Refactor code for calculating background image geometry

Source/core/paint/BackgroundImageGeometry.cpp

Index: Source/core/paint/BackgroundImageGeometry.cpp
diff --git a/Source/core/paint/BackgroundImageGeometry.cpp b/Source/core/paint/BackgroundImageGeometry.cpp
index b4a479509501fc3252b513c523a6802cd4ff8e55..d4a3bedff08bf0af15358b19fe13c291f3f5f1f4 100644
--- a/Source/core/paint/BackgroundImageGeometry.cpp
+++ b/Source/core/paint/BackgroundImageGeometry.cpp
@@ -5,14 +5,137 @@
 #include "config.h"
 #include "core/paint/BackgroundImageGeometry.h"
 
+#include "core/layout/LayoutBox.h"
+#include "core/layout/LayoutBoxModelObject.h"
+#include "core/layout/LayoutView.h"
+#include "core/layout/compositing/CompositedDeprecatedPaintLayerMapping.h"
+#include "core/paint/DeprecatedPaintLayer.h"
+#include "platform/LayoutUnit.h"
+#include "platform/geometry/LayoutRect.h"
+
 namespace blink {
 
+namespace {
+
+inline void applySubPixelHeuristicForTileSize(LayoutSize& tileSize, const IntSize& positioningAreaSize)
+{
+    tileSize.setWidth(positioningAreaSize.width() - tileSize.width() <= 1 ? tileSize.width().ceil() : tileSize.width().floor());
+    tileSize.setHeight(positioningAreaSize.height() - tileSize.height() <= 1 ? tileSize.height().ceil() : tileSize.height().floor());
+}
+
+// Return the amount of space to leave between image tiles for the background-repeat: space property.
+inline int getSpaceBetweenImageTiles(int areaSize, int tileSize)
+{
+    int numberOfTiles = areaSize / tileSize;
+    int space = -1;
+
+    if (numberOfTiles > 1) {
+        // Spec doesn't specify rounding, so use the same method as for background-repeat: round.
+        space = lroundf((areaSize - numberOfTiles * tileSize) / (float)(numberOfTiles - 1));
+    }
+
+    return space;
+}
+
+bool fixedBackgroundPaintsInLocalCoordinates(const LayoutObject& obj, const GlobalPaintFlags globalPaintFlags)
+{
+    if (!obj.isLayoutView())
+        return false;
+
+    const LayoutView& view = toLayoutView(obj);
+
+    if (globalPaintFlags & GlobalPaintFlattenCompositingLayers)
+        return false;
+
+    DeprecatedPaintLayer* rootLayer = view.layer();
+    if (!rootLayer || rootLayer->compositingState() == NotComposited)
+        return false;
+
+    return rootLayer->compositedDeprecatedPaintLayerMapping()->backgroundLayerPaintsFixedRootBackground();
+}
+
+IntSize calculateFillTileSize(const LayoutBoxModelObject& obj, const FillLayer& fillLayer, const IntSize& positioningAreaSize)
+{
+    StyleImage* image = fillLayer.image();
+    EFillSizeType type = fillLayer.size().type;
+
+    IntSize imageIntrinsicSize = obj.calculateImageIntrinsicDimensions(image, positioningAreaSize, LayoutBoxModelObject::ScaleByEffectiveZoom);
+    imageIntrinsicSize.scale(1 / image->imageScaleFactor(), 1 / image->imageScaleFactor());
+    switch (type) {
+    case SizeLength: {
+        LayoutSize tileSize(positioningAreaSize);
+
+        Length layerWidth = fillLayer.size().size.width();
+        Length layerHeight = fillLayer.size().size.height();
+
+        if (layerWidth.isFixed())
+            tileSize.setWidth(layerWidth.value());
+        else if (layerWidth.hasPercent())
+            tileSize.setWidth(valueForLength(layerWidth, positioningAreaSize.width()));
+
+        if (layerHeight.isFixed())
+            tileSize.setHeight(layerHeight.value());
+        else if (layerHeight.hasPercent())
+            tileSize.setHeight(valueForLength(layerHeight, positioningAreaSize.height()));
+
+        applySubPixelHeuristicForTileSize(tileSize, positioningAreaSize);
+
+        // If one of the values is auto we have to use the appropriate
+        // scale to maintain our aspect ratio.
