TLinearDDA Class Reference

#include <gdi.h>

Link against: gdi.lib

class TLinearDDA

Public Member Enumerations
enum	TLineMode { ECenter, ELeft }

Public Member Functions
	TLinearDDA()
	TLinearDDA(const TLinearDDA &)
IMPORT_C void	Construct(const TPoint &, const TPoint &, TLineMode)
IMPORT_C void	JumpToRect(const TRect &)
IMPORT_C void	JumpToXCoord(const TInt, TInt &)
IMPORT_C void	JumpToXCoord2(TInt, TInt &)
IMPORT_C void	JumpToYCoord(TInt &, const TInt)
IMPORT_C void	JumpToYCoord2(TInt &, TInt)
IMPORT_C TBool	NextStep(TPoint &)
IMPORT_C TBool	SingleScanline(TPoint &, TPoint &)
IMPORT_C TBool	SingleStep(TPoint &)

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

Member Enumeration Documentation

Enum TLineMode

LDDA Line mode.

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

Constructor & Destructor Documentation

TLinearDDA ( )

IMPORT_C

TLinearDDA

(

)

Constructs the default linear DDA.

No start or end point is defined for the line.

TLinearDDA ( const TLinearDDA & )

IMPORT_C

TLinearDDA

(

const TLinearDDA &

aLine

)

Copy constructs a linear DDA from the specified linear DDA.

Parameter	Description
aLine	The linear DDA to be copied.

Member Function Documentation

Construct ( const TPoint &, const TPoint &, TLineMode )

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.

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

JumpToRect ( const TRect & )

IMPORT_C void

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.

Parameter	Description
aRect	The rectangle to be jumped to.

JumpToXCoord ( const TInt, TInt & )

IMPORT_C void	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.

Parameter	Description
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

JumpToXCoord2 ( TInt, TInt & )

IMPORT_C void	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.

Parameter	Description
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

JumpToYCoord ( TInt &, const TInt )

IMPORT_C void	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.

Parameter	Description
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

JumpToYCoord2 ( TInt &, TInt )

IMPORT_C void	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.

Parameter	Description
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

NextStep ( TPoint & )

IMPORT_C TBool

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.

Parameter	Description
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.

Parameter

Description

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.

Returns: ETrue, when the position of the last pixel is returned; EFalse, otherwise.

SingleScanline ( TPoint &, TPoint & )

IMPORT_C TBool	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.

Parameter	Description
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.

Parameter

Description

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.

Returns: ETrue, when the position of the last scan line includes the end point; EFalse, otherwise.

SingleStep ( TPoint & )

IMPORT_C TBool

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.

Parameter	Description
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.

Parameter

Description

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.

Returns: ETrue, when the position of the last pixel is returned; EFalse, otherwise.