# NAME

Image::Leptonica::Func::shear

# VERSION

version 0.04

`shear.c`

```
shear.c
About arbitrary lines
PIX *pixHShear()
PIX *pixVShear()
About special 'points': UL corner and center
PIX *pixHShearCorner()
PIX *pixVShearCorner()
PIX *pixHShearCenter()
PIX *pixVShearCenter()
In place about arbitrary lines
l_int32 pixHShearIP()
l_int32 pixVShearIP()
Linear interpolated shear about arbitrary lines
PIX *pixHShearLI()
PIX *pixVShearLI()
Static helper
static l_float32 normalizeAngleForShear()
```

# FUNCTIONS

## pixHShear

PIX * pixHShear ( PIX *pixd, PIX *pixs, l_int32 yloc, l_float32 radang, l_int32 incolor )

```
pixHShear()
Input: pixd (<optional>, this can be null, equal to pixs,
or different from pixs)
pixs (no restrictions on depth)
yloc (location of horizontal line, measured from origin)
angle (in radians)
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd, always
Notes:
(1) There are 3 cases:
(a) pixd == null (make a new pixd)
(b) pixd == pixs (in-place)
(c) pixd != pixs
(2) For these three cases, use these patterns, respectively:
pixd = pixHShear(NULL, pixs, ...);
pixHShear(pixs, pixs, ...);
pixHShear(pixd, pixs, ...);
(3) This shear leaves the horizontal line of pixels at y = yloc
invariant. For a positive shear angle, pixels above this
line are shoved to the right, and pixels below this line
move to the left.
(4) With positive shear angle, this can be used, along with
pixVShear(), to perform a cw rotation, either with 2 shears
(for small angles) or in the general case with 3 shears.
(5) Changing the value of yloc is equivalent to translating
the result horizontally.
(6) This brings in 'incolor' pixels from outside the image.
(7) For in-place operation, pixs cannot be colormapped,
because the in-place operation only blits in 0 or 1 bits,
not an arbitrary colormap index.
(8) The angle is brought into the range [-pi, -pi]. It is
not permitted to be within MIN_DIFF_FROM_HALF_PI radians
from either -pi/2 or pi/2.
```

## pixHShearCenter

PIX * pixHShearCenter ( PIX *pixd, PIX *pixs, l_float32 radang, l_int32 incolor )

```
pixHShearCenter()
Input: pixd (<optional>, if not null, must be equal to pixs)
pixs
angle (in radians)
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd, or null on error.
Notes:
(1) See pixHShear() for usage.
(2) This does a horizontal shear about the center, with (+) shear
pushing increasingly leftward (-x) with increasing y.
```

## pixHShearCorner

PIX * pixHShearCorner ( PIX *pixd, PIX *pixs, l_float32 radang, l_int32 incolor )

```
pixHShearCorner()
Input: pixd (<optional>, if not null, must be equal to pixs)
pixs
angle (in radians)
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd, or null on error.
Notes:
(1) See pixHShear() for usage.
(2) This does a horizontal shear about the UL corner, with (+) shear
pushing increasingly leftward (-x) with increasing y.
```

## pixHShearIP

l_int32 pixHShearIP ( PIX *pixs, l_int32 yloc, l_float32 radang, l_int32 incolor )

```
pixHShearIP()
Input: pixs
yloc (location of horizontal line, measured from origin)
angle (in radians)
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: 0 if OK; 1 on error
Notes:
(1) This is an in-place version of pixHShear(); see comments there.
(2) This brings in 'incolor' pixels from outside the image.
(3) pixs cannot be colormapped, because the in-place operation
only blits in 0 or 1 bits, not an arbitrary colormap index.
(4) Does a horizontal full-band shear about the line with (+) shear
pushing increasingly leftward (-x) with increasing y.
```

## pixHShearLI

PIX * pixHShearLI ( PIX *pixs, l_int32 yloc, l_float32 radang, l_int32 incolor )

```
pixHShearLI()
Input: pixs (8 bpp or 32 bpp, or colormapped)
yloc (location of horizontal line, measured from origin)
angle (in radians, in range (-pi/2 ... pi/2))
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd (sheared), or null on error
Notes:
(1) This does horizontal shear with linear interpolation for
accurate results on 8 bpp gray, 32 bpp rgb, or cmapped images.
It is relatively slow compared to the sampled version
implemented by rasterop, but the result is much smoother.
(2) This shear leaves the horizontal line of pixels at y = yloc
invariant. For a positive shear angle, pixels above this
line are shoved to the right, and pixels below this line
move to the left.
(3) Any colormap is removed.
(4) The angle is brought into the range [-pi/2 + del, pi/2 - del],
where del == MIN_DIFF_FROM_HALF_PI.
```

