| class TLinearDDA |
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
| 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 &) |
| Private Member Functions | |
|---|---|
| void | UpdatePosition() |
| Public Member Enumerations | |
|---|---|
| enum | TLineMode { ECenter, ELeft } |
| Private Member Enumerations | |
|---|---|
| enum | TLineStatus { EInitialised, ECurrent, EComplete } |
| IMPORT_C | TLinearDDA | ( | ) |
Constructs the default linear DDA.
No start or end point is defined for the line.
| IMPORT_C | TLinearDDA | ( | const TLinearDDA & | aLine | ) |
Copy constructs a linear DDA from the specified linear DDA.
| const TLinearDDA & aLine | The linear DDA to be copied. |
| 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 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.
| const TRect & aRect | The rectangle to be jumped to. |
| 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.
| 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.
| 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.
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.
| 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.
| 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.
| TPoint & 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. |
| 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.
| TPoint & 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. |
| TPoint & 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. |
| 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.
| TPoint & 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. |
LDDA Line mode.
| ECenter |
Centres scan-lines in the pixel line |
| ELeft |
Starts at the beginning of a complete scan line. Used for bitmap scaling. |
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