C++ NativeImageSkia::hasResizedBitmap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.
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);
    }
}

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;

    // This is a very inexpensive operation. It will generate a new bitmap but
    // it will internally reference the old bitmap's pixels, adjusting the row
    // stride so the extra pixels appear as padding to the subsetted bitmap.
    SkBitmap srcSubset;
    SkIRect srcRect = enclosingIntRect(normSrcRect);
    bitmap->extractSubset(&srcSubset, srcRect);

    SkBitmap resampled;
    SkShader* shader;

    // 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 bit it will be.
    float destBitmapWidth, destBitmapHeight;
    TransformDimensions(patternTransform, srcRect.width(), srcRect.height(),
                        &destBitmapWidth, &destBitmapHeight);

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

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

    if (resampling == RESAMPLE_AWESOME) {
        // Do nice resampling.
        SkBitmap resampled;
        int width = static_cast<int>(destBitmapWidth);
        int height = static_cast<int>(destBitmapHeight);
        if (!srcRect.fLeft && !srcRect.fTop
            && srcRect.fRight == bitmap->width() && srcRect.fBottom == bitmap->height()
            && (bitmap->hasResizedBitmap(width, height)
                || bitmap->shouldCacheResampling(width, height, width, height))) {
            // resizedBitmap() caches resized image.
            resampled = bitmap->resizedBitmap(width, height);
        } else {
            resampled = skia::ImageOperations::Resize(srcSubset,
                skia::ImageOperations::RESIZE_LANCZOS3, 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.
        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);
}