+        if (layerWidth.isAuto() && !layerHeight.isAuto()) {
+            if (imageIntrinsicSize.height()) {
+                LayoutUnit adjustedWidth = imageIntrinsicSize.width() * tileSize.height() / imageIntrinsicSize.height();
+                if (imageIntrinsicSize.width() >= 1 && adjustedWidth < 1)
+                    adjustedWidth = 1;
+                tileSize.setWidth(adjustedWidth);
+            }
+        } else if (!layerWidth.isAuto() && layerHeight.isAuto()) {
+            if (imageIntrinsicSize.width()) {
+                LayoutUnit adjustedHeight = imageIntrinsicSize.height() * tileSize.width() / imageIntrinsicSize.width();
+                if (imageIntrinsicSize.height() >= 1 && adjustedHeight < 1)
+                    adjustedHeight = 1;
+                tileSize.setHeight(adjustedHeight);
+            }
+        } else if (layerWidth.isAuto() && layerHeight.isAuto()) {
+            // If both width and height are auto, use the image's intrinsic size.
+            tileSize = LayoutSize(imageIntrinsicSize);
+        }
+
+        tileSize.clampNegativeToZero();
+        return flooredIntSize(tileSize);
+    }
+    case SizeNone: {
+        // If both values are 'auto' then the intrinsic width and/or height of the image should be used, if any.
+        if (!imageIntrinsicSize.isEmpty())
+            return imageIntrinsicSize;
+
+        // If the image has neither an intrinsic width nor an intrinsic height, its size is determined as for 'contain'.
+        type = Contain;
+    }
+    case Contain:
+    case Cover: {
+        float horizontalScaleFactor = imageIntrinsicSize.width()
+            ? static_cast<float>(positioningAreaSize.width()) / imageIntrinsicSize.width() : 1;
+        float verticalScaleFactor = imageIntrinsicSize.height()
+            ? static_cast<float>(positioningAreaSize.height()) / imageIntrinsicSize.height() : 1;
+        float scaleFactor = type == Contain ? std::min(horizontalScaleFactor, verticalScaleFactor) : std::max(horizontalScaleFactor, verticalScaleFactor);
+        return IntSize(std::max(1l, lround(imageIntrinsicSize.width() * scaleFactor)), std::max(1l, lround(imageIntrinsicSize.height() * scaleFactor)));
+    }
+    }
+
+    ASSERT_NOT_REACHED();
+    return IntSize();
+}
+
+} // anonymous namespace
+
 void BackgroundImageGeometry::setNoRepeatX(int xOffset)
 {
     m_destRect.move(std::max(xOffset, 0), 0);
     m_phase.setX(-std::min(xOffset, 0));
     m_destRect.setWidth(m_tileSize.width() + std::min(xOffset, 0));
 }
+
 void BackgroundImageGeometry::setNoRepeatY(int yOffset)
 {
     m_destRect.move(0, std::max(yOffset, 0));
@@ -31,4 +154,181 @@ void BackgroundImageGeometry::clip(const IntRect& clipRect)
     m_destRect.intersect(clipRect);
 }
 
+void BackgroundImageGeometry::calculate(const LayoutBoxModelObject& obj, const LayoutBoxModelObject* paintContainer,
+    const GlobalPaintFlags globalPaintFlags, const FillLayer& fillLayer, const LayoutRect& paintRect,
+    LayoutObject* backgroundObject)
+{
+    LayoutUnit left = 0;
+    LayoutUnit top = 0;
+    IntSize positioningAreaSize;
+    IntRect snappedPaintRect = pixelSnappedIntRect(paintRect);
+    bool isLayoutView = obj.isLayoutView();
+    const LayoutBox* rootBox = nullptr;
+    if (isLayoutView) {
+        // It is only possible reach here when root element has a box.
+        Element* documentElement = obj.document().documentElement();
+        ASSERT(documentElement);
+        ASSERT(documentElement->layoutObject());
+        ASSERT(documentElement->layoutObject()->isBox());
+        rootBox = toLayoutBox(documentElement->layoutObject());
+    }
+    const LayoutBoxModelObject& positioningBox = isLayoutView ? static_cast<const LayoutBoxModelObject&>(*rootBox) : obj;
+
+    // Determine the background positioning area and set destRect to the background painting area.
