Restore caller GL state after output rendering

Step-image and parts-list helpers switched to the shared offscreen context
and left it current after rendering. Framebuffer release and destruction
also replaced a caller's existing binding with the default framebuffer.
This violated the output helpers' state-restoration contract on both
success and failure.

Capture the caller's context, surface, and framebuffer bindings in a scope
guard before asset waits and rendering. Restore them after the temporary
view is destroyed, preserving separate draw/read bindings where supported
and leaving no context current when the caller started without one.

Validation: full debug build and whitespace checks passed. A temporary
OpenGL regression harness verified step-image and parts-list success and
framebuffer creation failure with an alternate caller context, an alternate
surface on the shared context, nondefault framebuffer bindings, and no
initially current context.

common/lc_context.cpp

@@ -29,6 +29,51 @@ std::unique_ptr<QOffscreenSurface> lcContext::mOffscreenSurface;
 std::unique_ptr<lcContext> lcContext::mGlobalOffscreenContext;
 lcProgram lcContext::mPrograms[static_cast<int>(lcMaterialType::Count)];
 
+lcScopedGLContextState::lcScopedGLContextState()
+	: mContext(QOpenGLContext::currentContext()), mSurface(mContext ? mContext->surface() : nullptr)
+{
+	if (!mContext)
+		return;
+
+	QOpenGLFunctions* Functions = mContext->functions();
+	mSeparateFramebuffers = QOpenGLFramebufferObject::hasOpenGLFramebufferBlit();
+
+	if (mSeparateFramebuffers)
+	{
+		Functions->glGetIntegerv(GL_DRAW_FRAMEBUFFER_BINDING, &mDrawFramebuffer);
+		Functions->glGetIntegerv(GL_READ_FRAMEBUFFER_BINDING, &mReadFramebuffer);
+	}
+	else
+		Functions->glGetIntegerv(GL_FRAMEBUFFER_BINDING, &mDrawFramebuffer);
+}
+
+lcScopedGLContextState::~lcScopedGLContextState()
+{
+	QOpenGLContext* CurrentContext = QOpenGLContext::currentContext();
+
+	if (!mContext)
+	{
+		if (CurrentContext)
+			CurrentContext->doneCurrent();
+
+		return;
+	}
+
+	if (CurrentContext != mContext || mContext->surface() != mSurface)
+		if (!mContext->makeCurrent(mSurface))
+			return;
+
+	QOpenGLFunctions* Functions = mContext->functions();
+
+	if (mSeparateFramebuffers)
+	{
+		Functions->glBindFramebuffer(GL_DRAW_FRAMEBUFFER, mDrawFramebuffer);
+		Functions->glBindFramebuffer(GL_READ_FRAMEBUFFER, mReadFramebuffer);
+	}
+	else
+		Functions->glBindFramebuffer(GL_FRAMEBUFFER, mDrawFramebuffer);
+}
+
 lcContext::lcContext()
 {
 	mVertexBufferObject = 0;

common/lc_context.h

@@ -106,6 +106,24 @@ struct lcVertexAttribState
 	GLuint VertexBufferObject = 0;
 };
 
+// Restores caller state after temporary rendering, including a caller with no current context.
+class lcScopedGLContextState
+{
+public:
+	lcScopedGLContextState();
+	~lcScopedGLContextState();
+
+	lcScopedGLContextState(const lcScopedGLContextState&) = delete;
+	lcScopedGLContextState& operator=(const lcScopedGLContextState&) = delete;
+
+private:
+	QOpenGLContext* mContext;
+	QSurface* mSurface;
+	GLint mDrawFramebuffer = 0;
+	GLint mReadFramebuffer = 0;
+	bool mSeparateFramebuffers = false;
+};
+
 class lcContext : public QOpenGLFunctions
 {
 public:

common/lc_model.cpp

@@ -1695,6 +1695,8 @@ void lcModel::AddSubModelRenderMeshes(lcScene* Scene, const lcMatrix44& WorldMat
 
 QImage lcModel::GetStepImage(bool Zoom, int Width, int Height, lcStep Step)
 {
+	lcScopedGLContextState GLState;
+
 	WaitForAssets();
 
 	const lcResult<QImage> Image = RenderStepImageWithReadyAssets(Zoom, Width, Height, Step, nullptr);
@@ -1712,6 +1714,8 @@ QImage lcModel::GetStepImage(bool Zoom, int Width, int Height, lcStep Step)
 
 lcResult<QImage> lcModel::RenderStepImageWithReadyAssets(bool Zoom, int Width, int Height, lcStep Step, lcCamera* OutputCamera)
 {
+	lcScopedGLContextState GLState;
+
 	const lcView* ActiveView = gMainWindow ? gMainWindow->GetActiveView() : nullptr;
 	const lcStep CurrentStep = mCurrentStep;
 
@@ -1762,6 +1766,8 @@ lcResult<QImage> lcModel::RenderStepImageWithReadyAssets(bool Zoom, int Width, i
 
 QImage lcModel::GetPartsListImage(int MaxWidth, lcStep Step, quint32 BackgroundColor, QFont Font, QColor TextColor, bool KeepMissingParts) const
 {
+	lcScopedGLContextState GLState;
+
 	WaitForAssets();
 
 	lcPartsList PartsList;