分类：
2009-03-23 14:47:54
/** Enum describing how to treat edges when performing quick-reject tests
of a geometry against the current clip. Treating them as antialiased
(kAA_EdgeType) will take into account the extra pixels that may be drawn
if the edge does not lie exactly on a device pixel boundary (after being
transformed by the current matrix).
*/
//处理反锯齿问题
//判断当前的clip和给定的矩形是否有交错，添加antialiased参数会使得判断更精确
enum EdgeType {
/** Treat the edges as B&W (not antialiased) for the purposes of testing
against the current clip
*/
kBW_EdgeType,
/** Treat the edges as antialiased for the purposes of testing
against the current clip
*/
kAA_EdgeType
};
/** Return true if the specified rectangle, after being transformed by the
current matrix, would lie completely outside of the current clip. Call
this to check if an area you intend to draw into is clipped out (and
therefore you can skip making the draw calls).
@param rect the rect to compare with the current clip
@param et specifies how to treat the edges (see EdgeType)
@return true if the rect (transformed by the canvas' matrix) does not
intersect with the canvas' clip
*/
//判断当前的clip和给定的矩形是否有交错，如果没有交错，就返回true
bool quickReject(const SkRect& rect, EdgeType et) const;
/** Return true if the specified path, after being transformed by the
current matrix, would lie completely outside of the current clip. Call
this to check if an area you intend to draw into is clipped out (and
therefore you can skip making the draw calls). Note, for speed it may
return false even if the path itself might not intersect the clip
(i.e. the bounds of the path intersects, but the path does not).
@param path The path to compare with the current clip
@param et specifies how to treat the edges (see EdgeType)
@return true if the path (transformed by the canvas' matrix) does not
intersect with the canvas' clip
*/
bool quickReject(const SkPath& path, EdgeType et) const;
/** Return true if the horizontal band specified by top and bottom is
completely clipped out. This is a conservative calculation, meaning
that it is possible that if the method returns false, the band may still
in fact be clipped out, but the converse is not true. If this method
returns true, then the band is guaranteed to be clipped out.
@param top The top of the horizontal band to compare with the clip
@param bottom The bottom of the horizontal and to compare with the clip
@return true if the horizontal band is completely clipped out (i.e. does
not intersect the current clip)
*/
bool quickRejectY(SkScalar top, SkScalar bottom, EdgeType et) const;
/** Return the bounds of the current clip (in local coordinates) in the
bounds parameter, and return true if it is non-empty. This can be useful
in a way similar to quickReject, in that it tells you that drawing
outside of these bounds will be clipped out.
*/
//返回当前clip的边界矩形
bool getClipBounds(SkRect* bounds, EdgeType et = kAA_EdgeType) const;
/** Fill the entire canvas' bitmap (restricted to the current clip) with the
specified ARGB color, using the specified PorterDuff mode.
@param a the alpha component (0..255) of the color to fill the canvas
@param r the red component (0..255) of the color to fill the canvas
@param g the green component (0..255) of the color to fill the canvas
@param b the blue component (0..255) of the color to fill the canvas
@param mode the mode to apply the color in (defaults to SrcOver)
*/
//基于PorterDuff模式使用ARGB来填充整个canvas'的bitmap.
void drawARGB(U8CPU a, U8CPU r, U8CPU g, U8CPU b,
SkPorterDuff::Mode mode = SkPorterDuff::kSrcOver_Mode);
/** Fill the entire canvas' bitmap (restricted to the current clip) with the
specified color and porter-duff xfermode.
@param color the color to draw with
@param mode the mode to apply the color in (defaults to SrcOver)
*/
//基于PorterDuff模式使用SkColor来填充整个canvas'的bitmap.
void drawColor(SkColor color,
SkPorterDuff::Mode mode = SkPorterDuff::kSrcOver_Mode);
/** Fill the entire canvas' bitmap (restricted to the current clip) with the
specified paint.
@param paint The paint used to fill the canvas
*/
//基于PorterDuff模式使用SkPaint来填充整个canvas'的bitmap。注意这里的paint是有自己的一套绘画标准的。
virtual void drawPaint(const SkPaint& paint);
enum PointMode {
/** drawPoints draws each point separately */
kPoints_PointMode,
/** drawPoints draws each pair of points as a line segment */
kLines_PointMode,
/** drawPoints draws the array of points as a polygon */
kPolygon_PointMode
};
/** Draw a series of points, interpreted based on the PointMode mode. For
all modes, the count parameter is interpreted as the total number of
points. For kLine mode, count/2 line segments are drawn.
