Auto Exposure:

  - Filter results down to the three best.
  - Changing exposure based on distance to the target or at random.
  - Plumb exposure through the debug framework.
  - Refactor into target finder.

Change-Id: Ia083f56859938bf0825472fd15d248c545f6f2fc
diff --git a/y2019/jevois/camera/image_stream.h b/y2019/jevois/camera/image_stream.h
index 578e24f..dc52bd5 100644
--- a/y2019/jevois/camera/image_stream.h
+++ b/y2019/jevois/camera/image_stream.h
@@ -39,6 +39,11 @@
 
   void ReadEvent() override { reader_->HandleFrame(); }
 
+  bool SetExposure(int abs_exp) {
+    return reader_->SetCameraControl(V4L2_CID_EXPOSURE_ABSOLUTE,
+                                     "V4L2_CID_EXPOSURE_ABSOLUTE", abs_exp);
+  }
+
  private:
   std::unique_ptr<Reader> reader_;
 };
diff --git a/y2019/jevois/camera/reader.h b/y2019/jevois/camera/reader.h
index 53d83c7..c5498fe 100644
--- a/y2019/jevois/camera/reader.h
+++ b/y2019/jevois/camera/reader.h
@@ -33,10 +33,11 @@
   }
   int fd() { return fd_; }
 
+  bool SetCameraControl(uint32_t id, const char *name, int value);
+
  private:
   void QueueBuffer(v4l2_buffer *buf);
   void InitMMap();
-  bool SetCameraControl(uint32_t id, const char *name, int value);
   void Init();
   void Start();
   void MMapBuffers();
diff --git a/y2019/vision/debug_viewer.cc b/y2019/vision/debug_viewer.cc
index 4f0e747..c8d8234 100644
--- a/y2019/vision/debug_viewer.cc
+++ b/y2019/vision/debug_viewer.cc
@@ -195,6 +195,12 @@
       }
     }
 
+    int desired_exposure;
+    if (target_finder_.TestExposure(results, &desired_exposure)) {
+      printf("Switching exposure to %d.\n", desired_exposure);
+      SetExposure(desired_exposure);
+    }
+
     // If the target list is not empty then we found a target.
     return !results.empty();
   }
diff --git a/y2019/vision/target_finder.cc b/y2019/vision/target_finder.cc
index 5860e5c..f6e5ac4 100644
--- a/y2019/vision/target_finder.cc
+++ b/y2019/vision/target_finder.cc
@@ -555,6 +555,12 @@
       filtered.emplace_back(updatable_result);
     }
   }
+
+  // Sort the target list so that the widest (ie closest) target is first.
+  sort(filtered.begin(), filtered.end(),
+       [](const IntermediateResult &a, const IntermediateResult &b)
+           -> bool { return a.target_width > b.target_width; });
+
   frame_count_++;
   if (!filtered.empty()) {
     valid_result_count_++;
@@ -570,5 +576,61 @@
   return filtered;
 }
 
