```// Copyright (C) 2005  Davis E. King (davis@dlib.net), and Nils Labugt

#ifndef DLIB_GUI_CANVAS_DRAWINg_
#define DLIB_GUI_CANVAS_DRAWINg_

#include "canvas_drawing_abstract.h"
#include "../gui_core.h"
#include "../algs.h"
#include "../array2d.h"
#include "../pixel.h"
#include "../image_transforms/assign_image.h"
#include "../geometry.h"
#include <cmath>

namespace dlib
{

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
void draw_line (
const canvas& c,
const point& p1,
const point& p2,
const pixel_type& pixel,
const rectangle& area = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
rectangle valid_area(c.intersect(area));
long x1 = p1.x();
long y1 = p1.y();
long x2 = p2.x();
long y2 = p2.y();
if (x1 == x2)
{
// if the x coordinate is inside the canvas's area
if (x1 <= valid_area.right() && x1 >= valid_area.left())
{
// make sure y1 comes before y2
if (y1 > y2)
swap(y1,y2);

y1 = std::max(y1,valid_area.top());
y2 = std::min(y2,valid_area.bottom());
// this is a vertical line
for (long y = y1; y <= y2; ++y)
{
assign_pixel(c[y-c.top()][x1-c.left()], pixel);
}
}
}
else if (y1 == y2)
{
// if the y coordinate is inside the canvas's area
if (y1 <= valid_area.bottom() && y1 >= valid_area.top())
{
// make sure x1 comes before x2
if (x1 > x2)
swap(x1,x2);

x1 = std::max(x1,valid_area.left());
x2 = std::min(x2,valid_area.right());
// this is a horizontal line
for (long x = x1; x <= x2; ++x)
{
assign_pixel(c[y1-c.top()][x-c.left()], pixel);
}
}
}
else
{
rgb_alpha_pixel alpha_pixel;
assign_pixel(alpha_pixel, pixel);
const unsigned char max_alpha = alpha_pixel.alpha;

const long rise = (((long)y2) - ((long)y1));
const long run = (((long)x2) - ((long)x1));
if (std::abs(rise) < std::abs(run))
{
const double slope = ((double)rise)/run;

double first, last;

if (x1 > x2)
{
first = std::max(x2,valid_area.left());
last = std::min(x1,valid_area.right());
}
else
{
first = std::max(x1,valid_area.left());
last = std::min(x2,valid_area.right());
}

long y;
long x;
const double x1f = x1;
const double y1f = y1;
for (double i = first; i <= last; ++i)
{
const double dy = slope*(i-x1f) + y1f;
const double dx = i;

y = static_cast<long>(dy);
x = static_cast<long>(dx);

if (y >= valid_area.top() && y <= valid_area.bottom())
{
alpha_pixel.alpha = static_cast<unsigned char>((1.0-(dy-y))*max_alpha);
assign_pixel(c[y-c.top()][x-c.left()], alpha_pixel);
}
if (y+1 >= valid_area.top() && y+1 <= valid_area.bottom())
{
alpha_pixel.alpha = static_cast<unsigned char>((dy-y)*max_alpha);
assign_pixel(c[y+1-c.top()][x-c.left()], alpha_pixel);
}
}
}
else
{
const double slope = ((double)run)/rise;

double first, last;

if (y1 > y2)
{
first = std::max(y2,valid_area.top());
last = std::min(y1,valid_area.bottom());
}
else
{
first = std::max(y1,valid_area.top());
last = std::min(y2,valid_area.bottom());
}

long x;
long y;
const double x1f = x1;
const double y1f = y1;
for (double i = first; i <= last; ++i)
{
const double dx = slope*(i-y1f) + x1f;
const double dy = i;

y = static_cast<long>(dy);
x = static_cast<long>(dx);

if (x >= valid_area.left() && x <= valid_area.right())
{
alpha_pixel.alpha = static_cast<unsigned char>((1.0-(dx-x))*max_alpha);
assign_pixel(c[y-c.top()][x-c.left()], alpha_pixel);
}
if (x+1 >= valid_area.left() && x+1 <= valid_area.right())
{
alpha_pixel.alpha = static_cast<unsigned char>((dx-x)*max_alpha);
assign_pixel(c[y-c.top()][x+1-c.left()], alpha_pixel);
}
}
}
}

}
inline void draw_line (
const canvas& c,
const point& p1,
const point& p2
){ draw_line(c,p1,p2,0); }

// ----------------------------------------------------------------------------------------

void draw_sunken_rectangle (
const canvas& c,
const rectangle& border,
unsigned char alpha = 255
);

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
inline void draw_pixel (
const canvas& c,
const point& p,
