C++ NativeImageSkia::resizedBitmap方法代码示例

// Draws the given bitmap to the given canvas. The subset of the source bitmap
// identified by src_rect is drawn to the given destination rect. The bitmap
// will be resampled to resample_width * resample_height (this is the size of
// the whole image, not the subset). See shouldResampleBitmap for more.
//
// This does a lot of computation to resample only the portion of the bitmap
// that will only be drawn. This is critical for performance since when we are
// scrolling, for example, we are only drawing a small strip of the image.
// Resampling the whole image every time is very slow, so this speeds up things
// dramatically.
//
// Note: this code is only used when the canvas transformation is limited to
// scaling or translation.
static void drawResampledBitmap(SkCanvas& canvas, SkPaint& paint, const NativeImageSkia& bitmap, const SkIRect& srcIRect, const SkRect& destRect)
{
#if PLATFORM(CHROMIUM)
    TRACE_EVENT("drawResampledBitmap", &canvas, 0);
#endif
    // Apply forward transform to destRect to estimate required size of
    // re-sampled bitmap, and use only in calls required to resize, or that
    // check for the required size.
    SkRect destRectTransformed;
    canvas.getTotalMatrix().mapRect(&destRectTransformed, destRect);
    SkIRect destRectTransformedRounded;
    destRectTransformed.round(&destRectTransformedRounded);

    // Compute the visible portion of our rect.
    SkRect destRectVisibleSubset;
    ClipRectToCanvas(canvas, destRect, &destRectVisibleSubset);
    // ClipRectToCanvas often overshoots, resulting in a larger region than our
    // original destRect. Intersecting gets us back inside.
    if (!destRectVisibleSubset.intersect(destRect))
        return; // Nothing visible in destRect.

    // Compute the transformed (screen space) portion of the visible portion for
    // use below.
    SkRect destRectVisibleSubsetTransformed;
    canvas.getTotalMatrix().mapRect(&destRectVisibleSubsetTransformed, destRectVisibleSubset);
    SkRect destBitmapSubsetTransformed = destRectVisibleSubsetTransformed;
    destBitmapSubsetTransformed.offset(-destRectTransformed.fLeft,
                                       -destRectTransformed.fTop);
    SkIRect destBitmapSubsetTransformedRounded;
    destBitmapSubsetTransformed.round(&destBitmapSubsetTransformedRounded);

    // Transforms above plus rounding may cause destBitmapSubsetTransformedRounded
    // to go outside the image, so need to clip to avoid problems.
    if (!destBitmapSubsetTransformedRounded.intersect(
            0, 0, destRectTransformedRounded.width(), destRectTransformedRounded.height()))
        return; // Image is not visible.

    SkBitmap resampled = bitmap.resizedBitmap(srcIRect,
                                              destRectTransformedRounded.width(),
                                              destRectTransformedRounded.height(),
                                              destBitmapSubsetTransformedRounded);
    canvas.drawBitmapRect(resampled, 0, destRectVisibleSubset, &paint);
}

// This function is used to scale an image and extract a scaled fragment.
//
// ALGORITHM
//
// Because the scaled image size has to be integers, we approximate the real
// scale with the following formula (only X direction is shown):
//
// scaledImageWidth = round(scaleX * imageRect.width())
// approximateScaleX = scaledImageWidth / imageRect.width()
//
// With this method we maintain a constant scale factor among fragments in
// the scaled image. This allows fragments to stitch together to form the
// full scaled image. The downside is there will be a small difference
// between |scaleX| and |approximateScaleX|.
//
// A scaled image fragment is identified by:
//
// - Scaled image size
// - Scaled image fragment rectangle (IntRect)
//
// Scaled image size has been determined and the next step is to compute the
// rectangle for the scaled image fragment which needs to be an IntRect.
//
// scaledSrcRect = srcRect * (approximateScaleX, approximateScaleY)
// enclosingScaledSrcRect = enclosingIntRect(scaledSrcRect)
//
// Finally we extract the scaled image fragment using
// (scaledImageSize, enclosingScaledSrcRect).
//
static SkBitmap extractScaledImageFragment(const NativeImageSkia& bitmap, const SkRect& srcRect, float scaleX, float scaleY, SkRect* scaledSrcRect, SkIRect* enclosingScaledSrcRect)
{
    SkISize imageSize = SkISize::Make(bitmap.bitmap().width(), bitmap.bitmap().height());
    SkISize scaledImageSize = SkISize::Make(clampToInteger(roundf(imageSize.width() * scaleX)),
        clampToInteger(roundf(imageSize.height() * scaleY)));

