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126 lines
3.4 KiB
C
126 lines
3.4 KiB
C
/* Libart_LGPL - library of basic graphic primitives
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* Copyright (C) 1998 Raph Levien
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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#include <math.h>
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#include "art_misc.h"
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#include "art_point.h"
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#include "art_affine.h"
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#include "art_rgb_affine_private.h"
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/* Private functions for the rgb affine image compositors - primarily,
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the determination of runs, eliminating the need for source image
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bbox calculation in the inner loop. */
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/* Determine a "run", such that the inverse affine of all pixels from
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(x0, y) inclusive to (x1, y) exclusive fit within the bounds
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of the source image.
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Initial values of x0, x1, and result values stored in first two
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pointer arguments.
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*/
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#define EPSILON 1e-6
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void
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art_rgb_affine_run (int *p_x0, int *p_x1, int y,
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int src_width, int src_height,
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const double affine[6])
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{
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int x0, x1;
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double z;
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double x_intercept;
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int xi;
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x0 = *p_x0;
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x1 = *p_x1;
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/* do left and right edges */
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if (affine[0] > EPSILON)
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{
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z = affine[2] * (y + 0.5) + affine[4];
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x_intercept = -z / affine[0];
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xi = ceil (x_intercept + EPSILON - 0.5);
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if (xi > x0)
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x0 = xi;
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x_intercept = (-z + src_width) / affine[0];
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xi = ceil (x_intercept - EPSILON - 0.5);
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if (xi < x1)
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x1 = xi;
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}
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else if (affine[0] < -EPSILON)
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{
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z = affine[2] * (y + 0.5) + affine[4];
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x_intercept = (-z + src_width) / affine[0];
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xi = ceil (x_intercept + EPSILON - 0.5);
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if (xi > x0)
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x0 = xi;
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x_intercept = -z / affine[0];
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xi = ceil (x_intercept - EPSILON - 0.5);
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if (xi < x1)
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x1 = xi;
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}
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else
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{
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z = affine[2] * (y + 0.5) + affine[4];
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if (z < 0 || z >= src_width)
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{
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*p_x1 = *p_x0;
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return;
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}
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}
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/* do top and bottom edges */
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if (affine[1] > EPSILON)
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{
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z = affine[3] * (y + 0.5) + affine[5];
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x_intercept = -z / affine[1];
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xi = ceil (x_intercept + EPSILON - 0.5);
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if (xi > x0)
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x0 = xi;
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x_intercept = (-z + src_height) / affine[1];
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xi = ceil (x_intercept - EPSILON - 0.5);
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if (xi < x1)
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x1 = xi;
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}
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else if (affine[1] < -EPSILON)
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{
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z = affine[3] * (y + 0.5) + affine[5];
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x_intercept = (-z + src_height) / affine[1];
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xi = ceil (x_intercept + EPSILON - 0.5);
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if (xi > x0)
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x0 = xi;
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x_intercept = -z / affine[1];
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xi = ceil (x_intercept - EPSILON - 0.5);
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if (xi < x1)
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x1 = xi;
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}
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else
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{
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z = affine[3] * (y + 0.5) + affine[5];
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if (z < 0 || z >= src_height)
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{
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*p_x1 = *p_x0;
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return;
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}
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}
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*p_x0 = x0;
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*p_x1 = x1;
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}
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