const pixel_type& pixel
)
{
if (c.contains(p))
{
assign_pixel(c[p.y()-c.top()][p.x()-c.left()],pixel);
}
}

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
void draw_checkered (
const canvas& c,
const rectangle& a,
const pixel_type& pixel1,
const pixel_type& pixel2
)
{
rectangle area = a.intersect(c);
if (area.is_empty())
return;

for (long i = area.left(); i <= area.right(); ++i)
{
for (long j = area.top(); j <= area.bottom(); ++j)
{
canvas::pixel& p = c[j - c.top()][i - c.left()];
if ((j&0x1) ^ (i&0x1))
{
assign_pixel(p,pixel1);
}
else
{
assign_pixel(p,pixel2);
}
}
}
}

// ----------------------------------------------------------------------------------------

void draw_button_down (
const canvas& c,
const rectangle& btn,
unsigned char alpha = 255
);

// ----------------------------------------------------------------------------------------

void draw_button_up (
const canvas& c,
const rectangle& btn,
unsigned char alpha = 255
);

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
void draw_circle (
const canvas& c,
const point& center_point,
const pixel_type& pixel,
const rectangle& area = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
using std::sqrt;
rectangle valid_area(c.intersect(area));
const long x = center_point.x();
const long y = center_point.y();
{
long first_x = static_cast<long>(x - radius + 0.5);
long last_x = static_cast<long>(x + radius + 0.5);

// ensure that we only loop over the part of the x dimension that this
// canvas contains.
if (first_x < valid_area.left())
first_x = valid_area.left();
if (last_x > valid_area.right())
last_x = valid_area.right();

long top, bottom;

top = static_cast<long>(sqrt(std::max(rs - (first_x-x-0.5)*(first_x-x-0.5),0.0))+0.5);
top += y;
long last = top;

// draw the left half of the circle
long middle = std::min(x-1,last_x);
for (long i = first_x; i <= middle; ++i)
{
double a = i - x + 0.5;
// find the top of the arc
top = static_cast<long>(sqrt(std::max(rs - a*a,0.0))+0.5);
top += y;
long temp = top;

while(top >= last)
{
bottom = y - top + y;
if (top >= valid_area.top() && top <= valid_area.bottom() )
{
assign_pixel(c[top-c.top()][i-c.left()],pixel);
}

if (bottom >= valid_area.top() && bottom <= valid_area.bottom() )
{
assign_pixel(c[bottom-c.top()][i-c.left()],pixel);
}
--top;
}

last = temp;
}

middle = std::max(x,first_x);
top = static_cast<long>(sqrt(std::max(rs - (last_x-x+0.5)*(last_x-x+0.5),0.0))+0.5);
top += y;
last = top;
// draw the right half of the circle
for (long i = last_x; i >= middle; --i)
{
double a = i - x - 0.5;
// find the top of the arc
top = static_cast<long>(sqrt(std::max(rs - a*a,0.0))+0.5);
top += y;
long temp = top;

while(top >= last)
{
bottom = y - top + y;
if (top >= valid_area.top() && top <= valid_area.bottom() )
{
assign_pixel(c[top-c.top()][i-c.left()],pixel);
}

if (bottom >= valid_area.top() && bottom <= valid_area.bottom() )
{
assign_pixel(c[bottom-c.top()][i-c.left()],pixel);
}
--top;
}

last = temp;
}
}
else if (radius == 1 &&
x >= valid_area.left() && x <= valid_area.right() &&
y >= valid_area.top() && y <= valid_area.bottom() )
{
assign_pixel(c[y-c.top()][x-c.left()], pixel);
}
}
inline void draw_circle (
const canvas& c,
const point& center_point,
){ draw_circle(c, center_point, radius, 0); }

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
void draw_solid_circle (
const canvas& c,
const point& center_point,
const pixel_type& pixel,
const rectangle& area = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
using std::sqrt;
rectangle valid_area(c.intersect(area));
const long x = center_point.x();
const long y = center_point.y();
{
long first_x = static_cast<long>(x - radius + 0.5);
long last_x = static_cast<long>(x + radius + 0.5);

// ensure that we only loop over the part of the x dimension that this
// canvas contains.
