Anti-aliased line-drawing toy program

line-draw.cc

#include <vector>

#include <SDL3/SDL.h>
#include "SDL3_gfxPrimitives.h"

struct PointPair {
  SDL_Point begin, end;

  // Constructor required for emplace_back(); not POD.
  PointPair(SDL_Point a, SDL_Point b): begin(a), end(b) {}
};

int main() {
  SDL_Init(SDL_INIT_VIDEO);
  SDL_Window *w;
  SDL_Renderer *r;
  SDL_Point begin{}, end{};
  SDL_Event e;

  bool dragging = false, running = true;

  std::vector<PointPair> points;

  SDL_CreateWindowAndRenderer("Line Sketch", 800, 600, 0, &w, &r);

  while (running) {
    while (SDL_PollEvent(&e)) {
      switch (e.type) {
        case SDL_EVENT_KEY_DOWN:
          switch (e.key.key) {
            case SDLK_ESCAPE:
              running = false;
            break;
          }
        break;
        case SDL_EVENT_MOUSE_BUTTON_DOWN:
          if (e.button.button == SDL_BUTTON_LEFT)
          {
            dragging = true;

            begin.x = end.x = e.button.x;
            begin.y = end.y = e.button.y;
          }
        break;
        case SDL_EVENT_MOUSE_BUTTON_UP:
          if (e.button.button == SDL_BUTTON_LEFT)
          {
            dragging = false;
            points.emplace_back(begin, end);
          } else if (e.button.button == SDL_BUTTON_RIGHT) {
            points.clear();
          }
        break;
        case SDL_EVENT_MOUSE_MOTION:
          if (dragging)
          {
            end.x = e.motion.x;
            end.y = e.motion.y;
          }
        break;
        case SDL_EVENT_QUIT:
          running = false;
        break;
      }
    }

    SDL_SetRenderDrawColor(r, 0x0, 0x0, 0x0, 0x0);
    SDL_RenderClear(r);
    // SDL_SetRenderDrawColor(r, 0xFF, 0xFF, 0xFF, 0xFF);

    for (const auto& pair: points) {
      aalineColor(r, pair.begin.x, pair.begin.y, pair.end.x, pair.end.y, 0xFFFFFFFF);
    }

    if (dragging)
      aalineColor(r, begin.x, begin.y, end.x, end.y, 0xFFFFFFFF);

    // if (dragging)
    //   SDL_RenderLine(r, begin.x, begin.y, end.x, end.y);
    SDL_RenderPresent(r);
  }

  SDL_DestroyRenderer(r);
  SDL_DestroyWindow(w);
  SDL_Quit();
}