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LibWeb: Fix goofy CRC2D.arc() behaviour

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This PR corrects the signs of the start/end points that are passed
to the elliptical_arc_to(), it also removes the bogus path.close()
after creating the arc. Now .arc() seems to work correctly.
This commit is contained in:
MacDue 2023-05-27 20:18:31 +01:00 • committed by Andreas Kling
parent f7eb8eed34
commit 02d131bc4d
1 changed files with 11 additions and 8 deletions
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19
Userland/Libraries/LibWeb/HTML/Canvas/CanvasPath.cpp
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@ -53,7 +53,9 @@ WebIDL::ExceptionOr<void> CanvasPath::ellipse(float x, float y, float radius_x,
if (constexpr float tau = M_TAU; (!counter_clockwise && (end_angle - start_angle) >= tau)
|| (counter_clockwise && (start_angle - end_angle) >= tau)) {
start_angle = 0;
end_angle = tau;
// FIXME: elliptical_arc_to() incorrectly handles the case where the start/end points are very close.
// So we slightly fudge the numbers here to correct for that.
end_angle = tau * 0.9999f;
} else {
start_angle = fmodf(start_angle, tau);
end_angle = fmodf(end_angle, tau);
@ -63,8 +65,9 @@ WebIDL::ExceptionOr<void> CanvasPath::ellipse(float x, float y, float radius_x,
// To do so, we can pretend that the center of this ellipse is at (0, 0),
// and the whole coordinate system is rotated `rotation` radians around the x axis, centered on `center`.
// The sign of the resulting relative positions is just whether our angle is on one of the left quadrants.
auto sin_rotation = sinf(rotation);
auto cos_rotation = cosf(rotation);
float sin_rotation;
float cos_rotation;
AK::sincos(rotation, sin_rotation, cos_rotation);
auto resolve_point_with_angle = [&](float angle) {
auto tan_relative = tanf(angle);
@ -79,7 +82,9 @@ WebIDL::ExceptionOr<void> CanvasPath::ellipse(float x, float y, float radius_x,
auto relative_y_position = ab * tan_relative / sqrt;
// Make sure to set the correct sign
float sn = sinf(angle) >= 0 ? 1 : -1;
// -1 if 0 ≤ θ < 90° or 270°< θ ≤ 360°
// 1 if 90° < θ< 270°
float sn = cosf(angle) >= 0 ? 1 : -1;
relative_x_position *= sn;
relative_y_position *= sn;
@ -94,12 +99,10 @@ WebIDL::ExceptionOr<void> CanvasPath::ellipse(float x, float y, float radius_x,
m_path.move_to(start_point);
double delta_theta = end_angle - start_angle;
auto delta_theta = end_angle - start_angle;
// FIXME: This is still goofy for some values.
m_path.elliptical_arc_to(end_point, { radius_x, radius_y }, rotation, delta_theta > M_PI, !counter_clockwise);
m_path.elliptical_arc_to(end_point, { radius_x, radius_y }, rotation, delta_theta > AK::Pi<float>, !counter_clockwise);
m_path.close();
return {};
}