TLinearDDA Class Reference

Linear digital differential analyser. More...

#include <gdi.h>

Public Types
enum	TLineMode { ECenter , ELeft }
	LDDA Line mode. More...

Public Member Functions
IMPORT_C	TLinearDDA ()
	Constructs the default linear DDA.
IMPORT_C	TLinearDDA (const TLinearDDA &aLine)
	Copy constructs a linear DDA from the specified linear DDA.
IMPORT_C void	Construct (const TPoint &aStart, const TPoint &aFinish, TLineMode aMode=ECenter)
	Constructs a linear DDA, setting the start and end points of the line.
IMPORT_C TBool	SingleStep (TPoint &aPosition)
	Gets the pixel co-ordinates of the next pixel on the pixel line.
IMPORT_C TBool	SingleScanline (TPoint &aStartPosition, TPoint &aEndPosition)
	Gets the start and end pixel co-ordinates that define the next scan line.
IMPORT_C TBool	NextStep (TPoint &aPosition)
	Gets the pixel co-ordinates of the start of the next scan line.
IMPORT_C void	JumpToRect (const TRect &aRect)
	Jumps to start of a clipping rectangle.
IMPORT_C void	JumpToXCoord (const TInt aXCoord, TInt &aYCoord)
	Jumps to x co-ordinate.
IMPORT_C void	JumpToYCoord (TInt &aXCoord, const TInt aYCoord)
	Jumps to a y co-ordinate.
IMPORT_C void	JumpToXCoord2 (TInt aXCoord, TInt &aYCoord)
	Jumps to x co-ordinate.
IMPORT_C void	JumpToYCoord2 (TInt &aXCoord, TInt aYCoord)
	Jumps to a y co-ordinate.

Detailed Description

Linear digital differential analyser.

This is used to calculate the pixels which most closely approximate a specified straight line, or when scaling a bitmap. Note that a line is infinitely thin, and can only be approximated by pixels with real width and height.

Functions are provided for: pixel line traversing; jumping to a rectangle or co-ordinate

API status

Published to all clients. Released API.

Definition at line 436 of file gdi.h.

Member Enumeration Documentation

TLineMode

enum TLinearDDA::TLineMode

LDDA Line mode.

Enumerator
ECenter	Centres scan-lines in the pixel line.
ELeft	Starts at the beginning of a complete scan line. Used for bitmap scaling.

Definition at line 440 of file gdi.h.

Constructor & Destructor Documentation

TLinearDDA() [1/2]

IMPORT_C TLinearDDA::TLinearDDA

(

)

Constructs the default linear DDA.

No start or end point is defined for the line.

(generated from Symbian Developer Library)

TLinearDDA() [2/2]

IMPORT_C TLinearDDA::TLinearDDA

(

const TLinearDDA &

aLine

)

Copy constructs a linear DDA from the specified linear DDA.

Parameters

aLine

The linear DDA to be copied.

(generated from Symbian Developer Library)

Member Function Documentation

Construct()

IMPORT_C void TLinearDDA::Construct	(	const TPoint &	aStart,
		const TPoint &	aFinish,
		TLineMode	aMode = ECenter
	)

Constructs a linear DDA, setting the start and end points of the line.

Parameters

aStart	The start point of the line.
aFinish	The end point of the line.
aMode	The mode of the line; defaults to centred.

(generated from Symbian Developer Library)

JumpToRect()

IMPORT_C void TLinearDDA::JumpToRect

(

const TRect &

aRect

)

Jumps to start of a clipping rectangle.

This will accelerate the linear DDA to the vicinity of the specified rectangle. It is NOT guaranteed to reach the rectangle, but will reduce co-ordinates that are 1000's out to co-ordinates that are 10's out. Because of this, failure to intersect the rectangle may not be detected. If it is, or the line has not been constructed or has been run to completion, then a subsequent call to the stepping functions returns ETrue.

Parameters

aRect

The rectangle to be jumped to.

(generated from Symbian Developer Library)

JumpToXCoord()

IMPORT_C void TLinearDDA::JumpToXCoord	(	const TInt	aXCoord,
		TInt &	aYCoord
	)

Jumps to x co-ordinate.

The other co-ordinate of the intersection is returned through a reference argument. After a jump call, the line is ready to continue through calls to the stepping functions.

This function accelerates the Linear DDA stepping functions (e.g. SingleStep()) making them return EFalse when they reach the specified co-ordinate. If the line does not cross the co-ordinate, has not been constructed, has been run to completion or the intersection is the end point of the line then the stepping functions will return ETrue.

