TRegion Class Reference

#include <e32std.h>

class TRegion

Protected Attributes
TInt	iAllocedRects
TInt	iCount
TBool	iError

Protected Member Enumerations
enum	anonymous { ERRegionBuf }

Public Member Functions
IMPORT_C void	AddRect(const TRect &)
IMPORT_C TRect	BoundingRect()
TBool	CheckError()
IMPORT_C void	Clear()
IMPORT_C void	ClipRect(const TRect &)
IMPORT_C TBool	Contains(const TPoint &)
IMPORT_C void	Copy(const TRegion &)
TInt	Count()
IMPORT_C void	ForceError()
IMPORT_C void	Intersect(const TRegion &)
IMPORT_C void	Intersection(const TRegion &, const TRegion &)
IMPORT_C TBool	Intersects(const TRect &)
IMPORT_C TBool	IsContainedBy(const TRect &)
IMPORT_C TBool	IsEmpty()
IMPORT_C void	Offset(TInt, TInt)
IMPORT_C void	Offset(const TPoint &)
const TRect *	RectangleList()
IMPORT_C TInt	Sort()
IMPORT_C TInt	Sort(const TPoint &)
IMPORT_C void	SubRect(const TRect &, TRegion *)
IMPORT_C void	SubRegion(const TRegion &, TRegion *)
IMPORT_C void	Tidy()
IMPORT_C void	Union(const TRegion &)
IMPORT_C const TRect &	operator[](TInt)

Protected Member Functions
	TRegion(TInt)
	TRegion()
void	AppendRect(const TRect &)
void	AppendRegion(TRegion &)
void	DeleteRect(TRect *)
TRect *	ExpandRegion(TInt)
void	MergeRect(const TRect &, TBool)
IMPORT_C TRect *	RectangleListW()
TBool	SetListSize(TInt)
void	ShrinkRegion()
void	SubtractRegion(const TRegion &, TRegion *)

Detailed Description

Clipping region - abstract base class.

This abstract base class represents a 2-dimensional area which is used by Graphics, the graphics window server, and the text window server to define regions of the display which need to be updated, or regions within which all operations must occur.

A TRegion is defined in terms of an array of TRects and the more complex the region, the more TRects are required to represent it.

A clipping region initially has space allocated for five rectangles. If manipulations result in a region which requires more than this, an attempt is made to allocate more rectangles. If this cannot be done, an error flag is set, and all subsequent operations involving the region have no effect (except possibly to propagate the error flag to other regions). The CheckError() member function allows the error flag to be tested; Clear() can be used to clear it.

The redraw logic of application programs may use the TRegion in various ways:

1. minimally, they pass it to the graphics context as the clipping region; when a graphics context is activated to a window, the clipping region is set up automatically

2. if they wish to avoid redrawing objects which are outside the general area of the region, they may use TRegion::BoundingRect() to return the rectangle which bounds the clipping region, and draw only primitives that lie within that rectangle

3. if they wish to exercise finer control, they may extract the individual rectangles that comprise the clipping region using Operator[]().

Application programs may also manipulate clipping regions in order to constrain parts of their redrawing to narrower areas of the screen than the clipping region offered by the window server. To do this, functions that allow clipping region manipulation may be used; for example, adding or removing rectangles or finding the intersection or union of two regions.

Member Attribute Documentation

iAllocedRects

TInt

iAllocedRects

[protected]

iCount

TInt

iCount

[protected]

iError

TBool

iError

[protected]

Member Enumeration Documentation

Enum anonymous

Enumerator	Value	Description
ERRegionBuf	0x40000000

Constructor & Destructor Documentation

TRegion ( TInt )

IMPORT_C

TRegion

(

TInt

aAllocedRects

)

[protected]

TRegion ( )

TRegion

(

)

[protected, inline]

Member Function Documentation

AddRect ( const TRect & )

IMPORT_C void

AddRect

(

const TRect &

aRect

)

Adds a rectangle to this region.

Notes:

1. If this region's error flag is already set, this function has no effect.

2. If the operation causes the capacity of this region to be exceeded, or if memory allocation fails, the region is cleared, freeing up any memory which has been allocated; its error flag is also set.

Parameters
aRect	The rectangle to be added to this region.

AppendRect ( const TRect & )

void

AppendRect

(

const TRect &

aRect

)

[protected]

AppendRegion ( TRegion & )

void

AppendRegion

(

TRegion &

aRegion

)

[protected]

BoundingRect ( )

IMPORT_C TRect

BoundingRect

(

)

const

Gets the minimal rectangle that bounds the entire region.

Return Value: The region's minimal bounding rectangle.

CheckError ( )

TBool

CheckError

(

)

const [inline]

Tests whether the region's error flag is set.

The error flag may be set:

1. when an attempt to allocate more memory for the region fails

2. if an attempt is made to expand a fixed size region beyond its allocated size

3. if ForceError() has been called.

