include/core/SkMaskFilter.h

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef SkMaskFilter_DEFINED
#define SkMaskFilter_DEFINED

#include "SkFlattenable.h"
#include "SkMask.h"

class SkBlitter;
class SkBounder;
class SkMatrix;
class SkPath;
class SkRegion;

/** \class SkMaskFilter

    SkMaskFilter is the base class for object that perform transformations on
    an alpha-channel mask before drawing it. A subclass of SkMaskFilter may be
    installed into a SkPaint. Once there, each time a primitive is drawn, it
    is first scan converted into a SkMask::kA8_Format mask, and handed to the
    filter, calling its filterMask() method. If this returns true, then the
    new mask is used to render into the device.

    Blur and emboss are implemented as subclasses of SkMaskFilter.
*/
class SkMaskFilter : public SkFlattenable {
public:
    SkMaskFilter() {}

    /** Returns the format of the resulting mask that this subclass will return
        when its filterMask() method is called.
    */
    virtual SkMask::Format  getFormat() = 0;

    /** Create a new mask by filter the src mask.
        If src.fImage == null, then do not allocate or create the dst image
        but do fill out the other fields in dstMask.
        If you do allocate a dst image, use SkMask::AllocImage()
        If this returns false, dst mask is ignored.
        @param  dst the result of the filter. If src.fImage == null, dst should not allocate its image
        @param src the original image to be filtered.
        @param matrix the CTM
        @param margin   if not null, return the buffer dx/dy need when calculating the effect. Used when
                        drawing a clipped object to know how much larger to allocate the src before
                        applying the filter. If returning false, ignore this parameter.
        @return true if the dst mask was correctly created.
    */
    virtual bool filterMask(SkMask* dst, const SkMask& src, const SkMatrix&, SkIPoint* margin);

    /** Helper method that, given a path in device space, will rasterize it into a kA8_Format mask
        and then call filterMask(). If this returns true, the specified blitter will be called
        to render that mask. Returns false if filterMask() returned false.
        This method is not exported to java.
    */
    bool filterPath(const SkPath& devPath, const SkMatrix& devMatrix,
                    const SkRegion& devClip, SkBounder*, SkBlitter* blitter);

    virtual void flatten(SkFlattenableWriteBuffer& ) {}
protected:
    // empty for now, but lets get our subclass to remember to init us for the future
    SkMaskFilter(SkFlattenableReadBuffer&) {}
};

/** \class SkAutoMaskImage

    Stack class used to manage the fImage buffer in a SkMask.
    When this object loses scope, the buffer is freed with SkMask::FreeImage().
*/
class SkAutoMaskImage {
public:
    SkAutoMaskImage(SkMask* mask, bool alloc)
    {
        if (alloc)
            mask->fImage = SkMask::AllocImage(mask->computeImageSize());
        fImage = mask->fImage;
    }
    ~SkAutoMaskImage()
    {
        SkMask::FreeImage(fImage);
    }
private:
    uint8_t*    fImage;
};

#endif