    SkRect imageRect = SkRect::MakeWH(imageSize.width(), imageSize.height());
    SkRect scaledImageRect = SkRect::MakeWH(scaledImageSize.width(), scaledImageSize.height());

    SkMatrix scaleTransform;
    scaleTransform.setRectToRect(imageRect, scaledImageRect, SkMatrix::kFill_ScaleToFit);
    scaleTransform.mapRect(scaledSrcRect, srcRect);

    scaledSrcRect->intersect(scaledImageRect);
    *enclosingScaledSrcRect = enclosingIntRect(*scaledSrcRect);

    // |enclosingScaledSrcRect| can be larger than |scaledImageSize| because
    // of float inaccuracy so clip to get inside.
    enclosingScaledSrcRect->intersect(SkIRect::MakeSize(scaledImageSize));
    return bitmap.resizedBitmap(scaledImageSize, *enclosingScaledSrcRect);
}

void Image::drawPattern(GraphicsContext* context,
                        const FloatRect& floatSrcRect,
                        const AffineTransform& patternTransform,
                        const FloatPoint& phase,
                        ColorSpace styleColorSpace,
                        CompositeOperator compositeOp,
                        const FloatRect& destRect)
{
    FloatRect normSrcRect = normalizeRect(floatSrcRect);
    if (destRect.isEmpty() || normSrcRect.isEmpty())
        return; // nothing to draw

    NativeImageSkia* bitmap = nativeImageForCurrentFrame();
    if (!bitmap)
        return;

    SkIRect srcRect = enclosingIntRect(normSrcRect);

    // Figure out what size the bitmap will be in the destination. The
    // destination rect is the bounds of the pattern, we need to use the
    // matrix to see how big it will be.
    float destBitmapWidth, destBitmapHeight;
    TransformDimensions(patternTransform, srcRect.width(), srcRect.height(),
                        &destBitmapWidth, &destBitmapHeight);

    // Compute the resampling mode.
    ResamplingMode resampling;
    if (context->platformContext()->isAccelerated() || context->platformContext()->printing())
        resampling = RESAMPLE_LINEAR;
    else
        resampling = computeResamplingMode(context->platformContext(), *bitmap, srcRect.width(), srcRect.height(), destBitmapWidth, destBitmapHeight);

    // Load the transform WebKit requested.
    SkMatrix matrix(patternTransform);

    SkShader* shader;
    if (resampling == RESAMPLE_AWESOME) {
        // Do nice resampling.
        int width = static_cast<int>(destBitmapWidth);
        int height = static_cast<int>(destBitmapHeight);
        SkBitmap resampled = bitmap->resizedBitmap(srcRect, width, height);
        shader = SkShader::CreateBitmapShader(resampled, SkShader::kRepeat_TileMode, SkShader::kRepeat_TileMode);

        // Since we just resized the bitmap, we need to undo the scale set in
        // the image transform.
        matrix.setScaleX(SkIntToScalar(1));
        matrix.setScaleY(SkIntToScalar(1));
    } else {
        // No need to do nice resampling.
        SkBitmap srcSubset;
        bitmap->bitmap().extractSubset(&srcSubset, srcRect);
        shader = SkShader::CreateBitmapShader(srcSubset, SkShader::kRepeat_TileMode, SkShader::kRepeat_TileMode);
    }

    // We also need to translate it such that the origin of the pattern is the
    // origin of the destination rect, which is what WebKit expects. Skia uses
    // the coordinate system origin as the base for the patter. If WebKit wants
    // a shifted image, it will shift it from there using the patternTransform.
    float adjustedX = phase.x() + normSrcRect.x() *
                      narrowPrecisionToFloat(patternTransform.a());
    float adjustedY = phase.y() + normSrcRect.y() *
                      narrowPrecisionToFloat(patternTransform.d());
    matrix.postTranslate(SkFloatToScalar(adjustedX),
                         SkFloatToScalar(adjustedY));
    shader->setLocalMatrix(matrix);

