Export circuit png with dpi (#139)

New method QubitCircuit.draw() to export svg and png images. Density in dpi can be an argument from the user for conversion to png (defaults to 100dpi).

src/qutip_qip/circuit.py

@@ -6,6 +6,8 @@
 import numbers
 import warnings
 import inspect
+import os
+from functools import partialmethod
 
 import numpy as np
 from copy import deepcopy
@@ -2053,31 +2055,67 @@ def latex_code(self):
     # conversion is available, so the user doesn't get exceptions on display
     # because IPython tried to do something behind their back.
 
-    def _raw_png(self):
-        return _latex.image_from_latex(self.latex_code(), "png")
+    def _raw_img(self, file_type="png", dpi=100):
+        return _latex.image_from_latex(self.latex_code(), file_type, dpi)
 
     if "png" in _latex.CONVERTERS:
-        _repr_png_ = _raw_png
+        _repr_png_ = _raw_img
+
+    if "svg" in _latex.CONVERTERS:
+        _repr_svg_ = partialmethod(_raw_img, file_type="svg", dpi=None)
 
     @property
     def png(self):
         """
         Return the png file
         """
-        return DisplayImage(self._raw_png(), embed=True)
-
-    def _raw_svg(self):
-        return _latex.image_from_latex(self.latex_code(), "svg")
-
-    if "svg" in _latex.CONVERTERS:
-        _repr_svg_ = _raw_svg
+        return DisplayImage(self._repr_png_(), embed=True)
 
     @property
     def svg(self):
         """
         Return the svg file
         """
-        return DisplaySVG(self._raw_svg())
+        return DisplaySVG(self._repr_svg_())
+
+    def draw(
+        self,
+        file_type="png",
+        dpi=None,
+        file_name="exported_pic",
+        file_path="",
+    ):
+        """
+        Export circuit object as an image file in a supported format.
+
+        Parameters
+        ----------
+        file_type : Provide a supported image file_type eg: "svg"/"png".
+                   Default : "png".
+
+        dpi : Image density in Dots per inch(dpi)
+            Applicable for PNG, NA for SVG.
+            Default : None, though it's set to 100 internally for PNG
+
+        file_name : Filename of the exported image.
+                    Default : "exported_pic"
+
+        file_path : Path to which the file has to be exported.
+                    Default : ""
+                    Note : User should have write access to the location.
+        """
+
+        if file_type == "svg":
+            mode = "w"
+        else:
+            mode = "wb"
+            if file_type == "png" and not dpi:
+                dpi = 100
+        image_data = self._raw_img(file_type, dpi)
+        with open(
+            os.path.join(file_path, file_name + "." + file_type), mode
+        ) as f:
+            f.write(image_data)
 
     def _to_qasm(self, qasm_out):
         """

src/qutip_qip/circuit_latex.py

@@ -139,7 +139,7 @@ def _make_converter(configuration):
         return None
     mode = "rb" if configuration.binary else "r"
 
-    def converter(file_stem):
+    def converter(file_stem, dpi=100):
         """
         Convert a file located in the current directory named `<file_stem>.pdf`
         to an image format with the name `<file_stem>.xxx`, where `xxx` is
@@ -149,10 +149,17 @@ def converter(file_stem):
         ----------
         file_stem : str
             The basename of the PDF file to be converted.
+        dpi : int/float
+            Image density in dots per inch. Ignored for SVG.
         """
         in_file = file_stem + ".pdf"
         out_file = file_stem + "." + configuration.file_type
-        _run_command((which, *configuration.arguments, in_file, out_file))
+        if "-density" in configuration.arguments:
+            arguments = list(configuration.arguments)
+            arguments[arguments.index("-density") + 1] = str(dpi)
+        else:
+            arguments = configuration.arguments
+        _run_command((which, *arguments, in_file, out_file))
         with open(out_file, mode) as file:
             return file.read()
 
@@ -172,7 +179,7 @@ def converter(file_stem):
 
 if _pdflatex is not None:
 
-    def image_from_latex(code, file_type="png"):
+    def image_from_latex(code, file_type="png", dpi=100):
         """
         Convert the LaTeX `code` into an image format, defined by the
         `file_type`.  Returns a string or bytes object, depending on whether
@@ -240,7 +247,7 @@ def image_from_latex(code, file_type="png"):
                     raise ValueError(
                         "".join(["Unknown output format: '", file_type, "'."])
                     )
-                out = CONVERTERS[file_type](filename)
+                out = CONVERTERS[file_type](filename, dpi)
             finally:
                 # Leave the temporary directory before it is removed (necessary
                 # on Windows, but it doesn't hurt on POSIX).

tests/test_circuit.py

@@ -1,4 +1,6 @@
 import pytest
+import os
+import shutil
 import numpy as np
 from pathlib import Path
 
@@ -702,3 +704,32 @@ def test_latex_code_non_reversed(self):
         exp = ' &  &  \\meter & \\qw \\\\ \n &  ' + \
               '&  \\qw \\cwx[-1]  & \\qw \\\\ \n'
         assert qc.latex_code() == self._latex_template % exp
+
+    @pytest.mark.skipif(
+                shutil.which("pdflatex") is None,
+                reason="requires pdflatex"
+                )
+    def test_export_image(self):
+
+        def cleanup(*img_files):
+            for img_file in img_files:
+                if img_file in os.listdir('.'):
+                    os.remove(img_file)
+
+        file_png_200 = "exported_pic_200.png"
+        file_png_400 = "exported_pic_400.png"
+        file_svg = "exported_pic.svg"
+        cleanup(file_png_200, file_png_400, file_svg)
+
+        qc = QubitCircuit(2, reverse_states=False)
+        qc.add_gate("CSIGN", controls=[0], targets=[1])
+        qc.draw("png", 200, file_png_200.split('.')[0], "")
+        qc.draw("png", 400.5, file_png_400.split('.')[0], "")
+        qc.draw("svg", 450, file_svg.split('.')[0], "")
+
+        assert file_png_200 in os.listdir('.')
+        assert file_png_400 in os.listdir('.')
+        assert os.stat(file_png_200).st_size < os.stat(file_png_400).st_size
+        assert file_svg in os.listdir('.')
+
+        cleanup(file_png_200, file_png_400, file_svg)