Support decoding opaque to *premul

If a client requests unpremul or premul from an opaque SkCodec,
support it. The opaque image can be treated as any of them, though
it will be less efficient to draw than if the client had used
opaque.

Change the filling code (i.e. for incomplete images) to base its color on
the source alpha type. Prior to adding the support to decode opaque to
any, it was fine to use either source or dest (which would have yielded
the same result). If the client requests non-opaque, we do not want this
to switch the fill value from black to transparent. This also allows
simplifying the signatures for getFillValue and onGetFillValue.

In CodexTest, expect the same result when decoding opaque to *premul,
and compare to the opaque version.

BUG=skia:4616
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1641273003

Review URL: https://codereview.chromium.org/1641273003

1 files changed, 5 insertions, 6 deletions

diff --git a/include/codec/SkCodec.h b/include/codec/SkCodec.h
index 023ae51c49..edc8ec38fa 100644
--- a/include/codec/SkCodec.h
+++ b/include/codec/SkCodec.h
@@ -570,15 +570,14 @@ protected:
      * scanlines.  This allows the subclass to indicate what value to fill with.
      *
      * @param colorType Destination color type.
-     * @param alphaType Destination alpha type.
      * @return          The value with which to fill uninitialized pixels.
      *
      * Note that we can interpret the return value as an SkPMColor, a 16-bit 565 color,
      * an 8-bit gray color, or an 8-bit index into a color table, depending on the color
      * type.
      */
-    uint32_t getFillValue(SkColorType colorType, SkAlphaType alphaType) const {
-        return this->onGetFillValue(colorType, alphaType);
+    uint32_t getFillValue(SkColorType colorType) const {
+        return this->onGetFillValue(colorType);
     }
 
     /**
@@ -586,13 +585,13 @@ protected:
      * types that we support.  Note that for color types that do not use the full 32-bits,
      * we will simply take the low bits of the fill value.
      *
-     * kN32_SkColorType: Transparent or Black
+     * kN32_SkColorType: Transparent or Black, depending on the src alpha type
      * kRGB_565_SkColorType: Black
      * kGray_8_SkColorType: Black
      * kIndex_8_SkColorType: First color in color table
      */
-    virtual uint32_t onGetFillValue(SkColorType /*colorType*/, SkAlphaType alphaType) const {
-        return kOpaque_SkAlphaType == alphaType ? SK_ColorBLACK : SK_ColorTRANSPARENT;
+    virtual uint32_t onGetFillValue(SkColorType /*colorType*/) const {
+        return kOpaque_SkAlphaType == fSrcInfo.alphaType() ? SK_ColorBLACK : SK_ColorTRANSPARENT;
     }
 
     /**