feat: Add sketch creation with plane selection, oriented grid and labeled axes

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

src/ViewportWidget.h

@@ -5,17 +5,29 @@
 #include <QOpenGLFunctions>
 #include <QMatrix4x4>
 #include <QPoint>
+#include <QVector3D>
+#include <QRect>
 
 class ViewCube;
+class SketchGrid;
 
 class ViewportWidget : public QOpenGLWidget, protected QOpenGLFunctions
 {
     Q_OBJECT
 
 public:
+    enum class SketchPlane {
+        NONE,
+        XY,
+        XZ,
+        YZ
+    };
+
     explicit ViewportWidget(QWidget *parent = nullptr);
     ~ViewportWidget();
 
+    void startSketch(SketchPlane plane);
+
 protected:
     void initializeGL() override;
     void paintGL() override;
@@ -26,8 +38,13 @@ protected:
     void wheelEvent(QWheelEvent *event) override;
 
 private:
+    QVector3D project(const QVector3D& worldCoord, const QMatrix4x4& modelView, const QMatrix4x4& projection, const QRect& viewport);
+    void drawAxisLabels(QPainter& painter, const QMatrix4x4& modelView, const QMatrix4x4& projection);
+
     QMatrix4x4 projection;
     ViewCube* m_viewCube;
+    SketchGrid* m_sketchGrid = nullptr;
+    SketchPlane m_currentPlane = SketchPlane::NONE;
 
     float xRot = 0;
     float yRot = 0;