+    // destRect will be adjusted later if the background is non-repeating.
+    // FIXME: transforms spec says that fixed backgrounds behave like scroll inside transforms.
+    bool fixedAttachment = fillLayer.attachment() == FixedBackgroundAttachment;
+
+    if (RuntimeEnabledFeatures::fastMobileScrollingEnabled()) {
+        // As a side effect of an optimization to blit on scroll, we do not honor the CSS
+        // property "background-attachment: fixed" because it may result in rendering
+        // artifacts. Note, these artifacts only appear if we are blitting on scroll of
+        // a page that has fixed background images.
+        fixedAttachment = false;
+    }
+
+    if (!fixedAttachment) {
+        setDestRect(snappedPaintRect);
+
+        LayoutUnit right = 0;
+        LayoutUnit bottom = 0;
+        // Scroll and Local.
+        if (fillLayer.origin() != BorderFillBox) {
+            left = positioningBox.borderLeft();
+            right = positioningBox.borderRight();
+            top = positioningBox.borderTop();
+            bottom = positioningBox.borderBottom();
+            if (fillLayer.origin() == ContentFillBox) {
+                left += positioningBox.paddingLeft();
+                right += positioningBox.paddingRight();
+                top += positioningBox.paddingTop();
+                bottom += positioningBox.paddingBottom();
+            }
+        }
+
+        if (isLayoutView) {
+            // The background of the box generated by the root element covers the entire canvas and will
+            // be painted by the view object, but the we should still use the root element box for
+            // positioning.
+            positioningAreaSize = pixelSnappedIntSize(rootBox->size() - LayoutSize(left + right, top + bottom), rootBox->location());
+            // The input paint rect is specified in root element local coordinate (i.e. a transform
+            // is applied on the context for painting), and is expanded to cover the whole canvas.
+            // Since left/top is relative to the paint rect, we need to offset them back.
+            left -= paintRect.x();
+            top -= paintRect.y();
+        } else {
+            positioningAreaSize = pixelSnappedIntSize(paintRect.size() - LayoutSize(left + right, top + bottom), paintRect.location());
+        }
+    } else {
+        setHasNonLocalGeometry();
+
+        IntRect viewportRect = pixelSnappedIntRect(obj.viewRect());
+        if (fixedBackgroundPaintsInLocalCoordinates(obj, globalPaintFlags))
+            viewportRect.setLocation(IntPoint());
+        else if (FrameView* frameView = obj.view()->frameView())
+            viewportRect.setLocation(frameView->scrollPosition());
+
+        if (paintContainer) {
+            IntPoint absoluteContainerOffset = roundedIntPoint(paintContainer->localToAbsolute(FloatPoint()));
+            viewportRect.moveBy(-absoluteContainerOffset);
+        }
+
+        setDestRect(viewportRect);
+        positioningAreaSize = destRect().size();
+    }
+
+    const LayoutObject* clientForBackgroundImage = backgroundObject ? backgroundObject : &obj;
+    IntSize fillTileSize = calculateFillTileSize(positioningBox, fillLayer, positioningAreaSize);
+    fillLayer.image()->setContainerSizeForLayoutObject(clientForBackgroundImage, fillTileSize, obj.style()->effectiveZoom());
+    setTileSize(fillTileSize);
+
+    EFillRepeat backgroundRepeatX = fillLayer.repeatX();
+    EFillRepeat backgroundRepeatY = fillLayer.repeatY();
+    int availableWidth = positioningAreaSize.width() - tileSize().width();
+    int availableHeight = positioningAreaSize.height() - tileSize().height();
+
+    LayoutUnit computedXPosition = roundedMinimumValueForLength(fillLayer.xPosition(), availableWidth);
+    if (backgroundRepeatX == RoundFill && positioningAreaSize.width() > 0 && fillTileSize.width() > 0) {
+        long nrTiles = std::max(1l, lroundf((float)positioningAreaSize.width() / fillTileSize.width()));
+
+        // Round tile size per css3-background spec.
