typedef enum {PETSC_DRAW_MARKER_CROSS, PETSC_DRAW_MARKER_POINT,PETSC_DRAW_MARKER_PLUS,PETSC_DRAW_MARKER_CIRCLE} PetscDrawMarkerType;
PETSC_MARKER_CROSS - a small pixel based x symbol or the character x if that is not available
PETSC_MARKER_PLUS - a small pixel based + symbol or the character + if that is not available
PETSC_MARKER_CIRCLE - a small pixel based circle symbol or the character o if that is not available
PETSC_MARKER_POINT - the make obtained with PetscDrawPoint()