Allow setting alpha (transparency/opacity) for contour_plot

[jasongrout]

The object of this ticket is to allow an optional argument "alpha" to set the transparency / opacity for contour_plot, like it exists for other types of plots.

An initial patch enables an 'opacity' argument to the contour_plot function. It should be renamed 'alpha' for consistency with its name elsewhere.

Doctests need to be added, and a few examples need to be written.

Related tickets and discussions:

• #23104: implement alpha for streamline plots
• #21984: Deprecate the opacity argument for plot3d and use alpha
• Ask Sage question 41457: Fill colors with two contour plots

CC: @slel

Component: graphics

Keywords: alpha, transparency, opacity, plot, contour_plot

Author: Jason Grout

Issue created by migration from https://trac.sagemath.org/ticket/9491

[jasongrout]

Attachment: trac-9491-contour-alpha.patch.gz

[jasongrout]

comment:1

This patch was done in a rush, so there may be bugs in it.

[jasongrout]

comment:2

Comments from David Sanders on sage-support:

Firstly, with this code it seems not to be possible to make a region_plot without specifying opacity -- it looks like a default argument is missing somewhere.

[jasongrout]

comment:3

Replying to @jasongrout:

Comments from David Sanders on sage-support:

Firstly, with this code it seems not to be possible to make a region_plot without specifying opacity -- it looks like a default argument is missing somewhere.

I think that is correct.

[slel]

Description changed:

--- 
+++ 
@@ -1,3 +1,13 @@
-This patch enables an 'opacity' argument to the contour plot function.
+The object of this ticket is to allow an optional argument "alpha"
+to set the transparency / opacity for contour_plot, like it exists for
+other types of plots.

-Doctesting needs to be done, and a few examples need to be written.
+An initial patch enables an 'opacity' argument to the contour_plot function.
+It should be renamed 'alpha' for consistency with its name elsewhere.
+
+Doctests need to be added, and a few examples need to be written.
+
+Related tickets:
+
+- [#23104: implement alpha for streamline plots](https://github.com/sagemath/sage-prod/issues/23104)
+- [#21984: Deprecate the opacity argument for plot3d and use alpha](https://github.com/sagemath/sage-prod/issues/21984)

[slel]

Changed keywords from none to alpha, transparency, opacity, plot, contour_plot

[slel]

Description changed:

--- 
+++ 
@@ -7,7 +7,8 @@

 Doctests need to be added, and a few examples need to be written.

-Related tickets:
+Related tickets and discussions:

 - [#23104: implement alpha for streamline plots](https://github.com/sagemath/sage-prod/issues/23104)
 - [#21984: Deprecate the opacity argument for plot3d and use alpha](https://github.com/sagemath/sage-prod/issues/21984)
+- [Ask Sage question 41457: Fill colors with two contour plots](https://ask.sagemath.org/question/41457/fill-colors-with-two-contour-plots/)