libs/hwui/SkiaCanvas.cpp

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "SkiaCanvas.h"

#include "CanvasProperty.h"
#include "NinePatchUtils.h"
#include "VectorDrawable.h"
#include "hwui/Bitmap.h"
#include "hwui/MinikinUtils.h"
#include "pipeline/skia/AnimatedDrawables.h"

#include <SkDrawable.h>
#include <SkDeque.h>
#include <SkDrawFilter.h>
#include <SkGraphics.h>
#include <SkImage.h>
#include <SkImagePriv.h>
#include <SkRSXform.h>
#include <SkShader.h>
#include <SkTemplates.h>
#include <SkTextBlob.h>

#include <memory>

namespace android {

using uirenderer::PaintUtils;

Canvas* Canvas::create_canvas(const SkBitmap& bitmap) {
    return new SkiaCanvas(bitmap);
}

Canvas* Canvas::create_canvas(SkCanvas* skiaCanvas) {
    return new SkiaCanvas(skiaCanvas);
}

SkiaCanvas::SkiaCanvas() {}

SkiaCanvas::SkiaCanvas(SkCanvas* canvas)
    : mCanvas(canvas) {}

SkiaCanvas::SkiaCanvas(const SkBitmap& bitmap) {
    mCanvasOwned = std::unique_ptr<SkCanvas>(new SkCanvas(bitmap));
    mCanvas = mCanvasOwned.get();
}

SkiaCanvas::~SkiaCanvas() {}

void SkiaCanvas::reset(SkCanvas* skiaCanvas) {
    if (mCanvas != skiaCanvas) {
        mCanvas = skiaCanvas;
        mCanvasOwned.reset();
    }
    mSaveStack.reset(nullptr);
    mHighContrastText = false;
}

// ----------------------------------------------------------------------------
// Canvas state operations: Replace Bitmap
// ----------------------------------------------------------------------------

class ClipCopier : public SkCanvas::ClipVisitor {
public:
    explicit ClipCopier(SkCanvas* dstCanvas) : m_dstCanvas(dstCanvas) {}

    virtual void clipRect(const SkRect& rect, SkClipOp op, bool antialias) {
        m_dstCanvas->clipRect(rect, op, antialias);
    }
    virtual void clipRRect(const SkRRect& rrect, SkClipOp op, bool antialias) {
        m_dstCanvas->clipRRect(rrect, op, antialias);
    }
    virtual void clipPath(const SkPath& path, SkClipOp op, bool antialias) {
        m_dstCanvas->clipPath(path, op, antialias);
    }

private:
    SkCanvas* m_dstCanvas;
};

void SkiaCanvas::setBitmap(const SkBitmap& bitmap) {
    SkCanvas* newCanvas = new SkCanvas(bitmap);

    if (!bitmap.isNull()) {
        // Copy the canvas matrix & clip state.
        newCanvas->setMatrix(mCanvas->getTotalMatrix());

        ClipCopier copier(newCanvas);
        mCanvas->replayClips(&copier);
    }

    // deletes the previously owned canvas (if any)
    mCanvasOwned = std::unique_ptr<SkCanvas>(newCanvas);
    mCanvas = newCanvas;

    // clean up the old save stack
    mSaveStack.reset(nullptr);
}

// ----------------------------------------------------------------------------
// Canvas state operations
// ----------------------------------------------------------------------------

bool SkiaCanvas::isOpaque() {
    return mCanvas->imageInfo().isOpaque();
}

int SkiaCanvas::width() {
    return mCanvas->imageInfo().width();
}

int SkiaCanvas::height() {
    return mCanvas->imageInfo().height();
}

// ----------------------------------------------------------------------------
// Canvas state operations: Save (layer)
// ----------------------------------------------------------------------------

int SkiaCanvas::getSaveCount() const {
    return mCanvas->getSaveCount();
}

int SkiaCanvas::save(SaveFlags::Flags flags) {
    int count = mCanvas->save();
    recordPartialSave(flags);
    return count;
}

