port ok to SkPngEncoder

I can't tell you how excited I am to turn down the libpng settings...
anything that saves me a few seconds is a nice quality of life win.

This CL makes ok run in about half the time when producing .pngs.

Profile running `ok gm srgb png` before:
    10.59   s   16.5%    10.59   s          longest_match
    8.98    s   14.0%    8.98    s          png_setup_paeth_row
    8.93    s   13.9%    8.93    s          skia_png_write_find_filter
    7.75    s   12.1%    7.75    s          deflate_slow
    4.63    s    7.2%    4.63    s          std::wait_until(...) const
    959.00 ms    1.5%    959.00 ms          SkPathRef::validate() const
    935.00 ms    1.4%    935.00 ms          sk_to_srgb_hsw
    ...

After:
    2.35    s    8.7%    2.35    s          std::wait_until(...) const
    1.70    s    6.2%    1.70    s          longest_match
    1.19    s    4.4%    1.19    s          deflate_fast
    931.00 ms    3.4%    931.00 ms          SkPathRef::validate() const
    898.00 ms    3.3%    898.00 ms          sk_to_srgb_hsw
    ...

Change-Id: I425c30b2ecd97a0e4a4392779de6301db473ee47
Reviewed-on: https://skia-review.googlesource.com/15547
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Matt Sarett <msarett@google.com>

1 files changed, 16 insertions, 5 deletions

diff --git a/tools/ok_vias.cpp b/tools/ok_vias.cpp
index 20779cfd78..254e6b1a4f 100644
--- a/tools/ok_vias.cpp
+++ b/tools/ok_vias.cpp
@@ -8,6 +8,7 @@
 #include "SkImage.h"
 #include "SkOSFile.h"
 #include "SkPictureRecorder.h"
+#include "SkPngEncoder.h"
 #include "ok.h"
 #include <regex>
 
@@ -75,13 +76,23 @@ struct Png : Dst {
             return status;
         }
 
-        auto image = target->image();
-        sk_sp<SkData> png{image->encode()};
+        SkBitmap bm;
+        SkPixmap pm;
+        if (!target->image()->asLegacyBitmap(&bm, SkImage::kRO_LegacyBitmapMode) ||
+            !bm.peekPixels(&pm)) {
+            return Status::Failed;
+        }
 
         sk_mkdir(dir.c_str());
-        SkFILEWStream{(dir + "/" + src->name() + ".png").c_str()}
-            .write(png->data(), png->size());
-        return Status::OK;
+        SkFILEWStream dst{(dir + "/" + src->name() + ".png").c_str()};
+
+        SkPngEncoder::Options options;
+        options.fFilterFlags      = SkPngEncoder::FilterFlag::kNone;
+        options.fZLibLevel        = 1;
+        options.fUnpremulBehavior = pm.colorSpace() ? SkTransferFunctionBehavior::kRespect
+                                                    : SkTransferFunctionBehavior::kIgnore;
+        return SkPngEncoder::Encode(&dst, pm, options) ? Status::OK
+                                                       : Status::Failed;
     }
 
     sk_sp<SkImage> image() override {