Create images of different entities/layers

[f0rme]

Is it possible to output images of specific entities/entities with a given layer assigned to them without saving the DXF file each time?

My current approach is:

1. Assign a layer to a 'group' of entities.
2. Turn all other layers off.
3. Save the drawing .
4. Create an image of the drawing with the drawing addon.

Is it possible to not use step no. 3? Perhaps by using some entity data as an input rather than a drawing?

[mozman]

I am not sure I understand the question, because the simple way is:

1. Load DXF document or create a new one.
2. Assign a layer to a 'group' of entities.
3. Turn all other layers off.
4. Save the drawing.
5. Create an image of the drawing with the drawing addon.

[f0rme]

Thank you for your response. Chances are my question is terrible.
The issue I have when attempting your suggestion is that no changes are reflected unless the dxf file is saved before the creation of the image.
In other words the image created looks the same.

[mozman]

Please post a small example script and describe what you want to achieve.

[f0rme]

Here is a DXF with 4 polylines. I'd like to create an SVG image of each polyline.
My current approach is described above. What is your recommended solution?

Four Images:

[f0rme]

Some of the code below is just for me to see which layers are available.
Also, to determine how many images should be produced.

from readDXF import readDxfEasy
from makeImage import createSvg

filename = "dxfEg.dxf"

layer_no = 1
dwg, msp = readDxfEasy(filename)
 
for e in msp:
  if e.dxftype() == "LWPOLYLINE":
    e.dxf.layer = f"part_{layer_no}"
    layer_no += 1

for layer in dwg.layers:
  print(layer.dxf.name)
  #print(e.dxf.layer)

for num in range(1, layer_no):
  if layer.dxf.name != f'layer_{num}':
    layer.off()

    # I think my issue is here. Specifically using 'filename' as an input.
    createSvg(filename, num)

[mozman]

You have to create layer table entries, to switch layers on and off. Despite the fact that the DXF format does not require a layer table entry to be valid, you should always create layer table entries for all layers you plan to use.

Example shapes.dxf: each shape including the text has a different layer

shapes.zip

The following script...

import ezdxf
from ezdxf.addons.drawing.matplotlib import qsave

doc = ezdxf.readfile("shapes.dxf")
msp = doc.modelspace()

layer_names = ["Shape 1", "Shape 2", "Shape 3"]

for current_layer_name in layer_names:
    for name in layer_names:
        layer = doc.layers.get(name)
        if layer.dxf.name == current_layer_name:
            layer.on()
        else:
            layer.off()
    qsave(msp, f"{current_layer_name}.png")

creates these three images:

Another option to use a filter function, which also works with the Frontend.draw_layout() function.
The filter function returns True for all entities which should be rendered otherwise False to ignore the entity:

for current_layer_name in layer_names:
    qsave(
        msp,
        f"{current_layer_name}.png",
        filter_func=lambda e: e.dxf.layer == current_layer_name,
    )