imageskia.cpp

linux下开源浏览器WebKit的源码,市面上的很多商用浏览器都是移植自WebKit

/*
 * Copyright (c) 2008, Google Inc. All rights reserved.
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 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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#include "config.h"

#include "BitmapImage.h"
#include "BitmapImageSingleFrameSkia.h"
#include "ChromiumBridge.h"
#include "FloatConversion.h"
#include "FloatRect.h"
#include "GraphicsContext.h"
#include "Logging.h"
#include "NativeImageSkia.h"
#include "NotImplemented.h"
#include "PlatformContextSkia.h"
#include "PlatformString.h"
#include "SkiaUtils.h"
#include "SkShader.h"
#include "TransformationMatrix.h"

#include "skia/ext/image_operations.h"
#include "skia/ext/platform_canvas.h"

namespace WebCore {

// Used by computeResamplingMode to tell how bitmaps should be resampled.
enum ResamplingMode {
    // Nearest neighbor resampling. Used when we detect that the page is
    // trying to make a pattern by stretching a small bitmap very large.
    RESAMPLE_NONE,

    // Default skia resampling. Used for large growing of images where high
    // quality resampling doesn't get us very much except a slowdown.
    RESAMPLE_LINEAR,

    // High quality resampling.
    RESAMPLE_AWESOME,
};

static ResamplingMode computeResamplingMode(const NativeImageSkia& bitmap, int srcWidth, int srcHeight, float destWidth, float destHeight)
{
    int destIWidth = static_cast<int>(destWidth);
    int destIHeight = static_cast<int>(destHeight);

    // The percent change below which we will not resample. This usually means
    // an off-by-one error on the web page, and just doing nearest neighbor
    // sampling is usually good enough.
    const float kFractionalChangeThreshold = 0.025f;

    // Images smaller than this in either direction are considered "small" and
    // are not resampled ever (see below).
    const int kSmallImageSizeThreshold = 8;

    // The amount an image can be stretched in a single direction before we
    // say that it is being stretched so much that it must be a line or
    // background that doesn't need resampling.
    const float kLargeStretch = 3.0f;

    // Figure out if we should resample this image. We try to prune out some
    // common cases where resampling won't give us anything, since it is much
    // slower than drawing stretched.
    if (srcWidth == destIWidth && srcHeight == destIHeight) {
        // We don't need to resample if the source and destination are the same.
        return RESAMPLE_NONE;
    }

    if (srcWidth <= kSmallImageSizeThreshold
        || srcHeight <= kSmallImageSizeThreshold
        || destWidth <= kSmallImageSizeThreshold
        || destHeight <= kSmallImageSizeThreshold) {
        // Never resample small images. These are often used for borders and
        // rules (think 1x1 images used to make lines).
        return RESAMPLE_NONE;
    }

    if (srcHeight * kLargeStretch <= destHeight || srcWidth * kLargeStretch <= destWidth) {
        // Large image detected.

        // Don't resample if it is being stretched a lot in only one direction.
        // This is trying to catch cases where somebody has created a border
        // (which might be large) and then is stretching it to fill some part
        // of the page.
        if (srcWidth == destWidth || srcHeight == destHeight)
            return RESAMPLE_NONE;

        // The image is growing a lot and in more than one direction. Resampling
        // is slow and doesn't give us very much when growing a lot.
        return RESAMPLE_LINEAR;
    }

    if ((fabs(destWidth - srcWidth) / srcWidth < kFractionalChangeThreshold)
        && (fabs(destHeight - srcHeight) / srcHeight < kFractionalChangeThreshold)) {
        // It is disappointingly common on the web for image sizes to be off by
        // one or two pixels. We don't bother resampling if the size difference
        // is a small fraction of the original size.
        return RESAMPLE_NONE;
    }

    // When the image is not yet done loading, use linear. We don't cache the
    // partially resampled images, and as they come in incrementally, it causes
    // us to have to resample the whole thing every time.
    if (!bitmap.isDataComplete())
        return RESAMPLE_LINEAR;

    // Everything else gets resampled.
    return RESAMPLE_AWESOME;
}

// 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.
    resizedImageRect.set(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.
        gfx::Rect destBitmapSubset(destBitmapSubsetSkI.fLeft,
                                   destBitmapSubsetSkI.fTop,
                                   destBitmapSubsetSkI.width(),
                                   destBitmapSubsetSkI.height());

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

        // 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.
        SkRect offsetDestRect = {
            destBitmapSubset.x() + destRect.fLeft,
            destBitmapSubset.y() + destRect.fTop,
            destBitmapSubset.right() + destRect.fLeft,
            destBitmapSubset.bottom() + destRect.fTop };

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

static void paintSkBitmap(PlatformContextSkia* platformContext, const NativeImageSkia& bitmap, const SkIRect& srcRect, const SkRect& destRect, const SkPorterDuff::Mode& compOp)
{
    SkPaint paint;
    paint.setPorterDuffXfermode(compOp);
    paint.setFilterBitmap(true);

    skia::PlatformCanvas* canvas = platformContext->canvas();

    ResamplingMode resampling = platformContext->isPrinting() ? RESAMPLE_NONE :