RainbowRodDrawer.cs

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using System.Runtime.InteropServices;
using Microsoft.Xna.Framework;
using Terraria.Graphics.Shaders;
 
namespace Terraria.Graphics;
 
[StructLayout(LayoutKind.Sequential, Size = 1)]
public struct RainbowRodDrawer
{
    private static VertexStrip _vertexStrip = new VertexStrip();
 
    public void Draw(Projectile proj)
    {
        MiscShaderData miscShaderData = GameShaders.Misc["RainbowRod"];
        miscShaderData.UseSaturation(-2.8f);
        miscShaderData.UseOpacity(4f);
        miscShaderData.Apply();
        _vertexStrip.PrepareStripWithProceduralPadding(proj.oldPos, proj.oldRot, StripColors, StripWidth, -Main.screenPosition + proj.Size / 2f);
        _vertexStrip.DrawTrail();
        Main.pixelShader.CurrentTechnique.Passes[0].Apply();
    }
 
    private Color StripColors(float progressOnStrip)
    {
        Color value = Main.hslToRgb((progressOnStrip * 1.6f - Main.GlobalTimeWrappedHourly) % 1f, 1f, 0.5f);
        Color result = Color.Lerp(Color.White, value, Utils.GetLerpValue(-0.2f, 0.5f, progressOnStrip, clamped: true)) * (1f - Utils.GetLerpValue(0f, 0.98f, progressOnStrip));
        result.A = 0;
        return result;
    }
 
    private float StripWidth(float progressOnStrip)
    {
        float num = 1f;
        float lerpValue = Utils.GetLerpValue(0f, 0.2f, progressOnStrip, clamped: true);
        num *= 1f - (1f - lerpValue) * (1f - lerpValue);
        return MathHelper.Lerp(0f, 32f, num);
    }
}