color-lcms: add function to get params from parametric curvesets

Given a certain curveset, get_parametric_curveset_params() returns true
if the curveset contains parametric curves. Also, it returns the
parameters of the curveset (for each curve) and if the input should be
clamped or not.

This is not a generic function, it will specifically work for some well
behaved curveset. E.g. we return false if there are more than 3 curves
(one per color channel).

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>

libweston/color-lcms/color-curve-segments.c

@@ -572,3 +572,83 @@ curveset_print(cmsStage *stage, struct weston_log_scope *scope)
 		curve_print(data->TheCurves[i], scope);
 	}
 }
+
+bool
+get_parametric_curveset_params(struct weston_compositor *compositor,
+			       _cmsStageToneCurvesData *trc_data,
+			       cmsInt32Number *type,
+			       float curveset_params[3][10],
+			       bool *clamped_input)
+{
+	const cmsCurveSegment *seg, *seg0, *seg1, *seg2;
+	cmsInt32Number curve_types[3];
+	unsigned int i, j;
+
+	/* If there isn't a curve for each color channel, we define our curveset
+	 * as not being a parametric one. */
+	if (trc_data->nCurves != 3)
+		return false;
+
+	/* If at least one of the curves is being clamped to [0.0, 1.0], we
+	 * change clamped_input to true. Our expectation is that if one of the
+	 * curves is being clamped, all of them are. It makes no sense that it
+	 * gets clamped in a certain color channel and not in the others. */
+	*clamped_input = false;
+
+	for (i = 0; i < 3; i++) {
+		/* We handle curves with 1 or 3 segments. No more, no less. */
+		seg0 = cmsGetToneCurveSegment(0, trc_data->TheCurves[i]);
+		seg1 = cmsGetToneCurveSegment(1, trc_data->TheCurves[i]);
+		seg2 = cmsGetToneCurveSegment(2, trc_data->TheCurves[i]);
+
+		if (seg0 && !seg1) {
+			/* Case 1: we have a single segment (seg0).
+			 *
+			 * Ensure that the domain is (-inf, inf) and that the
+			 * seg type is not 0 (the type of sampled segments).
+			 */
+			if (!are_segment_breaks_equal(seg0->x0, -INFINITY) ||
+			    !are_segment_breaks_equal(seg0->x1, INFINITY) ||
+			    seg0->Type == 0)
+				return false;
+			seg = seg0;
+		} else if (seg0 && seg1 && seg2) {
+			/* Case 2: we have three segments. Clamped input.
+			 *
+			 * Ensure that the domain breaks are (-inf, 0.0],
+			 * (0.0, 1.0] and (1.0, inf] and that the 2nd segment
+			 * type is not 0 (the type of sampled segments).
+			 */
+			if (!are_segment_breaks_equal(seg0->x0, -INFINITY) ||
+			    !are_segment_breaks_equal(seg0->x1, 0.0) ||
+			    !are_segment_breaks_equal(seg1->x0, 0.0) ||
+			    !are_segment_breaks_equal(seg1->x1, 1.0) ||
+			    !are_segment_breaks_equal(seg2->x0, 1.0) ||
+			    !are_segment_breaks_equal(seg2->x1, INFINITY) ||
+			    seg1->Type == 0)
+				return false;
+			seg = seg1;
+			*clamped_input = true;
+		} else {
+			/* Neither 1 or 3 segments. So we don't define the
+			 * curveset as parametric. */
+			return false;
+		}
+
+		/* Copy the type and params from the segment that matters. We
+		 * don't use memcpy because we need to cast each cmsFloat64Number
+		 * to float. The precision loss doesn't matter. */
+		curve_types[i] = seg->Type;
+		for (j = 0; j < 10; j++)
+			curveset_params[i][j] = (float)seg->Params[j];
+	}
+
+	/* We only define our curveset as parametric when each of its curves are
+	 * of the same type for all the 3 channels. */
+	if (curve_types[0] != curve_types[1] || curve_types[0] != curve_types[2])
+		return false;
+
+	*type = curve_types[0];
+
+	return true;
+}

libweston/color-lcms/color-curve-segments.h

@@ -32,6 +32,13 @@
 
 #if HAVE_CMS_GET_TONE_CURVE_SEGMENT
 
+bool
+get_parametric_curveset_params(struct weston_compositor *compositor,
+			       _cmsStageToneCurvesData *trc_data,
+			       cmsInt32Number *type,
+			       float curveset_params[3][10],
+			       bool *clamped_input);
+
 void
 curveset_print(cmsStage *stage, struct weston_log_scope *scope);
 
@@ -47,6 +54,16 @@ join_powerlaw_curvesets(cmsContext context_id,
 
 # else /* HAVE_CMS_GET_TONE_CURVE_SEGMENT */
 
+static inline bool
+get_parametric_curveset_params(struct weston_compositor *compositor,
+			       _cmsStageToneCurvesData *trc_data,
+			       cmsInt32Number *type,
+			       float curveset_params[3][10],
+			       bool *clamped_input)
+{
+	return false;
+}
+
 static inline void
 curveset_print(cmsStage *stage, struct weston_log_scope *scope)
 {