Fix drawing SkAnimatedImages with transparency

Bug: b/74195953

Do not use SkBlendMode::kSrc, which overwrites the pixels that were
already present. Instead, blend normally.

Change-Id: Ie6843c6278212fddddd0ba0ae292fdb5eaf2342e
Reviewed-on: https://skia-review.googlesource.com/112200
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Leon Scroggins <scroggo@google.com>

src/android/SkAnimatedImage.cpp

@@ -289,7 +289,6 @@ void SkAnimatedImage::onDraw(SkCanvas* canvas) {
         SkAutoCanvasRestore acr(canvas, fPostProcess);
         canvas->concat(fMatrix);
         SkPaint paint;
-        paint.setBlendMode(SkBlendMode::kSrc);
         paint.setFilterQuality(kLow_SkFilterQuality);
         canvas->drawBitmap(fActiveFrame.fBitmap, 0, 0, &paint);
     }

tests/AnimatedImageTest.cpp

@@ -15,6 +15,7 @@
 #include "SkColor.h"
 #include "SkData.h"
 #include "SkImageInfo.h"
+#include "SkPicture.h"
 #include "SkRefCnt.h"
 #include "SkSize.h"
 #include "SkString.h"
@@ -27,6 +28,50 @@
 #include <memory>
 #include <vector>
 
+DEF_TEST(AnimatedImage_scaled, r) {
+    if (GetResourcePath().isEmpty()) {
+        return;
+    }
+
+    const char* file = "images/alphabetAnim.gif";
+    auto data = GetResourceAsData(file);
+    if (!data) {
+        ERRORF(r, "Could not get %s", file);
+        return;
+    }
+
+    auto codec = SkAndroidCodec::MakeFromCodec(SkCodec::MakeFromData(data));
+    if (!codec) {
+        ERRORF(r, "Could not create codec for %s", file);
+        return;
+    }
+
+    // Force the drawable follow its special case that requires scaling.
+    auto size = codec->getInfo().dimensions();
+    size.set(size.width() - 5, size.height() - 5);
+    auto rect = SkIRect::MakeSize(size);
+    auto image = SkAnimatedImage::Make(std::move(codec), size, rect, nullptr);
+    if (!image) {
+        ERRORF(r, "Failed to create animated image for %s", file);
+        return;
+    }
+
+    // Clear a bitmap to non-transparent and draw to it. pixels that are transparent
+    // in the image should not replace the original non-transparent color.
+    SkBitmap bm;
+    bm.allocPixels(SkImageInfo::MakeN32Premul(size.width(), size.height()));
+    bm.eraseColor(SK_ColorBLUE);
+    SkCanvas canvas(bm);
+    image->draw(&canvas);
+    for (int i = 0; i < size.width();  ++i)
+    for (int j = 0; j < size.height(); ++j) {
+        if (*bm.getAddr32(i, j) == SK_ColorTRANSPARENT) {
+            ERRORF(r, "Erased color underneath!");
+            return;
+        }
+    }
+}
+
 DEF_TEST(AnimatedImage, r) {
     if (GetResourcePath().isEmpty()) {
         return;