For kPoint mode, each point is drawn centered at its coordinate, and its
size is specified by the paint's stroke-width. It draws as a square,
unless the paint's cap-type is round, in which the points are drawn as
circles.
For kLine mode, each pair of points is drawn as a line segment,
respecting the paint's settings for cap/join/width.
For kPolygon mode, the entire array is drawn as a series of connected
line segments.
Note that, while similar, kLine and kPolygon modes draw slightly
differently than the equivalent path built with a series of moveto,
lineto calls, in that the path will draw all of its contours at once,
with no interactions if contours intersect each other (think XOR
xfermode). drawPoints always draws each element one at a time.
@param mode PointMode specifying how to draw the array of points.
@param count The number of points in the array
@param pts Array of points to draw
@param paint The paint used to draw the points
*/
//根据PointMode画一系列的点
//kPoints Mode: 在每个给定的坐标点画点。点的宽度由SkPaint的stroke-width决定。形状由SkPaint的cap-type决定，通常画正方形，如果指定圆形，就画圆形。
//kLines Mode: 画count/2的线段。如果传两个点，则画一条线段，如果传4个点，画两条线段: (pts[0] <--> pts[1]), (pts[2] <--> pts[3])。 注意pts[]的个数就是count的值。
//kPolygon Mode: 画多边形。如果传两个点，则画一条线段，如果传4个点，画三条线段: (pts[0] <--> pts[1]), (pts[1] <--> pts[2]), (pts[2] <--> pts[3])。 注意pts[]的个数就是count的值。
virtual void drawPoints(PointMode mode, size_t count, const SkPoint pts[],
const SkPaint& paint);
/** Helper method for drawing a single point. See drawPoints() for a more
details.
*/
void drawPoint(SkScalar x, SkScalar y, const SkPaint& paint);
/** Draws a single pixel in the specified color.
@param x The X coordinate of which pixel to draw
@param y The Y coordiante of which pixel to draw
@param color The color to draw
*/
void drawPoint(SkScalar x, SkScalar y, SkColor color);
/** Draw a line segment with the specified start and stop x,y coordinates,
using the specified paint. NOTE: since a line is always "framed", the
paint's Style is ignored.
@param x0 The x-coordinate of the start point of the line
@param y0 The y-coordinate of the start point of the line
@param x1 The x-coordinate of the end point of the line
@param y1 The y-coordinate of the end point of the line
@param paint The paint used to draw the line
*/
void drawLine(SkScalar x0, SkScalar y0, SkScalar x1, SkScalar y1,
const SkPaint& paint);
/** Draw the specified rectangle using the specified paint. The rectangle
will be filled or stroked based on the Style in the paint.
@param rect The rect to be drawn
@param paint The paint used to draw the rect
*/
virtual void drawRect(const SkRect& rect, const SkPaint& paint);
/** Draw the specified rectangle using the specified paint. The rectangle
will be filled or framed based on the Style in the paint.
@param rect The rect to be drawn
@param paint The paint used to draw the rect
*/
//画矩形，SkIRect和SkRect的区别是两者的坐标系统表示方法不同，SkIRect使用SkScalar来表示，SkRect使用int32_t来表示。
//SkScalar有两种表示方法：float和int32。如果使用float表示法，怎理论上将精度会提高
void drawIRect(const SkIRect& rect, const SkPaint& paint)
{
SkRect r;
r.set(rect); // promotes the ints to scalars
this->drawRect(r, paint);
}
/** Draw the specified rectangle using the specified paint. The rectangle
will be filled or framed based on the Style in the paint.
@param left The left side of the rectangle to be drawn
@param top The top side of the rectangle to be drawn
@param right The right side of the rectangle to be drawn
@param bottom The bottom side of the rectangle to be drawn
@param paint The paint used to draw the rect
*/
void drawRectCoords(SkScalar left, SkScalar top, SkScalar right,
SkScalar bottom, const SkPaint& paint);
/** Draw the specified oval using the specified paint. The oval will be
filled or framed based on the Style in the paint.
@param oval The rectangle bounds of the oval to be drawn
@param paint The paint used to draw the oval
*/
//画椭圆
void drawOval(const SkRect& oval, const SkPaint&);
/** Draw the specified circle using the specified paint. If radius is <= 0,
then nothing will be drawn. The circle will be filled
or framed based on the Style in the paint.
@param cx The x-coordinate of the center of the cirle to be drawn
@param cy The y-coordinate of the center of the cirle to be drawn
@param radius The radius of the cirle to be drawn
@param paint The paint used to draw the circle
*/
void drawCircle(SkScalar cx, SkScalar cy, SkScalar radius,
const SkPaint& paint);
/** Draw the specified arc, which will be scaled to fit inside the
specified oval. If the sweep angle is >= 360, then the oval is drawn
completely. Note that this differs slightly from SkPath::arcTo, which
treats the sweep angle mod 360.