// The SkiaCanvas::restore operation layers on the capability to preserve
// either (or both) the matrix and/or clip state after a SkCanvas::restore
// operation. It does this by explicitly saving off the clip & matrix state
// when requested and playing it back after the SkCanvas::restore.
void SkiaCanvas::restore() {
    const auto* rec = this->currentSaveRec();
    if (!rec) {
        // Fast path - no record for this frame.
        mCanvas->restore();
        return;
    }

    bool preserveMatrix = !(rec->saveFlags & SaveFlags::Matrix);
    bool preserveClip   = !(rec->saveFlags & SaveFlags::Clip);

    SkMatrix savedMatrix;
    if (preserveMatrix) {
        savedMatrix = mCanvas->getTotalMatrix();
    }

    const size_t clipIndex = rec->clipIndex;

    mCanvas->restore();
    mSaveStack->pop_back();

    if (preserveMatrix) {
        mCanvas->setMatrix(savedMatrix);
    }

    if (preserveClip) {
        this->applyPersistentClips(clipIndex);
    }
}

void SkiaCanvas::restoreToCount(int restoreCount) {
    while (mCanvas->getSaveCount() > restoreCount) {
        this->restore();
    }
}

static inline SkCanvas::SaveLayerFlags layerFlags(SaveFlags::Flags flags) {
    SkCanvas::SaveLayerFlags layerFlags = 0;

    // We intentionally ignore the SaveFlags::HasAlphaLayer and
    // SkCanvas::kIsOpaque_SaveLayerFlag flags because HWUI ignores it
    // and our Android client may use it incorrectly.
    // In Skia, this flag is purely for performance optimization.

    if (!(flags & SaveFlags::ClipToLayer)) {
        layerFlags |= SkCanvas::kDontClipToLayer_Legacy_SaveLayerFlag;
    }

    return layerFlags;
}

int SkiaCanvas::saveLayer(float left, float top, float right, float bottom,
            const SkPaint* paint, SaveFlags::Flags flags) {
    const SkRect bounds = SkRect::MakeLTRB(left, top, right, bottom);
    const SkCanvas::SaveLayerRec rec(&bounds, paint, layerFlags(flags));

    return mCanvas->saveLayer(rec);
}

int SkiaCanvas::saveLayerAlpha(float left, float top, float right, float bottom,
        int alpha, SaveFlags::Flags flags) {
    if (static_cast<unsigned>(alpha) < 0xFF) {
        SkPaint alphaPaint;
        alphaPaint.setAlpha(alpha);
        return this->saveLayer(left, top, right, bottom, &alphaPaint, flags);
    }
    return this->saveLayer(left, top, right, bottom, nullptr, flags);
}

class SkiaCanvas::Clip {
public:
    Clip(const SkRect& rect, SkClipOp op, const SkMatrix& m)
        : mType(Type::Rect), mOp(op), mMatrix(m), mRRect(SkRRect::MakeRect(rect)) {}
    Clip(const SkRRect& rrect, SkClipOp op, const SkMatrix& m)
        : mType(Type::RRect), mOp(op), mMatrix(m), mRRect(rrect) {}
    Clip(const SkPath& path, SkClipOp op, const SkMatrix& m)
        : mType(Type::Path), mOp(op), mMatrix(m), mPath(&path) {}

    void apply(SkCanvas* canvas) const {
        canvas->setMatrix(mMatrix);
        switch (mType) {
        case Type::Rect:
            canvas->clipRect(mRRect.rect(), mOp);
            break;
        case Type::RRect:
            canvas->clipRRect(mRRect, mOp);
            break;
        case Type::Path:
            canvas->clipPath(*mPath.get(), mOp);
            break;
        }
    }

private:
    enum class Type {
        Rect,
        RRect,
        Path,
    };

    Type        mType;
    SkClipOp    mOp;
    SkMatrix    mMatrix;

    // These are logically a union (tracked separately due to non-POD path).
    SkTLazy<SkPath> mPath;
    SkRRect         mRRect;
};

const SkiaCanvas::SaveRec* SkiaCanvas::currentSaveRec() const {
    const SaveRec* rec = mSaveStack
        ? static_cast<const SaveRec*>(mSaveStack->back())
        : nullptr;
    int currentSaveCount = mCanvas->getSaveCount();
    SkASSERT(!rec || currentSaveCount >= rec->saveCount);

    return (rec && rec->saveCount == currentSaveCount) ? rec : nullptr;
}

// ----------------------------------------------------------------------------
// functions to emulate legacy SaveFlags (i.e. independent matrix/clip flags)
// ----------------------------------------------------------------------------

void SkiaCanvas::recordPartialSave(SaveFlags::Flags flags) {
    // A partial save is a save operation which doesn't capture the full canvas state.
    // (either SaveFlags::Matrix or SaveFlags::Clip is missing).

