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-rw-r--r--bench/SkRasterPipelineBench.cpp22
-rw-r--r--src/core/SkSRGB.h30
-rw-r--r--src/opts/SkColorXform_opts.h43
-rw-r--r--tests/SRGBTest.cpp24
4 files changed, 48 insertions, 71 deletions
diff --git a/bench/SkRasterPipelineBench.cpp b/bench/SkRasterPipelineBench.cpp
index b3b87982af..0243940a10 100644
--- a/bench/SkRasterPipelineBench.cpp
+++ b/bench/SkRasterPipelineBench.cpp
@@ -139,24 +139,15 @@ static void SK_VECTORCALL srcover(SkRasterPipeline::Stage* st, size_t x,
st->next(x, r,g,b,a, dr,dg,db,da);
}
-static Sk4f clamp(const Sk4f& x) {
- return Sk4f::Min(Sk4f::Max(x, 0.0f), 255.0f);
-}
-
static void SK_VECTORCALL store_srgb(SkRasterPipeline::Stage* st, size_t x,
Sk4f r, Sk4f g, Sk4f b, Sk4f a,
Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
auto ptr = st->ctx<uint32_t*>() + x;
- r = clamp(sk_linear_to_srgb(r));
- g = clamp(sk_linear_to_srgb(g));
- b = clamp(sk_linear_to_srgb(b));
- a = clamp( 255.0f * a );
-
- ( SkNx_cast<int>(r)
- | SkNx_cast<int>(g) << 8
- | SkNx_cast<int>(b) << 16
- | SkNx_cast<int>(a) << 24 ).store(ptr);
+ ( sk_linear_to_srgb(r)
+ | sk_linear_to_srgb(g) << 8
+ | sk_linear_to_srgb(b) << 16
+ | Sk4f_round(255.0f*a) << 24).store(ptr);
}
static void SK_VECTORCALL store_srgb_tail(SkRasterPipeline::Stage* st, size_t x,
@@ -164,9 +155,8 @@ static void SK_VECTORCALL store_srgb_tail(SkRasterPipeline::Stage* st, size_t x,
Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
auto ptr = st->ctx<uint32_t*>() + x;
- auto rgba = sk_linear_to_srgb({r[0], g[0], b[0], 0});
- rgba = {rgba[0], rgba[1], rgba[2], 255.0f*a[0]};
- rgba = clamp(rgba);
+ Sk4i rgba = sk_linear_to_srgb({r[0], g[0], b[0], 0});
+ rgba = {rgba[0], rgba[1], rgba[2], (int)(255.0f * a[0] + 0.5f)};
SkNx_cast<uint8_t>(rgba).store(ptr);
}
diff --git a/src/core/SkSRGB.h b/src/core/SkSRGB.h
index d567a962d8..d3baa74631 100644
--- a/src/core/SkSRGB.h
+++ b/src/core/SkSRGB.h
@@ -14,37 +14,33 @@
*
* Current best practices:
* - for sRGB -> linear, lookup R,G,B in sk_linear_from_srgb;
- * - for linear -> sRGB, call sk_linear_to_srgb() for R,G,B, and round;
+ * - for linear -> sRGB, call sk_linear_to_srgb() for R,G,B;
* - the alpha channel is linear in both formats, needing at most *(1/255.0f) or *255.0f.
*
- * sk_linear_to_srgb()'s output requires rounding; it does not round for you.
- *
- * Given inputs in [0,1], sk_linear_to_srgb() will not underflow 0 but may overflow 255.
- * The overflow is small enough to be handled by rounding.
- * (But if you don't trust the inputs are in [0,1], you'd better clamp both sides immediately.)
- *
* sk_linear_to_srgb() will run a little faster than usual when compiled with SSE4.1+.
*/
extern const float sk_linear_from_srgb[256];
-static inline Sk4f sk_linear_to_srgb(const Sk4f& x) {
+static inline Sk4i sk_linear_to_srgb(const Sk4f& x) {
// Approximation of the sRGB gamma curve (within 1 when scaled to 8-bit pixels).