@param oval The bounds of oval used to define the shape of the arc
@param startAngle Starting angle (in degrees) where the arc begins
@param sweepAngle Sweep angle (in degrees) measured clockwise
@param useCenter true means include the center of the oval. For filling
this will draw a wedge. False means just use the arc.
@param paint The paint used to draw the arc
*/
void drawArc(const SkRect& oval, SkScalar startAngle, SkScalar sweepAngle,
bool useCenter, const SkPaint& paint);
/** Draw the specified round-rect using the specified paint. The round-rect
will be filled or framed based on the Style in the paint.
@param rect The rectangular bounds of the roundRect to be drawn
@param rx The x-radius of the oval used to round the corners
@param ry The y-radius of the oval used to round the corners
@param paint The paint used to draw the roundRect
*/
void drawRoundRect(const SkRect& rect, SkScalar rx, SkScalar ry,
const SkPaint& paint);
/** Draw the specified path using the specified paint. The path will be
filled or framed based on the Style in the paint.
@param path The path to be drawn
@param paint The paint used to draw the path
*/
//画路径，比较丰富
virtual void drawPath(const SkPath& path, const SkPaint& paint);
/** Draw the specified bitmap, with its top/left corner at (x,y), using the
specified paint, transformed by the current matrix. Note: if the paint
contains a maskfilter that generates a mask which extends beyond the
bitmap's original width/height, then the bitmap will be drawn as if it
were in a Shader with CLAMP mode. Thus the color outside of the original
width/height will be the edge color replicated.
@param bitmap The bitmap to be drawn
@param left The position of the left side of the bitmap being drawn
@param top The position of the top side of the bitmap being drawn
@param paint The paint used to draw the bitmap, or NULL
*/
//把指定的图像从left, top点起根据当前坐标系统画到当前canvas上。
//内部实现中，限定了宽和高必须小于32767，否则不画。内部是由了blit函数。
virtual void drawBitmap(const SkBitmap& bitmap, SkScalar left, SkScalar top,
const SkPaint* paint = NULL);
/** Draw the specified bitmap, with the specified matrix applied (before the
canvas' matrix is applied).
@param bitmap The bitmap to be drawn
@param src Optional: specify the subset of the bitmap to be drawn
@param dst The destination rectangle where the scaled/translated
image will be drawn
@param paint The paint used to draw the bitmap, or NULL
*/
//把指定的图像中src矩形画到当前canvas的dst矩形中去。
virtual void drawBitmapRect(const SkBitmap& bitmap, const SkIRect* src,
const SkRect& dst, const SkPaint* paint = NULL);
virtual void drawBitmapMatrix(const SkBitmap& bitmap, const SkMatrix& m,
const SkPaint* paint = NULL);
/** Draw the specified bitmap, with its top/left corner at (x,y),
NOT transformed by the current matrix. Note: if the paint
contains a maskfilter that generates a mask which extends beyond the
bitmap's original width/height, then the bitmap will be drawn as if it
were in a Shader with CLAMP mode. Thus the color outside of the original
width/height will be the edge color replicated.
@param bitmap The bitmap to be drawn
@param left The position of the left side of the bitmap being drawn
@param top The position of the top side of the bitmap being drawn
@param paint The paint used to draw the bitmap, or NULL
*/
virtual void drawSprite(const SkBitmap& bitmap, int left, int top,
const SkPaint* paint = NULL);
/** Draw the text, with origin at (x,y), using the specified paint.
The origin is interpreted based on the Align setting in the paint.
@param text The text to be drawn
@param byteLength The number of bytes to read from the text parameter
@param x The x-coordinate of the origin of the text being drawn
@param y The y-coordinate of the origin of the text being drawn
@param paint The paint used for the text (e.g. color, size, style)
*/
//根据SkPaint中的Align设置在(x,y)画字符。
virtual void drawText(const void* text, size_t byteLength, SkScalar x,
SkScalar y, const SkPaint& paint);
/** Draw the text, with each character/glyph origin specified by the pos[]
array. The origin is interpreted by the Align setting in the paint.
@param text The text to be drawn
@param byteLength The number of bytes to read from the text parameter
@param pos Array of positions, used to position each character
@param paint The paint used for the text (e.g. color, size, style)
*/
virtual void drawPosText(const void* text, size_t byteLength,
const SkPoint pos[], const SkPaint& paint);
/** Draw the text, with each character/glyph origin specified by the x
coordinate taken from the xpos[] array, and the y from the constY param.