    // Mask-out non canvas state bits.
    flags &= SaveFlags::MatrixClip;

    if (flags == SaveFlags::MatrixClip) {
        // not a partial save.
        return;
    }

    if (!mSaveStack) {
        mSaveStack.reset(new SkDeque(sizeof(struct SaveRec), 8));
    }

    SaveRec* rec = static_cast<SaveRec*>(mSaveStack->push_back());
    rec->saveCount = mCanvas->getSaveCount();
    rec->saveFlags = flags;
    rec->clipIndex = mClipStack.size();
}

template <typename T>
void SkiaCanvas::recordClip(const T& clip, SkClipOp op) {
    // Only need tracking when in a partial save frame which
    // doesn't restore the clip.
    const SaveRec* rec = this->currentSaveRec();
    if (rec && !(rec->saveFlags & SaveFlags::Clip)) {
        mClipStack.emplace_back(clip, op, mCanvas->getTotalMatrix());
    }
}

// Applies and optionally removes all clips >= index.
void SkiaCanvas::applyPersistentClips(size_t clipStartIndex) {
    SkASSERT(clipStartIndex <= mClipStack.size());
    const auto begin = mClipStack.cbegin() + clipStartIndex;
    const auto end = mClipStack.cend();

    // Clip application mutates the CTM.
    const SkMatrix saveMatrix = mCanvas->getTotalMatrix();

    for (auto clip = begin; clip != end; ++clip) {
        clip->apply(mCanvas);
    }

    mCanvas->setMatrix(saveMatrix);

    // If the current/post-restore save rec is also persisting clips, we
    // leave them on the stack to be reapplied part of the next restore().
    // Otherwise we're done and just pop them.
    const auto* rec = this->currentSaveRec();
    if (!rec || (rec->saveFlags & SaveFlags::Clip)) {
        mClipStack.erase(begin, end);
    }
}

// ----------------------------------------------------------------------------
// Canvas state operations: Matrix
// ----------------------------------------------------------------------------

void SkiaCanvas::getMatrix(SkMatrix* outMatrix) const {
    *outMatrix = mCanvas->getTotalMatrix();
}

void SkiaCanvas::setMatrix(const SkMatrix& matrix) {
    mCanvas->setMatrix(matrix);
}

void SkiaCanvas::concat(const SkMatrix& matrix) {
    mCanvas->concat(matrix);
}

void SkiaCanvas::rotate(float degrees) {
    mCanvas->rotate(degrees);
}

void SkiaCanvas::scale(float sx, float sy) {
    mCanvas->scale(sx, sy);
}

void SkiaCanvas::skew(float sx, float sy) {
    mCanvas->skew(sx, sy);
}

void SkiaCanvas::translate(float dx, float dy) {
    mCanvas->translate(dx, dy);
}

// ----------------------------------------------------------------------------
// Canvas state operations: Clips
// ----------------------------------------------------------------------------

// This function is a mirror of SkCanvas::getClipBounds except that it does
// not outset the edge of the clip to account for anti-aliasing. There is
// a skia bug to investigate pushing this logic into back into skia.
// (see https://code.google.com/p/skia/issues/detail?id=1303)
bool SkiaCanvas::getClipBounds(SkRect* outRect) const {
    SkIRect ibounds;
    if (!mCanvas->getDeviceClipBounds(&ibounds)) {
        return false;
    }

