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px4-firmware/nuttx/graphics/nxglib/nxglib_splitline.c

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/****************************************************************************
* graphics/nxglib/nxglib_splitline.c
*
* Copyright (C) 2011 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <string.h>
#include <errno.h>
#include <nuttx/nx/nxglib.h>
/****************************************************************************
* Pre-Processor Definitions
****************************************************************************/
#define SMALL_SIN 1966 /* 1966/65536 = 0.03 */
/****************************************************************************
* Private Types
****************************************************************************/
/****************************************************************************
* Private Data
****************************************************************************/
/****************************************************************************
* Public Data
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: nxgl_splitline
*
* Description:
* In the general case, a line with width can be represented as a
* parallelogram with a triangle at the top and bottom. Triangles and
* parallelograms are both degenerate versions of a trapeziod. This
* function breaks a wide line into triangles and trapezoids. This
* function also detects other degenerate cases:
*
* 1. If y1 == y2 then the line is horizontal and is better represented
* as a rectangle.
* 2. If x1 == x2 then the line is vertical and also better represented
* as a rectangle.
* 3. If the width of the line is 1, then there are no triangles at the
* top and bottome (this may also be the case if the width is narrow
* and the line is near vertical).
* 4. If the line is oriented is certain angles, it may consist only of
* the upper and lower triangles with no trapezoid in between. In
* this case, 3 trapezoids will be returned, but traps[1] will be
* degenerate.
*
* Input parameters:
* vector - A pointer to the vector described the line to be drawn.
* traps - A pointer to a array of trapezoids (size 3).
* rect - A pointer to a rectangle.
*
* Returned value:
* 0: Line successfully broken up into three trapezoids. Values in
* traps[0], traps[1], and traps[2] are valid.
* 1: Line successfully represented by one trapezoid. Value in traps[1]
* is valid.
* 2: Line successfully represented by one rectangle. Value in rect is
* valid
* <0: On errors, a negated errno value is returned.
*
****************************************************************************/
int nxgl_splitline(FAR struct nxgl_vector_s *vector,
FAR struct nxgl_trapezoid_s *traps,
FAR struct nxgl_rect_s *rect,
nxgl_coord_t linewidth)
{
struct nxgl_vector_s line;
nxgl_coord_t iheight;
nxgl_coord_t iwidth;
nxgl_coord_t iy;
nxgl_coord_t triheight;
nxgl_coord_t halfheight;
b16_t adjwidth;
b16_t xoffset;
b16_t halfoffset;
b16_t angle;
b16_t sinangle;
b16_t b16x;
/* First, check the linewidth */
if (linewidth < 1)
{
return -EINVAL;
}
/* Then make sure that the start position of the line is above the end
* position of the line... in raster order.
*/
if (vector->pt1.y < vector->pt2.y)
{
/* Vector is already in raster order */
memcpy(&line, vector, sizeof(struct nxgl_vector_s));
}
else if (vector->pt1.y > vector->pt2.y)
{
/* Swap the top and bottom */
line.pt1.x = vector->pt2.x;
line.pt1.y = vector->pt2.y;
line.pt2.x = vector->pt1.x;
line.pt2.y = vector->pt1.y;
}
else
{
/* First degenerate case: The line is horizontal. */
if (vector->pt1.x < vector->pt2.x)
{
rect->pt1.x = vector->pt1.x;
rect->pt2.x = vector->pt2.x;
}
else
{
rect->pt1.x = vector->pt2.x;
rect->pt2.x = vector->pt1.x;
}
/* The height of the rectangle is the width of the line, half above
* and half below.
*/
rect->pt1.y = vector->pt1.y - (linewidth >> 1);
rect->pt2.y = rect->pt1.y + linewidth - 1;
return 2;
}
/* Check if the line is vertical */
if (line.pt1.x == line.pt2.x)
{
/* Second degenerate case: The line is vertical. */
rect->pt1.y = line.pt1.y;
rect->pt2.y = line.pt2.y;
rect->pt1.x = line.pt1.x - (linewidth >> 1);
rect->pt2.x = rect->pt1.x + linewidth - 1;
return 2;
}
/* The final degenerate case */
if (linewidth == 1)
{
/* A line of width 1 is basically a single parallelogram of width 1 */
traps[1].top.x1 = itob16(line.pt1.x);
traps[1].top.x2 = traps[1].top.x1;
traps[1].top.y = line.pt1.y;
traps[1].bot.x1 = itob16(line.pt2.x);
traps[1].bot.x2 = traps[1].bot.x1;
traps[1].bot.y = line.pt2.y;
return 1;
}
/* Okay, then what remains is interesting.