if (first_x < valid_area.left())
first_x = valid_area.left();
if (last_x > valid_area.right())
last_x = valid_area.right();

long top, bottom;

top = static_cast<long>(sqrt(std::max(rs - (first_x-x-0.5)*(first_x-x-0.5),0.0))+0.5);
top += y;
long last = top;

// draw the left half of the circle
long middle = std::min(x-1,last_x);
for (long i = first_x; i <= middle; ++i)
{
double a = i - x + 0.5;
// find the top of the arc
top = static_cast<long>(sqrt(std::max(rs - a*a,0.0))+0.5);
top += y;
long temp = top;

while(top >= last)
{
bottom = y - top + y;
draw_line(c, point(i,top),point(i,bottom),pixel,area);
--top;
}

last = temp;
}

middle = std::max(x,first_x);
top = static_cast<long>(sqrt(std::max(rs - (last_x-x+0.5)*(last_x-x+0.5),0.0))+0.5);
top += y;
last = top;
// draw the right half of the circle
for (long i = last_x; i >= middle; --i)
{
double a = i - x - 0.5;
// find the top of the arc
top = static_cast<long>(sqrt(std::max(rs - a*a,0.0))+0.5);
top += y;
long temp = top;

while(top >= last)
{
bottom = y - top + y;
draw_line(c, point(i,top),point(i,bottom),pixel,area);
--top;
}

last = temp;
}
}
else if (radius == 1 &&
x >= valid_area.left() && x <= valid_area.right() &&
y >= valid_area.top() && y <= valid_area.bottom() )
{
assign_pixel(c[y-c.top()][x-c.left()], pixel);
}
}
inline void draw_solid_circle (
const canvas& c,
const point& center_point,
) { draw_solid_circle(c, center_point, radius, 0); }

// ----------------------------------------------------------------------------------------

namespace impl
{

template <typename alloc>
void get_convex_polygon_shape (
const std::vector<point>& points,
const long top,
const long bottom,
std::vector<double,alloc>& left_boundary,
std::vector<double,alloc>& right_boundary
)
/*!
requires
- 0 <= top <= bottom
ensures
- interprets points as the coordinates defining a convex polygon.  In
particular, we interpret points as a list of the vertices of the polygon
and assume they are ordered in clockwise order.
- #left_boundary.size() == bottom-top+1
- #right_boundary.size() == bottom-top+1
- for all top <= y <= bottom:
- #left_boundary[y-top] == the x coordinate for the left most side of
the polygon at coordinate y.
- #right_boundary[y-top] == the x coordinate for the right most side of
the polygon at coordinate y.
!*/
{
using std::min;
using std::max;

left_boundary.assign(bottom-top+1, std::numeric_limits<double>::infinity());
right_boundary.assign(bottom-top+1, -std::numeric_limits<double>::infinity());

// trace out the points along the edge of the polynomial and record them
for (unsigned long i = 0; i < points.size(); ++i)
{
const point p1 = points[i];
const point p2 = points[(i+1)%points.size()];

if (p1.y() == p2.y())
{
if (top <= p1.y() && p1.y() <= bottom)
{
const long y = p1.y() - top;
const double xmin = min(p1.x(), p2.x());
const double xmax = min(p1.x(), p2.x());
left_boundary[y]  = min(left_boundary[y], xmin);
right_boundary[y] = max(right_boundary[y], xmax);
}
}
else
{
// Here we trace out the line from p1 to p2 and record where it hits.