+bool TargetFinder::TestExposure(const std::vector<IntermediateResult> &results,
+                                int *desired_exposure) {
+  // TODO(ben): Add these values to config file.
+  constexpr double low_dist = 0.8;
+  constexpr double high_dist = 2.0;
+  constexpr int low_exposure  = 60;
+  constexpr int mid_exposure  = 300;
+  constexpr int high_exposure = 500;
+
+  bool needs_update = false;
+  if (results.size() > 0) {
+    // We are seeing a target so lets use an exposure
+    // based on the distance to that target.
+    // First result should always be the closest target.
+    if (results[0].extrinsics.z < low_dist) {
+      *desired_exposure = low_exposure;
+    } else if (results[0].extrinsics.z > high_dist) {
+      *desired_exposure = high_exposure;
+    } else {
+      *desired_exposure = mid_exposure;
+    }
+    if (*desired_exposure != current_exposure_) {
+      needs_update = true;
+      current_exposure_ = *desired_exposure;
+    }
+  } else {
+    // We don't see a target, but part of the problem might
+    // be the exposure setting. Lets try changing it and see
+    // if things get better.
+    const int offset = std::rand() % 10;
+
+    // At random with 3/X probability try a higher or lower.
+    if (offset == 0) {
+      if (low_exposure != current_exposure_) {
+        needs_update = true;
+        current_exposure_ = low_exposure;
+        *desired_exposure = low_exposure;
+      }
+    } else if (offset == 1) {
+      if (mid_exposure != current_exposure_) {
+        needs_update = true;
+        current_exposure_ = mid_exposure;
+        *desired_exposure = mid_exposure;
+      }
+    } else if (offset == 2) {
+      if (high_exposure != current_exposure_) {
+        needs_update = true;
+        current_exposure_ = high_exposure;
+        *desired_exposure = high_exposure;
+      }
+    }
+    // If one of our cases is not hit don't change anything.
+  }
+  return needs_update;
+}
+
 }  // namespace vision
 }  // namespace y2019
diff --git a/y2019/vision/target_finder.h b/y2019/vision/target_finder.h
index ff4c3f7..0f1575c 100644
--- a/y2019/vision/target_finder.h
+++ b/y2019/vision/target_finder.h
@@ -71,6 +71,9 @@
       const std::vector<IntermediateResult> &results, uint64_t print_rate,
       bool verbose);
 
+  bool TestExposure(const std::vector<IntermediateResult> &results,
+                    int *desired_exposure);
+
   // Get the local overlay for debug if we are doing that.
   aos::vision::PixelLinesOverlay *GetOverlay() { return &overlay_; }
 
@@ -104,6 +107,8 @@
   // Counts for logging.
   size_t frame_count_;
   size_t valid_result_count_;
+
+  int current_exposure_ = 0;
 };
 
 }  // namespace vision
diff --git a/y2019/vision/target_geometry.cc b/y2019/vision/target_geometry.cc
index de76acb..212759a 100644
--- a/y2019/vision/target_geometry.cc
+++ b/y2019/vision/target_geometry.cc
@@ -254,6 +254,7 @@
       ::aos::math::NormalizeAngle(IR.backup_extrinsics.r1);
   IR.backup_extrinsics.r2 =
       ::aos::math::NormalizeAngle(IR.backup_extrinsics.r2);
+  IR.target_width = target.width();
 
   // Ok, let's look at how perpendicular the corners are.
   // Vector from the outside to inside along the top on the left.
diff --git a/y2019/vision/target_sender.cc b/y2019/vision/target_sender.cc
index 79e2ca4..db33419 100644
--- a/y2019/vision/target_sender.cc
+++ b/y2019/vision/target_sender.cc
@@ -262,7 +262,10 @@
     results = finder.FilterResults(results, 30, verbose);
     LOG(INFO) << "Results: " << results.size();
 
-    // TODO: Select top 3 (randomly?)
+    int desired_exposure;
+    if (finder.TestExposure(results, &desired_exposure)) {
+      camera0->SetExposure(desired_exposure);
+    }
 
     frc971::jevois::CameraFrame frame{};
 
diff --git a/y2019/vision/target_types.h b/y2019/vision/target_types.h
index aba9300..990debc 100644
--- a/y2019/vision/target_types.h
+++ b/y2019/vision/target_types.h
@@ -48,6 +48,8 @@
   TargetComponent left;
   TargetComponent right;
 
+  double width() const { return left.inside.DistanceTo(right.inside); }
+
   // Returns a target.  The resulting target is in meters with 0, 0 centered
   // between the upper inner corners of the two pieces of tape, y being up and x
   // being to the right.
@@ -109,6 +111,9 @@
 struct IntermediateResult {
   ExtrinsicParams extrinsics;
 
+  // Width of the target in pixels. Distance from inner most points.
+  double target_width;
+
   // Error from solver calulations.
   double solver_error;