Roll skia/third_party/skcms 03457e1..42c2748 (1 commits)

https://skia.googlesource.com/skcms.git/+log/03457e1..42c2748

2018-04-30 mtklein@chromium.org handle L==N-1 special case in PolyTF fit


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TBR=brianosman@google.com

Change-Id: Ie06b99b89bd8f1ac24efe9c6149450f4f9942009
Reviewed-on: https://skia-review.googlesource.com/124528
Commit-Queue: skcms-skia-autoroll <skcms-skia-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Reviewed-by: skcms-skia-autoroll <skcms-skia-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>

3 files changed, 20 insertions, 11 deletions

diff --git a/third_party/skcms/src/PolyTF.c b/third_party/skcms/src/PolyTF.c
index b7b34c3d36..89e0cc40ca 100644
--- a/third_party/skcms/src/PolyTF.c
+++ b/third_party/skcms/src/PolyTF.c
@@ -94,13 +94,18 @@ static bool fit_poly_tf(const skcms_Curve* curve, skcms_PolyTF* tf) {
     }
 
     // Detect linear baseline: (ax + b)^g + e --> ax ~~> Cx
-    if (baseline.g == 1 && baseline.d == 0 && baseline.b + baseline.e == 0) {
-        tf->A = 0;
-        tf->B = 0;
-        tf->C = baseline.a;
-        tf->D = INFINITY_;   // Always use Cx, never Ax^3+Bx^2+(1-A-B)
-        return true;
+    if (baseline.g == 1 && baseline.d == 0) {
+        if (baseline.b + baseline.e == 0) {
+            tf->A = 0;
+            tf->B = 0;
+            tf->C = baseline.a;
+            tf->D = INFINITY_;   // Always use Cx, never Ax^3+Bx^2+(1-A-B)
+            return true;
+        } else {
+            return false;  // Just like baseline.f != 0 above, can't represent this offset.
+        }
     }
+
     // This case is less likely, but also guards against divide by zero below.
     if (tf->D == 1) {
         tf->A = 0;
@@ -112,7 +117,11 @@ static bool fit_poly_tf(const skcms_Curve* curve, skcms_PolyTF* tf) {
     // If the curve isn't parametric and we approximated instead, this should be exact.
     const int L = (int)(tf->D * (N-1)) + 1;
 
-    // TODO: handle special case of L == N-1 to avoid /0 in Gauss-Newton.
+    if (L == N-1) {
+        // All points but one fit the linear section.
+        // We could connect the last point with a quadratic, but let's just be lazy.
+        return false;
+    }
 
     skcms_TransferFunction inv;
     if (!skcms_TransferFunction_invert(&baseline, &inv)) {
diff --git a/third_party/skcms/src/TransferFunction.c b/third_party/skcms/src/TransferFunction.c
index b9bbf0b59b..14a7898f00 100644
--- a/third_party/skcms/src/TransferFunction.c
+++ b/third_party/skcms/src/TransferFunction.c
@@ -295,9 +295,9 @@ bool skcms_ApproximateCurve(const skcms_Curve* curve,
             // Degenerate case with only two points in the nonlinear segment. Solve directly.
             tf.g = 1;
             tf.a = (skcms_eval_curve((N-1)*x_scale, curve) - skcms_eval_curve((N-2)*x_scale, curve))
-                 * (N-1);
-            tf.b = skcms_eval_curve((N-1)*x_scale, curve)
-                 - tf.a * (N-2) * x_scale;
+                 / x_scale;
+            tf.b = skcms_eval_curve((N-2)*x_scale, curve)
+                 - tf.a * (N-2)*x_scale;
             tf.e = 0;
         } else {
             // Start by guessing a gamma-only curve through the midpoint.
diff --git a/third_party/skcms/version.sha1 b/third_party/skcms/version.sha1
index 91b45a81ee..db34bce1c4 100755
--- a/third_party/skcms/version.sha1
+++ b/third_party/skcms/version.sha1
@@ -1 +1 @@
-03457e177feaa237d742a795a7c050c0476c2cb5
\ No newline at end of file
+42c27486c1ffb16339be984eb6dde03e714a2c65
\ No newline at end of file