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LibGfx: Update Painter's bezier curve drawing algorithm.

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The new algorithm is an iterative one with an arbitrary threshold for splitting
curves. It splits curves evenly. This should theoretically be less accurate
than the existing recursive approach, but seems to give subjectively better
results in practice.
This commit is contained in:
Srimanta Barua 2020-06-06 15:31:34 +05:30 • committed by Andreas Kling
parent 0e9fb803c8
commit 186499cc25
Notes: sideshowbarker 2024-07-19 00:21:00 +09:00
3 changed files with 69 additions and 164 deletions
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49
Libraries/LibGfx/Painter.cpp
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@ -1282,45 +1282,22 @@ void Painter::draw_line(const IntPoint& p1, const IntPoint& p2, Color color, int
}
}
static void split_quadratic_bezier_curve(const FloatPoint& original_control, const FloatPoint& p1, const FloatPoint& p2, Function<void(const FloatPoint&, const FloatPoint&)>& callback)
{
auto po1_midpoint = original_control + p1;
po1_midpoint /= 2;
auto po2_midpoint = original_control + p2;
po2_midpoint /= 2;
auto new_segment = po1_midpoint + po2_midpoint;
new_segment /= 2;
Painter::for_each_line_segment_on_bezier_curve(po1_midpoint, p1, new_segment, callback);
Painter::for_each_line_segment_on_bezier_curve(po2_midpoint, new_segment, p2, callback);
}
static bool can_approximate_bezier_curve(const FloatPoint& p1, const FloatPoint& p2, const FloatPoint& control)
{
constexpr static int tolerance = 15;
auto p1x = 3 * control.x() - 2 * p1.x() - p2.x();
auto p1y = 3 * control.y() - 2 * p1.y() - p2.y();
auto p2x = 3 * control.x() - 2 * p2.x() - p1.x();
auto p2y = 3 * control.y() - 2 * p2.y() - p1.y();
p1x = p1x * p1x;
p1y = p1y * p1y;
p2x = p2x * p2x;
p2y = p2y * p2y;
return max(p1x, p2x) + max(p1y, p2y) <= tolerance;
}
void Painter::for_each_line_segment_on_bezier_curve(const FloatPoint& control_point, const FloatPoint& p1, const FloatPoint& p2, Function<void(const FloatPoint&, const FloatPoint&)>& callback)
{
if (can_approximate_bezier_curve(p1, p2, control_point)) {
callback(p1, p2);
} else {
split_quadratic_bezier_curve(control_point, p1, p2, callback);
float arbitrary = 15.0;
auto mid_point = FloatPoint::interpolate(p1, p2, 0.5);
float squared_distance = FloatPoint::squared_distance(control_point, mid_point);
size_t num_sections = 1 + floorf(sqrtf(arbitrary * squared_distance));
float delta = 1.0 / num_sections;
float t = 0.0;
FloatPoint p_cur = p1;
for (size_t i = 0; i < num_sections - 1; i++) {
t += delta;
FloatPoint pn = FloatPoint::interpolate(FloatPoint::interpolate(p1, control_point, t), FloatPoint::interpolate(control_point, p2, t), t);
callback(p_cur, pn);
p_cur = pn;
}
callback(p_cur, p2);
}
void Painter::for_each_line_segment_on_bezier_curve(const FloatPoint& control_point, const FloatPoint& p1, const FloatPoint& p2, Function<void(const FloatPoint&, const FloatPoint&)>&& callback)