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LibGfx: Add Painter::draw_circle_arc_intersecting()

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This adds a function to draw a circle specified by a center point (
relative to the given Rect) and a radius. The circle arc is only drawn
inside the specified Rect as to allow for circle arc segments.
Technically this was already possible using draw_elliptical_arc(), but
the algorithm is quite involved and lead to wonky arcs when trying to
draw circle arc segments.
This commit is contained in:
Tobias Christiansen 2021-05-16 16:14:33 +02:00 • committed by Andreas Kling
parent 819e0e0440
commit 8b63c2a10e
2 changed files with 44 additions and 0 deletions
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43
Userland/Libraries/LibGfx/Painter.cpp
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@ -384,6 +384,49 @@ void Painter::fill_rounded_corner(const IntRect& a_rect, int radius, Color color
}
}
void Painter::draw_circle_arc_intersecting(const IntRect& a_rect, const IntPoint& center, int radius, Color color, int thickness)
{
if (thickness <= 0)
return;
// Care about clipping
auto translated_a_rect = a_rect.translated(translation());
auto rect = translated_a_rect.intersected(clip_rect());
if (rect.is_empty())
return;
VERIFY(m_target->rect().contains(rect));
// We got cut on the top!
// FIXME: Also account for clipping on the x-axis
int clip_offset = 0;
if (translated_a_rect.y() < rect.y())
clip_offset = rect.y() - translated_a_rect.y();
if (thickness > radius)
thickness = radius;
int radius2 = radius * radius;
auto is_on_arc = [&](int x, int y) {
int distance2 = (center.x() - x) * (center.x() - x) + (center.y() - y) * (center.y() - y);
// Is within a circle of radius 1/2 around (x,y), so basically within the current pixel.
// Technically this is angle-dependent and should be between 1/2 and sqrt(2)/2, but this works.
return distance2 <= (radius2 + radius + 0.25) && distance2 >= (radius2 - radius + 0.25);
};
RGBA32* dst = m_target->scanline(rect.top()) + rect.left();
const size_t dst_skip = m_target->pitch() / sizeof(RGBA32);
for (int i = rect.height() - 1; i >= 0; --i) {
for (int j = 0; j < rect.width(); ++j)
if (is_on_arc(j, rect.height() - i + clip_offset))
dst[j] = color.value();
dst += dst_skip;
}
return draw_circle_arc_intersecting(a_rect, center, radius - 1, color, thickness - 1);
}
void Painter::fill_ellipse(const IntRect& a_rect, Color color)
{
VERIFY(scale() == 1); // FIXME: Add scaling support.