C++ FloatRect::uniteIfNonZero方法代码示例

void CCDamageTracker::extendDamageForLayer(CCLayerImpl* layer, FloatRect& targetDamageRect)
{
    // There are two ways that a layer can damage a region of the target surface:
    //   1. Property change (e.g. opacity, position, transforms):
    //        - the entire region of the layer itself damages the surface.
    //        - the old layer region also damages the surface, because this region is now exposed.
    //        - note that in many cases the old and new layer rects may overlap, which is fine.
    //
    //   2. Repaint/update: If a region of the layer that was repainted/updated, that
    //      region damages the surface.
    //
    // Property changes take priority over update rects.
    //
    // This method is called when we want to consider how a layer contributes to its
    // targetRenderSurface, even if that layer owns the targetRenderSurface itself.
    // To consider how a layer's targetSurface contributes to the ancestorSurface,
    // extendDamageForRenderSurface() must be called instead.

    bool layerIsNew = false;
    FloatRect oldRectInTargetSpace = removeRectFromCurrentFrame(layer->id(), layerIsNew);

    FloatRect rectInTargetSpace = CCMathUtil::mapClippedRect(layer->drawTransform(), FloatRect(FloatPoint::zero(), layer->contentBounds()));
    saveRectForNextFrame(layer->id(), rectInTargetSpace);

    if (layerIsNew || layerNeedsToRedrawOntoItsTargetSurface(layer)) {
        // If a layer is new or has changed, then its entire layer rect affects the target surface.
        targetDamageRect.uniteIfNonZero(rectInTargetSpace);

        // The layer's old region is now exposed on the target surface, too.
        // Note oldRectInTargetSpace is already in target space.
        targetDamageRect.uniteIfNonZero(oldRectInTargetSpace);
    } else if (!layer->updateRect().isEmpty()) {
        // If the layer properties havent changed, then the the target surface is only
        // affected by the layer's update area, which could be empty.
        FloatRect updateContentRect = layer->updateRect();
        float widthScale = layer->contentBounds().width() / static_cast<float>(layer->bounds().width());
        float heightScale = layer->contentBounds().height() / static_cast<float>(layer->bounds().height());
        updateContentRect.scale(widthScale, heightScale);

        FloatRect updateRectInTargetSpace = CCMathUtil::mapClippedRect(layer->drawTransform(), updateContentRect);
        targetDamageRect.uniteIfNonZero(updateRectInTargetSpace);
    }
}

void CCDamageTracker::updateDamageTrackingState(const Vector<CCLayerImpl*>& layerList, int targetSurfaceLayerID, bool targetSurfacePropertyChangedOnlyFromDescendant, const IntRect& targetSurfaceContentRect, CCLayerImpl* targetSurfaceMaskLayer, const WebKit::WebFilterOperations& filters)
{
    //
    // This function computes the "damage rect" of a target surface, and updates the state
    // that is used to correctly track damage across frames. The damage rect is the region
    // of the surface that may have changed and needs to be redrawn. This can be used to
    // scissor what is actually drawn, to save GPU computation and bandwidth.
    //
    // The surface's damage rect is computed as the union of all possible changes that
    // have happened to the surface since the last frame was drawn. This includes:
    //   - any changes for existing layers/surfaces that contribute to the target surface
    //   - layers/surfaces that existed in the previous frame, but no longer exist.
    //
    // The basic algorithm for computing the damage region is as follows:
    //
    //   1. compute damage caused by changes in active/new layers
    //       for each layer in the layerList:
    //           if the layer is actually a renderSurface:
    //               add the surface's damage to our target surface.
    //           else
    //               add the layer's damage to the target surface.
    //
    //   2. compute damage caused by the target surface's mask, if it exists.
    //
    //   3. compute damage caused by old layers/surfaces that no longer exist
    //       for each leftover layer:
    //           add the old layer/surface bounds to the target surface damage.
    //
    //   4. combine all partial damage rects to get the full damage rect.
    //
    // Additional important points:
    //
    // - This algorithm is implicitly recursive; it assumes that descendant surfaces have
    //   already computed their damage.
    //
    // - Changes to layers/surfaces indicate "damage" to the target surface; If a layer is
    //   not changed, it does NOT mean that the layer can skip drawing. All layers that
    //   overlap the damaged region still need to be drawn. For example, if a layer
    //   changed its opacity, then layers underneath must be re-drawn as well, even if
    //   they did not change.
    //
    // - If a layer/surface property changed, the old bounds and new bounds may overlap...
    //   i.e. some of the exposed region may not actually be exposing anything. But this
    //   does not artificially inflate the damage rect. If the layer changed, its entire
    //   old bounds would always need to be redrawn, regardless of how much it overlaps
    //   with the layer's new bounds, which also need to be entirely redrawn.
    //
    // - See comments in the rest of the code to see what exactly is considered a "change"
    //   in a layer/surface.
    //
    // - To correctly manage exposed rects, two RectMaps are maintained:
    //
    //      1. The "current" map contains all the layer bounds that contributed to the
    //         previous frame (even outside the previous damaged area). If a layer changes
    //         or does not exist anymore, those regions are then exposed and damage the
    //         target surface. As the algorithm progresses, entries are removed from the
    //         map until it has only leftover layers that no longer exist.
    //
    //      2. The "next" map starts out empty, and as the algorithm progresses, every
    //         layer/surface that contributes to the surface is added to the map.
    //
    //      3. After the damage rect is computed, the two maps are swapped, so that the
    //         damage tracker is ready for the next frame.
    //

