acdream/src/AcDream.App/Rendering/Wb/BindlessSupport.cs

using Silk.NET.OpenGL;
using Silk.NET.OpenGL.Extensions.ARB;
using AcDream.App.Rendering;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Thin wrapper around <see cref="ArbBindlessTexture"/> + capability detection
/// for the modern rendering path. Constructed once at startup via
/// <see cref="TryCreate"/>, which returns false if the extension isn't present.
/// </summary>
public sealed class BindlessSupport
{
    private readonly GL _gl;
    private readonly ArbBindlessTexture _ext;

    private BindlessSupport(GL gl, ArbBindlessTexture extension)
    {
        _gl = gl;
        _ext = extension;
    }

    public static bool TryCreate(GL gl, out BindlessSupport? support)
    {
        if (gl.TryGetExtension<ArbBindlessTexture>(out var ext))
        {
            support = new BindlessSupport(gl, ext);
            return true;
        }
        support = null;
        return false;
    }

    /// <summary>Get a 64-bit bindless handle for the texture and make it resident.
    /// Idempotent: handle is the same for a given texture name.</summary>
    public ulong GetResidentHandle(uint textureName)
    {
        ulong h = GlResourceCommand.Execute(
            _gl,
            $"get bindless handle for texture {textureName}",
            () => _ext.GetTextureHandle(textureName));
        if (h == 0)
            throw new InvalidOperationException(
                $"OpenGL returned no bindless handle for texture {textureName}.");

        bool resident = GlResourceCommand.Execute(
            _gl,
            $"query bindless handle {h} residency",
            () => _ext.IsTextureHandleResident(h));
        if (!resident)
        {
            GlResourceCommand.Execute(
                _gl,
                $"make bindless handle {h} resident",
                () => _ext.MakeTextureHandleResident(h));
        }
        return h;
    }

    /// <summary>Release residency for a handle. Call before deleting the underlying texture.</summary>
    public void MakeNonResident(ulong handle)
    {
        bool resident = GlResourceCommand.Execute(
            _gl,
            $"query bindless handle {handle} residency before release",
            () => _ext.IsTextureHandleResident(handle));
        if (!resident)
            return;

        GlResourceCommand.Execute(
            _gl,
            $"make bindless handle {handle} non-resident",
            () => _ext.MakeTextureHandleNonResident(handle));
    }

    // Phase N.5b note: a `SetSamplerHandleUniform` wrapper was added in T6
    // and removed when terrain rendering surfaced GL_INVALID_OPERATION on
    // NVIDIA Windows for the `uniform sampler2DArray` + glProgramUniformHandleARB
    // combination. The replacement pattern (uvec2 handle uniform + GLSL
    // sampler-from-handle constructor — see terrain_modern.frag) lives at the
    // call site via plain `_gl.ProgramUniform2(program, loc, low, high)`. If
    // you re-introduce a sampler-handle helper, restrict it to drivers known
    // to accept the direct sampler-uniform path.

    /// <summary>Detect <c>GL_ARB_shader_draw_parameters</c> in addition to bindless.
    /// N.5's vertex shader uses <c>gl_BaseInstanceARB</c> and <c>gl_DrawIDARB</c>
    /// from this extension.</summary>
    public bool HasShaderDrawParameters(GL gl)
    {
        return gl.IsExtensionPresent("GL_ARB_shader_draw_parameters");
    }
}