Region is a compressed one bit mask. Region describes an aliased clipping area on integer boundaries. Region can also describe an array of integer rectangles.
Canvas uses Region to reduce the current clip. Region may be drawn to Canvas; Paint determines if Region is filled or stroked, its Color, and so on.
Region may be constructed from IRect array or Path. Diagonal lines and curves in Path become integer rectangle edges. Regions operators compute union, intersection, difference, and so on. Canvas allows only intersection and difference; successive clips can only reduce available Canvas area.
SkRegion describes the set of pixels used to clip Canvas. SkRegion is compact, efficiently storing a single integer rectangle, or a run length encoded array of rectangles. SkRegion may reduce the current Canvas_Clip, or may be drawn as one or more integer rectangles. SkRegion iterator returns the scan lines or rectangles contained by it, optionally intersecting a bounding rectangle.
Returns sequence of rectangles, sorted along y-axis, then x-axis, that make up Region.
Initializes SkRegion::Iterator with an empty SkRegion. done() on SkRegion::Iterator returns true. Call reset() to initialized SkRegion::Iterator at a later time.
empty SkRegion iterator
rect={1,2,3,4}
reset SkRegion
Sets SkRegion::Iterator to return elements of SkIRect array in region.
SkRegion iterator
rect={1,2,3,4}
reset SkRegion Cliperator Spanerator
SkPoint SkRegion::Iterator to start of SkRegion. Returns true if SkRegion was set; otherwise, returns false.
true if SkRegion was set
#Volatile
empty iter rewind success=false
empty iter rect={0,0,0,0}
empty region rewind success=true
empty region rect={0,0,0,0}
after set rect rect={1,2,3,4}
after rewind rewind success=true
after rewind rect={1,2,3,4}
reset
Resets iterator, using the new SkRegion.
empty region: done=true after set rect: done=true after reset: done=false
rewind
Returns true if SkRegion::Iterator is pointing to final SkIRect in SkRegion.
true if data parsing is complete
done=true done=false
next rect
Advances SkRegion::Iterator to next SkIRect in SkRegion if it is not done.
rect={1,2,3,4}
rect={5,6,7,8}
done rect
Returns SkIRect element in SkRegion. Does not return predictable results if SkRegion is empty.
part of SkRegion as SkIRect
#Volatile
rect={0,0,0,0}
rect={1,2,3,4}
next done
Returns SkRegion if set; otherwise, returns nullptr.
iterated SkRegion
Iterator reset
Returns the sequence of rectangles, sorted along y-axis, then x-axis, that make up Region intersected with the specified clip rectangle.
Sets SkRegion::Cliperator to return elements of SkIRect array in SkRegion within clip.
SkRegion iterator
rect={1,2,2,3}
SkRegion Iterator Spanerator
Returns true if SkRegion::Cliperator is pointing to final SkIRect in SkRegion.
true if data parsing is complete
empty region done=true after add rect done=false
next rect
Advances iterator to next SkIRect in SkRegion contained by clip.
rect={1,3,3,4}
rect={5,6,7,7}
done
Returns SkIRect element in SkRegion, intersected with clip passed to SkRegion::Cliperator constructor. Does not return predictable results if SkRegion is empty.
part of SkRegion inside clip as SkIRect
#Volatile
empty region rect={1094713344,1065353216,0,-1}
after set rect rect={1,2,3,3}
next done
Returns the line segment ends within Region that intersect a horizontal line.
Sets SkRegion::Spanerator to return line segments in SkRegion on scan line.
SkRegion iterator
SkRegion Iterator Cliperator
Advances iterator to next span intersecting SkRegion within line segment provided in constructor. Returns true if interval was found.
true if interval was found
empty region: result=false after set rect: result=true left=2 right=3
done
Constructs an empty SkRegion. SkRegion is set to empty bounds at (0, 0) with zero width and height.
empty SkRegion
region bounds: {0, 0, 0, 0}
setEmpty
Constructs a copy of an existing region. Copy constructor makes two regions identical by value. Internally, region and the returned result share pointer values. The underlying SkRect array is copied when modified.
Creating a SkRegion copy is very efficient and never allocates memory. SkRegion are always copied by value from the interface; the underlying shared pointers are not exposed.
copy of SkRegion
region bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}
after region set empty:
region bounds: {0,0,0,0}
region2 bounds: {1,2,3,4}
setRegion operator=(const SkRegion& region)
Constructs a rectangular SkRegion matching the bounds of rect.
rectangular SkRegion
setRect setRegion
Releases ownership of any shared data and deletes data if SkRegion is sole owner.
region2 bounds: {1,2,3,4}
SkRegion() SkRegion(const SkRegion& region) SkRegion(const SkIRect& rect) operator=(const SkRegion& region)
Constructs a copy of an existing region. Makes two regions identical by value. Internally, region and the returned result share pointer values. The underlying SkRect array is copied when modified.
