+LICENSE

After the so-called "avalanche", where the fractal has finished
forming as there are no more candidates for toppling, we no longer
need the threads to be working.  As an intensive operation, it makes
no sense to continue processing when we are sure there is no further
dynamic behaviour possible.

Using a tick based solution, every DELTA ticks we check if the
avalanche is completed.  If so, we clean up all the threads AND ensure
that we no longer need to be checking for avalanches.

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2023 Aryadev Chavali
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Makefile

@@ -1,7 +1,7 @@
 CC=gcc
 CFLAGS=-Wall -Wextra -pedantic -ggdb -fsanitize=address
 LIBS=-lm -lraylib
-OBJECTS=main.o
+OBJECTS=files.o main.o
 OUT=sandpile.out
 ARGS=
 

files.c

@@ -0,0 +1,50 @@
+/* file-handler.c
+ * Created: 2023-08-25
+ * Author: Aryadev Chavali
+ * Description: Implementations of writing and loading state->from files
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include <stb/stb_image_write.h>
+
+#include "./lib.h"
+
+#define CHUNK_SIZE 1024
+
+bool write_to_png(state_t *state, const char *filepath)
+{
+  unsigned char *image_data =
+      calloc(3 * state->dwidth * state->dwidth, sizeof(*image_data));
+
+  size_t image_ptr = 0;
+
+  for (size_t i = 0; i < state->dwidth; ++i)
+    for (size_t j = 0; j < state->dwidth; ++j, image_ptr += 3)
+    {
+      unsigned char colour[3] = {0};
+      uint64_t sandpile       = state->data[(i * state->dwidth) + j];
+      if (sandpile == 0)
+        colour[0] = colour[1] = colour[2] = 0;
+      else if (sandpile == 1)
+        colour[0] = colour[2] = 255;
+      else if (sandpile == 2)
+      {
+        colour[0] = 255;
+        colour[1] = colour[2] = 20;
+      }
+      else if (sandpile == 3)
+      {
+        colour[2] = 255;
+        colour[0] = colour[1] = 20;
+      }
+
+      memcpy(image_data + image_ptr, colour, sizeof(*colour) * 3);
+    }
+
+  stbi_write_png(filepath, state->dwidth, state->dwidth, 3, image_data,
+                 3 * state->dwidth);
+  free(image_data);
+  return true;
+}

lib.h

@@ -2,21 +2,22 @@
 #define LIB_H
 
 #include <stdbool.h>
+#include <stdint.h>
 #include <stdlib.h>
 
 typedef struct State
 {
   // Sandpiles
-  unsigned char *data;
+  uint64_t *data;
   size_t dwidth;
 
   size_t window_len;
-  int multiplier;
+  double multiplier;
 
   bool thread_alive;
+  uint64_t payload;
 } state_t;
 
-bool load_from_file(state_t *state, const char *filepath);
-bool write_to_file(state_t *state, const char *filepath);
+bool write_to_png(state_t *state, const char *filepath);
 
 #endif

main.c

@@ -15,14 +15,23 @@
 
 #include "./lib.h"
 
-void step(state_t *state)
+struct StepArg
 {
-  state->data[((state->dwidth / 2) * state->dwidth) + (state->dwidth / 2)]++;
-  for (size_t i = 0; i < state->dwidth; ++i)
-    for (size_t j = 0; j < state->dwidth; ++j)
+  state_t *state;
+  size_t x_min, x_max, y_min, y_max;
+};
+
+pthread_mutex_t mutex;
+
+void step(struct StepArg arg)
+{
+  state_t *state = arg.state;
+  for (size_t i = arg.x_min; i < arg.x_max; ++i)
+    for (size_t j = arg.y_min; j < arg.y_max; ++j)
       if (state->data[(i * state->dwidth) + j] >= 4)
       {
-        unsigned char *references[] = {
+        pthread_mutex_lock(&mutex);
+        uint64_t *references[] = {
             (j == 0) ? NULL : &state->data[((i)*state->dwidth) + j - 1],
             (i == state->dwidth - 1)
                 ? NULL
@@ -33,36 +42,65 @@ void step(state_t *state)
             (i == 0) ? NULL : &state->data[((i - 1) * state->dwidth) + j]};
         for (size_t k = 0; k < 4; ++k)
           if (references[k])
-            *references[k] += 1;
-        state->data[(i * state->dwidth) + j] = 0;
+            *references[k] += state->data[(i * state->dwidth) + j] / 4;
+        state->data[(i * state->dwidth) + j] %= 4;
+        pthread_mutex_unlock(&mutex);
       }
 }
 
 void *compute_thread(void *input)
 {
-  state_t *state = input;
-  while (state->thread_alive)
-    step(state);
+  struct StepArg *arg = input;
+  while (arg->state->thread_alive)
+    step(*arg);
   return NULL;
 }
 
