restructure

mandelbrot.c

@@ -2,31 +2,35 @@
 #include <complex.h>
 #include <stdbool.h>
 
-int main(int argc, char *argv[]) {
-  SDL_Surface *screen = NULL;
-  if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
-    printf("Error: Could not initialize SDL: %s.\n", SDL_GetError());
-    exit(1);
-  }
-  screen = SDL_SetVideoMode(1280, 800, 32, SDL_SWSURFACE);
+/* Compute the out-coloring based on the iteration counter. */
+Uint32 outcolor(int it) {
+  return 0x00010001 * it;
+}
 
-  if (SDL_MUSTLOCK(screen)) {
-    SDL_LockSurface(screen);
+/* Compute the in-coloring. */
+Uint32 incolor() {
+  return 0x00000000; /* black */
+}
+
+void drawmandelbrot(SDL_Surface *surface) {
+  if (SDL_MUSTLOCK(surface)) {
+    SDL_LockSurface(surface);
   }
-  Uint32 *pixels = (Uint32 *) screen->pixels;
-  for (int i = 0; i < screen->w * screen->h; i++) {
-    int y = i / screen->w;
-    int x = i % screen->w;
+  Uint32 *pixels = (Uint32 *) surface->pixels;
+
+  for (int i = 0; i < surface->w * surface->h; i++) {
+    int y = i / surface->w;
+    int x = i % surface->w;
 
-    float complex c = ((3.0 * x / screen->w) - 2.0)
-        + I * ((2.0 * y / screen->h) - 1.0);
+    float complex c = ((3.0 * x / surface->w) - 2.0)
+        + I * ((2.0 * y / surface->h) - 1.0);
 
     bool diverges = false;
     float complex z = 0;
     int it;
     for (it = 1; it < 256; it++) {
       z = cpowf(z, 2) + c;
-      if (cabs(z) > 100) {
+      if (cabs(z) > 2) {
         diverges = true;
         break;
       }
@@ -34,28 +38,43 @@ int main(int argc, char *argv[]) {
 
     Uint32 color;
     if (diverges) {
-      color = 0x00010001 * it;
+      color = outcolor(it);
     } else {
-      color = 0x00000000;
+      color = incolor();
     }
 
     pixels[i] = color;
-    if (y % 10 == 0)
-      SDL_Flip(screen);
+
+    /* Update the screen every 10 lines. */
+    if (y % 10 == 0) {
+      SDL_Flip(surface);
+    }
   }
 
+  if (SDL_MUSTLOCK(surface)) {
+    SDL_UnlockSurface(surface);
+  }
+  SDL_Flip(surface);
+}
+
+int main(int argc, char *argv[]) {
+  /* Set up SDL. */
+  if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
+    fprintf(stderr, "Error: Could not initialize SDL: %s.\n", SDL_GetError());
+    exit(1);
+  }
+  SDL_Surface *screen = SDL_SetVideoMode(320, 240, 32, SDL_SWSURFACE);
+  
+  /* Do the mandelbrot. */
+  drawmandelbrot(screen);
+
   /* Save BMP */
   char *file = "mandelbrot.bmp";
   if (SDL_SaveBMP(screen, file) != 0) {
     fprintf(stderr, "Could not write %s!\n", file);
   }
 
-  if (SDL_MUSTLOCK(screen)) {
-    SDL_UnlockSurface(screen);
-  }
-  SDL_Flip(screen);
-
+  /* Quit. */
   SDL_Delay(20000);
-
   SDL_Quit();
 }