Creating a SkRegion copy is very efficient and never allocates memory. SkRegion are always copied by value from the interface; the underlying shared pointers are not exposed.
SkRegion to copy by value
region1 bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}
set swap SkRegion(const SkRegion& region)
Compares SkRegion and other; returns true if they enclose exactly the same area.
true if SkRegion pair are equivalent
empty one == two set rect one != two set empty one == two
operator!=(const SkRegion& other) const operator=(const SkRegion& region)
Compares SkRegion and other; returns true if they do not enclose the same area.
true if SkRegion pair are not equivalent
empty one == two set rect one != two union rect one == two
operator==(const SkRegion& other) const operator=(const SkRegion& region)
Sets SkRegion to src, and returns true if src bounds is not empty. This makes SkRegion and src identical by value. Internally, SkRegion and src share pointer values. The underlying SkRect array is copied when modified.
Creating a SkRegion copy is very efficient and never allocates memory. SkRegion are always copied by value from the interface; the underlying shared pointers are not exposed.
copy of src
region1 bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}
operator=(const SkRegion& region) swap SkRegion(const SkRegion& region)
Exchanges SkIRect array of SkRegion and other. swap() internally exchanges pointers, so it is lightweight and does not allocate memory.
swap() usage has largely been replaced by operator=(const SkRegion& region). SkPath do not copy their content on assignment until they are written to, making assignment as efficient as swap().
region1 bounds: {0,0,0,0}
region2 bounds: {1,2,3,4}
operator=(const SkRegion& region) set SkRegion(const SkRegion& region)
Returns true if SkRegion is empty. Empty SkRegion has bounds width or height less than or equal to zero. SkRegion() constructs empty SkRegion; setEmpty() and setRect() with dimensionless data make SkRegion empty.
true if bounds has no width or height
initial: region is empty set rect: region is not empty set empty: region is empty
isRect isComplex operator==(const SkRegion& other) const
Returns true if SkRegion is one SkIRect with positive dimensions.
true if SkRegion contains one SkIRect
initial: region is not rect set rect: region is rect set empty: region is not rect
isEmpty isComplex
Returns true if SkRegion is described by more than one rectangle.
true if SkRegion contains more than one SkIRect
initial: region is not complex set rect: region is not complex op rect: region is complex
isEmpty isRect
Returns minimum and maximum axes values of SkIRect array. Returns (0, 0, 0, 0) if SkRegion is empty.
combined bounds of all SkIRect elements
bounds: {1,2,4,5}
isEmpty isRect
Returns a value that increases with the number of elements in SkRegion. Returns zero if SkRegion is empty. Returns one if SkRegion equals SkIRect; otherwise, returns value greater than one indicating that SkRegion is complex.
Call to compare SkRegion for relative complexity.
relative complexity
initial: region complexity 0 set rect: region complexity 1 op rect: region complexity 3
isRect isComplex
Appends outline of SkRegion to path. Returns true if SkRegion is not empty; otherwise, returns false, and leaves path unmodified.
true if path changed
isEmpty isComplex
Constructs an empty SkRegion. SkRegion is set to empty bounds at (0, 0) with zero width and height. Always returns false.
false
region bounds: {1,2,3,4}
after region set empty:
region bounds: {0,0,0,0}
SkRegion()
Constructs a rectangular SkRegion matching the bounds of rect. If rect is empty, constructs empty and returns false.
true if rect is not empty
region is not empty region is empty setEmpty: false
SkRegion(const SkIRect& rect)
Constructs SkRegion with bounds (left, top, right, bottom). Returns true if left is less than right and top is less than bottom; otherwise, constructs empty SkRegion and returns false.
rectangular SkRegion
set to: 1,2,3,4: success:true {1,2,3,4}
set to: 3,2,1,4: success:false {0,0,0,0}
SkRegion(const SkIRect& rect)
Constructs SkRegion as the union of SkIRect in rects array. If count is zero, constructs empty SkRegion. Returns false if constructed SkRegion is empty.
May be faster than repeated calls to op().
true if constructed SkRegion is not empty
setRect op
Constructs a copy of an existing region. Makes two regions identical by value. Internally, region and the returned result share pointer values. The underlying SkRect array is copied when modified.
Creating a SkRegion copy is very efficient and never allocates memory. SkRegion are always copied by value from the interface; the underlying shared pointers are not exposed.