Use Clear() to unset the error flag, clear the region and free all allocated memory.

Return Value: True, if the error flag is set; false, otherwise.

Clear ( )

IMPORT_C void

Clear

(

)

Clears this region.

This frees up any memory which has been allocated and unsets the error flag.

ClipRect ( const TRect & )

IMPORT_C void

ClipRect

(

const TRect &

aRect

)

Clips the region to the specified rectangle.

The resulting region is the area of overlap between the region and the rectangle. If there is no overlap, all rectangles within this region are deleted and the resulting region is empty.

Parameters
aRect	The rectangle to which this region is to be clipped.

Contains ( const TPoint & )

IMPORT_C TBool

Contains

(

const TPoint &

aPoint

)

const

Tests whether a point is located within the region.

If the point is located on the top or left hand side of any rectangle in the region, it is considered to be within that rectangle and within the region.

If the point is located on the right hand side or bottom of a rectangle, it is considered to be outside that rectangle, and may be outside the region.

Parameters
aPoint	The specified point.

Return Value: True, if the point is within the region; false, otherwise.

Copy ( const TRegion & )

IMPORT_C void

Copy

(

const TRegion &

aRegion

)

Copies another region to this region.

The state of the specified region's error flag is also copied.

Parameters
aRegion	The region to be copied.

Count ( )

TInt

Count

(

)

const [inline]

Gets the number of rectangles in this region.

Return Value: The number of rectangles.

DeleteRect ( TRect * )

void

DeleteRect

(

TRect *

aRect

)

[protected]

ExpandRegion ( TInt )

TRect *

ExpandRegion

(

TInt

aCount

)

[protected]

Ensure that the region is big enough to hold aCount rectangles. Any allocation increase is for at least the granularity count of rectangles. Similar to SetListSize, but always preserves existing iCount rectangles.

Parameters
aCount	number of rectangles the region is expected to hold

Return Value: NULL if region is not big enough, otherwise pointer to the Rect array.

ForceError ( )

IMPORT_C void

ForceError

(

)

Sets the error flag, and clears the region.

This frees up memory allocated to the region.

Intersect ( const TRegion & )

IMPORT_C void

Intersect

(

const TRegion &

aRegion

)

Replaces this region with the area of intersection between it and the specified region.

Note that if the error flag of either this region or the specified region is set, then this region is cleared and its error flag is set. This frees up allocated memory.

Parameters
aRegion	The region to be intersected with this region.

Intersection ( const TRegion &, const TRegion & )

IMPORT_C void	Intersection	(	const TRegion &	aRegion,
			const TRegion &	aRegion2
		)

Replaces this region with the area of intersection between two specified regions.

Notes:

1. If the error flag of either of the two specified regions is set, then this region is cleared and its error flag is set. This frees up allocated memory.

2. If this region's error flag is already set, then the function has no effect.

Parameters
aRegion	The first region.
aRegion2	The second region.

Intersects ( const TRect & )

IMPORT_C TBool

Intersects

(

const TRect &

aRect

)

const

Tests whether where there is any intersection between this region and the specified rectangle.

Parameters
aRect	The specified rectangle.

Return Value: True, if there is an intersection; false, otherwise.

IsContainedBy ( const TRect & )

IMPORT_C TBool

IsContainedBy

(

const TRect &

aRect

)

const

Tests whether the region is fully enclosed within the specified rectangle.

Parameters
aRect	The specified rectangle.

Return Value: True, if the region is fully enclosed within the rectangle (their sides may touch); false, otherwise.

IsEmpty ( )

IMPORT_C TBool

IsEmpty

(

)

const

Tests whether the region is empty.

Return Value: True, if the region is empty and its error flag is unset; false, otherwise.

MergeRect ( const TRect &, TBool )

void	MergeRect	(	const TRect &	aRect,
			TBool	aEnclosed
		)	[protected]

Merges a rectangle with this region.

If requested it looks for a rectangle in the region that covers the new rectangle, if found method returns immediately. Otherwise, or if an enclosing rectangle is not found, the new aRect is subtracted from all intersecting rectangles, and then aRect is appended to the region.

Parameters
aRect	The rectangular area to be added to this region.
aEnclosed	Whether to look for a rectangle in the region that covers the new aRect.

Offset ( TInt, TInt )

IMPORT_C void	Offset	(	TInt	aXoffset,
			TInt	aYoffset
		)

Moves the region by adding X and Y offsets to the co-ordinates of its corners.

The size of the region is not changed.

Parameters
aXoffset	The number of pixels by which to move the region horizontally. If negative, the region moves leftwards.
aYoffset	The number of pixels by which to move the region vertically. If negative, the region moves upwards.

Offset ( const TPoint & )

IMPORT_C void

Offset

(

const TPoint &

aOffset

)

Moves the region by adding a TPoint offset to the co-ordinates of its corners.

