osu-lazer/osu.Game/Screens/Edit/Compose/Components/LinedPositionSnapGrid.cs

// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using System;
using System.Collections.Generic;
using System.Linq;
using osu.Framework.Graphics;
using osu.Framework.Graphics.Shapes;
using osu.Framework.Utils;
using osuTK;

namespace osu.Game.Screens.Edit.Compose.Components
{
    public abstract partial class LinedPositionSnapGrid : PositionSnapGrid
    {
        protected void GenerateGridLines(Vector2 step, Vector2 drawSize)
        {
            int index = 0;
            var currentPosition = StartPosition.Value;

            // Make lines the same width independent of display resolution.
            float lineWidth = DrawWidth / ScreenSpaceDrawQuad.Width;
            float lineLength = drawSize.Length * 2;

            List<Box> generatedLines = new List<Box>();

            while (lineDefinitelyIntersectsBox(currentPosition, step.PerpendicularLeft, drawSize) ||
                   isMovingTowardsBox(currentPosition, step, drawSize))
            {
                var gridLine = new Box
                {
                    Colour = Colour4.White,
                    Alpha = 0.1f,
                    Origin = Anchor.Centre,
                    RelativeSizeAxes = Axes.None,
                    Width = lineWidth,
                    Height = lineLength,
                    Position = currentPosition,
                    Rotation = MathHelper.RadiansToDegrees(MathF.Atan2(step.Y, step.X)),
                };

                generatedLines.Add(gridLine);

                index += 1;
                currentPosition = StartPosition.Value + index * step;
            }

            if (generatedLines.Count == 0)
                return;

            generatedLines.First().Alpha = 0.2f;

            AddRangeInternal(generatedLines);
        }

        private bool isMovingTowardsBox(Vector2 currentPosition, Vector2 step, Vector2 box)
        {
            return (currentPosition + step).LengthSquared < currentPosition.LengthSquared ||
                   (currentPosition + step - box).LengthSquared < (currentPosition - box).LengthSquared;
        }

        private bool lineDefinitelyIntersectsBox(Vector2 lineStart, Vector2 lineDir, Vector2 box)
        {
            var p2 = lineStart + lineDir;

            double d1 = det(Vector2.Zero);
            double d2 = det(new Vector2(box.X, 0));
            double d3 = det(new Vector2(0, box.Y));
            double d4 = det(box);

            return definitelyDifferentSign(d1, d2) || definitelyDifferentSign(d3, d4) ||
                   definitelyDifferentSign(d1, d3) || definitelyDifferentSign(d2, d4);

            double det(Vector2 p) => (p.X - lineStart.X) * (p2.Y - lineStart.Y) - (p.Y - lineStart.Y) * (p2.X - lineStart.X);

            bool definitelyDifferentSign(double a, double b) => !Precision.AlmostEquals(a, 0) &&
                                                                !Precision.AlmostEquals(b, 0) &&
                                                                Math.Sign(a) != Math.Sign(b);
        }
    }
}