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LibGfx: Put the Midpoint Ellipse Algorithm in its own function

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Lucas CHOLLET 2023-01-01 15:55:57 +01:00 committed by Andreas Kling
parent 9c5915b5b4
commit d2372464a2
Notes: sideshowbarker 2024-07-17 09:48:50 +09:00 
Author: https://github.com/LucasChollet
Commit: https://github.com/SerenityOS/serenity/commit/d2372464a2
Pull-request: https://github.com/SerenityOS/serenity/pull/16780
1 changed files with 53 additions and 48 deletions
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101
Userland/Libraries/LibGfx/Painter.cpp
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@ -472,6 +472,55 @@ void Painter::draw_circle_arc_intersecting(IntRect const& a_rect, IntPoint cente
return draw_circle_arc_intersecting(a_rect, center, radius - 1, color, thickness - 1);
}
// The callback will only be called for a quarter of the ellipse, the user is intended to deduce other points.
// As the coordinate space is relative to the center of the rectangle, it's simply (x, y), (x, -y), (-x, y) and (-x, -y).
static void on_each_ellipse_point(IntRect const& rect, Function<void(IntPoint)>&& callback)
{
// Note: This is an implementation of the Midpoint Ellipse Algorithm.
double const a = rect.width() / 2;
double const a_square = a * a;
double const b = rect.height() / 2;
double const b_square = b * b;
int x = 0;
auto y = static_cast<int>(b);
double dx = 2 * b_square * x;
double dy = 2 * a_square * y;
// For region 1:
auto decision_parameter = b_square - a_square * b + .25 * a_square;
while (dx < dy) {
callback({ x, y });
if (decision_parameter >= 0) {
y--;
dy -= 2 * a_square;
decision_parameter -= dy;
}
x++;
dx += 2 * b_square;
decision_parameter += dx + b_square;
}
// For region 2:
decision_parameter = b_square * ((x + 0.5) * (x + 0.5)) + a_square * ((y - 1) * (y - 1)) - a_square * b_square;
while (y >= 0) {
callback({ x, y });
if (decision_parameter <= 0) {
x++;
dx += 2 * b_square;
decision_parameter += dx;
}
y--;
dy -= 2 * a_square;
decision_parameter += a_square - dy;
}
}
void Painter::fill_ellipse(IntRect const& a_rect, Color color)
{
VERIFY(scale() == 1); // FIXME: Add scaling support.
@ -498,57 +547,13 @@ void Painter::draw_ellipse_intersecting(IntRect const& rect, Color color, int th
auto const center = rect.center();
auto const draw_real_world_x4 = [this, &color, thickness, center](int x, int y) {
IntPoint const directions[4] = { { x, y }, { x, -y }, { -x, y }, { -x, -y } };
for (auto const& delta : directions) {
on_each_ellipse_point(rect, [this, &color, thickness, center](IntPoint position) {
IntPoint const directions[4] = { { position.x(), position.y() }, { position.x(), -position.y() }, { -position.x(), position.y() }, { -position.x(), -position.y() } };
for (auto const delta : directions) {
auto const point = center + delta;
draw_line(point, point, color, thickness);
}
};
// Note: This is an implementation of the Midpoint Ellipse Algorithm:
double const a = rect.width() / 2;
double const a_square = a * a;
double const b = rect.height() / 2;
double const b_square = b * b;
int x = 0;
auto y = static_cast<int>(b);
double dx = 2 * b_square * x;
double dy = 2 * a_square * y;
// For region 1:
auto decision_parameter = b_square - a_square * b + .25 * a_square;
while (dx < dy) {
draw_real_world_x4(x, y);
if (decision_parameter >= 0) {
y--;
dy -= 2 * a_square;
decision_parameter -= dy;
}
x++;
dx += 2 * b_square;
decision_parameter += dx + b_square;
}
// For region 2:
decision_parameter = b_square * ((x + 0.5) * (x + 0.5)) + a_square * ((y - 1) * (y - 1)) - a_square * b_square;
while (y >= 0) {
draw_real_world_x4(x, y);
if (decision_parameter <= 0) {
x++;
dx += 2 * b_square;
decision_parameter += dx;
}
y--;
dy -= 2 * a_square;
decision_parameter += a_square - dy;
}
});
}
template<typename RectType, typename Callback>