SkPNGImageEncoder encodes all SkColorTypes

src/images/SkImageDecoder_libpng.cpp

Index: src/images/SkImageDecoder_libpng.cpp
diff --git a/src/images/SkImageDecoder_libpng.cpp b/src/images/SkImageDecoder_libpng.cpp
index a03ed10453f70d8053dc72bafee1bae8f8f5ae3f..fe72d8a9d881bf483138bf15b000680250e07550 100644
--- a/src/images/SkImageDecoder_libpng.cpp
+++ b/src/images/SkImageDecoder_libpng.cpp
@@ -827,7 +827,24 @@ private:
     typedef SkImageEncoder INHERITED;
 };
 
-bool SkPNGImageEncoder::onEncode(SkWStream* stream, const SkBitmap& bitmap, int /*quality*/) {
+bool SkPNGImageEncoder::onEncode(SkWStream* stream,
+                                 const SkBitmap& originalBitmap,
+                                 int /*quality*/) {
+    SkBitmap copy;
+    bool useCopy = false;

[scroggo, 2015/12/07 17:05:45]

I don't think this variable is necessary. Instead you could say something like:

SkBitmap bmStorage;
const SkBitmap* bitmap;

switch (ct) {
  // All your cases:
    bitmap = &originalBitmap;
    break;
  default:
    copyTo();
    bitmap = &bitmapStorage;
    break;
}

[hal.canary, 2015/12/07 21:34:38]

done.

+    switch (originalBitmap.colorType()) {
+        case kIndex_8_SkColorType:
+        case kN32_SkColorType:
+        case kARGB_4444_SkColorType:
+        case kRGB_565_SkColorType:
+            break;
+        default:

[scroggo, 2015/12/07 17:05:45]

So basically, what we are now supporting are:

- The other swizzle for N32 (the ironic thing here is that we might copy to the
opposite of what libpng wants - maybe add a FIXME?)
- Gray (again, this probably deserves a FIXME - we could actually encoded it to
gray, rather than copying)
- Alpha8 (not really sure what to do here, but maybe copying to N32 is as good
as anything? Android uses ALPHA_8 to mean gray, since gray did not exist when
they wanted it; maybe it would be interesting to abuse gray here? not sure...)

[hal.canary, 2015/12/07 21:34:38]

I added TODOs and assigned them to you.

+            if (originalBitmap.copyTo(&copy, kN32_SkColorType)) {
+                useCopy = true;
+            }
+    }
+    const SkBitmap& bitmap = useCopy ? copy : originalBitmap;
+
     SkColorType ct = bitmap.colorType();
 
     const bool hasAlpha = !bitmap.isOpaque();