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Another couple of Matlab bugs and workarounds

Every now and then I come across some internal Matlab bugs. In many cases I find a workaround and move on, sometimes bothering to report the bugs to MathWorks support, but often not. In truth, it’s a bit frustrating to hear the standard response that the issue [or "unexpected behavior", but never "bug" - apparently that's a taboo word] “has been reported to the development team and they will consider fixing it in one of the future releases of MATLAB”.

To date I’ve reported dozens of bugs and as far as I can tell, few if any of them have actually been fixed, years after I’ve reported them. None of them appear on Matlab’s official bug parade, which is only a small subset of the full list that MathWorks keeps hidden for some unknown reason (is it possible that someone’s ashamed of their bugs? nuh, couldn’t be…). Never mind, I don’t take it personally, I simply find a workaround and move on. I’ve already posted about this before. Today I’ll discuss two additional bugs I’ve run across once-too-often, and my workarounds:

Nothing really earth-shattering, but annoying nonetheless.
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Categories: Desktop, Figure window, Low risk of breaking in future versions, Stock Matlab function, Undocumented feature
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Plot markers transparency and color gradient

Last week I explained how to customize plot-lines with transparency and color gradient. Today I wish to show how we can achieve similar effects with plot markers. Note that this discussion (like the preceding several posts) deal exclusively with HG2, Matlab’s new graphics system starting with R2014b (well yes, we can also turn HG2 on in earlier releases).

As Paul has noted in a comment last week, we cannot simply set a 4th (alpha transparency) element to the MarkerFaceColor and MarkerEdgeColor properties:

>> x=1:10; y=10*x; hLine=plot(x,y,'o-');
>> hLine.MarkerFaceColor = [0.5,0.5,0.5];      % This is ok
>> hLine.MarkerFaceColor = [0.5,0.5,0.5,0.3];  % Not ok
While setting the 'MarkerFaceColor' property of Line:
Color value must be a 3 element numeric vector

Standard Matlab plot markers

Standard Matlab plot markers

Lost cause? – not in a long shot. We simply need to be a bit more persuasive, using the hidden MarkerHandle property:
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Categories: Handle graphics, Medium risk of breaking in future versions, Stock Matlab function, Undocumented feature
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Plot line transparency and color gradient

In the past few weeks, I discussed the new HG2 axes Backdrop and Baseline properties with their associated ability to specify the transparency level using a fourth (undocumented) element in their Color.

In other words, color in HG2 can still be specified as an RGB triplet (e.g., [1,0,0] to symbolize bright red), but also via a 4-element quadruplet RGBA, where the 4th element (Alpha) signifies the opacity level (0.0=fully transparent, 0.5=semi-transparent, 1.0=opaque). So, for example, [1, 0, 0, 0.3] means a 70%-transparent red.

This Alpha element is not documented anywhere as being acceptable, but appears to be supported almost universally in HG2 wherever a color element can be specified. In some rare cases (e.g., for patch objects) Matlab has separate Alpha properties that are fully documented, but in any case nowhere have I seen documented that we can directly set the alpha value in the color property, especially for objects (such as plot lines) that do not officially support transparency. If anyone finds a documented reference anywhere, please let me know – perhaps I simply missed it.

Here is a simple visualization:

xlim([1,5]);
hold('on');
h1a = plot(1:5,     11:15, '.-', 'LineWidth',10, 'DisplayName',' 0.5');
h1b = plot(1.5:5.5, 11:15, '.-', 'LineWidth',10, 'DisplayName',' 1.0', 'Color',h1a.Color);  % 100% opaque
h1a.Color(4) = 0.5;  % 50% transparent
h2a = plot(3:7,  15:-1:11, '.-r', 'LineWidth',8, 'DisplayName',' 0.3'); h2a.Color(4)=0.3;  % 70% transparent
h2b = plot(2:6,  15:-1:11, '.-r', 'LineWidth',8, 'DisplayName',' 0.7'); h2b.Color(4)=0.7;  % 30% transparent
h2c = plot(1:5,  15:-1:11, '.-r', 'LineWidth',8, 'DisplayName',' 1.0');  % 100% opaque = 0% transparent
legend('show','Location','west')

Transparent HG2 plot lines

Transparent HG2 plot lines

Now for the fun part: we can make color-transition (gradient) effects along the line, using its hidden Edge property:
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Categories: Handle graphics, Medium risk of breaking in future versions, Stock Matlab function, Undocumented feature
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Customizing axes part 4 – additional properties

In the past three weeks I explained how HG2 (in R2014b) enables us to customize the axes rulers, back-drop, baselines, box and grid-lines in ways that were previously impossible in HG1 (R2014a or earlier). Today I will conclude the mini-series on axes customizations by describing other useful undocumented customizations of the HG2 axes:

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Categories: Handle graphics, Medium risk of breaking in future versions, Stock Matlab function, Undocumented feature
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Customizing axes part 3 – Backdrop

In the past two weeks I explained how HG2 (in R2014b) enables us to customize the axes rulers, baselines, box and grid-lines in ways that were previously impossible in HG1 (R2014a or earlier). Today I will describe another useful undocumented property of the HG2 axes – Backdrop.

