C++ DrawingContext::raw方法代码示例

/**
 * Rasterize items.
 * This method submits the drawing opeartions required to draw this item
 * to the supplied DrawingContext, restricting drawing the specified area.
 *
 * This method does some common tasks and calls the item-specific rendering
 * function, _renderItem(), to render e.g. paths or bitmaps.
 *
 * @param flags Rendering options. This deals mainly with cache control.
 */
unsigned
DrawingItem::render(DrawingContext &dc, Geom::IntRect const &area, unsigned flags, DrawingItem *stop_at)
{
    bool outline = _drawing.outline();
    bool render_filters = _drawing.renderFilters();

    // stop_at is handled in DrawingGroup, but this check is required to handle the case
    // where a filtered item with background-accessing filter has enable-background: new
    if (this == stop_at) return RENDER_STOP;

    // If we are invisible, return immediately
    if (!_visible) return RENDER_OK;
    if (_ctm.isSingular(1e-18)) return RENDER_OK;

    // TODO convert outline rendering to a separate virtual function
    if (outline) {
        _renderOutline(dc, area, flags);
        return RENDER_OK;
    }

    // carea is the area to paint
    Geom::OptIntRect carea = Geom::intersect(area, _drawbox);
    if (!carea) return RENDER_OK;

    if (_antialias) {
        cairo_set_antialias(dc.raw(), CAIRO_ANTIALIAS_DEFAULT);
    } else {
        cairo_set_antialias(dc.raw(), CAIRO_ANTIALIAS_NONE);
    }

    // render from cache if possible
    if (_cached) {
        if (_cache) {
            _cache->prepare();
            set_cairo_blend_operator( dc, _mix_blend_mode );

            _cache->paintFromCache(dc, carea);
            if (!carea) return RENDER_OK;
        } else {
            // There is no cache. This could be because caching of this item
            // was just turned on after the last update phase, or because
            // we were previously outside of the canvas.
            Geom::OptIntRect cl = _drawing.cacheLimit();
            cl.intersectWith(_drawbox);
            if (cl) {
                _cache = new DrawingCache(*cl);
            }
        }
    } else {
        // if our caching was turned off after the last update, it was already
        // deleted in setCached()
    }

    // determine whether this shape needs intermediate rendering.
    bool needs_intermediate_rendering = false;
    bool &nir = needs_intermediate_rendering;
    bool needs_opacity = (_opacity < 0.995);

    // this item needs an intermediate rendering if:
    nir |= (_clip != NULL); // 1. it has a clipping path
    nir |= (_mask != NULL); // 2. it has a mask
    nir |= (_filter != NULL && render_filters); // 3. it has a filter
    nir |= needs_opacity; // 4. it is non-opaque
    nir |= (_cache != NULL); // 5. it is cached
    nir |= (_mix_blend_mode != SP_CSS_BLEND_NORMAL); // 6. Blend mode not normal
    nir |= (_isolation == SP_CSS_ISOLATION_ISOLATE); // 7. Explicit isolatiom

    /* How the rendering is done.
     *
     * Clipping, masking and opacity are done by rendering them to a surface
     * and then compositing the object's rendering onto it with the IN operator.
     * The object itself is rendered to a group.
     *
     * Opacity is done by rendering the clipping path with an alpha
     * value corresponding to the opacity. If there is no clipping path,
     * the entire intermediate surface is painted with alpha corresponding
     * to the opacity value.
     */

    // Short-circuit the simple case.
    // We also use this path for filter background rendering, because masking, clipping,
    // filters and opacity do not apply when rendering the ancestors of the filtered
    // element
    if ((flags & RENDER_FILTER_BACKGROUND) || !needs_intermediate_rendering) {
        return _renderItem(dc, *carea, flags & ~RENDER_FILTER_BACKGROUND, stop_at);
    }

    // iarea is the bounding box for intermediate rendering
    // Note 1: Pixels inside iarea but outside carea are invalid
    //         (incomplete filter dependence region).
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