libcamera: controls: Add AE related controls

AeMeteringMode, AeConstraintMode, and AeExposureMode are new enum type
controls used to specify operating modes in the AE algorithm. All modes
may not be supported by all platforms.

ExposureValue is a new control used to set the log2 exposure adjustment
for the AE algorithm.

Lux is a new control that returns the current lux estimate.

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

src/libcamera/control_ids.yaml

@@ -25,6 +25,109 @@ controls:
 
         \sa AeEnable
 
+  # AeMeteringMode needs further attention:
+  # - Auto-generate max enum value.
+  # - Better handling of custom types.
+  - AeMeteringMode:
+      type: int32_t
+      description: |
+        Specify a metering mode for the AE algorithm to use. The metering
+        modes determine which parts of the image are used to determine the
+        scene brightness. Metering modes may be platform specific and not
+        all metering modes may be supported.
+      enum:
+        - name: MeteringCentreWeighted
+          value: 0
+          description: Centre-weighted metering mode.
+        - name: MeteringSpot
+          value: 1
+          description: Spot metering mode.
+        - name: MeteringMatrix
+          value: 2
+          description: Matrix metering mode.
+        - name: MeteringCustom
+          value: 3
+          description: Custom metering mode.
+        - name: MeteringModeMax
+          value: 3
+          description: Maximum allowed value (place any new values above here).
+
+  # AeConstraintMode needs further attention:
+  # - Auto-generate max enum value.
+  # - Better handling of custom types.
+  - AeConstraintMode:
+      type: int32_t
+      description: |
+        Specify a constraint mode for the AE algorithm to use. These determine
+        how the measured scene brightness is adjusted to reach the desired
+        target exposure. Constraint modes may be platform specific, and not
+        all constraint modes may be supported.
+      enum:
+        - name: ConstraintNormal
+          value: 0
+          description: Default constraint mode.
+            This mode aims to balance the exposure of different parts of the
+            image so as to reach a reasonable average level. However, highlights
+            in the image may appear over-exposed and lowlights may appear
+            under-exposed.
+        - name: ConstraintHighlight
+          value: 1
+          description: Highlight constraint mode.
+            This mode adjusts the exposure levels in order to try and avoid
+            over-exposing the brightest parts (highlights) of an image.
+            Other non-highlight parts of the image may appear under-exposed.
+        - name: ConstraintShadows
+          value: 2
+          description: Shadows constraint mode.
+            This mode adjusts the exposure levels in order to try and avoid
+            under-exposing the dark parts (shadows) of an image. Other normally
+            exposed parts of the image may appear over-exposed.
+        - name: ConstraintCustom
+          value: 3
+          description: Custom constraint mode.
+        - name: ConstraintModeMax
+          value: 3
+          description: Maximum allowed value (place any new values above here).
+
+  # AeExposureMode needs further attention:
+  # - Auto-generate max enum value.
+  # - Better handling of custom types.
+  - AeExposureMode:
+      type: int32_t
+      description: |
+        Specify an exposure mode for the AE algorithm to use. These specify
+        how the desired total exposure is divided between the shutter time
+        and the sensor's analogue gain. The exposure modes are platform
+        specific, and not all exposure modes may be supported.
+      enum:
+        - name: ExposureNormal
+          value: 0
+          description: Default exposure mode.
+        - name: ExposureShort
+          value: 1
+          description: Exposure mode allowing only short exposure times.
+        - name: ExposureLong
+          value: 2
+          description: Exposure mode allowing long exposure times.
+        - name: ExposureCustom
+          value: 3
+          description: Custom exposure mode.
+        - name: ExposureModeMax
+          value: 3
+          description: Maximum allowed value (place any new values above here).
+
+  - ExposureValue:
+      type: float
+      description: |
+        Specify an Exposure Value (EV) parameter. The EV parameter will only be
+        applied if the AE algorithm is currently enabled.
+
+        By convention EV adjusts the exposure as log2. For example
+        EV = [-2, -1, 0.5, 0, 0.5, 1, 2] results in an exposure adjustment
+        of [1/4x, 1/2x, 1/sqrt(2)x, 1x, sqrt(2)x, 2x, 4x].
+
+        \sa AeEnable
+
   - ExposureTime:
       type: int32_t
       description: |
@@ -55,6 +158,12 @@ controls:
         Specify a fixed contrast parameter. Normal contrast is given by the
         value 1.0; larger values produce images with more contrast.
 
+  - Lux:
+      type: float
+      description: |
+        Report an estimate of the current illuminance level in lux. The Lux
+        control can only be returned in metadata.
+
   - AwbEnable:
       type: bool
       description: |