test scalePixels and unpremul

Bug: skia:5733
Change-Id: I6c661408198f6a536e1e55ba01d976948446b8eb
Reviewed-on: https://skia-review.googlesource.com/70280
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>

1 files changed, 27 insertions, 2 deletions

diff --git a/src/core/SkPixmap.cpp b/src/core/SkPixmap.cpp
index bd6436e72a..5648405445 100644
--- a/src/core/SkPixmap.cpp
+++ b/src/core/SkPixmap.cpp
@@ -228,6 +228,10 @@ bool SkPixmap::erase(const SkColor4f& origColor, const SkIRect* subset) const {
     return true;
 }
 
+static void set_alphatype(SkPixmap* dst, const SkPixmap& src, SkAlphaType at) {
+    dst->reset(src.info().makeAlphaType(at), src.addr(), src.rowBytes());
+}
+
 bool SkPixmap::scalePixels(const SkPixmap& dst, SkFilterQuality quality) const {
     // Can't do anthing with empty src or dst
     if (this->width() <= 0 || this->height() <= 0 || dst.width() <= 0 || dst.height() <= 0) {
@@ -239,13 +243,34 @@ bool SkPixmap::scalePixels(const SkPixmap& dst, SkFilterQuality quality) const {
         return this->readPixels(dst);
     }
 
+    // Temp storage in case we need to edit the requested alphatypes
+    SkPixmap storage_src, storage_dst;
+    const SkPixmap* srcPtr = this;
+    const SkPixmap* dstPtr = &dst;
+
+    // Trick: if src and dst are both unpremul, we can give the correct result if we change both
+    //        to premul (or opaque), since the draw will not try to blend or otherwise interpret
+    //        the pixels' alpha.
+    //
+    // Today this works except in kHigh_SkFilterQuality, where we incorrectly clamp assuming the
+    // colors are premul. TODO: fix the HQ mode.
+    //
+    if (srcPtr->alphaType() == kUnpremul_SkAlphaType &&
+        dstPtr->alphaType() == kUnpremul_SkAlphaType)
+    {
+        set_alphatype(&storage_src, *this, kPremul_SkAlphaType);
+        set_alphatype(&storage_dst, dst,   kPremul_SkAlphaType);
+        srcPtr = &storage_src;
+        dstPtr = &storage_dst;
+    }
+
     SkBitmap bitmap;
-    if (!bitmap.installPixels(*this)) {
+    if (!bitmap.installPixels(*srcPtr)) {
         return false;
     }
     bitmap.setIsVolatile(true); // so we don't try to cache it
 
-    auto surface(SkSurface::MakeRasterDirect(dst.info(), dst.writable_addr(), dst.rowBytes()));
+    auto surface(SkSurface::MakeRasterDirect(dstPtr->info(), dstPtr->writable_addr(), dstPtr->rowBytes()));
     if (!surface) {
         return false;
     }