// x = m*y + b
const double m = (p2.x() - p1.x())/(double)(p2.y()-p1.y());
const double b = p1.x() - m*p1.y(); // because: x1 = m*y1 + b

const long ymin = max(top,min(p1.y(), p2.y()));
const long ymax = min(bottom,max(p1.y(), p2.y()));
for (long y = ymin; y <= ymax; ++y)
{
const double x = m*y + b;
const unsigned long idx = y-top;
left_boundary[idx]  = min(left_boundary[idx], x);
right_boundary[idx] = max(right_boundary[idx], x);
}
}
}
}

// ------------------------------------------------------------------------------------

}

template <typename pixel_type>
void draw_solid_convex_polygon (
const canvas& c,
const std::vector<point>& polygon,
const pixel_type& pixel,
const rectangle& area = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
using std::max;
using std::min;
const rectangle valid_area(c.intersect(area));

rectangle bounding_box;
for (unsigned long i = 0; i < polygon.size(); ++i)
bounding_box += polygon[i];

// Don't do anything if the polygon is totally outside the area we can draw in
// right now.
if (bounding_box.intersect(valid_area).is_empty())
return;

rgb_alpha_pixel alpha_pixel;
assign_pixel(alpha_pixel, pixel);
const unsigned char max_alpha = alpha_pixel.alpha;

// we will only want to loop over the part of left_boundary that is part of the
// valid_area.
long top = max(valid_area.top(),bounding_box.top());
long bottom = min(valid_area.bottom(),bounding_box.bottom());

// Since we look at the adjacent rows of boundary information when doing the alpha
// blending, we want to make sure we always have some boundary information unless
// we are at the absolute edge of the polygon.
const long top_offset = (top == bounding_box.top()) ? 0 : 1;
const long bottom_offset = (bottom == bounding_box.bottom()) ? 0 : 1;
if (top != bounding_box.top())
top -= 1;
if (bottom != bounding_box.bottom())
bottom += 1;

std::vector<double> left_boundary;
std::vector<double> right_boundary;
impl::get_convex_polygon_shape(polygon, top, bottom, left_boundary, right_boundary);

// draw the polygon row by row
for (unsigned long i = top_offset; i < left_boundary.size(); ++i)
{
long left_x = static_cast<long>(std::ceil(left_boundary[i]));
long right_x = static_cast<long>(std::floor(right_boundary[i]));

left_x = max(left_x, valid_area.left());
right_x = min(right_x, valid_area.right());

if (i < left_boundary.size()-bottom_offset)
{
// draw the main body of the polygon
for (long x = left_x; x <= right_x; ++x)
{
const long y = i+top;
assign_pixel(c[y-c.top()][x-c.left()], pixel);
}
}

if (i == 0)
continue;

// Now draw anti-aliased edges so they don't look all pixely.

// Alpha blend the edges on the left side.
double delta = left_boundary[i-1] - left_boundary[i];
if (std::abs(delta) <= 1)
{
if (std::floor(left_boundary[i]) != left_x)
{
const point p(static_cast<long>(std::floor(left_boundary[i])), i+top);
rgb_alpha_pixel temp = alpha_pixel;
temp.alpha = max_alpha-static_cast<unsigned char>((left_boundary[i]-p.x())*max_alpha);
if (valid_area.contains(p))
assign_pixel(c[p.y()-c.top()][p.x()-c.left()],temp);
}
}
else if (delta < 0)  // on the bottom side
{
for (long x = static_cast<long>(std::ceil(left_boundary[i-1])); x < left_x; ++x)
{
const point p(x, i+top);
rgb_alpha_pixel temp = alpha_pixel;
temp.alpha = static_cast<unsigned char>((x-left_boundary[i-1])/std::abs(delta)*max_alpha);
if (valid_area.contains(p))
assign_pixel(c[p.y()-c.top()][p.x()-c.left()],temp);
}
}
else // on the top side
{
const long old_left_x = static_cast<long>(std::ceil(left_boundary[i-1]));
for (long x = left_x; x < old_left_x; ++x)
{
const point p(x, i+top-1);
rgb_alpha_pixel temp = alpha_pixel;
temp.alpha = static_cast<unsigned char>((x-left_boundary[i])/delta*max_alpha);
if (valid_area.contains(p))
assign_pixel(c[p.y()-c.top()][p.x()-c.left()],temp);
}
}

// Alpha blend the edges on the right side
delta = right_boundary[i-1] - right_boundary[i];
if (std::abs(delta) <= 1)
{
if (std::ceil(right_boundary[i]) != right_x)
{
const point p(static_cast<long>(std::ceil(right_boundary[i])), i+top);
rgb_alpha_pixel temp = alpha_pixel;
temp.alpha = max_alpha-static_cast<unsigned char>((p.x()-right_boundary[i])*max_alpha);
