libcamera: Rename "shutter speed" to "exposure time"

The terms "shutter" and "shutter speed" are used through libcamera to
mean "exposure time". This is confusing, both due to "speed" being used
as "time" while it should be the inverse (i.e. a maximum speed should
correspond to the minimum time), and due to "shutter speed" and
"exposure time" being used in different places with the same meaning.

To improve clarity of the code base and the documentation, use "exposure
time" consistently to replace "shutter speed".

This rename highlighted another vocabulary issue in libcamera. The
ExposureModeHelper::splitExposure() function used to document that it
splits "exposure time into shutter time and gain". It has been reworded
to "split exposure into exposure time and gain". That is not entirely
satisfactory, as "exposure" has a defined meaning in photography (see
https://en.wikipedia.org/wiki/Exposure_(photography)) that is not
expressed as a duration. This issue if left to be addressed separately.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/src/ipa/ipu3/ipu3.cpp b/src/ipa/ipu3/ipu3.cpp
index 89c3192c..44c98cbf 100644
--- a/src/ipa/ipu3/ipu3.cpp
+++ b/src/ipa/ipu3/ipu3.cpp
@@ -112,7 +112,7 @@ namespace ipa::ipu3 {
  * blue gains to apply to generate a neutral grey frame overall.
  *
  * AGC is handled by calculating a histogram of the green channel to estimate an
- * analogue gain and shutter time which will provide a well exposed frame. A
+ * analogue gain and exposure time which will provide a well exposed frame. A
  * low-pass IIR filter is used to smooth the changes to the sensor to reduce
  * perceivable steps.
  *
@@ -215,13 +215,13 @@ void IPAIPU3::updateSessionConfiguration(const ControlInfoMap &sensorControls)
 
 	/*
 	 * When the AGC computes the new exposure values for a frame, it needs
-	 * to know the limits for shutter speed and analogue gain.
+	 * to know the limits for exposure time and analogue gain.
 	 * As it depends on the sensor, update it with the controls.
 	 *
-	 * \todo take VBLANK into account for maximum shutter speed
+	 * \todo take VBLANK into account for maximum exposure time
 	 */
-	context_.configuration.agc.minShutterSpeed = minExposure * context_.configuration.sensor.lineDuration;
-	context_.configuration.agc.maxShutterSpeed = maxExposure * context_.configuration.sensor.lineDuration;
+	context_.configuration.agc.minExposureTime = minExposure * context_.configuration.sensor.lineDuration;
+	context_.configuration.agc.maxExposureTime = maxExposure * context_.configuration.sensor.lineDuration;
 	context_.configuration.agc.minAnalogueGain = camHelper_->gain(minGain);
 	context_.configuration.agc.maxAnalogueGain = camHelper_->gain(maxGain);
 }