The origin is interpreted by the Align setting in the paint.
@param text The text to be drawn
@param byteLength The number of bytes to read from the text parameter
@param xpos Array of x-positions, used to position each character
@param constY The shared Y coordinate for all of the positions
@param paint The paint used for the text (e.g. color, size, style)
*/
virtual void drawPosTextH(const void* text, size_t byteLength,
const SkScalar xpos[], SkScalar constY,
const SkPaint& paint);
/** Draw the text, with origin at (x,y), using the specified paint, along
the specified path. The paint's Align setting determins where along the
path to start the text.
@param text The text to be drawn
@param byteLength The number of bytes to read from the text parameter
@param path The path the text should follow for its baseline
@param hOffset The distance along the path to add to the text's
starting position
@param vOffset The distance above(-) or below(+) the path to
position the text
@param paint The paint used for the text
*/
void drawTextOnPathHV(const void* text, size_t byteLength,
const SkPath& path, SkScalar hOffset,
SkScalar vOffset, const SkPaint& paint);
/** Draw the text, with origin at (x,y), using the specified paint, along
the specified path. The paint's Align setting determins where along the
path to start the text.
@param text The text to be drawn
@param byteLength The number of bytes to read from the text parameter
@param path The path the text should follow for its baseline
@param matrix (may be null) Applied to the text before it is
mapped onto the path
@param paint The paint used for the text
*/
virtual void drawTextOnPath(const void* text, size_t byteLength,
const SkPath& path, const SkMatrix* matrix,
const SkPaint& paint);
/** Draw the picture into this canvas. This method effective brackets the
playback of the picture's draw calls with save/restore, so the state
of this canvas will be unchanged after this call. This contrasts with
the more immediate method SkPicture::draw(), which does not bracket
the canvas with save/restore, thus the canvas may be left in a changed
state after the call.
@param picture The recorded drawing commands to playback into this
canvas.
*/
virtual void drawPicture(SkPicture& picture);
enum VertexMode {
kTriangles_VertexMode,
kTriangleStrip_VertexMode,
kTriangleFan_VertexMode
};
/** Draw the array of vertices, interpreted as triangles (based on mode).
@param vmode How to interpret the array of vertices
@param vertexCount The number of points in the vertices array (and
corresponding texs and colors arrays if non-null)
@param vertices Array of vertices for the mesh
@param texs May be null. If not null, specifies the coordinate
in texture space for each vertex.
@param colors May be null. If not null, specifies a color for each
vertex, to be interpolated across the triangle.
@param xmode Used if both texs and colors are present. In this
case the colors are combined with the texture using mode,
before being drawn using the paint. If mode is null, then
the porter-duff MULTIPLY mode is used.
@param indices If not null, array of indices to reference into the
vertex (texs, colors) array.
@param indexCount number of entries in the indices array (if not null)
@param paint Specifies the shader/texture if present.
*/
virtual void drawVertices(VertexMode vmode, int vertexCount,
const SkPoint vertices[], const SkPoint texs[],
const SkColor colors[], SkXfermode* xmode,
const uint16_t indices[], int indexCount,
const SkPaint& paint);
//////////////////////////////////////////////////////////////////////////
/** Get the current bounder object.
The bounder's reference count is unchaged.
@return the canva's bounder (or NULL).
*/
SkBounder* getBounder() const { return fBounder; }
/** Set a new bounder (or NULL).
Pass NULL to clear any previous bounder.
As a convenience, the parameter passed is also returned.
If a previous bounder exists, its reference count is decremented.
If bounder is not NULL, its reference count is incremented.
@param bounder the new bounder (or NULL) to be installed in the canvas
@return the set bounder object
*/
virtual SkBounder* setBounder(SkBounder* bounder);
/** Get the current filter object. The filter's reference count is not
affected. The filter is part of the state this is affected by
save/restore.
@return the canvas' filter (or NULL).
*/
//获得当前canvas对应device的filter。filter的作用不明朗？
SkDrawFilter* getDrawFilter() const;
/** Set the new filter (or NULL). Pass NULL to clear any existing filter.
As a convenience, the parameter is returned. If an existing filter
exists, its refcnt is decrement. If the new filter is not null, its
refcnt is incremented. The filter is part of the state this is affected
by save/restore.
@param filter the new filter (or NULL)
@return the new filter
*/
virtual SkDrawFilter* setDrawFilter(SkDrawFilter* filter);
//////////////////////////////////////////////////////////////////////////
/** Return the current matrix on the canvas.
This does not account for the translate in any of the devices.
