tests/color_util: add TRANSFER_FN_IDENTITY

This will be useful to make a curve in a color pipeline pass-through
without needing to special-case skipping the curve.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

tests/color_util.c

@@ -167,6 +167,9 @@ apply_tone_curve(enum transfer_fn fn, float r)
 	float ret = 0;
 
 	switch(fn) {
+	case TRANSFER_FN_IDENTITY:
+		ret = r;
+		break;
 	case TRANSFER_FN_SRGB_EOTF:
 		ret = sRGB_EOTF(r);
 		break;

tests/color_util.h

@@ -58,6 +58,7 @@ struct lcmsMAT3 {
 };
 
 enum transfer_fn {
+	TRANSFER_FN_IDENTITY,
 	TRANSFER_FN_SRGB_EOTF,
 	TRANSFER_FN_SRGB_EOTF_INVERSE,
 	TRANSFER_FN_ADOBE_RGB_EOTF,