Drawing / Export Addon¶
This add-on provides the functionality to render a DXF document to produce a rasterized or vector-graphic image which can be saved to a file or viewed interactively depending on the backend being used.
The module provides two example scripts in the folder
examples/addons/drawing which can be run to save rendered
images to files or view an interactive visualisation
Example for the usage of the
import sys import matplotlib.pyplot as plt from ezdxf import recover from ezdxf.addons.drawing import RenderContext, Frontend from ezdxf.addons.drawing.matplotlib import MatplotlibBackend # Safe loading procedure (requires ezdxf v0.14): try: doc, auditor = recover.readfile('your.dxf') except IOError: print(f'Not a DXF file or a generic I/O error.') sys.exit(1) except ezdxf.DXFStructureError: print(f'Invalid or corrupted DXF file.') sys.exit(2) # The auditor.errors attribute stores severe errors, # which may raise exceptions when rendering. if not auditor.has_errors: fig = plt.figure() ax = fig.add_axes([0, 0, 1, 1]) ctx = RenderContext(doc) out = MatplotlibBackend(ax) Frontend(ctx, out).draw_layout(doc.modelspace(), finalize=True) fig.savefig('your.png', dpi=300)
Simplified render workflow but with less control:
from ezdxf import recover from ezdxf.addons.drawing import matplotlib # Exception handling left out for compactness: doc, auditor = recover.readfile('your.dxf') if not auditor.has_errors: matplotlib.qsave(doc.modelspace(), 'your.png')
Additional options for the drawing add-on can be passed by the config
argument of the
__init__(). Not every
option will be supported by all backends.
Configuration options for the
the size to draw POINT entities (in drawing units) set to None to use the $PDSIZE value from the dxf document header
0 5% of draw area height <0 Specifies a percentage of the viewport size >0 Specifies an absolute size None use the $PDMODE value from the dxf document header
whether to use metric or imperial units as enum
0 use imperial units (in, ft, yd, …) 1 use metric units (ISO meters) None use the $MEASUREMENT value from the dxf document header
whether to show or filter out POINT entities on the defpoints layer
the action to take when a proxy graphic is encountered
the method to use when drawing styled lines (eg dashed, dotted etc)
the method to use when drawing HATCH entities
the length to use when drawing infinite lines
set to 0.0 for a constant minimal width the current result is correct, in SVG the line width is 0.7 points for 0.25mm as required, but it often looks too thick
the minimum line width in 1/300 inch, set to None for let the the backend choose.
the minimum length for a dash when drawing a styled line (default value is arbitrary)
Max flattening distance in drawing units see Path.flattening documentation. The backend implementation should calculate an appropriate value, like 1 screen- or paper pixel on the output medium, but converted into drawing units. Sets Path() approximation accuracy
Approximate a full circle by n segments, arcs have proportional less segments. Only used for approximation of arcs in banded polylines.
draw all lines as solid regardless of the linetype style
use the closest approximation available to the backend for rendering styled lines
analyse and render styled lines as accurately as possible. This approach is slower and is not well suited to interactive applications.
The action to take when a HATCH entity is encountered
do not show HATCH entities at all
show only the outline of HATCH entities
show HATCH entities but draw with solid fill regardless of the pattern
show HATCH entities using the closest approximation available to the current backend
The action to take when an entity with a proxy graphic is encountered
To get proxy graphics support proxy graphics have to be loaded: Set the global option
True, which is the default value.
This can not prevent drawing proxy graphic inside of blocks, because this is outside of the domain of the drawing add-on!
do not display proxy graphics (skip_entity will be called instead)
if the entity cannot be rendered directly (eg if not implemented) but a proxy is present: display the proxy
display proxy graphics even for entities where direct rendering is available
The rendering is performed in two stages. The front-end traverses the DXF document
structure, converting each encountered entity into primitive drawing commands.
These commands are fed to a back-end which implements the interface:
PyQtBackend (QGraphicsScene based) and a
MatplotlibBackend are implemented.
Although the resulting images will not be pixel-perfect with AutoCAD (which was taken as the ground truth when developing this add-on) great care has been taken to achieve similar behavior in some areas:
- The algorithm for determining color should match AutoCAD. However, the color
palette is not stored in the dxf file, so the chosen colors may be different
to what is expected. The
RenderContextclass supports passing a plot style table (CTB-file) as custom color palette but uses the same palette as AutoCAD by default.
- Text rendering is quite accurate, text positioning, alignment and word wrapping are very faithful. Differences may occur if a different font from what was used by the CAD application but even in that case, for supported backends, measurements are taken of the font being used to match text as closely as possible.
- Visibility determination (based on which layers are visible) should match AutoCAD
examples/addons/drawing/cad_viewer.py for an advanced use of the module.
examples/addons/drawing/draw_cad.py for a simple use of the module.
drawing.md in the ezdxf repository for additional behaviours documented
during the development of this add-on.
- Rich text formatting is ignored (drawn as plain text)
- If the backend does not match the font then the exact text placement and wrapping may appear slightly different
- MULTILEADER renders only proxy graphic if available
- relative size of POINT entities cannot be replicated exactly
- only basic support for:
- infinite lines (rendered as lines with a finite length)
- VIEWPORT and OLE2FRAME entities (rendered as rectangles)
- 3D entities are projected into the xy-plane and 3D text is not supported
- vertical text (will render as horizontal text)
- multiple columns of text (placement of additional columns may be incorrect)