Rewrite owf=auto code to be more general.

- Change the definition to be a bit more general. The mapping from resolution
  to owf frames stays mostly the same however, but should handle weird
  resolutions better.
- Move everything to config module.
- Fix handling of tiles. It had a bug where owf for tiles was always
  threads * 4/3 - 1. Works as intended now.

src/config.c

@@ -602,3 +602,59 @@ int config_validate(config *cfg)
   }
   return 1;
 }
+
+int size_of_wpp_ends(int threads)
+{
+  // Based on the shape of the area where all threads can't yet run in parallel.
+  return 4 * threads * threads - 2 * threads;
+}
+
+int config_set_owf_auto(config *cfg)
+{
+  if (cfg->wpp) {
+    // If wpp is on, select owf such that less than 15% of the
+    // frame is covered by the are threads can not work at the same time.
+    const int lcu_width = CEILDIV(cfg->width, LCU_WIDTH);
+    const int lcu_height = CEILDIV(cfg->height, LCU_WIDTH);
+    
+    // Find the largest number of threads per frame that satifies the
+    // the condition: wpp start/stop inefficiency takes up  less than 15%
+    // of frame area.
+    int threads_per_frame = 1;
+    const int wpp_treshold = lcu_width * lcu_height * 15 / 100;
+    while ((threads_per_frame + 1) * 2 < lcu_width &&
+           threads_per_frame + 1 < lcu_height &&
+           size_of_wpp_ends(threads_per_frame + 1) < wpp_treshold)
+    {
+      ++threads_per_frame;
+    }
+    
+    const int threads = (cfg->threads > 1 ? cfg->threads : 1);
+    const int frames = CEILDIV(threads, threads_per_frame);
+
+    // Convert from number of parallel frames to number of additional frames.
+    cfg->owf = CLIP(0, threads - 1, frames - 1);
+  } else {
+    // If wpp is not on, select owf such that there is enough
+    // tiles for twice the number of threads.
+
+    int tiles_per_frame = 1;
+    if (cfg->tiles_width_count > 0) {
+      tiles_per_frame *= cfg->tiles_width_count + 1;
+    }
+    if (cfg->tiles_height_count > 0) {
+      tiles_per_frame *= cfg->tiles_height_count + 1;
+    }
+    int threads = (cfg->threads > 1 ? cfg->threads : 1);
+    int frames = CEILDIV(threads * 2, tiles_per_frame);
+
+    // Limit number of frames to 1.25x the number of threads for the case
+    // where there is only 1 tile per frame.
+    frames = CLIP(1, threads * 4 / 3, frames);
+    cfg->owf = frames - 1;
+  }
+
+  fprintf(stderr, "--owf=auto value set to %d.\n", cfg->owf);
+  
+  return 1;
+}

src/config.h

@@ -89,5 +89,6 @@ int config_init(config *cfg);
 int config_destroy(config *cfg);
 int config_read(config *cfg,int argc, char *argv[]);
 int config_validate(config *cfg);
+int config_set_owf_auto(config *cfg);
 
 #endif

src/encmain.c

@@ -195,49 +195,9 @@ int main(int argc, char *argv[])
   }
 
   if (cfg->owf == -1) {
-    if (cfg->wpp) {
-      // If --owf=auto and wpp is on, select owf according to the lesser dimension.
-      // An ok rule for all intra seems to be to always have at least 4 wpp
-      // streams per thread. For a single frame that would mean that all threads
-      // are working for at least half of the frame.
-      int lcu_width = (cfg->width + LCU_WIDTH - 1) / LCU_WIDTH;
-      int lcu_height = (cfg->height + LCU_WIDTH - 1) / LCU_WIDTH;
-      int min_dimension = MIN(lcu_width, lcu_height);
-      int threads = (cfg->threads > 1 ? cfg->threads : 1);
-
-      // Find the largest number of threads per frame that satifies the
-      // the condition that there are 4 wpp streams per thread.
-      int threads_per_frame = 1;
-      while (min_dimension / (threads_per_frame + 1) >= 4) {
-        ++threads_per_frame;
-      }
-
-      // Get ceil(threads / threads_per_frame).
-      int frames = (threads + threads_per_frame - 1) / threads_per_frame;
-      cfg->owf = CLIP(0, threads - 1, frames - 1);
-    } else {
-      // If --owf=auto and wpp is not on, select owf such that there is enough
-      // tiles for twice the number of threads. That should make sure there are
-      // always some tiles to work on.
-
-      int tiles_per_frame = 1;
-      if (cfg->tiles_width_split != NULL) {
-        tiles_per_frame *= cfg->tiles_width_count;
-      }
-      if (cfg->tiles_height_split != NULL) {
-        tiles_per_frame *= cfg->tiles_height_count;
-      }
-      int threads = (cfg->threads > 1 ? cfg->threads : 1);
-      // Get ceil(threads * 2 / tiles_per_frame).
-      int frames = (threads * 2 + tiles_per_frame - 1) / tiles_per_frame;
-
-      // Limit number of frames to 1.25x the number of threads for the case
-      // where there is only 1 tile per frame.
-      frames = CLIP(1, threads * 4 / 3, frames);
-      cfg->owf = frames - 1;
+    if (!config_set_owf_auto(cfg)) {
+      goto exit_failure;
     }
-
-    fprintf(stderr, "--owf=auto value set to %d.\n", cfg->owf);
   }
 
   // Do more validation to make sure the parameters we have make sense.

src/global.h

@@ -124,6 +124,7 @@ typedef int16_t coefficient;
 #define CU_WIDTH_FROM_DEPTH(depth) (LCU_WIDTH >> depth)
 #define WITHIN(val, min_val, max_val) ((min_val) <= (val) && (val) <= (max_val))
 #define PU_INDEX(x_pu, y_pu) (((x_pu) % 2)  + 2 * ((y_pu) % 2))
+#define CEILDIV(x,y) (((x) + (y) - 1) / (y))
 
 #define LOG2_LCU_WIDTH 6
 // CU_TO_PIXEL = y * lcu_width * pic_width + x * lcu_width