabs(near) * std::tan(fov * 0.5) * 2;
}

float MinusRenderer::calculate_width(const float height, const float ratio) {
  return height * ratio;
}

TransformMatrix MinusRenderer::squish_tranform() {
  // Frustum to Cuboid
  return TransformMatrix{{near_, 0, 0, 0},
                         {0, near_, 0, 0},
                         {0, 0, near_ + far_, -near_ * far_},
                         {0, 0, 1, 0}};
}

TransformMatrix MinusRenderer::orthographic_tranform() {
  const auto right = width_ * 0.5;
  const auto left = -right;
  const auto top = height_ * 0.5;
  const auto bottom = -top;

  TransformMatrix m{{1, 0, 0, -0.5 * (right - left)},
                    {0, 1, 0, -0.5 * (top - bottom)},
                    {0, 0, 1, -0.5 * (far_ - near_)},
                    {0, 0, 0, 1}};

  m = TransformMatrix{{2 / (right - left), 0, 0, 0},
                      {0, 2 / (top - bottom), 0, 0},
                      {0, 0, 2 / std::fabs(far_ - near_), 0},
                      {0, 0, 0, 1}} *
      m;

  return m;
}

TransformMatrix MinusRenderer::view_port_transform(const float width,
                                                   const float height) {
  return TransformMatrix{{width * 0.5, 0, 0, width * 0.5},
                         {0, height * 0.5, 0, height * 0.5},
                         {0, 0, 1, 0},
                         {0, 0, 0, 1}};
}

void MinusRenderer::model_transform(const TransformMatrix &m) {
  for (auto &t : primitives_) {
    t.affine_transform(m);
  }
}

cv::Mat MinusRenderer::render(const int resolution_width,
                              const int resolution_height) {
  std::vector<Triangle> primitives;
  for (const auto &t : primitives_) {
    primitives.push_back(t);
  }
  for (auto &t : primitives) {
    t.projective_transform(squish_tranform());
    t.affine_transform(orthographic_tranform());
    t.affine_transform(
        view_port_transform(resolution_width, resolution_height));
  }

  Rasterizer rasterizer{resolution_width, resolution_height};
  const auto &pixels = rasterizer.rasterize(primitives);
  assert(!pixels.empty());
  cv::Mat color_image(pixels.size(), (pixels[0]).size(), CV_8UC3);

  for (int i = 0; i < pixels.size(); ++i) {
    const auto &row = pixels[i];
    for (int j = 0; j < row.size(); ++j) {
      auto &pixel_color = color_image.at<cv::Vec3b>(pixels.size() - i - 1, j);
      pixel_color =
          cv::Vec3b{static_cast<unsigned char>(
                        row[j].x() * std::numeric_limits<char>::max()),
                    static_cast<unsigned char>(
                        row[j].y() * std::numeric_limits<char>::max()),
                    static_cast<unsigned char>(
                        row[j].z() * std::numeric_limits<char>::max())};
    }
  }
  return color_image;
}