if (valid_area.contains(p))
assign_pixel(c[p.y()-c.top()][p.x()-c.left()],temp);
}
}
else if (delta < 0) // on the top side
{
for (long x = static_cast<long>(std::floor(right_boundary[i-1]))+1; x <= right_x; ++x)
{
const point p(x, i+top-1);
rgb_alpha_pixel temp = alpha_pixel;
temp.alpha = static_cast<unsigned char>((right_boundary[i]-x)/std::abs(delta)*max_alpha);
if (valid_area.contains(p))
assign_pixel(c[p.y()-c.top()][p.x()-c.left()],temp);
}
}
else // on the bottom side
{
const long old_right_x = static_cast<long>(std::floor(right_boundary[i-1]));
for (long x = right_x+1; x <= old_right_x; ++x)
{
const point p(x, i+top);
rgb_alpha_pixel temp = alpha_pixel;
temp.alpha = static_cast<unsigned char>((right_boundary[i-1]-x)/delta*max_alpha);
if (valid_area.contains(p))
assign_pixel(c[p.y()-c.top()][p.x()-c.left()],temp);
}
}
}
}
inline void draw_solid_convex_polygon (
const canvas& c,
const std::vector<point>& polygon
) { draw_solid_convex_polygon(c, polygon, 0); }

// ----------------------------------------------------------------------------------------

template <
typename image_type
>
void draw_image (
const canvas& c,
const point& p,
const image_type& img,
const rectangle& area_ = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
const long x = p.x();
const long y = p.y();
rectangle rect(x,y,num_columns(img)+x-1,num_rows(img)+y-1);
rectangle area = c.intersect(rect).intersect(area_);
if (area.is_empty())
return;

for (long row = area.top(); row <= area.bottom(); ++row)
{
for (long col = area.left(); col <= area.right(); ++col)
{
assign_pixel(c[row-c.top()][col-c.left()], img[row-rect.top()][col-rect.left()]);
}
}
}

// ----------------------------------------------------------------------------------------

template <
typename image_type
>
void draw_image (
const canvas& c,
const rectangle& rect,
const image_type& img,
const rectangle& area_ = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
const rectangle area = c.intersect(rect).intersect(area_);
if (area.is_empty() || num_columns(img) * num_rows(img) == 0)
return;

const matrix<long,1> x = matrix_cast<long>(round(linspace(0, num_columns(img)-1, rect.width())));
const matrix<long,1> y = matrix_cast<long>(round(linspace(0, num_rows(img)-1, rect.height())));

for (long row = area.top(); row <= area.bottom(); ++row)
{
const long r = y(row-rect.top());
long cc = area.left() - rect.left();
for (long col = area.left(); col <= area.right(); ++col)
{
assign_pixel(c[row-c.top()][col-c.left()], img[r][x(cc++)]);
}
}
}

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
void draw_rounded_rectangle (
const canvas& c,
const rectangle& rect,
const pixel_type& color,
const rectangle& area_ = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
if ( rect.intersect ( c ).is_empty() )
return;

draw_line ( c, point(rect.left() + radius + 1, rect.bottom()),
point(rect.right() - radius - 1, rect.bottom()), color,area_ );

draw_line ( c, point(rect.left() + radius + 1, rect.top()),
point(rect.right() - radius - 1, rect.top()), color,area_ );

draw_line ( c, point(rect.left(), rect.top() + radius + 1),
point(rect.left(), rect.bottom() - radius - 1), color,area_ );

draw_line ( c, point(rect.right(), rect.top() + radius + 1),
point(rect.right(), rect.bottom() - radius - 1), color,area_ );

unsigned x = radius, y = 0, old_x = x;

point p;
while ( x > y )
{
p = point(rect.left() + radius - y, rect.top() + radius - x);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.right() - radius + y, rect.top() + radius - x);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.right() - radius + y, rect.bottom() - radius + x);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.left() + radius - y, rect.bottom() - radius + x);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.left() + radius - x, rect.top() + radius - y);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.right() - radius + x, rect.top() + radius - y);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.right() - radius + x, rect.bottom() - radius + y);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.left() + radius - x, rect.bottom() - radius + y);