+        fillTileSize.setWidth(lroundf(positioningAreaSize.width() / (float)nrTiles));
+
+        // Maintain aspect ratio if background-size: auto is set
+        if (fillLayer.size().size.height().isAuto() && backgroundRepeatY != RoundFill) {
+            fillTileSize.setHeight(fillTileSize.height() * positioningAreaSize.width() / (nrTiles * fillTileSize.width()));
+        }
+
+        setTileSize(fillTileSize);
+        setPhaseX(tileSize().width() ? tileSize().width() - roundToInt(computedXPosition + left) % tileSize().width() : 0);
+        setSpaceSize(IntSize());
+    }
+
+    LayoutUnit computedYPosition = roundedMinimumValueForLength(fillLayer.yPosition(), availableHeight);
+    if (backgroundRepeatY == RoundFill && positioningAreaSize.height() > 0 && fillTileSize.height() > 0) {
+        long nrTiles = std::max(1l, lroundf((float)positioningAreaSize.height() / fillTileSize.height()));
+
+        // Round tile size per css3-background spec.
+        fillTileSize.setHeight(lroundf(positioningAreaSize.height() / (float)nrTiles));
+
+        // Maintain aspect ratio if background-size: auto is set
+        if (fillLayer.size().size.width().isAuto() && backgroundRepeatX != RoundFill) {
+            fillTileSize.setWidth(fillTileSize.width() * positioningAreaSize.height() / (nrTiles * fillTileSize.height()));
+        }
+
+        setTileSize(fillTileSize);
+        setPhaseY(tileSize().height() ? tileSize().height() - roundToInt(computedYPosition + top) % tileSize().height() : 0);
+        setSpaceSize(IntSize());
+    }
+
+    if (backgroundRepeatX == RepeatFill) {
+        int xOffset = fillLayer.backgroundXOrigin() == RightEdge ? availableWidth - computedXPosition : computedXPosition;
+        setPhaseX(tileSize().width() ? tileSize().width() - roundToInt(xOffset + left) % tileSize().width() : 0);
+        setSpaceSize(IntSize());
+    } else if (backgroundRepeatX == SpaceFill && fillTileSize.width() > 0) {
+        int space = getSpaceBetweenImageTiles(positioningAreaSize.width(), tileSize().width());
+        int actualWidth = tileSize().width() + space;
+
+        if (space >= 0) {
+            computedXPosition = roundedMinimumValueForLength(Length(), availableWidth);
+            setSpaceSize(IntSize(space, 0));
+            setPhaseX(actualWidth ? actualWidth - roundToInt(computedXPosition + left) % actualWidth : 0);
+        } else {
+            backgroundRepeatX = NoRepeatFill;
+        }
+    }
+    if (backgroundRepeatX == NoRepeatFill) {
+        int xOffset = fillLayer.backgroundXOrigin() == RightEdge ? availableWidth - computedXPosition : computedXPosition;
+        setNoRepeatX(left + xOffset);
+        setSpaceSize(IntSize(0, spaceSize().height()));
+    }
+
+    if (backgroundRepeatY == RepeatFill) {
+        int yOffset = fillLayer.backgroundYOrigin() == BottomEdge ? availableHeight - computedYPosition : computedYPosition;
+        setPhaseY(tileSize().height() ? tileSize().height() - roundToInt(yOffset + top) % tileSize().height() : 0);
+        setSpaceSize(IntSize(spaceSize().width(), 0));
+    } else if (backgroundRepeatY == SpaceFill && fillTileSize.height() > 0) {
+        int space = getSpaceBetweenImageTiles(positioningAreaSize.height(), tileSize().height());
+        int actualHeight = tileSize().height() + space;
+
+        if (space >= 0) {
+            computedYPosition = roundedMinimumValueForLength(Length(), availableHeight);
+            setSpaceSize(IntSize(spaceSize().width(), space));
+            setPhaseY(actualHeight ? actualHeight - roundToInt(computedYPosition + top) % actualHeight : 0);
+        } else {
+            backgroundRepeatY = NoRepeatFill;
+        }
+    }
+    if (backgroundRepeatY == NoRepeatFill) {
+        int yOffset = fillLayer.backgroundYOrigin() == BottomEdge ? availableHeight - computedYPosition : computedYPosition;
+        setNoRepeatY(top + yOffset);
+        setSpaceSize(IntSize(spaceSize().width(), 0));
+    }
+
+    if (fixedAttachment)
+        useFixedAttachment(snappedPaintRect.location());
+
+    clip(snappedPaintRect);
+}
+
 } // namespace blink