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Made the version of draw_line() that draws onto a regular image use alpha 

blending for drawing diagonal lines.
This commit is contained in:
Davis King 2014-08-17 17:26:44 -04:00
parent 413096982b
commit 0b5cb827e2
1 changed files with 44 additions and 28 deletions
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72
dlib/image_transforms/draw.h
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@ -68,6 +68,13 @@ namespace dlib
}
else
{
// This part is a little more complicated because we are going to perform alpha
// blending so the diagonal lines look nice.
const rectangle valid_area = get_rect(c);
rgb_alpha_pixel alpha_pixel;
assign_pixel(alpha_pixel, val);
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))
@ -80,13 +87,13 @@ namespace dlib
if (x1 > x2)
{
first = x2;
last = x1;
first = std::max(x2,valid_area.left());
last = std::min(x1,valid_area.right());
}
else
{
first = x1;
last = x2;
first = std::max(x1,valid_area.left());
last = std::min(x2,valid_area.right());
}
long y;
@ -95,18 +102,23 @@ namespace dlib
const double y1f = y1;
for (double i = first; i <= last; ++i)
{
y = static_cast<long>(slope*(i-x1f) + y1f);
x = static_cast<long>(i);
const double dy = slope*(i-x1f) + y1f;
const double dx = i;
y = static_cast<long>(dy);
x = static_cast<long>(dx);
if (y < 0 || y >= c.nr())
continue;
if (x < 0 || x >= c.nc())
continue;
assign_pixel(c[y][x] , val);
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][x], 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][x], alpha_pixel);
}
}
}
else
@ -119,33 +131,37 @@ namespace dlib
if (y1 > y2)
{
first = y2;
last = y1;
first = std::max(y2,valid_area.top());
last = std::min(y1,valid_area.bottom());
}
else
{
first = y1;
last = y2;
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)
{
x = static_cast<long>(slope*(i-y1f) + x1f);
y = static_cast<long>(i);
const double dx = slope*(i-y1f) + x1f;
const double dy = i;
y = static_cast<long>(dy);
x = static_cast<long>(dx);
if (x < 0 || x >= c.nc())
continue;
if (y < 0 || y >= c.nr())
continue;
assign_pixel(c[y][x] , val);
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][x], 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][x+1], alpha_pixel);
}
}
}
}