Add NIF previewer plugin with Linux-specific fixes

Vendored from github.com/Parapets/mo2-preview_nif and adapted for Linux:

- BSA texture resolution via MO2 virtual tree with case-insensitive
  fallback walk (Linux FS is case-sensitive; NIFs reference textures
  with arbitrary case against files on disk)
- Process-wide cached BSA candidate list, keyed by profile path,
  priority-sorted, filtering disabled mods
- Path backslash normalization before loose-file lookup
- Polygon offset on SLSF1_Decal-flagged shapes to break z-ties with
  coincident base meshes (road decals, moss overlays)
- Opaque framebuffer via glColorMask alpha lock so alpha-blended shapes
  can't bleed the dialog background through the preview area
- QMouseEvent::globalPosition().toPoint() for Qt6 compatibility

Preview dialog behavior (organizercore.cpp):
- Switch previewFile and previewFileWithAlternatives from stack-allocated
  exec() to heap + ApplicationModal + show() + WA_DeleteOnClose.
- Parent passed as nullptr so preview lifetime is decoupled from the
  stack-allocated ModInfoDialog that spawns it. Nested exec() inside
  the enclosing dialog's exec() was softlocking on close.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

1 files changed, 236 insertions, 0 deletions

diff --git a/libs/preview_nif/src/NifExtensions.h b/libs/preview_nif/src/NifExtensions.h
new file mode 100644
index 0000000..cd529e5
--- /dev/null
+++ b/libs/preview_nif/src/NifExtensions.h
@@ -0,0 +1,236 @@
+#pragma once
+
+#include <QOpenGLFunctions>
+#include <NifFile.hpp>
+#include <cstdint>
+#include <cstring>
+
+struct SLSF1
+{
+    SLSF1() = delete;
+
+    enum BSLightingShaderFlags1 : std::uint32_t
+    {
+        Specular                = 1U << 0,
+        Skinned                 = 1U << 1,
+        TempRefraction          = 1U << 2,
+        VertexAlpha             = 1U << 3,
+        GreyscaleToPaletteColor = 1U << 4,
+        GreyscaleToPaletteAlpha = 1U << 5,
+        UseFalloff              = 1U << 6,
+        EnvironmentMapping      = 1U << 7,
+        ReceiveShadows          = 1U << 8,
+        CastShadows             = 1U << 9,
+        FacegenDetailMap        = 1U << 10,
+        Parallax                = 1U << 11,
+        ModelSpaceNormals       = 1U << 12,
+        NonProjectiveShadows    = 1U << 13,
+        Landscape               = 1U << 14,
+        Refraction              = 1U << 15,
+        FireRefraction          = 1U << 16,
+        EyeEnvironmentMapping   = 1U << 17,
+        HairSoftLighting        = 1U << 18,
+        ScreendoorAlphaFade     = 1U << 19,
+        LocalmapHideSecret      = 1U << 20,
+        FaceGenRGBTint          = 1U << 21,
+        OwnEmit                 = 1U << 22,
+        ProjectedUV             = 1U << 23,
+        MultipleTextures        = 1U << 24,
+        RemappableTextures      = 1U << 25,
+        Decal                   = 1U << 26,
+        DynamicDecal            = 1U << 27,
+        ParallaxOcclusion       = 1U << 28,
+        ExternalEmittance       = 1U << 29,
+        SoftEffect              = 1U << 30,
+        ZBufferTest             = 1U << 31,
+    };
+};
+
+struct SLSF2
+{
+    SLSF2() = delete;
+
+    enum BSLightingShaderFlags2 : std::uint32_t
+    {
+        ZBufferWrite                = 1U << 0,
+        LODLandscape                = 1U << 1,
+        LODObjects                  = 1U << 2,
+        NoFade                      = 1U << 3,
+        DoubleSided                 = 1U << 4,
+        VertexColors                = 1U << 5,
+        GlowMap                     = 1U << 6,
+        AssumeShadowmask            = 1U << 7,
+        PackedTangent               = 1U << 8,
+        MultiIndexSnow              = 1U << 9,
+        VertexLighting              = 1U << 10,
+        UniformScale                = 1U << 11,
+        FitSlope                    = 1U << 12,
+        Billboard                   = 1U << 13,
+        NoLODLandBlend              = 1U << 14,
+        EnvMapLightFade             = 1U << 15,
+        Wireframe                   = 1U << 16,
+        WeaponBlood                 = 1U << 17,
+        HideOnLocalMap              = 1U << 18,
+        PremultAlpha                = 1U << 19,
+        CloudLOD                    = 1U << 20,
+        AnisotropicLighting         = 1U << 21,
+        NoTransparencyMultisampling = 1U << 22,
+        Unused01                    = 1U << 23,
+        MultiLayerParallax          = 1U << 24,
+        SoftLighting                = 1U << 25,
+        RimLighting                 = 1U << 26,
+        BackLighting                = 1U << 27,
+        Unused02                    = 1U << 28,
+        TreeAnim                    = 1U << 29,