    SkPaint paint;
    paint.setShader(shader)->unref();
    paint.setXfermodeMode(WebCoreCompositeToSkiaComposite(compositeOp));
    paint.setFilterBitmap(resampling == RESAMPLE_LINEAR);

    context->platformContext()->paintSkPaint(destRect, paint);
}

// Draws the given bitmap to the given canvas. The subset of the source bitmap
// identified by src_rect is drawn to the given destination rect. The bitmap
// will be resampled to resample_width * resample_height (this is the size of
// the whole image, not the subset). See shouldResampleBitmap for more.
//
// This does a lot of computation to resample only the portion of the bitmap
// that will only be drawn. This is critical for performance since when we are
// scrolling, for example, we are only drawing a small strip of the image.
// Resampling the whole image every time is very slow, so this speeds up things
// dramatically.
static void drawResampledBitmap(SkCanvas& canvas, SkPaint& paint, const NativeImageSkia& bitmap, const SkIRect& srcIRect, const SkRect& destRect)
{
    // First get the subset we need. This is efficient and does not copy pixels.
    SkBitmap subset;
    bitmap.extractSubset(&subset, srcIRect);
    SkRect srcRect;
    srcRect.set(srcIRect);

    // Whether we're doing a subset or using the full source image.
    bool srcIsFull = srcIRect.fLeft == 0 && srcIRect.fTop == 0
        && srcIRect.width() == bitmap.width()
        && srcIRect.height() == bitmap.height();

    // We will always draw in integer sizes, so round the destination rect.
    SkIRect destRectRounded;
    destRect.round(&destRectRounded);
    SkIRect resizedImageRect =  // Represents the size of the resized image.
        { 0, 0, destRectRounded.width(), destRectRounded.height() };

    if (srcIsFull && bitmap.hasResizedBitmap(destRectRounded.width(), destRectRounded.height())) {
        // Yay, this bitmap frame already has a resized version.
        SkBitmap resampled = bitmap.resizedBitmap(destRectRounded.width(), destRectRounded.height());
        canvas.drawBitmapRect(resampled, 0, destRect, &paint);
        return;
    }

    // Compute the visible portion of our rect.
    SkRect destBitmapSubsetSk;
    ClipRectToCanvas(canvas, destRect, &destBitmapSubsetSk);
    destBitmapSubsetSk.offset(-destRect.fLeft, -destRect.fTop);

    // The matrix inverting, etc. could have introduced rounding error which
    // causes the bounds to be outside of the resized bitmap. We round outward
    // so we always lean toward it being larger rather than smaller than we
    // need, and then clamp to the bitmap bounds so we don't get any invalid
    // data.
    SkIRect destBitmapSubsetSkI;
    destBitmapSubsetSk.roundOut(&destBitmapSubsetSkI);
    if (!destBitmapSubsetSkI.intersect(resizedImageRect))
        return;  // Resized image does not intersect.

    if (srcIsFull && bitmap.shouldCacheResampling(
            resizedImageRect.width(),
            resizedImageRect.height(),
            destBitmapSubsetSkI.width(),
            destBitmapSubsetSkI.height())) {
        // We're supposed to resize the entire image and cache it, even though
        // we don't need all of it.
        SkBitmap resampled = bitmap.resizedBitmap(destRectRounded.width(),
                                                  destRectRounded.height());
        canvas.drawBitmapRect(resampled, 0, destRect, &paint);
    } else {
        // We should only resize the exposed part of the bitmap to do the
        // minimal possible work.

        // Resample the needed part of the image.
        SkBitmap resampled = skia::ImageOperations::Resize(subset,
            skia::ImageOperations::RESIZE_LANCZOS3,
            destRectRounded.width(), destRectRounded.height(),
            destBitmapSubsetSkI);

        // Compute where the new bitmap should be drawn. Since our new bitmap
        // may be smaller than the original, we have to shift it over by the
        // same amount that we cut off the top and left.
        destBitmapSubsetSkI.offset(destRect.fLeft, destRect.fTop);
        SkRect offsetDestRect;
        offsetDestRect.set(destBitmapSubsetSkI);

        canvas.drawBitmapRect(resampled, 0, offsetDestRect, &paint);
    }
}