feat: ipa: simple: awb: keep the gains across reconfigurationfedora-45-libcamera-sp12in2main

fixes the issue with green tinted photos on front camera

2 files changed, 66 insertions, 0 deletions

diff --git a/README.md b/README.md
index 0b3b0ca..880b7ca 100644
--- a/README.md
+++ b/README.md
@@ -36,6 +36,9 @@ which matches the kernel driver, where `OV02C10_REG_ANALOG_GAIN` runs from
 | Patch | Fixes |
 | --- | --- |
 | `patches/0001-libipa-camera_sensor-add-ov02c10.patch` | Adds the `ov02c10` `CameraSensorHelper` (gain `code/16`, black level `0x40` at 10 bits) and its `camera_sensor_properties` entry. |
+| `patches/0002-pipeline-simple-capture-bayer-order-from-mbus-code.patch` | Takes the capture device's Bayer order from the media bus code the pipeline reports instead of deriving it from the transform, so the rear camera streams. |
+| `patches/0003-ipa-simple-data-add-ov02c10-tuning-file.patch` | Adds `ov02c10.yaml`, enabling a CCM for the front camera. Hand-tuned, not measured against a colour target. |
+| `patches/0004-ipa-simple-awb-keep-gains-across-reconfiguration.patch` | Keeps the AWB gains over a reconfiguration, so a still captured right after one is not rendered with the sensor's raw white balance. |
 
 ## Versioning
 
diff --git a/patches/0004-ipa-simple-awb-keep-gains-across-reconfiguration.patch b/patches/0004-ipa-simple-awb-keep-gains-across-reconfiguration.patch
new file mode 100644
index 0000000..8bc5628
--- /dev/null
+++ b/patches/0004-ipa-simple-awb-keep-gains-across-reconfiguration.patch
@@ -0,0 +1,63 @@
+ipa: simple: awb: Keep the gains across a reconfiguration
+
+Awb::configure() resets the colour gains to 1.0, so every reconfiguration
+throws away the white balance the previous one had converged on and the first
+frames of the new configuration are rendered with the sensor's raw white
+balance.
+
+An application that reconfigures the camera and captures immediately therefore
+gets a tinted image, which is what taking a still picture with GNOME Snapshot
+does on the Surface Pro 12in: its preview is correctly balanced, and the
+picture it writes is heavily green, because the still is captured at a
+different resolution than the preview and the frame it keeps is the first one
+after the reconfiguration. Captured through PipeWire, the front camera needs
+two frames to converge:
+
+  frame  R/G    B/G
+      0  0.709  0.805
+      1  0.516  0.734
+      2  1.045  0.920
+     44  1.044  0.905
+
+The gains describe the scene in front of the sensor, not the stream
+configuration, so keep them and only initialise them once.
+
+--- a/src/ipa/simple/algorithms/awb.h
++++ b/src/ipa/simple/algorithms/awb.h
+@@ -29,6 +29,9 @@
+ 		     IPAFrameContext &frameContext,
+ 		     const SwIspStats *stats,
+ 		     ControlList &metadata) override;
++
++private:
++	bool initialised_ = false;
+ };
+ 
+ } /* namespace ipa::soft::algorithms */
+--- a/src/ipa/simple/algorithms/awb.cpp
++++ b/src/ipa/simple/algorithms/awb.cpp
+@@ -26,8 +26,24 @@
+ int Awb::configure(IPAContext &context,
+ 		   [[maybe_unused]] const IPAConfigInfo &configInfo)
+ {
++	/*
++	 * Initialise the gains on the first configuration only.
++	 *
++	 * A camera can be reconfigured while it keeps looking at the same
++	 * scene, which is what an application does when it captures a still
++	 * picture at a different resolution than the one its preview runs at.
++	 * Discarding the gains that the previous configuration converged on
++	 * then paints the first frames of the new one with the sensor's raw
++	 * white balance, and an application that captures straight away gets a
++	 * tinted picture. The gains are a property of the scene rather than of
++	 * the stream configuration, so carry them over.
++	 */
++	if (initialised_)
++		return 0;
++
+ 	auto &gains = context.activeState.awb.gains;
+ 	gains = { { 1.0, 1.0, 1.0 } };
++	initialised_ = true;
+ 
+ 	return 0;
+ }