SkImage-only bitmap patterns

Source/platform/graphics/ImagePattern.cpp

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "platform/graphics/ImagePattern.h"
+
+#include "platform/graphics/Image.h"
+#include "platform/graphics/skia/SkiaUtils.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkImage.h"
+#include "third_party/skia/include/core/SkPicture.h"
+#include "third_party/skia/include/core/SkPictureRecorder.h"
+#include "third_party/skia/include/core/SkShader.h"
+
+namespace blink {
+
+PassRefPtr<ImagePattern> ImagePattern::create(PassRefPtr<Image> image, RepeatMode repeatMode)
+{
+    return adoptRef(new ImagePattern(image, repeatMode));
+}
+
+ImagePattern::ImagePattern(PassRefPtr<Image> image, RepeatMode repeatMode)
+    : Pattern(repeatMode)
+    , m_tileImage(image->imageForCurrentFrame())
+{
+    if (m_tileImage) {
+        // TODO(fmalita): mechanism to extract the actual SkImageInfo from an SkImage?
+        const SkImageInfo info =
+            SkImageInfo::MakeN32Premul(m_tileImage->width(), m_tileImage->height());
+        adjustExternalMemoryAllocated(info.getSafeSize(info.minRowBytes()));
+    }
+}
+
+PassRefPtr<SkShader> ImagePattern::createShader()
+{
+    if (!m_tileImage)
+        return adoptRef(SkShader::CreateColorShader(SK_ColorTRANSPARENT));
+
+    SkMatrix localMatrix = affineTransformToSkMatrix(m_patternSpaceTransformation);
+
+    if (isRepeatXY()) {
+        return adoptRef(m_tileImage->newShader(SkShader::kRepeat_TileMode,
+            SkShader::kRepeat_TileMode, &localMatrix));
+    }
+
+    // Skia does not have a "draw the tile only once" option. Clamp_TileMode
+    // repeats the last line of the image after drawing one tile. To avoid
+    // filling the space with arbitrary pixels, this workaround forces the
+    // image to have a line of transparent pixels on the "repeated" edge(s),
+    // thus causing extra space to be transparent filled.
+    SkISize tileSize = SkISize::Make(
+        m_tileImage->width() + (isRepeatX() ? 0 : 1),
+        m_tileImage->height() + (isRepeatY() ? 0 : 1));
+
+    SkPictureRecorder recorder;
+    SkCanvas* canvas =
+        recorder.beginRecording(SkRect::MakeIWH(tileSize.width(), tileSize.height()));
+
+    SkPaint paint;
+    paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+    canvas->drawImage(m_tileImage.get(), 0, 0, &paint);
+    RefPtr<SkPicture> tilePicture = adoptRef(recorder.endRecording());
+    RefPtr<SkImage> tileImage =
+        adoptRef(SkImage::NewFromPicture(tilePicture.get(), tileSize, nullptr, nullptr));

[Justin Novosad, 2015/08/17 15:03:24]

Why is it necessary to go through a picture here?

[f(malita), 2015/08/17 15:09:30]

It is a way to avoid record-time rasterization.  Not strictly necessary (we
could allocate an expanded raster surface here and draw the image, equivalent to
the previous behavior) - but it seems desirable to avoid this sort of thing on
the main thread.

+
+    if (!tileImage)
+        return adoptRef(SkShader::CreateColorShader(SK_ColorTRANSPARENT));
+
+    return adoptRef(tileImage->newShader(
+        isRepeatX() ? SkShader::kRepeat_TileMode : SkShader::kClamp_TileMode,
+        isRepeatY() ? SkShader::kRepeat_TileMode : SkShader::kClamp_TileMode,
+        &localMatrix));
+}
+
+} // namespace