SkRegion to copy by value
region bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}
after region set empty:
region bounds: {1,2,3,4}
region2 bounds: {0,0,0,0}
SkRegion(const SkRegion& region)
Constructs SkRegion to match outline of path within clip. Returns false if constructed SkRegion is empty.
Constructed SkRegion draws the same pixels as path through clip when anti-aliasing is disabled.
true if constructed SkRegion is not empty
setRects op
Returns true if SkRegion intersects rect. Returns false if either rect or SkRegion is empty, or do not intersect.
true if rect and SkRegion have area in common
contains SkRect::intersects
Returns true if SkRegion intersects other. Returns false if either other or SkRegion is empty, or do not intersect.
true if other and SkRegion have area in common
contains SkRect::intersects
Returns true if SkIPoint (x, y) is inside SkRegion. Returns false if SkRegion is empty.
true if (x, y) is inside SkRegion
intersects SkRect::contains
Returns true if other is completely inside SkRegion. Returns false if SkRegion or other is empty.
true if other is inside SkRegion
intersects SkRect::contains
Returns true if other is completely inside SkRegion. Returns false if SkRegion or other is empty.
true if other is inside SkRegion
intersects SkRect::contains
Returns true if SkRegion is a single rectangle and contains r. May return false even though SkRegion contains r.
true quickly if r points are equal or inside
quickContains 1: true quickContains 2: true quickContains 3: false
contains quickReject intersects
Returns true if SkRegion is a single rectangle and contains SkIRect (left, top, right, bottom). Returns false if SkRegion is empty or SkIRect (left, top, right, bottom) is empty. May return false even though SkRegion contains (left, top, right, bottom).
true quickly if SkIRect are equal or inside
quickContains 1: true quickContains 2: true quickContains 3: false
contains quickReject intersects
Returns true if SkRegion does not intersect rect. Returns true if rect is empty or SkRegion is empty. May return false even though SkRegion does not intersect rect.
true if rect does not intersect
quickReject 1: true quickReject 2: true quickReject 3: false
quickContains contains intersects
Returns true if SkRegion does not intersect rgn. Returns true if rgn is empty or SkRegion is empty. May return false even though SkRegion does not intersect rgn.
true if rgn does not intersect
quickReject 1: true quickReject 2: true quickReject 3: false
quickContains contains intersects
Offsets SkRegion by ivector (dx, dy). Has no effect if SkRegion is empty.
SkCanvas::translate SkIRect::offset SkPath::offset
Offsets SkRegion by ivector (dx, dy), writing result to dst. SkRegion may be passed as dst parameter, translating SkRegion in place. Has no effect if dst is nullptr. If SkRegion is empty, sets dst to empty.
SkCanvas::translate SkIRect::offset SkPath::offset
The logical operations that can be performed when combining two Regions.
SkPathOp
Replaces SkRegion with the result of SkRegion op rect. Returns true if replaced SkRegion is not empty.
kDifference_Op, kIntersect_Op, kUnion_Op, kXOR_Op, kReverseDifference_Op, kReplace_Op
false if result is empty
setRects Op
Replaces SkRegion with the result of SkRegion op SkIRect (left, top, right, bottom). Returns true if replaced SkRegion is not empty.
kDifference_Op, kIntersect_Op, kUnion_Op, kXOR_Op, kReverseDifference_Op, kReplace_Op
false if result is empty
setRects Op
Replaces SkRegion with the result of SkRegion op rgn. Returns true if replaced SkRegion is not empty.
kDifference_Op, kIntersect_Op, kUnion_Op, kXOR_Op, kReverseDifference_Op, kReplace_Op
false if result is empty
setRects Op
Replaces SkRegion with the result of rect op rgn. Returns true if replaced SkRegion is not empty.
kDifference_Op, kIntersect_Op, kUnion_Op, kXOR_Op, kReverseDifference_Op, kReplace_Op
false if result is empty
setRects Op
Replaces SkRegion with the result of rgn op rect. Returns true if replaced SkRegion is not empty.
kDifference_Op, kIntersect_Op, kUnion_Op, kXOR_Op, kReverseDifference_Op, kReplace_Op
false if result is empty
setRects Op
Replaces SkRegion with the result of rgna op rgnb. Returns true if replaced SkRegion is not empty.
kDifference_Op, kIntersect_Op, kUnion_Op, kXOR_Op, kReverseDifference_Op, kReplace_Op
false if result is empty
setRects Op
Writes SkRegion to buffer, and returns number of bytes written. If buffer is nullptr, returns number number of bytes that would be written.
size of SkRegion
readFromMemory
Constructs SkRegion from buffer of size length. Returns bytes read. Returned value will be multiple of four or zero if length was too small.
bytes read
writeToMemory