-int main(void)
+bool completed_avalanche(state_t *state)
 {
-  state_t state    = {NULL, 512, 512, 0, true};
+  for (size_t i = 0; i < state->dwidth; ++i)
+    for (size_t j = 0; j < state->dwidth; ++j)
+      if (state->data[(i * state->dwidth) + j] >= 4)
+        return false;
+  return true;
+}
+
+int main(int argc, char *argv[])
+{
+  // Setup "default" state
+  state_t state    = {NULL, 512, 512, 0, true, pow(2, 16)};
   state.data       = calloc(state.dwidth * state.dwidth, sizeof(*state.data));
   state.multiplier = state.window_len / state.dwidth;
+  state.data[(state.dwidth * state.dwidth / 2) + (state.dwidth / 2)] =
+      state.payload;
 
   const float zoom = 0.125f;
   Camera2D camera  = {0};
   camera.zoom      = 1.0f;
 
-  pthread_t step_thread;
-  pthread_create(&step_thread, NULL, &compute_thread, &state);
+  // Initialise mutex for threads to use
+  pthread_mutex_init(&mutex, NULL);
+  // Setup quadrants (for threads)
+  struct StepArg a = {&state, 0, state.dwidth / 2, 0, state.dwidth / 2};
+  struct StepArg b = {&state, 0, state.dwidth / 2, state.dwidth / 2,
+                      state.dwidth};
+  struct StepArg c = {&state, state.dwidth / 2, state.dwidth, 0,
+                      state.dwidth / 2};
+  struct StepArg d = {&state, state.dwidth / 2, state.dwidth, state.dwidth / 2,
+                      state.dwidth};
+  // Setup threads
+  pthread_t thread_a, thread_b, thread_c, thread_d;
+  pthread_create(&thread_a, NULL, &compute_thread, &a);
+  pthread_create(&thread_b, NULL, &compute_thread, &b);
+  pthread_create(&thread_c, NULL, &compute_thread, &c);
+  pthread_create(&thread_d, NULL, &compute_thread, &d);
 
   InitWindow(state.window_len, state.window_len, "Abelian sand pile");
   SetTargetFPS(60);
 
-  while (!WindowShouldClose())
+  const int DELTA = 100;
+  bool done       = false;
+  for (uint64_t ticks = 0, prev_ticks = 0; !WindowShouldClose(); ++ticks)
   {
     if (IsKeyPressed(KEY_UP) || IsKeyDown(KEY_UP))
     {
@@ -85,6 +123,21 @@ int main(void)
         camera.zoom = zoom;
     }
 
+    if (ticks - prev_ticks > DELTA && !done)
+    {
+      printf("Checking if avalanche is complete!\n");
+      if (completed_avalanche(&state))
+      {
+        state.thread_alive = false;
+        pthread_join(thread_a, NULL);
+        pthread_join(thread_b, NULL);
+        pthread_join(thread_c, NULL);
+        pthread_join(thread_d, NULL);
+        done = true;
+      }
+      prev_ticks = ticks;
+    }
+
     if (IsMouseButtonDown(MOUSE_BUTTON_LEFT))
     {
       Vector2 delta = Vector2Scale(GetMouseDelta(), -1.0f / camera.zoom);
@@ -97,16 +150,16 @@ int main(void)
     for (size_t i = 0; i < state.dwidth; ++i)
       for (size_t j = 0; j < state.dwidth; ++j)
       {
-        Color c                = {0};
-        unsigned char sandpile = state.data[(i * state.dwidth) + j];
+        Color c           = {0};
+        uint64_t sandpile = state.data[(i * state.dwidth) + j];
         if (sandpile == 0)
           c = BLACK;
         else if (sandpile == 1)
-          c = GREEN;
+          c = MAGENTA;
         else if (sandpile == 2)
-          c = PURPLE;
+          c = RED;
         else if (sandpile == 3)
-          c = YELLOW;
+          c = BLUE;
 
         DrawRectangle(i * state.multiplier, j * state.multiplier,
                       state.multiplier, state.multiplier, c);
@@ -116,7 +169,16 @@ int main(void)
   }
 
   if (state.thread_alive)
-    pthread_cancel(step_thread);
+  {
+    state.thread_alive = false;
+    pthread_join(thread_a, NULL);
+    pthread_join(thread_b, NULL);
+    pthread_join(thread_c, NULL);
+    pthread_join(thread_d, NULL);
+  }
+
   CloseWindow();
+  write_to_png(&state, "data.png");
+  free(state.data);
   return 0;
 }