Re-implement QGraphicsTransform to use QMatrix4x4

QTransform-based transformations create problems when performing
X and Y axis rotations because they aren't using true 3D.  This
change modifies QGraphicsTransform and its sub-classes to use
QMatrix4x4 as the standard transformation matrix, with a project()
function to project back to 2D when required.

Reviewed-by: trustme

1 files changed, 6 insertions, 5 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem_p.h b/src/gui/graphicsview/qgraphicsitem_p.h
index 43d690f..38cb757 100644
--- a/src/gui/graphicsview/qgraphicsitem_p.h
+++ b/src/gui/graphicsview/qgraphicsitem_p.h
@@ -500,16 +500,17 @@ struct QGraphicsItemPrivate::TransformData
             return transform * *postmultiplyTransform;
         }
 
-        QTransform x(transform);
+        QMatrix4x4 x(transform);
         for (int i = 0; i < graphicsTransforms.size(); ++i)
             graphicsTransforms.at(i)->applyTo(&x);
         x.translate(xOrigin, yOrigin);
-        x.rotate(rotation, Qt::ZAxis);
-        x.scale(scale, scale);
+        x.rotate(rotation, 0, 0, 1);
+        x.scale(scale);
         x.translate(-xOrigin, -yOrigin);
+        QTransform t = QGraphicsTransform::project(x);
         if (postmultiplyTransform)
-            x *= *postmultiplyTransform;
-        return x;
+            t *= *postmultiplyTransform;
+        return t;
     }
 };