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LibGfx+LibWeb: Wire up CanvasRenderingContext2D.ellipse()

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Note that this is *extremely* naive, and not very good at being correct.
This commit is contained in:
AnotherTest 2021-04-15 18:41:13 +04:30 • committed by Andreas Kling
parent 6c05d6d370
commit 801daf47f0
6 changed files with 104 additions and 12 deletions
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59
Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp
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@ -188,6 +188,65 @@ void CanvasRenderingContext2D::quadratic_curve_to(float cx, float cy, float x, f
m_path.quadratic_bezier_curve_to({ cx, cy }, { x, y });
}
void CanvasRenderingContext2D::arc(float x, float y, float radius, float start_angle, float end_angle, bool counter_clockwise)
{
ellipse(x, y, radius, radius, 0, start_angle, end_angle, counter_clockwise);
}
void CanvasRenderingContext2D::ellipse(float x, float y, float radius_x, float radius_y, float rotation, float start_angle, float end_angle, bool counter_clockwise)
{
if ((!counter_clockwise && (end_angle - start_angle) >= M_TAU)
|| (counter_clockwise && (start_angle - end_angle) >= M_TAU)) {
start_angle = 0;
end_angle = M_TAU;
} else {
start_angle = fmodf(start_angle, M_TAU);
end_angle = fmodf(end_angle, M_TAU);
}
// Then, figure out where the ends of the arc are.
// 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);
auto resolve_point_with_angle = [&](float angle) {
auto tan_relative = tanf(angle);
auto tan2 = tan_relative * tan_relative;
auto ab = radius_x * radius_y;
auto a2 = radius_x * radius_x;
auto b2 = radius_y * radius_y;
auto sqrt = sqrtf(b2 + a2 * tan2);
auto relative_x_position = ab / sqrt;
auto relative_y_position = ab * tan_relative / sqrt;
// Make sure to set the correct sign
float sn = sinf(angle) >= 0 ? 1 : -1;
relative_x_position *= sn;
relative_y_position *= sn;
// Now rotate it (back) around the center point by 'rotation' radians, then move it back to our actual origin.
auto relative_rotated_x_position = relative_x_position * cos_rotation - relative_y_position * sin_rotation;
auto relative_rotated_y_position = relative_x_position * sin_rotation + relative_y_position * cos_rotation;
return Gfx::FloatPoint { relative_rotated_x_position + x, relative_rotated_y_position + y };
};
auto start_point = resolve_point_with_angle(start_angle);
auto end_point = resolve_point_with_angle(end_angle);
m_path.move_to(start_point);
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.close();
}
void CanvasRenderingContext2D::rect(float x, float y, float width, float height)
{
m_path.move_to({ x, y });