The size of the region is not changed.

Parameters
aOffset	The offset by which the region is moved. The region is moved horizontally by aOffset.iX pixels and vertically by aOffset.iY pixels.

RectangleList ( )

const TRect *

RectangleList

(

)

const [inline]

Gets a pointer to the array of rectangles defining this region.

RectangleListW ( )

IMPORT_C TRect *

RectangleListW

(

)

[protected]

SetListSize ( TInt )

TBool

SetListSize

(

TInt

aCount

)

[protected]

Ensure that the region is big enough to hold aCount rectangles.

Parameters
aCount	number of rectangles the region is expected to hold

Return Value: ETrue if region is big enough, EFalse if fixed size region is too small or alloc failed.

ShrinkRegion ( )

void

ShrinkRegion

(

)

[protected]

After an RRegion's iCount has reduced try to release some memory. Hysteresis rule: reduce allocated memory to iCount, but only if the released memory will also be at least the granularity.

Sort ( )

IMPORT_C TInt

Sort

(

)

Sorts the region's array of rectangles according to their vertical position on the screen.

The sort uses the bottom right hand corner co-ordinates of the rectangles. The co-ordinates of the top and left hand sides are irrelevant to the sort operation.

Higher rectangles take precedence over lower ones. For rectangles at the same vertical position, the leftmost takes priority.

Note that the sort order may need to be different from the default if, for example, a region is moved downwards so that lower non-overlapping rectangles need to be redrawn (and sorted) before higher ones. In this case, use the second overload of this function.

Return Value: KErrNone, if the operation is successful; KErrGeneral, otherwise.

Sort ( const TPoint & )

IMPORT_C TInt

Sort

(

const TPoint &

aOffset

)

Sorts the region's array of rectangles according to a specified sort order.

The sort uses the bottom right hand co-ordinates of the rectangles. The co-ordinates of the top and left hand sides are irrelevant to the sort operation

The order of the sort is determined by whether the iX and iY members of aOffset are positive, or zero or less. If aOffset.iY is greater than zero, lower rectangles take precedence over higher rectangles in the list order. Otherwise, higher rectangles take precedence. For rectangles of equal height, aOffset.iX becomes relevant to the sort. If is greater than zero, rightmost rectangles take precedence. Otherwise, leftmost rectangles take precedence.

Parameters
aOffset	A point whose iX and iY members determine the order of the sort.

Return Value: KErrNone, if the operation is successful; KErrGeneral, otherwise.

SubRect ( const TRect &, TRegion * )

IMPORT_C void	SubRect	(	const TRect &	aRect,
			TRegion *	aSubtractedRegion = 0
		)

Removes a rectangle from this region.

If there is no intersection between the rectangle and this region, then this region is unaffected.

Parameters
aRect	The rectangular area to be removed from this region.
aSubtractedRegion	A pointer to a region. If this is supplied, the removed rectangle is added to it. By default this pointer is NULL.

SubRegion ( const TRegion &, TRegion * )

IMPORT_C void	SubRegion	(	const TRegion &	aRegion,
			TRegion *	aSubtractedRegion = 0
		)

Removes a region.

If there is no area of intersection between the two regions, this region is unaffected.

Parameters
aRegion	The region to be removed from this region. If aRegion's error flag is set, then this region is cleared, freeing up any allocated memory, and the error flag is set.
aSubtractedRegion	If specified, then on return contains the area removed from this region.

SubtractRegion ( const TRegion &, TRegion * )

void	SubtractRegion	(	const TRegion &	aRegion,
			TRegion *	aSubtractedRegion = 0
		)	[protected]

Removes a region.

If there is no area of intersection between the two regions, this region is unaffected.

Parameters
aRegion	The region to be removed from this region. If aRegion's error flag is set, then this region is cleared, freeing up any allocated memory, and the error flag is set.
aSubtractedRegion	If specified, then on return contains the area removed from this region.

Tidy ( )

IMPORT_C void

Tidy

(

)

Merges all rectangles within this region which share an adjacent edge of the same length.

The function subsequently checks for allocated but unused memory, if this memory is at least as large as the granularity it is released to the system.

Union ( const TRegion & )

IMPORT_C void

Union

(

const TRegion &

aRegion

)

Replaces this region with the union of it and the specified region.

Note that if the error flag of either this region or the specified region is set, then this region is cleared and its error flag is set. This frees up allocated memory.

Parameters
aRegion	The region to be joined to this region.

operator[] ( TInt )

IMPORT_C const TRect &

operator[]

(

TInt

aIndex

)

const

Gets a rectangle from the region.

Parameters
aIndex	The index of a rectangle within the region's array of rectangles. Indexes are relative to zero.

Return Value: The specified rectangle.

Panic Codes
USER	81, if aIndex is greater than or equal to the number of rectangles in the region.