*
* iheight = |y2 - y1|
* iwidth = |x2 - x1|
*/
iheight = line.pt2.y - line.pt1.y + 1;
if (line.pt1.x < line.pt2.x)
{
iwidth = line.pt2.x - line.pt1.x + 1;
}
else
{
iwidth = line.pt1.x - line.pt2.x + 1;
}
/* Triangle height: linewidth * cosA
* Adjusted width: triheight / sinA
* X offset : linewidth * linewidth / adjusted line width
*/
angle = b16atan2(itob16(iheight), itob16(iwidth));
triheight = b16toi(linewidth * b16cos(angle) + b16HALF);
halfheight = (triheight >> 1);
/* If the sine of the angle is tiny (i.e., the line is nearly horizontal),
* then we cannot compute the adjusted width. In this case, just use
* the width of the line bounding box.
*/
sinangle = b16sin(angle);
if (sinangle < SMALL_SIN)
{
adjwidth = itob16(iwidth);
xoffset = 0;
}
else
{
adjwidth = b16divb16(itob16(linewidth), sinangle);
xoffset = itob16(linewidth * linewidth);
xoffset = b16divb16(xoffset, adjwidth);
}
halfoffset = (xoffset >> 1);
/* Return the top triangle (if there is one). NOTE that the horizontal
* (z) positions are represented with 16 bits of fraction. The vertical
* (y) positions, on the other hand, are integer.
*/
if (triheight > 0)
{
if (line.pt1.x < line.pt2.x)
{
/* Line is going "south east" */
b16x = itob16(line.pt1.x) - halfoffset;
iy = line.pt1.y + halfheight;
traps[0].top.x1 = b16x + xoffset;
traps[0].top.x2 = traps[0].top.x1;
traps[0].top.y = iy - triheight + 1;
traps[0].bot.x1 = b16x;
traps[0].bot.x2 = b16x + adjwidth - b16ONE;
traps[0].bot.y = iy;
b16x = itob16(line.pt2.x) + halfoffset;
iy = line.pt2.y - halfheight;
traps[2].top.x1 = b16x - adjwidth + b16ONE;
traps[2].top.x2 = b16x;
traps[2].top.y = iy;
traps[2].bot.x1 = b16x - xoffset;
traps[2].bot.x2 = traps[2].bot.x1;
traps[2].bot.y = iy + triheight - 1;
}
else
{
/* Line is going "south west" */
b16x = itob16(line.pt1.x) + halfoffset;
iy = line.pt1.y + halfheight;
traps[0].top.x1 = b16x - xoffset;
traps[0].top.x2 = traps[0].top.x1;
traps[0].top.y = iy - triheight + 1;
traps[0].bot.x1 = b16x - adjwidth + b16ONE;
traps[0].bot.x2 = b16x;
traps[0].bot.y = iy;
b16x = itob16(line.pt2.x) - halfoffset;
iy = line.pt2.y - halfheight;
traps[2].top.x1 = b16x;
traps[2].top.x2 = b16x + adjwidth - b16ONE;
traps[2].top.y = iy;
traps[2].bot.x1 = b16x + xoffset;
traps[2].bot.x2 = traps[2].bot.x1;
traps[2].bot.y = iy + triheight - 1;
}
/* The center parallelogram is the horizontal edge of each triangle.
* Note the minor inefficency: that horizontal edges are drawn twice.
*/
traps[1].top.x1 = traps[0].bot.x1;
traps[1].top.x2 = traps[0].bot.x2;
traps[1].top.y = traps[0].bot.y;
traps[1].bot.x1 = traps[2].top.x1;
traps[1].bot.x2 = traps[2].top.x2;
traps[1].bot.y = traps[2].top.y;
return 0;
}
/* The line is too vertical to have any significant triangular top or
* bottom. Just return the center parallelogram.
*/
traps[1].top.x1 = itob16(line.pt1.x) - halfoffset;
traps[1].top.x2 = traps[1].top.x1 + adjwidth - 1;
traps[1].top.y = line.pt1.y;
traps[1].bot.x1 = itob16(line.pt2.x) - halfoffset;
traps[1].bot.x2 = traps[1].bot.x1 + adjwidth - 1;
traps[1].bot.y = line.pt2.y;
return 1;
}
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