Increase precision of equality checking for color space transfer fns

BUG=skia:

Change-Id: I7b921d34539c071e63a47fb7151dc1dcdaa08cb3
Reviewed-on: https://skia-review.googlesource.com/9636
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

1 files changed, 25 insertions, 19 deletions

diff --git a/src/core/SkColorSpacePriv.h b/src/core/SkColorSpacePriv.h
index 0f5af2781e..4a63ddfa14 100644
--- a/src/core/SkColorSpacePriv.h
+++ b/src/core/SkColorSpacePriv.h
@@ -58,6 +58,12 @@ static inline bool color_space_almost_equal(float a, float b) {
     return SkTAbs(a - b) < 0.01f;
 }
 
+// Let's use a stricter version for transfer functions.  Worst case, these are encoded
+// in ICC format, which offers 16-bits of fractional precision.
+static inline bool transfer_fn_almost_equal(float a, float b) {
+    return SkTAbs(a - b) < 0.001f;
+}
+
 static inline bool is_zero_to_one(float v) {
     // Because we allow a value just barely larger than 1, the client can use an
     // entirely linear transfer function.
@@ -115,37 +121,37 @@ static inline bool is_valid_transfer_fn(const SkColorSpaceTransferFn& coeffs) {
 }
 
 static inline bool is_almost_srgb(const SkColorSpaceTransferFn& coeffs) {
-    return color_space_almost_equal(1.0f / 1.055f,   coeffs.fA) &&
-           color_space_almost_equal(0.055f / 1.055f, coeffs.fB) &&
-           color_space_almost_equal(1.0f / 12.92f,   coeffs.fC) &&
-           color_space_almost_equal(0.04045f,        coeffs.fD) &&
-           color_space_almost_equal(0.00000f,        coeffs.fE) &&
-           color_space_almost_equal(0.00000f,        coeffs.fF) &&
-           color_space_almost_equal(2.40000f,        coeffs.fG);
+    return transfer_fn_almost_equal(1.0f / 1.055f,   coeffs.fA) &&
+           transfer_fn_almost_equal(0.055f / 1.055f, coeffs.fB) &&
+           transfer_fn_almost_equal(1.0f / 12.92f,   coeffs.fC) &&
+           transfer_fn_almost_equal(0.04045f,        coeffs.fD) &&
+           transfer_fn_almost_equal(0.00000f,        coeffs.fE) &&
+           transfer_fn_almost_equal(0.00000f,        coeffs.fF) &&
+           transfer_fn_almost_equal(2.40000f,        coeffs.fG);
 }
 
 static inline bool is_almost_2dot2(const SkColorSpaceTransferFn& coeffs) {
-    return color_space_almost_equal(1.0f, coeffs.fA) &&
-           color_space_almost_equal(0.0f, coeffs.fB) &&
-           color_space_almost_equal(0.0f, coeffs.fE) &&
-           color_space_almost_equal(2.2f, coeffs.fG) &&
+    return transfer_fn_almost_equal(1.0f, coeffs.fA) &&
+           transfer_fn_almost_equal(0.0f, coeffs.fB) &&
+           transfer_fn_almost_equal(0.0f, coeffs.fE) &&
+           transfer_fn_almost_equal(2.2f, coeffs.fG) &&
            coeffs.fD <= 0.0f;
 }
 
 static inline bool is_almost_linear(const SkColorSpaceTransferFn& coeffs) {
     // OutputVal = InputVal ^ 1.0f
     const bool linearExp =
-           color_space_almost_equal(1.0f, coeffs.fA) &&
-           color_space_almost_equal(0.0f, coeffs.fB) &&
-           color_space_almost_equal(0.0f, coeffs.fE) &&
-           color_space_almost_equal(1.0f, coeffs.fG) &&
-           coeffs.fD <= 0.0f;
+            transfer_fn_almost_equal(1.0f, coeffs.fA) &&
+            transfer_fn_almost_equal(0.0f, coeffs.fB) &&
+            transfer_fn_almost_equal(0.0f, coeffs.fE) &&
+            transfer_fn_almost_equal(1.0f, coeffs.fG) &&
+            coeffs.fD <= 0.0f;
 
     // OutputVal = 1.0f * InputVal
     const bool linearFn =
-           color_space_almost_equal(1.0f, coeffs.fC) &&
-           color_space_almost_equal(0.0f, coeffs.fF) &&
-           coeffs.fD >= 1.0f;
+            transfer_fn_almost_equal(1.0f, coeffs.fC) &&
+            transfer_fn_almost_equal(0.0f, coeffs.fF) &&
+            coeffs.fD >= 1.0f;
 
     return linearExp || linearFn;
 }