acdream/src/AcDream.App/Rendering/SamplerCache.cs

using System;
using Silk.NET.OpenGL;

namespace AcDream.App.Rendering;

/// <summary>
/// Two persistent GL sampler objects (Repeat + ClampToEdge) created once
/// per GL context. Renderers <see cref="GL.BindSampler"/> the appropriate
/// one to a texture unit instead of mutating per-texture
/// <c>GL_TEXTURE_WRAP_S/T</c> state — sampler state overrides the
/// texture's own wrap parameters, so two renderers can share the same
/// texture handle but sample it with different wrap modes safely.
///
/// <para>
/// Ported from
/// <c>references/WorldBuilder/Chorizite.OpenGLSDLBackend/OpenGLGraphicsDevice.cs:115-132</c>.
/// Filter modes match <see cref="TextureCache"/>'s upload defaults
/// (Linear / Linear, no mipmaps) so binding either sampler doesn't
/// change the visual filtering behavior — only the wrap behavior at
/// UVs outside [0, 1].
/// </para>
///
/// <para>
/// Lifetime: created once at GL init, disposed with the GL context.
/// Anything that binds a sampler MUST unbind it (<c>BindSampler(unit, 0)</c>)
/// before yielding to a renderer that doesn't use samplers, otherwise
/// the bound sampler's wrap mode will silently override that renderer's
/// per-texture wrap state.
/// </para>
/// </summary>
public sealed class SamplerCache : IDisposable
{
    private readonly GL _gl;
    private readonly ResourceCleanupGroup _resources;

    /// <summary>Sampler with WrapS = WrapT = Repeat. The default for textures uploaded by <see cref="TextureCache"/>.</summary>
    public uint Wrap { get; }

    /// <summary>Sampler with WrapS = WrapT = ClampToEdge. Used by sky meshes whose authored UVs are strictly in [0, 1] to avoid bilinear-filter bleed at seam edges.</summary>
    public uint Clamp { get; }

    public SamplerCache(GL gl)
    {
        _gl = gl ?? throw new ArgumentNullException(nameof(gl));
        var resources = new ResourceCleanupGroup();
        uint wrap = 0;
        uint clamp = 0;
        try
        {
            wrap = GlResourceCommand.CreateName(
                _gl,
                "repeat sampler",
                _gl.GenSampler,
                _gl.DeleteSampler);
            uint ownedWrap = wrap;
            resources.Add(
                "repeat sampler",
                () => GlResourceCommand.Execute(
                    _gl,
                    $"delete repeat sampler {ownedWrap}",
                    () => _gl.DeleteSampler(ownedWrap)));
            Configure(wrap, TextureWrapMode.Repeat, "repeat sampler");

            clamp = GlResourceCommand.CreateName(
                _gl,
                "clamp sampler",
                _gl.GenSampler,
                _gl.DeleteSampler);
            uint ownedClamp = clamp;
            resources.Add(
                "clamp sampler",
                () => GlResourceCommand.Execute(
                    _gl,
                    $"delete clamp sampler {ownedClamp}",
                    () => _gl.DeleteSampler(ownedClamp)));
            Configure(clamp, TextureWrapMode.ClampToEdge, "clamp sampler");
        }
        catch (Exception constructionFailure)
        {
            resources.RollbackConstructionAndThrow(
                "SamplerCache construction failed and its sampler prefix did not cleanly roll back.",
                constructionFailure);
        }

        Wrap = wrap;
        Clamp = clamp;
        _resources = resources;
    }

    private void Configure(uint sampler, TextureWrapMode wrap, string name) =>
        GlResourceCommand.Execute(_gl, $"configure {name}", () =>
        {
            _gl.SamplerParameter(sampler, SamplerParameterI.WrapS, (int)wrap);
            _gl.SamplerParameter(sampler, SamplerParameterI.WrapT, (int)wrap);
            _gl.SamplerParameter(sampler, SamplerParameterI.MinFilter, (int)TextureMinFilter.Linear);
            _gl.SamplerParameter(sampler, SamplerParameterI.MagFilter, (int)TextureMagFilter.Linear);
        });

    public void Dispose()
    {
        _resources.RetryCleanup();
    }
}