    // These functions cannot be bypassed with early-exits, even if we know what the
    // damage will be for this frame, because we need to update the damage tracker state
    // to correctly track the next frame.
    FloatRect damageFromActiveLayers = trackDamageFromActiveLayers(layerList, targetSurfaceLayerID);
    FloatRect damageFromSurfaceMask = trackDamageFromSurfaceMask(targetSurfaceMaskLayer);
    FloatRect damageFromLeftoverRects = trackDamageFromLeftoverRects();

    FloatRect damageRectForThisUpdate;

    if (m_forceFullDamageNextUpdate || targetSurfacePropertyChangedOnlyFromDescendant) {
        damageRectForThisUpdate = targetSurfaceContentRect;
        m_forceFullDamageNextUpdate = false;
    } else {
        // FIXME: can we clamp this damage to the surface's content rect? (affects performance, but not correctness)
        damageRectForThisUpdate = damageFromActiveLayers;
        damageRectForThisUpdate.uniteIfNonZero(damageFromSurfaceMask);
        damageRectForThisUpdate.uniteIfNonZero(damageFromLeftoverRects);

        if (filters.hasFilterThatMovesPixels())
            expandRectWithFilters(damageRectForThisUpdate, filters);
    }

    // Damage accumulates until we are notified that we actually did draw on that frame.
    m_currentDamageRect.uniteIfNonZero(damageRectForThisUpdate);

    // The next history map becomes the current map for the next frame. Note this must
    // happen every frame to correctly track changes, even if damage accumulates over
    // multiple frames before actually being drawn.
    swap(m_currentRectHistory, m_nextRectHistory);
}

void CCDamageTracker::extendDamageForRenderSurface(CCLayerImpl* layer, FloatRect& targetDamageRect)
{
    // There are two ways a "descendant surface" can damage regions of the "target surface":
    //   1. Property change:
    //        - a surface's geometry can change because of
    //            - changes to descendants (i.e. the subtree) that affect the surface's content rect
    //            - changes to ancestor layers that propagate their property changes to their entire subtree.
    //        - just like layers, both the old surface rect and new surface rect will
    //          damage the target surface in this case.
    //
    //   2. Damage rect: This surface may have been damaged by its own layerList as well, and that damage
    //      should propagate to the target surface.
    //

    CCRenderSurface* renderSurface = layer->renderSurface();

    bool surfaceIsNew = false;
    FloatRect oldSurfaceRect = removeRectFromCurrentFrame(layer->id(), surfaceIsNew);

    FloatRect surfaceRectInTargetSpace = renderSurface->drawableContentRect(); // already includes replica if it exists.
    saveRectForNextFrame(layer->id(), surfaceRectInTargetSpace);

    FloatRect damageRectInLocalSpace;
    if (surfaceIsNew || renderSurface->surfacePropertyChanged() || layer->layerSurfacePropertyChanged()) {
        // The entire surface contributes damage.
        damageRectInLocalSpace = renderSurface->contentRect();

        // The surface's old region is now exposed on the target surface, too.
        targetDamageRect.uniteIfNonZero(oldSurfaceRect);
    } else {
        // Only the surface's damageRect will damage the target surface.
        damageRectInLocalSpace = renderSurface->damageTracker()->currentDamageRect();
    }

    // If there was damage, transform it to target space, and possibly contribute its reflection if needed.
    if (!damageRectInLocalSpace.isEmpty()) {
        const WebTransformationMatrix& drawTransform = renderSurface->drawTransform();
        FloatRect damageRectInTargetSpace = CCMathUtil::mapClippedRect(drawTransform, damageRectInLocalSpace);
        targetDamageRect.uniteIfNonZero(damageRectInTargetSpace);

        if (layer->replicaLayer()) {
            const WebTransformationMatrix& replicaDrawTransform = renderSurface->replicaDrawTransform();
            targetDamageRect.uniteIfNonZero(CCMathUtil::mapClippedRect(replicaDrawTransform, damageRectInLocalSpace));
        }
    }

    // If there was damage on the replica's mask, then the target surface receives that damage as well.
    if (layer->replicaLayer() && layer->replicaLayer()->maskLayer()) {
        CCLayerImpl* replicaMaskLayer = layer->replicaLayer()->maskLayer();

        bool replicaIsNew = false;
        removeRectFromCurrentFrame(replicaMaskLayer->id(), replicaIsNew);

        const WebTransformationMatrix& replicaDrawTransform = renderSurface->replicaDrawTransform();
        FloatRect replicaMaskLayerRect = CCMathUtil::mapClippedRect(replicaDrawTransform, FloatRect(FloatPoint::zero(), FloatSize(replicaMaskLayer->bounds().width(), replicaMaskLayer->bounds().height())));
        saveRectForNextFrame(replicaMaskLayer->id(), replicaMaskLayerRect);

        // In the current implementation, a change in the replica mask damages the entire replica region.
        if (replicaIsNew || replicaMaskLayer->layerPropertyChanged() || !replicaMaskLayer->updateRect().isEmpty())
            targetDamageRect.uniteIfNonZero(replicaMaskLayerRect);
    }

    // If the layer has a background filter, this may cause pixels in our surface to be expanded, so we will need to expand any damage
    // at or below this layer. We expand the damage from this layer too, as we need to readback those pixels from the surface with only
    // the contents of layers below this one in them. This means we need to redraw any pixels in the surface being used for the blur in
    // this layer this frame.
    if (layer->backgroundFilters().hasFilterThatMovesPixels())
        expandDamageRectInsideRectWithFilters(targetDamageRect, surfaceRectInTargetSpace, layer->backgroundFilters());
}