    SkMatrix inverse;
    // if we can't invert the CTM, we can't return local clip bounds
    if (!mCanvas->getTotalMatrix().invert(&inverse)) {
        if (outRect) {
            outRect->setEmpty();
        }
        return false;
    }

    if (NULL != outRect) {
        SkRect r = SkRect::Make(ibounds);
        inverse.mapRect(outRect, r);
    }
    return true;
}

bool SkiaCanvas::quickRejectRect(float left, float top, float right, float bottom) const {
    SkRect bounds = SkRect::MakeLTRB(left, top, right, bottom);
    return mCanvas->quickReject(bounds);
}

bool SkiaCanvas::quickRejectPath(const SkPath& path) const {
    return mCanvas->quickReject(path);
}

bool SkiaCanvas::clipRect(float left, float top, float right, float bottom, SkClipOp op) {
    SkRect rect = SkRect::MakeLTRB(left, top, right, bottom);
    this->recordClip(rect, op);
    mCanvas->clipRect(rect, op);
    return !mCanvas->isClipEmpty();
}

bool SkiaCanvas::clipPath(const SkPath* path, SkClipOp op) {
    SkRRect roundRect;
    if (path->isRRect(&roundRect)) {
        this->recordClip(roundRect, op);
        mCanvas->clipRRect(roundRect, op);
    } else {
        this->recordClip(*path, op);
        mCanvas->clipPath(*path, op);
    }
    return !mCanvas->isClipEmpty();
}

// ----------------------------------------------------------------------------
// Canvas state operations: Filters
// ----------------------------------------------------------------------------

SkDrawFilter* SkiaCanvas::getDrawFilter() {
    return mCanvas->getDrawFilter();
}

void SkiaCanvas::setDrawFilter(SkDrawFilter* drawFilter) {
    mCanvas->setDrawFilter(drawFilter);
}

// ----------------------------------------------------------------------------
// Canvas draw operations
// ----------------------------------------------------------------------------

void SkiaCanvas::drawColor(int color, SkBlendMode mode) {
    mCanvas->drawColor(color, mode);
}

void SkiaCanvas::drawPaint(const SkPaint& paint) {
    mCanvas->drawPaint(paint);
}

// ----------------------------------------------------------------------------
// Canvas draw operations: Geometry
// ----------------------------------------------------------------------------

void SkiaCanvas::drawPoints(const float* points, int count, const SkPaint& paint,
                            SkCanvas::PointMode mode) {
    if (CC_UNLIKELY(count < 2 || paint.nothingToDraw())) return;
    // convert the floats into SkPoints
    count >>= 1;    // now it is the number of points
    std::unique_ptr<SkPoint[]> pts(new SkPoint[count]);
    for (int i = 0; i < count; i++) {
        pts[i].set(points[0], points[1]);
        points += 2;
    }
    mCanvas->drawPoints(mode, count, pts.get(), paint);
}


void SkiaCanvas::drawPoint(float x, float y, const SkPaint& paint) {
    mCanvas->drawPoint(x, y, paint);
}

void SkiaCanvas::drawPoints(const float* points, int count, const SkPaint& paint) {
    this->drawPoints(points, count, paint, SkCanvas::kPoints_PointMode);
}

void SkiaCanvas::drawLine(float startX, float startY, float stopX, float stopY,
                          const SkPaint& paint) {
    mCanvas->drawLine(startX, startY, stopX, stopY, paint);
}

void SkiaCanvas::drawLines(const float* points, int count, const SkPaint& paint) {
    if (CC_UNLIKELY(count < 4 || paint.nothingToDraw())) return;
    this->drawPoints(points, count, paint, SkCanvas::kLines_PointMode);
}

void SkiaCanvas::drawRect(float left, float top, float right, float bottom,
        const SkPaint& paint) {
    if (CC_UNLIKELY(paint.nothingToDraw())) return;
    mCanvas->drawRectCoords(left, top, right, bottom, paint);

}

void SkiaCanvas::drawRegion(const SkRegion& region, const SkPaint& paint) {
    if (CC_UNLIKELY(paint.nothingToDraw())) return;
    mCanvas->drawRegion(region, paint);
}

void SkiaCanvas::drawRoundRect(float left, float top, float right, float bottom,
        float rx, float ry, const SkPaint& paint) {
    if (CC_UNLIKELY(paint.nothingToDraw())) return;
    SkRect rect = SkRect::MakeLTRB(left, top, right, bottom);
    mCanvas->drawRoundRect(rect, rx, ry, paint);
}

void SkiaCanvas::drawCircle(float x, float y, float radius, const SkPaint& paint) {
    if (CC_UNLIKELY(radius <= 0 || paint.nothingToDraw())) return;
    mCanvas->drawCircle(x, y, radius, paint);
}

