1
2/*
3 * Copyright 2006 The Android Open Source Project
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9
10#ifndef SkMaskFilter_DEFINED
11#define SkMaskFilter_DEFINED
12
13#include "SkFlattenable.h"
14#include "SkMask.h"
15
16class SkBlitter;
17class SkBounder;
18class SkMatrix;
19class SkPath;
20class SkRasterClip;
21
22/** \class SkMaskFilter
23
24    SkMaskFilter is the base class for object that perform transformations on
25    an alpha-channel mask before drawing it. A subclass of SkMaskFilter may be
26    installed into a SkPaint. Once there, each time a primitive is drawn, it
27    is first scan converted into a SkMask::kA8_Format mask, and handed to the
28    filter, calling its filterMask() method. If this returns true, then the
29    new mask is used to render into the device.
30
31    Blur and emboss are implemented as subclasses of SkMaskFilter.
32*/
33class SkMaskFilter : public SkFlattenable {
34public:
35    SkMaskFilter() {}
36
37    /** Returns the format of the resulting mask that this subclass will return
38        when its filterMask() method is called.
39    */
40    virtual SkMask::Format getFormat() = 0;
41
42    /** Create a new mask by filter the src mask.
43        If src.fImage == null, then do not allocate or create the dst image
44        but do fill out the other fields in dstMask.
45        If you do allocate a dst image, use SkMask::AllocImage()
46        If this returns false, dst mask is ignored.
47        @param  dst the result of the filter. If src.fImage == null, dst should not allocate its image
48        @param src the original image to be filtered.
49        @param matrix the CTM
50        @param margin   if not null, return the buffer dx/dy need when calculating the effect. Used when
51                        drawing a clipped object to know how much larger to allocate the src before
52                        applying the filter. If returning false, ignore this parameter.
53        @return true if the dst mask was correctly created.
54    */
55    virtual bool filterMask(SkMask* dst, const SkMask& src, const SkMatrix&,
56                            SkIPoint* margin);
57
58    virtual void flatten(SkFlattenableWriteBuffer& ) {}
59
60    enum BlurType {
61        kNone_BlurType,    //!< this maskfilter is not a blur
62        kNormal_BlurType,  //!< fuzzy inside and outside
63        kSolid_BlurType,   //!< solid inside, fuzzy outside
64        kOuter_BlurType,   //!< nothing inside, fuzzy outside
65        kInner_BlurType,   //!< fuzzy inside, nothing outside
66    };
67
68    struct BlurInfo {
69        SkScalar fRadius;
70        bool     fIgnoreTransform;
71        bool     fHighQuality;
72    };
73
74    /**
75     *  Optional method for maskfilters that can be described as a blur. If so,
76     *  they return the corresponding BlurType and set the fields in BlurInfo
77     *  (if not null). If they cannot be described as a blur, they return
78     *  kNone_BlurType and ignore the info parameter.
79     */
80    virtual BlurType asABlur(BlurInfo*) const;
81
82    /**
83     * The fast bounds function is used to enable the paint to be culled early
84     * in the drawing pipeline. This function accepts the current bounds of the
85     * paint as its src param and the filter adjust those bounds using its
86     * current mask and returns the result using the dest param. Callers are
87     * allowed to provide the same struct for both src and dest so each
88     * implementation must accomodate that behavior.
89     *
90     *  The default impl calls filterMask with the src mask having no image,
91     *  but subclasses may override this if they can compute the rect faster.
92     */
93    virtual void computeFastBounds(const SkRect& src, SkRect* dest);
94
95protected:
96    // empty for now, but lets get our subclass to remember to init us for the future
97    SkMaskFilter(SkFlattenableReadBuffer&) {}
98
99private:
100    friend class SkDraw;
101
102    /** Helper method that, given a path in device space, will rasterize it into a kA8_Format mask
103     and then call filterMask(). If this returns true, the specified blitter will be called
104     to render that mask. Returns false if filterMask() returned false.
105     This method is not exported to java.
106     */
107    bool filterPath(const SkPath& devPath, const SkMatrix& devMatrix,
108                    const SkRasterClip&, SkBounder*, SkBlitter* blitter);
109};
110
111#endif
112
113