plaffine.c File Reference

#include "plplotP.h"

Go to the source code of this file.

Functions
void	plP_affine_identity (PLFLT *affine_vector)
void	plP_affine_translate (PLFLT *affine_vector, PLFLT xtranslate, PLFLT ytranslate)
void	plP_affine_scale (PLFLT *affine_vector, PLFLT xscale, PLFLT yscale)
void	plP_affine_rotate (PLFLT *affine_vector, PLFLT angle)
void	plP_affine_xskew (PLFLT *affine_vector, PLFLT angle)
void	plP_affine_yskew (PLFLT *affine_vector, PLFLT angle)
void	plP_affine_multiply (PLFLT *affine_vectorA, PLFLT_VECTOR affine_vectorB, PLFLT_VECTOR affine_vectorC)

Detailed Description

These function perform variuos affine transformations.

For background on these affine functions see SVG specification, e.g., http://www.w3.org/TR/SVGTiny12/coords.html#EstablishingANewUserSpace. Affine 3x3 matrices with elements A_i,j always have a last row of 0, 0, 1 so the elements are conveniently stored in a vector in the order A_1_1, A_2_1, A_1_2, A_2_2, A_1_3, A_2_3, with the last row implied.

N.B. The PLplot affine interpretation of translate, scale, etc., is as actions on coordinate systems, rather than actions on objects. This is identical to the SVG specficiation interpretation. However, the SVG specification interprets the affine matrix as follows: old_coord_vector = affine_matrix * new_coordinate vector. In PLplot we use the alternative interpretation new_coord_vector = affine_matrix * old_coordinate vector. The result is all affine matrices below are the inverses of the SVG equivalents.

N.B. All PLplot affine functions below return the affine matrix result (in vector form) as the first argument). It is the calling routine's responsibility to provide the space for all affine matrix arguments, i.e., a PLFLT array with a dimension of 6.

Definition in file plaffine.c.

Function Documentation

void plP_affine_identity

(

PLFLT *

affine_vector

)

Returns affine identity matrix

Parameters

affine_vector

Initialize a (pre-allocated) transform matrix.

Definition at line 56 of file plaffine.c.

void plP_affine_multiply	(	PLFLT *	affine_vectorA,
		PLFLT_VECTOR	affine_vectorB,
		PLFLT_VECTOR	affine_vectorC
	)

Multiply two affine transformation matrices to form a third.

A = B * C

Parameters

affine_vectorA	Pre-allocated storage for the result of multiplying matrix affine_vectorB by matrix affine_vectorC.
affine_vectorB	First matrix to multiply.
affine_vectorC	Second matrix to multiply.

Definition at line 184 of file plaffine.c.

void plP_affine_rotate	(	PLFLT *	affine_vector,
		PLFLT	angle
	)

Rotate new coordinate system axes relative to the old. angle is in degrees.

Parameters

affine_vector	Pre-allocated storage for a rotation matrix.
angle	Amount to rotate in degrees.

Definition at line 123 of file plaffine.c.

void plP_affine_scale	(	PLFLT *	affine_vector,
		PLFLT	xscale,
		PLFLT	yscale
	)

Scale new coordinate system axes relative to the old.

Parameters

affine_vector	Pre-allocate storage for a scale matrix.
xscale	Amount to scale in x.
yscale	Amount to scale in y.

Definition at line 93 of file plaffine.c.

void plP_affine_translate	(	PLFLT *	affine_vector,
		PLFLT	xtranslate,
		PLFLT	ytranslate
	)

Translate new coordinate system axes relative to the old.

Parameters

affine_vector	Pre-allocated storage for a translation matrix.
xtranslate	Amount to translate in x.
ytranslate	Amount to translate in y.

Definition at line 73 of file plaffine.c.

void plP_affine_xskew	(	PLFLT *	affine_vector,
		PLFLT	angle
	)

Skew new X coordinate axis relative to the old. angle is in degrees.

Parameters

affine_vector	Pre-allocated storage for a skew (in x) matrix.
angle	Amount to skew in degrees.

Definition at line 143 of file plaffine.c.

void plP_affine_yskew	(	PLFLT *	affine_vector,
		PLFLT	angle
	)

Skew new Y coordinate axis relative to the old. angle is in degrees.

Parameters

affine_vector	Pre-allocated storage for a skew (in y) matrix.
angle	Amount to skew in degrees.

Definition at line 162 of file plaffine.c.