void SkiaCanvas::drawOval(float left, float top, float right, float bottom, const SkPaint& paint) {
    if (CC_UNLIKELY(paint.nothingToDraw())) return;
    SkRect oval = SkRect::MakeLTRB(left, top, right, bottom);
    mCanvas->drawOval(oval, paint);
}

void SkiaCanvas::drawArc(float left, float top, float right, float bottom,
        float startAngle, float sweepAngle, bool useCenter, const SkPaint& paint) {
    if (CC_UNLIKELY(paint.nothingToDraw())) return;
    SkRect arc = SkRect::MakeLTRB(left, top, right, bottom);
    mCanvas->drawArc(arc, startAngle, sweepAngle, useCenter, paint);
}

void SkiaCanvas::drawPath(const SkPath& path, const SkPaint& paint) {
    if (CC_UNLIKELY(paint.nothingToDraw())) return;
    mCanvas->drawPath(path, paint);
}

void SkiaCanvas::drawVertices(SkCanvas::VertexMode vertexMode, int vertexCount,
                              const float* verts, const float* texs, const int* colors,
                              const uint16_t* indices, int indexCount, const SkPaint& paint) {
#ifndef SK_SCALAR_IS_FLOAT
    SkDEBUGFAIL("SkScalar must be a float for these conversions to be valid");
#endif
    const int ptCount = vertexCount >> 1;
    mCanvas->drawVertices(SkVertices::MakeCopy(vertexMode, ptCount, (SkPoint*)verts,
                                               (SkPoint*)texs, (SkColor*)colors,
                                               indexCount, indices),
                          SkBlendMode::kModulate, paint);
}

// ----------------------------------------------------------------------------
// Canvas draw operations: Bitmaps
// ----------------------------------------------------------------------------

void SkiaCanvas::drawBitmap(Bitmap& bitmap, float left, float top, const SkPaint* paint) {
    SkBitmap skBitmap;
    bitmap.getSkBitmap(&skBitmap);
    mCanvas->drawBitmap(skBitmap, left, top, paint);
}

void SkiaCanvas::drawBitmap(Bitmap& hwuiBitmap, const SkMatrix& matrix, const SkPaint* paint) {
    SkBitmap bitmap;
    hwuiBitmap.getSkBitmap(&bitmap);
    SkAutoCanvasRestore acr(mCanvas, true);
    mCanvas->concat(matrix);
    mCanvas->drawBitmap(bitmap, 0, 0, paint);
}

void SkiaCanvas::drawBitmap(Bitmap& hwuiBitmap, float srcLeft, float srcTop,
                            float srcRight, float srcBottom, float dstLeft, float dstTop,
                            float dstRight, float dstBottom, const SkPaint* paint) {
    SkBitmap bitmap;
    hwuiBitmap.getSkBitmap(&bitmap);
    SkRect srcRect = SkRect::MakeLTRB(srcLeft, srcTop, srcRight, srcBottom);
    SkRect dstRect = SkRect::MakeLTRB(dstLeft, dstTop, dstRight, dstBottom);
    mCanvas->drawBitmapRect(bitmap, srcRect, dstRect, paint);
}

void SkiaCanvas::drawBitmapMesh(Bitmap& hwuiBitmap, int meshWidth, int meshHeight,
        const float* vertices, const int* colors, const SkPaint* paint) {
    SkBitmap bitmap;
    hwuiBitmap.getSkBitmap(&bitmap);
    const int ptCount = (meshWidth + 1) * (meshHeight + 1);
    const int indexCount = meshWidth * meshHeight * 6;
    uint32_t flags = SkVertices::kHasTexCoords_BuilderFlag;
    if (colors) {
        flags |= SkVertices::kHasColors_BuilderFlag;
    }
    SkVertices::Builder builder(SkCanvas::kTriangles_VertexMode, ptCount, indexCount, flags);
    memcpy(builder.positions(), vertices, ptCount * sizeof(SkPoint));
    if (colors) {
        memcpy(builder.colors(), colors, ptCount * sizeof(SkColor));
    }
    SkPoint* texs = builder.texCoords();
    uint16_t* indices = builder.indices();

