Region

最新推荐文章于 2022-06-04 11:59:35 发布

原创最新推荐文章于 2022-06-04 11:59:35 发布 · 879 阅读

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本文深入解析了SurfaceFlinger中computeVisibleRegions函数的工作原理，该函数负责计算每一层的可见区域、覆盖区域及脏区域，并更新各层的状态。通过详细的代码注释，读者能够了解到如何处理透明和不透明表面，以及如何计算各层之间的相对位置。

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void SurfaceFlinger::computeVisibleRegions(
        const LayerVector& currentLayers, uint32_t layerStack,
        Region& outDirtyRegion, Region& outOpaqueRegion)
{
    ATRACE_CALL();

    Region aboveOpaqueLayers;
    Region aboveCoveredLayers;
    Region dirty;

    outDirtyRegion.clear();

    size_t i = currentLayers.size();
    while (i--) {
        const sp<Layer>& layer = currentLayers[i];

        // start with the whole surface at its current location
        const Layer::State& s(layer->drawingState());

        // only consider the layers on the given layer stack
        if (s.layerStack != layerStack)
            continue;

        /*
         * opaqueRegion: area of a surface that is fully opaque.
         */
        Region opaqueRegion;

        /*
         * visibleRegion: area of a surface that is visible on screen
         * and not fully transparent. This is essentially the layer's
         * footprint minus the opaque regions above it.
                 * Areas covered by a translucent surface are considered visible.
         */
        Region visibleRegion;

        /*
         * coveredRegion: area of a surface that is covered by all
         * visible regions above it (which includes the translucent areas).
         */
        Region coveredRegion;

        /*
         * transparentRegion: area of a surface that is hinted to be completely
         * transparent. This is only used to tell when the layer has no visible
         * non-transparent regions and can be removed from the layer list. It
         * does not affect the visibleRegion of this layer or any layers
         * beneath it. The hint may not be correct if apps don't respect the
         * SurfaceView restrictions (which, sadly, some don't).
         */
        Region transparentRegion;


        // handle hidden surfaces by setting the visible region to empty
        if (CC_LIKELY(layer->isVisible())) {
            const bool translucent = !layer->isOpaque();
            Rect bounds(s.transform.transform(layer->computeBounds()));
            visibleRegion.set(bounds);
            if (!visibleRegion.isEmpty()) {
                // Remove the transparent area from the visible region
                if (translucent) {
                    const Transform tr(s.transform);
                    if (tr.transformed()) {
                        if (tr.preserveRects()) {

                        if (tr.preserveRects()) {
                            // transform the transparent region
                            transparentRegion = tr.transform(s.activeTransparentRegion);
                        } else {
                            // transformation too complex, can't do the
                            // transparent region optimization.
                            transparentRegion.clear();
                        }
                    } else {
                        transparentRegion = s.activeTransparentRegion;
                    }
                }

                // compute the opaque region
                const int32_t layerOrientation = s.transform.getOrientation();
                if (s.alpha==255 && !translucent &&
                        ((layerOrientation & Transform::ROT_INVALID) == false)) {
                    // the opaque region is the layer's footprint
                    opaqueRegion = visibleRegion;
                }
            }
        }

        // Clip the covered region to the visible region
        coveredRegion = aboveCoveredLayers.intersect(visibleRegion);

        // Update aboveCoveredLayers for next (lower) layer
        aboveCoveredLayers.orSelf(visibleRegion);

        // subtract the opaque region covered by the layers above us
        visibleRegion.subtractSelf(aboveOpaqueLayers);

        // compute this layer's dirty region
        if (layer->contentDirty) {
            // we need to invalidate the whole region
            dirty = visibleRegion;
            // as well, as the old visible region
            dirty.orSelf(layer->visibleRegion);
            layer->contentDirty = false;
        } else {
            /* compute the exposed region:
             *   the exposed region consists of two components:
             *   1) what's VISIBLE now and was COVERED before
             *   2) what's EXPOSED now less what was EXPOSED before
             *
             * note that (1) is conservative, we start with the whole
             * visible region but only keep what used to be covered by
             * something -- which mean it may have been exposed.
             *
             * (2) handles areas that were not covered by anything but got
             * exposed because of a resize.
             */
            const Region newExposed = visibleRegion - coveredRegion;
            const Region oldVisibleRegion = layer->visibleRegion;
            const Region oldCoveredRegion = layer->coveredRegion;
            const Region oldExposed = oldVisibleRegion - oldCoveredRegion;
            dirty = (visibleRegion&oldCoveredRegion) | (newExposed-oldExposed);
        }
        dirty.subtractSelf(aboveOpaqueLayers);

        // accumulate to the screen dirty region

        outDirtyRegion.orSelf(dirty);

        // Update aboveOpaqueLayers for next (lower) layer
        aboveOpaqueLayers.orSelf(opaqueRegion);

        // Store the visible region in screen space
        layer->setVisibleRegion(visibleRegion);
        layer->setCoveredRegion(coveredRegion);
        layer->setVisibleNonTransparentRegion(
                visibleRegion.subtract(transparentRegion));
    }

    outOpaqueRegion = aboveOpaqueLayers;
}

Region:

可以包含多个rect -》 mStorge;

opengl绘制的时候可以仅仅绘制这些独立的，甚至是隔开的区域；

mbounds分裂

最重要的函数：
void Region::boolean_operation(int op, Region& dst,
        const Region& lhs,
        const Region& rhs, int dx, int dy)
{    SkRegion::Op sk_op;
    switch (op) {
        case op_or: sk_op = SkRegion::kUnion_Op; name="OR"; break;
        case op_xor: sk_op = SkRegion::kUnion_XOR; name="XOR"; break;
        case op_and: sk_op = SkRegion::kIntersect_Op; name="AND"; break;
        case op_nand: sk_op = SkRegion::kDifference_Op; name="NAND"; break;
    }
    sk_dst.op(sk_lhs, sk_rhs, sk_op);     //调用skia的函数

}

数据成员
Rect mBounds; 
Vector<Rect>    mStorage;



isEmpty                             Returns true if the rectangle is empty (left >= right or top >= bottom)
    
mBounds    inline  bool        isEmpty() const     { return mBounds.isEmpty();  }
    inline  bool        isRect() const      { return mStorage.isEmpty(); }

    inline  Rect        getBounds() const   { return mBounds; }
    inline  Rect        bounds() const      { return getBounds(); }
Region::const_iterator Region::begin() const {
    return isRect() ? &mBounds : mStorage.array();
}

Region::const_iterator Region::end() const {
    if (isRect()) {
        if (isEmpty()) {
            return &mBounds;
        } else {
            return &mBounds + 1;
        }
    } else {
        return mStorage.array() + mStorage.size();
    }
}