+        EffectLighting              = 1U << 30,
+        HDLODObjects                = 1U << 31,
+    };
+};
+
+struct TriShape
+{
+    TriShape() = delete;
+
+    enum NiAVObjectFlags : std::uint32_t
+    {
+        Hidden                            = 1U << 0,
+        SelectiveUpdate                   = 1U << 1,
+        SelectiveUpdateTransforms         = 1U << 2,
+        SelectiveUpdateController         = 1U << 3,
+        SelectiveUpdateRigid              = 1U << 4,
+        DisplayUIObject                   = 1U << 5,
+        DisableSorting                    = 1U << 6,
+        SelectiveUpdateTransformsOverride = 1U << 7,
+        SaveExternalGeomData              = 1U << 9,
+        NoDecals                          = 1U << 10,
+        AlwaysDraw                        = 1U << 11,
+        MeshLODFO4                        = 1U << 12,
+        FixedBound                        = 1U << 13,
+        TopFadeNode                       = 1U << 14,
+        IgnoreFade                        = 1U << 15,
+        NoAnimSyncX                       = 1U << 16,
+        NoAnimSyncY                       = 1U << 17,
+        NoAnimSyncZ                       = 1U << 18,
+        NoAnimSyncS                       = 1U << 19,
+        NoDismember                       = 1U << 20,
+        NoDismemberValidity               = 1U << 21,
+        RenderUse                         = 1U << 22,
+        MaterialsApplied                  = 1U << 23,
+        HighDetail                        = 1U << 24,
+        ForceUpdate                       = 1U << 25,
+        PreProcessedNode                  = 1U << 26,
+        MeshLODSkyrim                     = 1U << 27,
+    };
+};
+
+struct NiAlphaPropertyFlags
+{
+public:
+    NiAlphaPropertyFlags(std::uint16_t flags = 0)
+    {
+        std::memcpy(this, &flags, sizeof(NiAlphaPropertyFlags));
+    }
+
+    bool isAlphaBlendEnabled()
+    {
+        return m_AlphaBlendEnable;
+    }
+
+    GLenum sourceBlendingFactor()
+    {
+        return getBlendMode(m_SrcBlendMode);
+    }
+
+    GLenum destinationBlendingFactor()
+    {
+        return getBlendMode(m_DstBlendMode);
+    }
+
+    bool isAlphaTestEnabled()
+    {
+        return m_AlphaTestEnable;
+    }
+
+    GLenum alphaTestMode()
+    {
+        return getTestMode(m_AlphaTestMode);
+    }
+
+    bool isTriangleSortDisabled()
+    {
+        return m_NoSort;
+    }
+
+private:
+    static std::uint32_t getBlendMode(std::uint16_t flags)
+    {
+        switch (flags) {
+            case 0: return GL_ONE;
+            case 1: return GL_ZERO;
+            case 2: return GL_SRC_COLOR;
+            case 3: return GL_ONE_MINUS_SRC_COLOR;
+            case 4: return GL_DST_COLOR;
+            case 5: return GL_ONE_MINUS_DST_COLOR;
+            case 6: return GL_SRC_ALPHA;
+            case 7: return GL_ONE_MINUS_SRC_ALPHA;
+            case 8: return GL_DST_ALPHA;
+            case 9: return GL_ONE_MINUS_DST_ALPHA;
+            default: return GL_ONE;
+        };
+    }
+
+    static std::uint32_t getTestMode(std::uint16_t flags)
+    {
+        switch (flags) {
+            case 0: return GL_ALWAYS;
+            case 1: return GL_LESS;
+            case 2: return GL_EQUAL;
+            case 3: return GL_LEQUAL;
+            case 4: return GL_GREATER;
+            case 5: return GL_NOTEQUAL;
+            case 6: return GL_GEQUAL;
+            case 7: return GL_NEVER;
+            default: return GL_ALWAYS;
+        }
+    };
+
+    std::uint16_t m_AlphaBlendEnable : 1;
+    std::uint16_t m_SrcBlendMode : 4;
+    std::uint16_t m_DstBlendMode : 4;
+    std::uint16_t m_AlphaTestEnable : 1;
+    std::uint16_t m_AlphaTestMode : 3;
+    std::uint16_t m_NoSort : 1;
+};
+static_assert(sizeof(NiAlphaPropertyFlags) == 2);
+
+inline nifly::MatTransform GetShapeTransformToGlobal(
+    nifly::NifFile* nifFile,
+    nifly::NiShape* niShape)
+{
+    nifly::MatTransform xform = niShape->GetTransformToParent();
+    nifly::NiNode* parent = nifFile->GetParentNode(niShape);
+    while (parent) {
+        xform = parent->GetTransformToParent().ComposeTransforms(xform);
+        parent = nifFile->GetParentNode(parent);
+    }
+
+    return xform;
+}
+
+inline nifly::BoundingSphere GetBoundingSphere(
+    nifly::NifFile* nifFile,
+    nifly::NiShape* niShape)
+{
+    if (auto vertices = nifFile->GetVertsForShape(niShape)) {
+        auto bounds = nifly::BoundingSphere(*vertices);
+
+        auto xform = GetShapeTransformToGlobal(nifFile, niShape);
+
+        bounds.center = xform.ApplyTransform(bounds.center);
+        bounds.radius = xform.ApplyTransformToDist(bounds.radius);
+        return bounds;
+    }
+    else {
+        return nifly::BoundingSphere();
+    }
+}