Improve Pi Non-GPU-accel exposure (#148)

Changes exposure setters to accept a floating point input (rather than integer)
Updates the UI to change exposure in increments of 0.1 (rather than 1.0)
Updates quirky PI camera logic to use the raw_ interface with scaling/offset logic matching the GPU-accelerated pi3 camera logic from Declan.
Adds logic to disable auto-white-balance in the PI camera, which should yield more consistent vision processing results.

photon-server/src/main/java/org/photonvision/vision/camera/FileVisionSource.java

@@ -89,7 +89,7 @@ public class FileVisionSource implements VisionSource {
         }
 
         @Override
-        public void setExposure(int exposure) {}
+        public void setExposure(double exposure) {}
 
         @Override
         public void setBrightness(int brightness) {}

photon-server/src/main/java/org/photonvision/vision/camera/USBCameraSource.java

@@ -28,7 +28,6 @@ import org.photonvision.common.configuration.CameraConfiguration;
 import org.photonvision.common.configuration.ConfigManager;
 import org.photonvision.common.logging.LogGroup;
 import org.photonvision.common.logging.Logger;
-import org.photonvision.common.util.math.MathUtils;
 import org.photonvision.vision.frame.FrameProvider;
 import org.photonvision.vision.frame.provider.USBFrameProvider;
 import org.photonvision.vision.processes.VisionSource;
@@ -60,6 +59,18 @@ public class USBCameraSource implements VisionSource {
 
         usbCameraSettables = new USBCameraSettables(config);
         usbFrameProvider = new USBFrameProvider(cvSink, usbCameraSettables);
+
+        if (cameraQuirks.hasQuirk(CameraQuirk.PiCam)) {
+            // Pick a bunch of reasonable setting defaults for vision processing.
+            camera.getProperty("exposure_dynamic_framerate").set(0);
+            camera.getProperty("auto_exposure_bias").set(0);
+            camera.getProperty("image_stabilization").set(0);
+            camera.getProperty("iso_sensitivity").set(0);
+            camera.getProperty("iso_sensitivity_auto").set(0);
+            camera.getProperty("exposure_metering_mode").set(0);
+            camera.getProperty("scene_mode").set(0);
+            camera.getProperty("power_line_frequency").set(2);
+        }
     }
 
     @Override
@@ -80,17 +91,40 @@ public class USBCameraSource implements VisionSource {
             calculateFrameStaticProps();
         }
 
+        private int timeToPiCamV2RawExposure(double time_us) {
+            int retVal =
+                    (int) Math.round(time_us / 100.0); // PiCamV2 needs exposure time in units of 100us/bit
+            return Math.min(Math.max(retVal, 1), 10000); // Cap to allowable range for parameter
+        }
+
+        private double pctToExposureTimeUs(double pct_in) {
+            // Mirror the photonvision raspicam driver's algorithm for picking an exposure time
+            // from a 0-100% input
+            final double PADDING_LOW_US = 100;
+            final double PADDING_HIGH_US = 200;
+            return PADDING_LOW_US
+                    + (pct_in / 100.0) * ((1e6 / (double) camera.getVideoMode().fps) - PADDING_HIGH_US);
+        }
+
         @Override
-        public void setExposure(int exposure) {
+        public void setExposure(double exposure) {
             try {
+                int scaledExposure = 1;
                 if (cameraQuirks.hasQuirk(CameraQuirk.PiCam)) {
+                    camera.getProperty("white_balance_auto_preset").set(2); // Auto white-balance off
                     camera.getProperty("auto_exposure").set(1); // auto exposure off
-                    camera
-                            .getProperty("exposure_time_absolute")
-                            .set(MathUtils.safeDivide(10000, exposure)); // exposure time is a range, 0-10000
+
+                    scaledExposure =
+                            (int) Math.round(timeToPiCamV2RawExposure(pctToExposureTimeUs(exposure)));
+                    logger.debug("Setting camera raw exposure to " + Integer.toString(scaledExposure));
+                    camera.getProperty("raw_exposure_time_absolute").set(scaledExposure);
+                    camera.getProperty("raw_exposure_time_absolute").set(scaledExposure);
+
                 } else {
-                    camera.setExposureManual(exposure);
-                    camera.setExposureManual(exposure);
+                    scaledExposure = (int) Math.round(exposure);
+                    logger.debug("Setting camera exposure to " + Integer.toString(scaledExposure));
+                    camera.setExposureManual(scaledExposure);
+                    camera.setExposureManual(scaledExposure);
                 }
             } catch (VideoException e) {
                 logger.error("Failed to set camera exposure!", e);

photon-server/src/main/java/org/photonvision/vision/pipeline/CVPipelineSettings.java

@@ -39,7 +39,7 @@ public class CVPipelineSettings implements Cloneable {
     public ImageFlipMode inputImageFlipMode = ImageFlipMode.NONE;
     public ImageRotationMode inputImageRotationMode = ImageRotationMode.DEG_0;
     public String pipelineNickname = "New Pipeline";
-    public int cameraExposure = 50;
+    public double cameraExposure = 50;
     public int cameraBrightness = 50;
     public int cameraGain = 50;
     public int cameraVideoModeIndex = 0;

photon-server/src/main/java/org/photonvision/vision/processes/VisionSourceSettables.java

@@ -42,7 +42,7 @@ public abstract class VisionSourceSettables {
         return configuration;
     }
 
-    public abstract void setExposure(int exposure);
+    public abstract void setExposure(double exposure);
 
     public abstract void setBrightness(int brightness);