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, 105 insertions, 0 deletions

diff --git a/libs/preview_nif/src/OpenGLShape.h b/libs/preview_nif/src/OpenGLShape.h
new file mode 100644
index 0000000..b53e96d
--- /dev/null
+++ b/libs/preview_nif/src/OpenGLShape.h
@@ -0,0 +1,105 @@
+#pragma once
+
+#include "ShaderManager.h"
+#include "TextureManager.h"
+
+#include <Geometry.hpp>
+#include <NifFile.hpp>
+
+#include <QOpenGLBuffer>
+#include <QOpenGLShaderProgram>
+#include <QOpenGLTexture>
+#include <QOpenGLVertexArrayObject>
+#include <QWidget>
+
+enum TextureSlot
+{
+    BaseMap = 0,
+    NormalMap = 1,
+    GlowMap = 2,
+    LightMask = 2,
+    HeightMap = 3,
+    DetailMask = 3,
+    EnvironmentMap = 4,
+    EnvironmentMask = 5,
+    TintMask = 6,
+    InnerMap = 6,
+    BacklightMap = 7,
+    SpecularMap = 7,
+};
+
+struct OpenGLShape
+{
+public:
+    OpenGLShape(
+        nifly::NifFile* nifFile,
+        nifly::NiShape* niShape,
+        TextureManager* textureManager);
+
+    void destroy();
+    void setupShaders(QOpenGLShaderProgram* program);
+
+    static QVector2D convertVector2(nifly::Vector2 vector);
+    static QVector3D convertVector3(nifly::Vector3 vector);
+    static QColor convertColor(nifly::Color4 color);
+    static QMatrix4x4 convertTransform(nifly::MatTransform transform);
+
+    ShaderManager::ShaderType shaderType = ShaderManager::SKDefault;
+
+    QOpenGLVertexArrayObject* vertexArray = nullptr;
+
+    QOpenGLBuffer* vertexBuffers[ATTRIB_COUNT] { nullptr };
+
+    QOpenGLBuffer* indexBuffer = nullptr;
+    GLsizei elements = 0;
+
+    std::array<QOpenGLTexture*, 13> textures { nullptr };
+
+    QMatrix4x4 modelMatrix;
+    QVector3D specColor{ 1.0f, 1.0f, 1.0f };
+    float specStrength = 1.0f ;
+    float specGlossiness = 1.0f;
+    float fresnelPower;
+
+    float paletteScale;
+
+    bool hasGlowMap = false;
+    QColor glowColor = QColorConstants::White;
+    float glowMult = 1.0f;
+
+    float alpha = 1.0f;
+    QVector3D tintColor{ 1.0f, 1.0f, 1.0f };
+
+    QVector2D uvScale{ 1.0f, 1.0f };
+    QVector2D uvOffset{ 0.0f, 0.0f };
+
+    bool hasEmit = false;
+    bool hasSoftlight = false;
+    bool hasBacklight = false;
+    bool hasRimlight = false;
+    bool hasTintColor = false;
+    bool hasWeaponBlood = false;
+
+    bool doubleSided = false;
+    float softlight = 0.3f;
+    float backlightPower = 0.0f;
+    float rimPower = 2.0f;
+    float subsurfaceRolloff;
+    float envReflection = 1.0f;
+
+    QVector2D innerScale;
+    float innerThickness;
+    float outerRefraction;
+    float outerReflection;
+
+    bool zBufferWrite = true;
+    bool zBufferTest = true;
+    bool isDecal = false;
+
+    bool alphaBlendEnable = false;
+    GLenum srcBlendMode = GL_ONE;
+    GLenum dstBlendMode = GL_ONE;
+    bool alphaTestEnable = false;
+    GLenum alphaTestMode = GL_GREATER;
+    float alphaThreshold = 0.0f;
+};