## pixVShear

PIX * pixVShear ( PIX *pixd, PIX *pixs, l_int32 xloc, l_float32 radang, l_int32 incolor )

```
pixVShear()
Input: pixd (<optional>, this can be null, equal to pixs,
or different from pixs)
pixs (no restrictions on depth)
xloc (location of vertical line, measured from origin)
angle (in radians; not too close to +-(pi / 2))
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd, or null on error
Notes:
(1) There are 3 cases:
(a) pixd == null (make a new pixd)
(b) pixd == pixs (in-place)
(c) pixd != pixs
(2) For these three cases, use these patterns, respectively:
pixd = pixVShear(NULL, pixs, ...);
pixVShear(pixs, pixs, ...);
pixVShear(pixd, pixs, ...);
(3) This shear leaves the vertical line of pixels at x = xloc
invariant. For a positive shear angle, pixels to the right
of this line are shoved downward, and pixels to the left
of the line move upward.
(4) With positive shear angle, this can be used, along with
pixHShear(), to perform a cw rotation, either with 2 shears
(for small angles) or in the general case with 3 shears.
(5) Changing the value of xloc is equivalent to translating
the result vertically.
(6) This brings in 'incolor' pixels from outside the image.
(7) For in-place operation, pixs cannot be colormapped,
because the in-place operation only blits in 0 or 1 bits,
not an arbitrary colormap index.
(8) The angle is brought into the range [-pi, -pi]. It is
not permitted to be within MIN_DIFF_FROM_HALF_PI radians
from either -pi/2 or pi/2.
```

## pixVShearCenter

PIX * pixVShearCenter ( PIX *pixd, PIX *pixs, l_float32 radang, l_int32 incolor )

```
pixVShearCenter()
Input: pixd (<optional>, if not null, must be equal to pixs)
pixs
angle (in radians)
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd, or null on error.
Notes:
(1) See pixVShear() for usage.
(2) This does a vertical shear about the center, with (+) shear
pushing increasingly downward (+y) with increasing x.
```

## pixVShearCorner

PIX * pixVShearCorner ( PIX *pixd, PIX *pixs, l_float32 radang, l_int32 incolor )

```
pixVShearCorner()
Input: pixd (<optional>, if not null, must be equal to pixs)
pixs
angle (in radians)
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd, or null on error.
Notes:
(1) See pixVShear() for usage.
(2) This does a vertical shear about the UL corner, with (+) shear
pushing increasingly downward (+y) with increasing x.
```

## pixVShearIP

l_int32 pixVShearIP ( PIX *pixs, l_int32 xloc, l_float32 radang, l_int32 incolor )

```
pixVShearIP()
Input: pixs (all depths; not colormapped)
xloc (location of vertical line, measured from origin)
angle (in radians)
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: 0 if OK; 1 on error
Notes:
(1) This is an in-place version of pixVShear(); see comments there.
(2) This brings in 'incolor' pixels from outside the image.
(3) pixs cannot be colormapped, because the in-place operation
only blits in 0 or 1 bits, not an arbitrary colormap index.
(4) Does a vertical full-band shear about the line with (+) shear
pushing increasingly downward (+y) with increasing x.
```

## pixVShearLI

PIX * pixVShearLI ( PIX *pixs, l_int32 xloc, l_float32 radang, l_int32 incolor )

```
pixVShearLI()
Input: pixs (8 bpp or 32 bpp, or colormapped)
xloc (location of vertical line, measured from origin)
angle (in radians, in range (-pi/2 ... pi/2))
incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK);
Return: pixd (sheared), or null on error
Notes:
(1) This does vertical shear with linear interpolation for
accurate results on 8 bpp gray, 32 bpp rgb, or cmapped images.
It is relatively slow compared to the sampled version
implemented by rasterop, but the result is much smoother.
(2) This shear leaves the vertical line of pixels at x = xloc
invariant. For a positive shear angle, pixels to the right
of this line are shoved downward, and pixels to the left
of the line move upward.
(3) Any colormap is removed.
(4) The angle is brought into the range [-pi/2 + del, pi/2 - del],
where del == MIN_DIFF_FROM_HALF_PI.
```

# AUTHOR

Zakariyya Mughal <zmughal@cpan.org>

# COPYRIGHT AND LICENSE

This software is copyright (c) 2014 by Zakariyya Mughal.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.