    // cons up texture coordinates and indices
    {
        const SkScalar w = SkIntToScalar(bitmap.width());
        const SkScalar h = SkIntToScalar(bitmap.height());
        const SkScalar dx = w / meshWidth;
        const SkScalar dy = h / meshHeight;

        SkPoint* texsPtr = texs;
        SkScalar y = 0;
        for (int i = 0; i <= meshHeight; i++) {
            if (i == meshHeight) {
                y = h;  // to ensure numerically we hit h exactly
            }
            SkScalar x = 0;
            for (int j = 0; j < meshWidth; j++) {
                texsPtr->set(x, y);
                texsPtr += 1;
                x += dx;
            }
            texsPtr->set(w, y);
            texsPtr += 1;
            y += dy;
        }
        SkASSERT(texsPtr - texs == ptCount);
    }

    // cons up indices
    {
        uint16_t* indexPtr = indices;
        int index = 0;
        for (int i = 0; i < meshHeight; i++) {
            for (int j = 0; j < meshWidth; j++) {
                // lower-left triangle
                *indexPtr++ = index;
                *indexPtr++ = index + meshWidth + 1;
                *indexPtr++ = index + meshWidth + 2;
                // upper-right triangle
                *indexPtr++ = index;
                *indexPtr++ = index + meshWidth + 2;
                *indexPtr++ = index + 1;
                // bump to the next cell
                index += 1;
            }
            // bump to the next row
            index += 1;
        }
        SkASSERT(indexPtr - indices == indexCount);
    }

    // double-check that we have legal indices
#ifdef SK_DEBUG
    {
        for (int i = 0; i < indexCount; i++) {
            SkASSERT((unsigned)indices[i] < (unsigned)ptCount);
        }
    }
#endif

    // cons-up a shader for the bitmap
    SkPaint tmpPaint;
    if (paint) {
        tmpPaint = *paint;
    }

    sk_sp<SkImage> image = SkMakeImageFromRasterBitmap(bitmap, kNever_SkCopyPixelsMode);
    tmpPaint.setShader(image->makeShader(SkShader::kClamp_TileMode, SkShader::kClamp_TileMode));

    mCanvas->drawVertices(builder.detach(), SkBlendMode::kModulate, tmpPaint);
}

void SkiaCanvas::drawNinePatch(Bitmap& hwuiBitmap, const Res_png_9patch& chunk,
        float dstLeft, float dstTop, float dstRight, float dstBottom, const SkPaint* paint) {

    SkBitmap bitmap;
    hwuiBitmap.getSkBitmap(&bitmap);

    SkCanvas::Lattice lattice;
    NinePatchUtils::SetLatticeDivs(&lattice, chunk, bitmap.width(), bitmap.height());

    lattice.fFlags = nullptr;
    int numFlags = 0;
    if (chunk.numColors > 0 && chunk.numColors == NinePatchUtils::NumDistinctRects(lattice)) {
        // We can expect the framework to give us a color for every distinct rect.
        // Skia requires a flag for every rect.
        numFlags = (lattice.fXCount + 1) * (lattice.fYCount + 1);
    }

    SkAutoSTMalloc<25, SkCanvas::Lattice::Flags> flags(numFlags);
    if (numFlags > 0) {
        NinePatchUtils::SetLatticeFlags(&lattice, flags.get(), numFlags, chunk);
    }

    lattice.fBounds = nullptr;
    SkRect dst = SkRect::MakeLTRB(dstLeft, dstTop, dstRight, dstBottom);
    mCanvas->drawBitmapLattice(bitmap, lattice, dst, paint);
}

void SkiaCanvas::drawVectorDrawable(VectorDrawableRoot* vectorDrawable) {
    vectorDrawable->drawStaging(this);
}

// ----------------------------------------------------------------------------
// Canvas draw operations: Text
// ----------------------------------------------------------------------------

void SkiaCanvas::drawGlyphs(const uint16_t* text, const float* positions, int count,
        const SkPaint& paint, float x, float y,
        float boundsLeft, float boundsTop, float boundsRight, float boundsBottom,
        float totalAdvance) {
     if (!text || !positions || count <= 0 || paint.nothingToDraw()) return;
    // Set align to left for drawing, as we don't want individual
    // glyphs centered or right-aligned; the offset above takes
    // care of all alignment.
    SkPaint paintCopy(paint);
    paintCopy.setTextAlign(SkPaint::kLeft_Align);