Parameters

aXCoord	x co-ordinate to jump to
aYCoord	On return, this parameter holds the y co-ordinate which corresponds to the specified x co-ordinate

(generated from Symbian Developer Library)

JumpToXCoord2()

IMPORT_C void TLinearDDA::JumpToXCoord2	(	TInt	aXCoord,
		TInt &	aYCoord
	)

Jumps to x co-ordinate.

This works in the same way as TLinearDDA::JumpToXCoord except that it make sure that using the NextStep function does not return the same value twice.

TLinearDDA::JumpToXCoord(TInt, TInt&)

Parameters

aXCoord	x co-ordinate to jump to
aYCoord	On return, this parameter holds the y co-ordinate which corresponds to the specified x co-ordinate

(generated from Symbian Developer Library)

JumpToYCoord()

IMPORT_C void TLinearDDA::JumpToYCoord	(	TInt &	aXCoord,
		const TInt	aYCoord
	)

Jumps to a y co-ordinate.

The other co-ordinate of the intersection is returned through a reference argument. After a jump call, the line is ready to continue through calls to the stepping functions.

This function accelerates the Linear DDA stepping functions (e.g. SingleStep()) making them return EFalse when they reach the specified co-ordinate. If the line does not cross the co-ordinate, has not been constructed, has been run to completion or the intersection is the end point of the line then they will return ETrue.

Parameters

aXCoord	On return, this parameter holds the x co-ordinate which corresponds to the specified y co-ordinate.
aYCoord	y co-ordinate to jump to

(generated from Symbian Developer Library)

JumpToYCoord2()

IMPORT_C void TLinearDDA::JumpToYCoord2	(	TInt &	aXCoord,
		TInt	aYCoord
	)

Jumps to a y co-ordinate.

This works in the same way as TLinearDDA::JumpToYCoord except that it make sure that using the NextStep function does not return the same value twice.

TLinearDDA::JumpToYCoord(TInt&, TInt)

Parameters

aXCoord	On return, this parameter holds the x co-ordinate which corresponds to the specified y co-ordinate.
aYCoord	y co-ordinate to jump to

(generated from Symbian Developer Library)

NextStep()

IMPORT_C TBool TLinearDDA::NextStep

(

TPoint &

aPosition

)

Gets the pixel co-ordinates of the start of the next scan line.

The best line that joins the start and end points is formed from all the scan lines returned by this function.

The function is called repeatedly until the start position of all scanlines has been returned.

The start and end points passed to the constructor of this object define the boundaries of the line. Successive scan lines move from the start point to the end point.

Parameters

aPosition

On entry to the first call, this can be a reference to any point. On return from the first call, this is the position of the pixel that defines the leftmost position of the first scan line. On return from subsequent calls, this is the position of the pixel that defines the leftmost position of the next scan line. On return from the final call, this is the position of the last pixel in the line, as specified during construction.

(generated from Symbian Developer Library)

SingleScanline()

IMPORT_C TBool TLinearDDA::SingleScanline	(	TPoint &	aStartPosition,
		TPoint &	aEndPosition
	)

Gets the start and end pixel co-ordinates that define the next scan line.

The best line that joins the start and end points is formed from all the scan lines returned by this function.

The function is called repeatedly until the position of all scanlines has been returned.

The start and end points passed to the constructor of this object define the boundaries of the line. Successive scan lines move from the start point to the end point.

Parameters

aStartPosition

On entry to the first call, this can be a reference to any point. On return from the first call, this is the position of the pixel that defines the leftmost position of the first scan line. On return from subsequent calls, this is the position of the pixel that defines the leftmost position of the next scan line. On return from the final call, either this or aEndPosition is set to the end point, as specified during construction.

aEndPosition

On entry to the first call, this can be a reference to any point. On return from the first call, this is the position of the pixel that defines the rightmost position of the first scan line. On return from subsequent calls, this is the position of the pixel that defines the rightmost position of the next scan line. On return from the final call, either this or aStartPosition is set to the end point, as specified during construction.

(generated from Symbian Developer Library)

SingleStep()

IMPORT_C TBool TLinearDDA::SingleStep

(

TPoint &

aPosition

)

Gets the pixel co-ordinates of the next pixel on the pixel line.

The function is called repeatedly until the whole line has been traversed or, if JumpToRect() has been called, until the part of the line inside the rectangle has been traversed. Note that, for performance reasons, JumpToRect() may fail to detect the intersection of the line with the rectangle accurately and SingleStep() may return more points than strictly necessary.

Parameters

aPosition

On entry to the first call, this can be a reference to any point. On return from the first call, this is the position of the first pixel in the line, as specified during construction of this object. On return from subsequent calls, this is the position of subsequent pixels in the line, as calculated by the function. On return from the final call, this is the position of the last pixel in the line, as specified during construction of this object.

(generated from Symbian Developer Library)

---

The documentation for this class was generated from the following files:

• gdi.h
• gdi.h.dox