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, 74 insertions, 0 deletions

diff --git a/libs/preview_nif/src/ShaderManager.cpp b/libs/preview_nif/src/ShaderManager.cpp
new file mode 100644
index 0000000..2109b44
--- /dev/null
+++ b/libs/preview_nif/src/ShaderManager.cpp
@@ -0,0 +1,74 @@
+#include "ShaderManager.h"
+
+#include <QOpenGLContext>
+
+ShaderManager::ShaderManager(MOBase::IOrganizer* moInfo) : m_MOInfo{ moInfo }
+{}
+
+QOpenGLShaderProgram* ShaderManager::getProgram(ShaderType type)
+{
+    if (type == None) {
+        return nullptr;
+    }
+
+    if (m_Programs[type] == nullptr) {
+        m_Programs[type] = loadProgram(type);
+    }
+
+    return m_Programs[type];
+}
+
+QOpenGLShaderProgram* ShaderManager::loadProgram(ShaderType type)
+{
+    QString vert;
+    QString frag;
+
+    switch (type) {
+    case SKDefault:
+        vert = "default.vert";
+        frag = "sk_default.frag";
+        break;
+    case SKMSN:
+        vert = "sk_msn.vert";
+        frag = "sk_msn.frag";
+        break;
+    case SKMultilayer:
+        vert = "default.vert";
+        frag = "sk_multilayer.frag";
+        break;
+    case SKEffectShader:
+        vert = "sk_effectshader.vert";
+        frag = "sk_effectshader.frag";
+        break;
+    case FO4Default:
+        vert = "default.vert";
+        frag = "fo4_default.frag";
+        break;
+    case FO4EffectShader:
+        vert = "default.vert";
+        frag = "fo4_effectshader.frag";
+        break;
+    default:
+        return nullptr;
+    }
+
+    auto game = m_MOInfo->managedGame();
+    auto dataPath = MOBase::IOrganizer::getPluginDataPath();
+    auto vertexShader = QString("%1/shaders/%2").arg(dataPath).arg(vert);
+    auto fragmentShader = QString("%1/shaders/%2").arg(dataPath).arg(frag);
+
+    auto program = new QOpenGLShaderProgram(QOpenGLContext::currentContext());
+    program->addShaderFromSourceFile(QOpenGLShader::Vertex, vertexShader);
+    program->addShaderFromSourceFile(QOpenGLShader::Fragment, fragmentShader);
+
+    program->bindAttributeLocation("position", AttribPosition);
+    program->bindAttributeLocation("normal", AttribNormal);
+    program->bindAttributeLocation("tangent", AttribTangent);
+    program->bindAttributeLocation("bitangent", AttribBitangent);
+    program->bindAttributeLocation("texCoord", AttribTexCoord);
+    program->bindAttributeLocation("color", AttribColor);
+
+    program->link();
+
+    return program;
+}