Tons of changes: can now simulate the mandelbrot for n iterations

Essentially using a naive threaded solution with a naive escape
routine for choosing whether a given location is actually in the
Mandelbrot set.  I think the colouring solution is quite unique: I use
a scaled quadratic function which ensures maximum colouring is given
to those with medium number of iterations.  I'll try a linear ratio
next.  Currently we start properly lagging at ~2^20 iterations, which
is why I'm looking for a better way to draw and compute escapes.

main.c

@@ -4,26 +4,174 @@
  * Description: Entrypoint of program
  */
 
+#include <math.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+
+#include <pthread.h>
+#include <unistd.h>
 
 #include <raylib.h>
 #include <raymath.h>
 
-#define WIDTH  512
-#define HEIGHT 512
+#define WIDTH       1024
+#define HEIGHT      1024
+#define MAX_THREADS 4
+uint64_t MAX_ITER = 1 << 2;
 
+Color cells[WIDTH * HEIGHT];
+pthread_t threads[MAX_THREADS];
+pthread_mutex_t mutex;
+
+#define SQUARE(a) (a * a)
+
+Color iter_to_colour(size_t iterations)
+{
+  if (iterations == MAX_ITER)
+    return BLACK;
+
+  // quadratic ratio
+  float ratio = Remap(iterations * (MAX_ITER - iterations), 0,
+                      SQUARE(MAX_ITER) / 4, 0, 1);
+
+  return (Color){255 * SQUARE(ratio), 10, 255 * SQUARE(1 - ratio), 255};
+}
+
+struct ThreadArg
+{
+  size_t x_0, x_t;
+  size_t y_0, y_t;
+  bool done;
+};
+
+void *generate_colours(void *state)
+{
+  struct ThreadArg *ptr = (struct ThreadArg *)state;
+  ptr->done             = false;
+  for (size_t i = ptr->x_0; i < ptr->x_t; ++i)
+    for (size_t j = ptr->y_0; j < ptr->y_t; ++j)
+    {
+      Vector2 init   = {Remap(i, 0, WIDTH, -1.5, 0.5),
+                        Remap(j, 0, HEIGHT, -1, 1)};
+      Vector2 update = {0};
+      size_t iterations;
+      for (iterations = 0;
+           iterations < MAX_ITER && Vector2LengthSqr(update) <= 4; ++iterations)
+      {
+        double new_x = SQUARE(update.x) - SQUARE(update.y) + init.x;
+        update.y     = (2 * update.x * update.y) + init.y;
+        update.x     = new_x;
+      }
+      Color c                = iter_to_colour(iterations);
+      cells[(i * WIDTH) + j] = c;
+    }
+  ptr->done = true;
+  return NULL;
+}
+
+void threads_start_render(struct ThreadArg *args)
+{
+  for (size_t i = 0; i < MAX_THREADS; ++i)
+    pthread_create(&threads[i], NULL, &generate_colours, &args[i]);
+}
+
+bool threads_done(struct ThreadArg *args)
+{
+  for (size_t i = 0; i < MAX_THREADS; ++i)
+    if (!args[i].done)
+      return false;
+  return true;
+}
+
+void threads_cancel_render(void)
+{
+  for (size_t i = 0; i < MAX_THREADS; ++i)
+    pthread_join(threads[i], NULL);
+}
+
+#define ZOOM_INC 0.3f
+#define MOVE_INC WIDTH / 50
 int main(void)
 {
   InitWindow(WIDTH, HEIGHT, "Mandelbrot simulation");
-  for (size_t ticks = 0; !WindowShouldClose(); ++ticks)
+  Camera2D camera = {0};
+  camera.zoom     = 1.0f;
+
+  Image img = GenImageColor(WIDTH, HEIGHT, BLACK);
+  ImageFormat(&img, PIXELFORMAT_UNCOMPRESSED_R8G8B8A8);
+  /* Texture2D texture = LoadTextureFromImage(img); */
+  UnloadImage(img);
+
+  SetTargetFPS(60);
+
+  pthread_mutex_init(&mutex, NULL);
+  struct ThreadArg args[] = {{0, WIDTH / 2, 0, HEIGHT, false},
+                             {WIDTH / 2, WIDTH, 0, HEIGHT / 4, false},
+                             {WIDTH / 2, WIDTH, HEIGHT / 4, HEIGHT / 2, false},
+                             {WIDTH / 2, WIDTH, HEIGHT / 2, HEIGHT, false}};
+  threads_start_render(args);
+
+  const size_t delta = 1;
+
+  for (size_t prev = 0, ticks = 0; !WindowShouldClose(); ++ticks)
   {
+    if (IsKeyPressed(KEY_UP) || IsKeyDown(KEY_UP))
+      camera.target.y -= MOVE_INC;
+    else if (IsKeyPressed(KEY_DOWN) || IsKeyDown(KEY_DOWN))
+      camera.target.y += MOVE_INC;
+    else if (IsKeyPressed(KEY_RIGHT) || IsKeyDown(KEY_RIGHT))
+      camera.target.x += MOVE_INC;
+    else if (IsKeyPressed(KEY_LEFT) || IsKeyDown(KEY_LEFT))
+      camera.target.x -= MOVE_INC;
+    else if (IsKeyPressed(KEY_N) || IsKeyDown(KEY_N))
+    {
+      camera.zoom += ZOOM_INC;
+      if (camera.zoom > 3.0f)
+        camera.zoom = 3.0f;
+    }
+    else if (IsKeyPressed(KEY_M) || IsKeyDown(KEY_M))
+    {
+      camera.zoom -= ZOOM_INC;
+      if (camera.zoom < 0.1f)
+        camera.zoom = 0.1f;
+    }
+    else if (IsKeyPressed(KEY_SPACE))
+    {
+      while (!threads_done(args))
+        continue;
+      memset(cells, 0, WIDTH * HEIGHT);
+      MAX_ITER *= 2;
+      threads_cancel_render();
+      threads_start_render(args);
+    }
+
+    if (ticks - prev > delta)
+    {
+      prev = ticks;
+      /* UpdateTexture(texture, cells); */
+    }
+
     BeginDrawing();
+    BeginMode2D(camera);
     ClearBackground(BLACK);
-    DrawText("Hello, world!", 100, 100, 50, RAYWHITE);
+    char iters[128];
+    sprintf(iters, "iterations=%lu", MAX_ITER);
+    /* DrawTexture(texture, 1024, 1024, BLUE); */
+    for (size_t i = 0; i < WIDTH; ++i)
+    {
+      for (size_t j = 0; j < HEIGHT; ++j)
+      {
+        DrawPixel(i, j, cells[(i * WIDTH) + j]);
+      }
+    }
+    DrawText(iters, 200, 200, 50, RAYWHITE);
+    EndMode2D();
     EndDrawing();
   }
+  threads_cancel_render();
+  /* UnloadTexture(texture); */
   CloseWindow();
   return 0;
 }