- // For 0.00000f <= x < 0.00349f, 12.92 * x
- // For 0.00349f <= x <= 1.00000f, 0.679*(x.^0.5) + 0.423*x.^(0.25) - 0.101
- // Note that 0.00349 was selected because it is a point where both functions produce the
- // same pixel value when rounded.
+ //
+ // Tuned by brute force to minimize the number of bytes that fail to round trip,
+ // here 0 (of 256), and then to minimize the number of points halfway between bytes
+ // (in linear space) that fail to hit the right byte, here 131 (of 255), and to
+ // minimize the number of monotonicity regressions over the range [0,1], here 0.
+
auto rsqrt = x.rsqrt(),
sqrt = rsqrt.invert(),
ftrt = rsqrt.rsqrt();
- auto lo = (12.92f * 255.0f) * x;
+ auto lo = (13.0471f * 255.0f) * x;
- auto hi = (-0.101115084998961f * 255.0f) +
- (+0.678513029959381f * 255.0f) * sqrt +
- (+0.422602055039580f * 255.0f) * ftrt;
+ auto hi = (-0.0974983f * 255.0f)
+ + (+0.687999f * 255.0f) * sqrt
+ + (+0.412999f * 255.0f) * ftrt;
- return (x < 0.00349f).thenElse(lo, hi);
+ return SkNx_cast<int>( (x < 0.0048f).thenElse(lo, hi) );
}
#endif//SkSRGB_DEFINED
diff --git a/src/opts/SkColorXform_opts.h b/src/opts/SkColorXform_opts.h
index 3bb11f5599..af683e105f 100644
--- a/src/opts/SkColorXform_opts.h
+++ b/src/opts/SkColorXform_opts.h
@@ -16,20 +16,20 @@
namespace SK_OPTS_NS {
-static Sk4f linear_to_2dot2(const Sk4f& x) {
+static Sk4f clamp_0_1(const Sk4f& x) {
+ // The order of the arguments is important here. We want to make sure that NaN
+ // clamps to zero. Note that max(NaN, 0) = 0, while max(0, NaN) = NaN.
+ return Sk4f::Min(Sk4f::Max(x, 0.0f), 1.0f);
+}
+
+static Sk4i linear_to_2dot2(const Sk4f& x) {
// x^(29/64) is a very good approximation of the true value, x^(1/2.2).
auto x2 = x.rsqrt(), // x^(-1/2)
x32 = x2.rsqrt().rsqrt().rsqrt().rsqrt(), // x^(-1/32)
x64 = x32.rsqrt(); // x^(+1/64)
// 29 = 32 - 2 - 1
- return 255.0f * x2.invert() * x32 * x64.invert();
-}
-
-static Sk4f clamp_0_to_255(const Sk4f& x) {
- // The order of the arguments is important here. We want to make sure that NaN
- // clamps to zero. Note that max(NaN, 0) = 0, while max(0, NaN) = NaN.
