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, 48 insertions, 0 deletions

diff --git a/libs/preview_nif/src/ShaderManager.h b/libs/preview_nif/src/ShaderManager.h
new file mode 100644
index 0000000..3c38ba1
--- /dev/null
+++ b/libs/preview_nif/src/ShaderManager.h
@@ -0,0 +1,48 @@
+#pragma once
+
+#include <imoinfo.h>
+#include <QOpenGLShaderProgram>
+
+enum VertexAttrib
+{
+    AttribPosition = 0,
+    AttribNormal = 1,
+    AttribTangent = 2,
+    AttribBitangent = 3,
+    AttribTexCoord = 4,
+    AttribColor = 5,
+
+    ATTRIB_COUNT,
+};
+
+class ShaderManager
+{
+public:
+    enum ShaderType
+    {
+        None = -1,
+        SKDefault,
+        SKMSN,
+        SKMultilayer,
+        SKEffectShader,
+        FO4Default,
+        FO4EffectShader,
+
+        SHADER_COUNT,
+    };
+
+    ShaderManager(MOBase::IOrganizer* moInfo);
+    ~ShaderManager() = default;
+    ShaderManager(const ShaderManager&) = delete;
+    ShaderManager(ShaderManager&&) = delete;
+    ShaderManager& operator=(const ShaderManager&) = delete;
+    ShaderManager& operator=(ShaderManager&&) = delete;
+
+    QOpenGLShaderProgram* getProgram(ShaderType type);
+
+private:
+    QOpenGLShaderProgram* loadProgram(ShaderType type);
+
+    MOBase::IOrganizer* m_MOInfo;
+    QOpenGLShaderProgram* m_Programs[SHADER_COUNT] { nullptr };
+};