if (area_.contains(p)) draw_pixel (c, p , color );
y++;
old_x = x;
x = square_root ( ( radius * radius - y * y ) * 4 ) / 2;
}

if ( x == y && old_x != x )
{
p = point(rect.left() + radius - y, rect.top() + radius - x);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.right() - radius + y, rect.top() + radius - x);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.right() - radius + y, rect.bottom() - radius + x);
if (area_.contains(p)) draw_pixel (c, p , color );
p = point(rect.left() + radius - y, rect.bottom() - radius + x);
if (area_.contains(p)) draw_pixel (c, p , color );
}
}

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
const canvas& c,
const rectangle& rect,
const pixel_type& top_color,
const pixel_type& bottom_color,
const rectangle& area = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())

)
{
rectangle valid_area(c.intersect(area.intersect(rect)));
if ( valid_area.is_empty() )
return;

unsigned long m_prev = 0, m = radius, c_div = valid_area.height() - 1;

const long c_top = valid_area.top();
const long c_bottom = valid_area.bottom();

for ( long y = c_top; y <= c_bottom;y++ )
{

unsigned long c_s = y - c_top;

unsigned long c_t = c_bottom - y;

if ( c_div == 0 )
{
// only a single round, just take the average color
c_div = 2;
c_s = c_t = 1;
}

rgb_alpha_pixel color;
vector_to_pixel(color,
((pixel_to_vector<unsigned long>(top_color)*c_t + pixel_to_vector<unsigned long>(bottom_color)*c_s)/c_div));

unsigned long s = y - rect.top();

unsigned long t = rect.bottom() - y;

if ( s < radius )
{
m = radius - square_root ( ( radius * radius - ( radius - s ) * ( radius - s ) ) * 4 ) / 2;

if ( s == m && m + 1 < m_prev )  // these are hacks to remove distracting artefacts at small radii
m++;
}
else if ( t < radius )
{
m = radius - square_root ( ( radius * radius - ( radius - t ) * ( radius - t ) ) * 4 ) / 2;

if ( t == m && m == m_prev )
m++;
}
else
{
m = 0;
}

m_prev = m;

draw_line ( c, point(rect.left() + m, y),
point(rect.right() - m, y), color, valid_area );
}
}

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
void draw_rectangle (
const canvas& c,
rectangle rect,
const pixel_type& pixel,
const rectangle& area = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
// top line
draw_line(c, point(rect.left(),rect.top()),
point(rect.right(),rect.top()),
pixel, area);

// bottom line
draw_line(c, point(rect.left(),rect.bottom()),
point(rect.right(),rect.bottom()),
pixel, area);

// left line
draw_line(c, point(rect.left(),rect.top()),
point(rect.left(),rect.bottom()),
pixel, area);

// right line
draw_line(c, point(rect.right(),rect.top()),
point(rect.right(),rect.bottom()),
pixel, area);
}
inline void draw_rectangle (
const canvas& c,
rectangle rect
){ draw_rectangle(c, rect, 0); }

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
void fill_rect (
const canvas& c,
const rectangle& rect,
const pixel_type& pixel
)
{
rectangle area = rect.intersect(c);
for (long y = area.top(); y <= area.bottom(); ++y)
{
for (long x = area.left(); x <= area.right(); ++x)
{
assign_pixel(c[y-c.top()][x-c.left()], pixel);
}
}
}

// ----------------------------------------------------------------------------------------

template <typename pixel_type>
const canvas& c,
const rectangle& rect,
const pixel_type& pixel_top,
const pixel_type& pixel_bottom,
const rectangle& area_ = rectangle(std::numeric_limits<long>::min(), std::numeric_limits<long>::min(),
std::numeric_limits<long>::max(), std::numeric_limits<long>::max())
)
{
rectangle area = rect.intersect(c).intersect(area_);
pixel_type pixel;

const long s = rect.bottom()-rect.top();

for (long y = area.top(); y <= area.bottom(); ++y)
{
const long t = rect.bottom()-y;
const long b = y-rect.top();
vector_to_pixel(pixel,
((pixel_to_vector<long>(pixel_top)*t +
pixel_to_vector<long>(pixel_bottom)*b)/s));

for (long x = area.left(); x <= area.right(); ++x)
{
assign_pixel(c[y-c.top()][x-c.left()], pixel);
}
}
}

// ----------------------------------------------------------------------------------------

}

#ifdef NO_MAKEFILE
#include "canvas_drawing.cpp"
#endif

#endif // DLIB_GUI_CANVAS_DRAWINg_

```