این یه باگه تو ماری من کار نکردم ولی توضیحات خودشون اینه :
BUG ID 34729 - Mari displays a rendering error on the canvas when it is unable to create a shader
. More information has been included to help
you determine the cause of the error.
Some solutions might be to hide
groups and layers, or to cache parts of your layer stack until a shader
can be created.