sequence: rather than a static divider in config, default to a heuristically generated one

app/config/config.cpp

@@ -110,7 +110,6 @@ void Config::SetDefaults()
   config_map_["DefaultSequenceAudioFrequency"] = 48000;
   config_map_["DefaultSequenceAudioLayout"] = QVariant::fromValue(static_cast<uint64_t>(AV_CH_LAYOUT_STEREO));
   config_map_["DefaultSequencePreviewFormat"] = PixelFormat::PIX_FMT_RGBA16F;
-  config_map_["DefaultSequencePreviewDivider"] = 3;
 
   // Online/offline settings
   config_map_["OnlinePixelFormat"] = PixelFormat::PIX_FMT_RGBA32F;

app/core.cpp

@@ -809,6 +809,11 @@ QList<uint64_t> Core::SupportedChannelLayouts()
   return channel_layouts;
 }
 
+QList<int> Core::SupportedDividers()
+{
+  return {1, 2, 3, 4, 6, 8, 12, 16};
+}
+
 QString Core::FrameRateToString(const rational &frame_rate)
 {
   return tr("%1 FPS").arg(frame_rate.toDouble());

app/core.h

@@ -178,6 +178,11 @@ public:
    */
   static QList<uint64_t> SupportedChannelLayouts();
 
+  /**
+   * @brief Return a list of supported dividers
+   */
+  static QList<int> SupportedDividers();
+
   /**
    * @brief Convert rational frame rate (i.e. flipped timebase) to a user-friendly string
    */

app/dialog/sequence/sequencedialogparametertab.cpp

@@ -90,7 +90,7 @@ SequenceDialogParameterTab::SequenceDialogParameterTab(Sequence* sequence, QWidg
   }
 
   // Set up preview dividers
-  divider_list_ = {1, 2, 3, 4, 6, 8, 12, 16};
+  divider_list_ = Core::SupportedDividers();
   foreach (int d, divider_list_) {
     QString name;
 

app/project/item/sequence/sequence.cpp

@@ -238,11 +238,14 @@ void Sequence::set_audio_params(const AudioParams &params)
 
 void Sequence::set_default_parameters()
 {
-  set_video_params(VideoParams(Config::Current()["DefaultSequenceWidth"].toInt(),
-                                        Config::Current()["DefaultSequenceHeight"].toInt(),
+  int width = Config::Current()["DefaultSequenceWidth"].toInt();
+  int height = Config::Current()["DefaultSequenceHeight"].toInt();
+
+  set_video_params(VideoParams(width,
+                               height,
                                Config::Current()["DefaultSequenceFrameRate"].value<rational>(),
                                static_cast<PixelFormat::Format>(Config::Current()["DefaultSequencePreviewFormat"].toInt()),
-                                        Config::Current()["DefaultSequencePreviewDivider"].toInt()));
+                               VideoParams::generate_auto_divider(width, height)));
   set_audio_params(AudioParams(Config::Current()["DefaultSequenceAudioFrequency"].toInt(),
                    Config::Current()["DefaultSequenceAudioLayout"].toULongLong(),
                    SampleFormat::kInternalFormat));
@@ -266,7 +269,7 @@ void Sequence::set_parameters_from_footage(const QList<Footage *> footage)
                                        vs->height(),
                                        vs->frame_rate().flipped(),
                                        static_cast<PixelFormat::Format>(Config::Current()["DefaultSequencePreviewFormat"].toInt()),
-                                                Config::Current()["DefaultSequencePreviewDivider"].toInt()));
+                                       VideoParams::generate_auto_divider(vs->width(), vs->height())));
           found_video_params = true;
         }
         break;
@@ -281,7 +284,7 @@ void Sequence::set_parameters_from_footage(const QList<Footage *> footage)
                                        is->height(),
                                        video_params().time_base(),
                                        static_cast<PixelFormat::Format>(Config::Current()["DefaultSequencePreviewFormat"].toInt()),
-                                                Config::Current()["DefaultSequencePreviewDivider"].toInt()));
+                                       VideoParams::generate_auto_divider(is->width(), is->height())));
         }
         break;
       case Stream::kAudio:

app/render/videoparams.cpp

@@ -22,6 +22,8 @@
 
 #include <QtMath>
 
+#include "core.h"
+
 OLIVE_NAMESPACE_ENTER
 
 VideoParams::VideoParams() :
@@ -48,6 +50,44 @@ VideoParams::VideoParams(const int &width, const int &height, const rational &ti
   calculate_effective_size();
 }
 
+int VideoParams::generate_auto_divider(qint64 width, qint64 height)
+{
+  // Arbitrary pixel count (from 640x360)
+  const int target_res = 230400;
+
+  qint64 megapixels = width * height;
+
+  double squared_divider = double(megapixels) / double(target_res);
+  double divider = qSqrt(squared_divider);
+
+  QList<int> supported_dividers = Core::SupportedDividers();
+
+  if (divider <= supported_dividers.first()) {
+    return supported_dividers.first();
+  } else if (divider >= supported_dividers.last()) {
+    return supported_dividers.last();
+  } else {
+    for (int i=1; i<supported_dividers.size(); i++) {
+      int prev_divider = supported_dividers.at(i-1);
+      int next_divider = supported_dividers.at(i);
+
+      if (divider >= prev_divider && divider <= next_divider) {
+        double prev_diff = qAbs(prev_divider - divider);
+        double next_diff = qAbs(next_divider - divider);
+
+        if (prev_diff < next_diff) {
+          return prev_divider;
+        } else {
+          return next_divider;
+        }
+      }
+    }
+
+    // "Safe" fallback
+    return 2;
+  }
+}
+
 bool VideoParams::operator==(const VideoParams &rhs) const
 {
   return width() == rhs.width()

app/render/videoparams.h

@@ -68,6 +68,8 @@ public:
     return format_;
   }
 
+  static int generate_auto_divider(qint64 width, qint64 height);
+
   bool is_valid() const;
 
   bool operator==(const VideoParams& rhs) const;

app/widget/viewer/footageviewer.cpp

@@ -88,14 +88,17 @@ void FootageViewerWidget::SetFootage(Footage *footage)
                                                  video_stream->height(),
                                                  video_stream->frame_rate().flipped(),
                                                  static_cast<PixelFormat::Format>(Config::Current()["DefaultSequencePreviewFormat"].toInt()),
-                                                          Config::Current()["DefaultSequencePreviewDivider"].toInt()));
+                                                 VideoParams::generate_auto_divider(video_stream->width(), video_stream->height())));
       NodeParam::ConnectEdge(video_node_->output(), viewer_node_->texture_input());
     } else {
-      viewer_node_->set_video_params(VideoParams(Config::Current()["DefaultSequenceWidth"].toInt(),
-                                     Config::Current()["DefaultSequenceHeight"].toInt(),
+      int width = Config::Current()["DefaultSequenceWidth"].toInt();
+      int height = Config::Current()["DefaultSequenceHeight"].toInt();
+
+      viewer_node_->set_video_params(VideoParams(width,
+                                                 height,
                                                  Config::Current()["DefaultSequenceFrameRate"].value<rational>(),
                                                  static_cast<PixelFormat::Format>(Config::Current()["DefaultSequencePreviewFormat"].toInt()),
-                                     Config::Current()["DefaultSequencePreviewDivider"].toInt()));
+                                                 VideoParams::generate_auto_divider(width, height)));
     }
 
     if (audio_stream) {