@return The current matrix on the canvas.
*/
const SkMatrix& getTotalMatrix() const;
/** Return the current device clip (concatenation of all clip calls).
This does not account for the translate in any of the devices.
@return the current device clip (concatenation of all clip calls).
*/
const SkRegion& getTotalClip() const;
/** May be overridden by subclasses. This returns a compatible device
for this canvas, with the specified config/width/height. If isOpaque
is true, then the underlying bitmap is optimized to assume that every
pixel will be drawn to, and thus it does not need to clear the alpha
channel ahead of time (assuming the specified config supports per-pixel
alpha.) If isOpaque is false, then the bitmap should clear its alpha
channel.
*/
//创建device。注意，这个函数可以由子类覆盖。也就是说为2D加速提供了可能。
virtual SkDevice* createDevice(SkBitmap::Config, int width, int height,
bool isOpaque, bool isForLayer);
///////////////////////////////////////////////////////////////////////////
/** After calling saveLayer(), there can be any number of devices that make
up the top-most drawing area. LayerIter can be used to iterate through
those devices. Note that the iterator is only valid until the next API
call made on the canvas. Ownership of all pointers in the iterator stays
with the canvas, so none of them should be modified or deleted.
*/
class LayerIter /*: SkNoncopyable*/ {
public:
/** Initialize iterator with canvas, and set values for 1st device */
LayerIter(SkCanvas*, bool skipEmptyClips);
~LayerIter();
/** Return true if the iterator is done */
bool done() const { return fDone; }
/** Cycle to the next device */
void next();
// These reflect the current device in the iterator
SkDevice* device() const;
const SkMatrix& matrix() const;
const SkRegion& clip() const;
const SkPaint& paint() const;
int x() const;
int y() const;
private:
// used to embed the SkDrawIter object directly in our instance, w/o
// having to expose that class def to the public. There is an assert
// in our constructor to ensure that fStorage is large enough
// (though needs to be a compile-time-assert!). We use intptr_t to work
// safely with 32 and 64 bit machines (to ensure the storage is enough)
intptr_t fStorage[12];
class SkDrawIter* fImpl; // this points at fStorage
SkPaint fDefaultPaint;
bool fDone;
};
protected:
// all of the drawBitmap variants call this guy
virtual void commonDrawBitmap(const SkBitmap&, const SkMatrix& m,
const SkPaint& paint);
private:
class MCRec;
//这个变量是整个canvas的layer stack.贯穿整个canvas始终
SkDeque fMCStack;
// points to top of stack
MCRec* fMCRec;
// the first N recs that can fit here mean we won't call malloc
uint32_t fMCRecStorage[32];//这里是canvas的缓存机制。
SkBounder* fBounder;
void prepareForDeviceDraw(SkDevice*);
bool fDeviceCMDirty; // cleared by updateDeviceCMCache()
void updateDeviceCMCache();
friend class SkDrawIter; // needs setupDrawForLayerDevice()
SkDevice* init(SkDevice*);
void internalDrawBitmap(const SkBitmap&, const SkMatrix& m,
const SkPaint* paint);
void drawDevice(SkDevice*, int x, int y, const SkPaint*);
// shared by save() and saveLayer()
int internalSave(SaveFlags flags);
void internalRestore();
/* These maintain a cache of the clip bounds in local coordinates,
(converted to 2s-compliment if floats are slow).
*/
mutable SkRectCompareType fLocalBoundsCompareType;
mutable bool fLocalBoundsCompareTypeDirty;
const SkRectCompareType& getLocalClipBoundsCompareType() const {
if (fLocalBoundsCompareTypeDirty) {
this->computeLocalClipBoundsCompareType();
fLocalBoundsCompareTypeDirty = false;
}
return fLocalBoundsCompareType;
}
void computeLocalClipBoundsCompareType() const;
};
/** Stack helper class to automatically call restoreToCount() on the canvas
when this object goes out of scope. Use this to guarantee that the canvas
is restored to a known state.
*/
class SkAutoCanvasRestore : SkNoncopyable {
public:
SkAutoCanvasRestore(SkCanvas* canvas, bool doSave) : fCanvas(canvas) {
SkASSERT(canvas);
fSaveCount = canvas->getSaveCount();
if (doSave) {
canvas->save();
}
}
~SkAutoCanvasRestore() {
fCanvas->restoreToCount(fSaveCount);
}
private:
SkCanvas* fCanvas;
int fSaveCount;
};
SkCanvas包含有device，device可以由外部设定。具体如何设定需要再研究。SkCanvas包含会根据给定的paint来draw相应的图形图像。是skia的中心。
