libcamera: shaders: Add support for black level compensation

Add the ability to apply a int blacklevel subtraction against the
demosaiced data prior to application of colour correction data.

Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Robert Mader <robert.mader@collabora.com>
Tested-by: Hans de Goede <johannes.goede@oss.qualcomm.com> # ThinkPad T14s gen 6 (arm64) ov02c10 + X1c gen 12 ov08x40
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com> # Lenovo X13s
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/shaders/bayer_1x_packed.frag

@@ -66,6 +66,7 @@ uniform vec2 tex_bayer_first_red;
 
 uniform sampler2D tex_y;
 uniform mat3 ccm;
+uniform vec3 blacklevel;
 
 void main(void)
 {
@@ -213,6 +214,8 @@ void main(void)
 			vec3(patterns.y, C, patterns.x) :
 			vec3(patterns.wz, C));
 
+	rgb = rgb - blacklevel;
+
 	/*
 	 *   CCM is a 3x3 in the format
 	 *

src/libcamera/shaders/bayer_unpacked.frag

@@ -25,6 +25,7 @@ varying vec4            center;
 varying vec4            yCoord;
 varying vec4            xCoord;
 uniform mat3            ccm;
+uniform vec3            blacklevel;
 
 void main(void) {
     vec3 rgb;
@@ -108,6 +109,8 @@ void main(void) {
             vec3(PATTERN.w, C, PATTERN.z) :
             vec3(PATTERN.yx, C));
 
+    rgb = rgb - blacklevel;
+
     /*
      *   CCM is a 3x3 in the format
      *