    SkRect bounds = SkRect::MakeLTRB(boundsLeft + x, boundsTop + y,
                                     boundsRight + x, boundsBottom + y);

    SkTextBlobBuilder builder;
    const SkTextBlobBuilder::RunBuffer& buffer = builder.allocRunPos(paintCopy, count, &bounds);
    // TODO: we could reduce the number of memcpy's if the this were exposed further up
    //       in the architecture.
    memcpy(buffer.glyphs, text, count * sizeof(uint16_t));
    memcpy(buffer.pos, positions, (count << 1) * sizeof(float));

    sk_sp<SkTextBlob> textBlob(builder.make());
    mCanvas->drawTextBlob(textBlob, 0, 0, paintCopy);
    drawTextDecorations(x, y, totalAdvance, paintCopy);
}

void SkiaCanvas::drawLayoutOnPath(const minikin::Layout& layout, float hOffset, float vOffset,
        const SkPaint& paint, const SkPath& path, size_t start, size_t end) {
    const int N = end - start;
    SkAutoSTMalloc<1024, uint8_t> storage(N * (sizeof(uint16_t) + sizeof(SkRSXform)));
    SkRSXform* xform = (SkRSXform*)storage.get();
    uint16_t* glyphs = (uint16_t*)(xform + N);
    SkPathMeasure meas(path, false);

    for (size_t i = start; i < end; i++) {
        glyphs[i - start] = layout.getGlyphId(i);
        float x = hOffset + layout.getX(i);
        float y = vOffset + layout.getY(i);

        SkPoint pos;
        SkVector tan;
        if (!meas.getPosTan(x, &pos, &tan)) {
            pos.set(x, y);
            tan.set(1, 0);
        }
        xform[i - start].fSCos = tan.x();
        xform[i - start].fSSin = tan.y();
        xform[i - start].fTx   = pos.x() - tan.y() * y;
        xform[i - start].fTy   = pos.y() + tan.x() * y;
    }

    this->asSkCanvas()->drawTextRSXform(glyphs, sizeof(uint16_t) * N, xform, nullptr, paint);
}

// ----------------------------------------------------------------------------
// Canvas draw operations: Animations
// ----------------------------------------------------------------------------

void SkiaCanvas::drawRoundRect(uirenderer::CanvasPropertyPrimitive* left,
        uirenderer::CanvasPropertyPrimitive* top, uirenderer::CanvasPropertyPrimitive* right,
        uirenderer::CanvasPropertyPrimitive* bottom, uirenderer::CanvasPropertyPrimitive* rx,
        uirenderer::CanvasPropertyPrimitive* ry, uirenderer::CanvasPropertyPaint* paint) {
    sk_sp<uirenderer::skiapipeline::AnimatedRoundRect> drawable(
            new uirenderer::skiapipeline::AnimatedRoundRect(left, top, right, bottom, rx, ry, paint));
    mCanvas->drawDrawable(drawable.get());
}

void SkiaCanvas::drawCircle(uirenderer::CanvasPropertyPrimitive* x, uirenderer::CanvasPropertyPrimitive* y,
        uirenderer::CanvasPropertyPrimitive* radius, uirenderer::CanvasPropertyPaint* paint) {
    sk_sp<uirenderer::skiapipeline::AnimatedCircle> drawable(new uirenderer::skiapipeline::AnimatedCircle(x, y, radius, paint));
    mCanvas->drawDrawable(drawable.get());
}

// ----------------------------------------------------------------------------
// Canvas draw operations: View System
// ----------------------------------------------------------------------------

void SkiaCanvas::drawLayer(uirenderer::DeferredLayerUpdater* layerUpdater) {
    LOG_ALWAYS_FATAL("SkiaCanvas can't directly draw Layers");
}

void SkiaCanvas::drawRenderNode(uirenderer::RenderNode* renderNode) {
    LOG_ALWAYS_FATAL("SkiaCanvas can't directly draw RenderNodes");
}

void SkiaCanvas::callDrawGLFunction(Functor* functor,
        uirenderer::GlFunctorLifecycleListener* listener) {
    LOG_ALWAYS_FATAL("SkiaCanvas can't directly draw GL Content");
}

} // namespace android