- return Sk4f::Min(Sk4f::Max(x, 0.0f), 255.0f);
+ return Sk4f_round(255.0f * x2.invert() * x32 * x64.invert());
}
enum DstGamma {
@@ -79,21 +79,18 @@ static void color_xform_RGB1(void* dst, const uint32_t* src, int len,
auto store_4 = [&dstReds, &dstGreens, &dstBlues, &dst, &dstTables] {
if (kSRGB_DstGamma == kDstGamma || k2Dot2_DstGamma == kDstGamma) {
- Sk4f (*linear_to_curve)(const Sk4f&) =
+ Sk4i (*linear_to_curve)(const Sk4f&) =
(kSRGB_DstGamma == kDstGamma) ? sk_linear_to_srgb : linear_to_2dot2;
- dstReds = linear_to_curve(dstReds);
- dstGreens = linear_to_curve(dstGreens);
- dstBlues = linear_to_curve(dstBlues);
+ auto reds = linear_to_curve(clamp_0_1(dstReds));
+ auto greens = linear_to_curve(clamp_0_1(dstGreens));
+ auto blues = linear_to_curve(clamp_0_1(dstBlues));
- dstReds = clamp_0_to_255(dstReds);
- dstGreens = clamp_0_to_255(dstGreens);
- dstBlues = clamp_0_to_255(dstBlues);
- auto rgba = (Sk4f_round(dstReds) << SK_R32_SHIFT)
- | (Sk4f_round(dstGreens) << SK_G32_SHIFT)
- | (Sk4f_round(dstBlues) << SK_B32_SHIFT)
- | (Sk4i{ 0xFF << SK_A32_SHIFT});
+ auto rgba = (reds << SK_R32_SHIFT)
+ | (greens << SK_G32_SHIFT)
+ | (blues << SK_B32_SHIFT)
+ | (Sk4i{0xFF} << SK_A32_SHIFT);
rgba.store((uint32_t*) dst);
dst = SkTAddOffset<void>(dst, 4 * sizeof(uint32_t));
@@ -155,15 +152,13 @@ static void color_xform_RGB1(void* dst, const uint32_t* src, int len,
auto dstPixel = rXgXbX*r + rYgYbY*g + rZgZbZ*b;
if (kSRGB_DstGamma == kDstGamma || k2Dot2_DstGamma == kDstGamma) {
- Sk4f (*linear_to_curve)(const Sk4f&) =
+ Sk4i (*linear_to_curve)(const Sk4f&) =
(kSRGB_DstGamma == kDstGamma) ? sk_linear_to_srgb : linear_to_2dot2;
- dstPixel = linear_to_curve(dstPixel);
-
- dstPixel = clamp_0_to_255(dstPixel);
+ auto pixel = linear_to_curve(clamp_0_1(dstPixel));
uint32_t rgba;
- SkNx_cast<uint8_t>(Sk4f_round(dstPixel)).store(&rgba);
+ SkNx_cast<uint8_t>(pixel).store(&rgba);
rgba |= 0xFF000000;
*((uint32_t*) dst) = SkSwizzle_RGBA_to_PMColor(rgba);
dst = SkTAddOffset<void>(dst, sizeof(uint32_t));
diff --git a/tests/SRGBTest.cpp b/tests/SRGBTest.cpp
index 65bfc59b42..43ec02700f 100644
--- a/tests/SRGBTest.cpp
+++ b/tests/SRGBTest.cpp
@@ -11,28 +11,24 @@
#include <math.h>
static uint8_t linear_to_srgb(float l) {
- // Round float to int, truncate that to uint8_t.
- return (uint8_t)Sk4f_round( sk_linear_to_srgb(Sk4f{l}) )[0];
+ return (uint8_t)sk_linear_to_srgb(Sk4f{l})[0];
}
DEF_TEST(sk_linear_to_srgb, r) {
- // Should map 0 -> 0 and 1 -> 1.
- REPORTER_ASSERT(r, 0 == linear_to_srgb(0.0f));
- REPORTER_ASSERT(r, 255 == linear_to_srgb(1.0f));
+ // All bytes should round trip.
+ for (int i = 0; i < 256; i++) {
+ int actual = linear_to_srgb(sk_linear_from_srgb[i]);
+ if (i != actual) {
+ ERRORF(r, "%d -> %d\n", i, actual);
+ }
+ }
// Should be monotonic between 0 and 1.
- // We don't bother checking denorm values.
- int tolerated_regressions = 0;
-#if defined(SK_ARM_HAS_NEON)
- // Values around 0.166016 are usually 72 but drop briefly (41 floats) down to 71.
- tolerated_regressions = 1;
-#endif
uint8_t prev = 0;
- for (float f = FLT_MIN; f <= 1.0f; ) {
+ for (float f = FLT_MIN; f <= 1.0f; ) { // We don't bother checking denorm values.
uint8_t srgb = linear_to_srgb(f);
- REPORTER_ASSERT(r, srgb >= prev || tolerated_regressions > 0);
- if (srgb < prev) { tolerated_regressions--; }
+ REPORTER_ASSERT(r, srgb >= prev);
prev = srgb;
union { float flt; uint32_t bits; } pun = { f };
generated by cgit v1.2.3 (git 2.39.1) at 2024-05-28 22:53:50 +0000