Subtexture.cs

using System;
using System.Numerics;

namespace Foster.Framework;

/// <summary>
/// A Subtexture, representing a rectangular segment of a Texture
/// </summary>
public class Subtexture
{
    /// <summary>
    /// The Texture coordinates. These are set automatically based on the Source rectangle
    /// </summary>
    public readonly Vector2[] TexCoords = new Vector2[4];

    /// <summary>
    /// The draw coordinates. These are set automatically based on the Source and Frame rectangle
    /// </summary>
    public readonly Vector2[] DrawCoords = new Vector2[4];

    /// <summary>
    /// The Texture this Subtexture is... a subtexture of
    /// </summary>
    public Texture? Texture
    {
        get => texture;
        set
        {
            if (texture != value)
            {
                texture = value;
                UpdateCoords();
            }
        }
    }

    /// <summary>
    /// The source rectangle to sample from the Texture
    /// </summary>
    public Rect Source
    {
        get => source;
        set
        {
            source = value;
            UpdateCoords();
        }
    }

    /// <summary>
    /// The frame of the Subtexture. This is useful if you trim transparency and want to store the original size of the image
    /// For example, if the original image was (64, 64), but the trimmed version is (32, 48), the Frame may be (-16, -8, 64, 64)
    /// </summary>
    public Rect Frame
    {
        get => frame;
        set
        {
            frame = value;
            UpdateCoords();
        }
    }

    /// <summary>
    /// The Draw Width of the Subtexture
    /// </summary>
    public float Width => frame.Width;

    /// <summary>
    /// The Draw Height of the Subtexture
    /// </summary>
    public float Height => frame.Height;

    private Texture? texture;
    private Rect frame;
    private Rect source;

    public Subtexture()
    {

    }

    public Subtexture(Texture texture)
        : this(texture, new Rect(0, 0, texture.Width, texture.Height))
    {

    }

    public Subtexture(Texture texture, Rect source)
        : this(texture, source, new Rect(0, 0, source.Width, source.Height))
    {

    }

    public Subtexture(Texture texture, Rect source, Rect frame)
    {
        this.texture = texture;
        this.source = source;
        this.frame = frame;

        UpdateCoords();
    }

    public void Reset(Texture texture, Rect source, Rect frame)
    {
        this.texture = texture;
        this.source = source;
        this.frame = frame;

        UpdateCoords();
    }

    public (Rect Source, Rect Frame) GetClip(in Rect clip)
    {
        (Rect Source, Rect Frame) result;

        result.Source = (clip + Source.Position + Frame.Position).OverlapRect(Source);

        result.Frame.X = MathF.Min(0, Frame.X + clip.X);
        result.Frame.Y = MathF.Min(0, Frame.Y + clip.Y);
        result.Frame.Width = clip.Width;
        result.Frame.Height = clip.Height;

        return result;
    }

    public (Rect Source, Rect Frame) GetClip(float x, float y, float w, float h)
    {
        return GetClip(new Rect(x, y, w, h));
    }

    public Subtexture GetClipSubtexture(Rect clip)
    {
        var (source, frame) = GetClip(clip);
        return new Subtexture(Texture!, source, frame);
    }

    private void UpdateCoords()
    {
        DrawCoords[0].X = -frame.X;
        DrawCoords[0].Y = -frame.Y;
        DrawCoords[1].X = -frame.X + source.Width;
        DrawCoords[1].Y = -frame.Y;
        DrawCoords[2].X = -frame.X + source.Width;
        DrawCoords[2].Y = -frame.Y + source.Height;
        DrawCoords[3].X = -frame.X;
        DrawCoords[3].Y = -frame.Y + source.Height;

        if (texture != null)
        {
            var tx0 = source.X / texture.Width;
            var ty0 = source.Y / texture.Height;
            var tx1 = source.Right / texture.Width;
            var ty1 = source.Bottom / texture.Height;

            TexCoords[0].X = tx0;
            TexCoords[0].Y = ty0;
            TexCoords[1].X = tx1;
            TexCoords[1].Y = ty0;
            TexCoords[2].X = tx1;
            TexCoords[2].Y = ty1;
            TexCoords[3].X = tx0;
            TexCoords[3].Y = ty1;
        }
    }

}