HG2 axes Backdrop with custom tint

HG2 axes Backdrop with custom tint


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Categories: Handle graphics, Medium risk of breaking in future versions, Stock Matlab function, Undocumented feature
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Customizing axes part 2

Last week I explained how HG2 (in R2014b) enables us to customize the axes rulers in ways that were previously impossible in HG1 (R2014a or earlier). Today I will describe other useful undocumented customizations of the HG2 axes:

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Categories: Handle graphics, Low risk of breaking in future versions, Stock Matlab function, Undocumented feature
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Customizing axes rulers

Over 4 years have passed since I’ve posted my scoop on Matlab’s upcoming new graphics system (a.k.a. HG2, Handle Graphics version 2). At that time HG2 was still far from usable, but that has changed when I posted my HG2 update last year. Numerous user feedbacks, by email and blog comments, were reported and the MathWorks developers have listened and improved the code. HG2 was finally released with Matlab R2014b last Friday, and it seems at first glance to be a beauty. I hope my posts and the feedbacks have contributed, but in any case the MathWorks dev group deserves big kudos for releasing a totally new system that provides important usability and aesthetic improvements [almost] without sacrificing performance or backward-compatibility. Trust me, it’s not an easy achievement.

Customized HG2 plot

Customized HG2 plot


One of the nice things that I like about HG2 is that it provides numerous new ways to customize the objects in ways that were impossible (or nearly so) in the old HG1. In R2014b, the leap was large enough that MathWorks wisely chose to limit the official new properties to a bare minimum, for maximal HG1 compatibility. I assume that this will remain also in R2015a, which I expect to be a release devoted to bug fixing and stabilization rather than to new features. I expect the new features to start becoming official in R2015b onward. Such a measured roadmap is to be expected from a responsible engineering company such as MathWorks. So in fact there is no need at all to be disappointed at the relative lack of new functional features. They are all there already, just not yet official, and this is just as it should be.

That being said, if we are aware of the risk that these features might change in the upcoming years until they become official (if ever), then we can start using them today. Experience with this blog has shown that the vast majority of such undocumented features remain working unchanged for years, and some of them eventually become documented. For example, uitab/uitabgroup, on which I posted over 4 years ago, and which has existed almost unchanged since 2005, finally became official in R2014b after many years of running in unofficial form.

In the next few weeks I intend to present a series of posts that highlight some of the undocumented customizations in HG2. I’ll start with some new axes features, followed by plotting aspects.
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Categories: Handle graphics, Low risk of breaking in future versions, Stock Matlab function, Undocumented feature
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Customizing combobox popups

Last week I explained how we can use display custom items in a standard Matlab combobox (popup/dropdown), using its underlying Java component. Today I will show how we can use this Java component for other nice customizations of the combobox’s popup:

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Categories: GUI, Java, Medium risk of breaking in future versions, UI controls, Undocumented feature
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Customizing listbox/combobox items

Last week I wrote about using a variety of techniques to customize listbox items with an attached checkbox icon. Some of these methods used a standard Matlab listbox uicontrol, others used other controls. Today I wish to extend the discussion and show how Matlab listbox and combobox (pop-up) items can be customized in a variety of ways.

To add icons to listbox/combobox items, we could use standard HTML, as I’ve shown last week. This is the simplest method, requires no Java knowledge, and it usually works well. The problem is that when a listbox/combobox has numerous items (hundreds or more), it may start getting sluggish. In such case it is faster to use a dedicated Java cell-renderer that sets the icon, font, colors, tooltip and other aspects on an item-by-item basis. This runs faster and enables far greater customizability than what is possible with HTML. The drawback is that it requires some Java programming. No free lunch…

Listbox and combobox cell-renderers need to extend javax.swing.ListCellRenderer, similarly to uitable cell-renderers. This is basically a simple Java class that minimally contains just an empty constructor and a getListCellRendererComponent() method with a predefined signature. getListCellRendererComponent() is automatically called by the Swing render engine separately for each listbox item, and gets as input args a JList reference, the item value (typically a string), an integer list index, a boolean flag indicating whether the item is currently selected, and another flag indicating whether the item is currently in focus. getListCellRendererComponent() uses these parameters to customize and return a java.awt.Component, which is typically (but not necessarily) a standard Swing JLabel.

Here is a simple example that displays a folder of icon files in a Matlab listbox and combobox. Each item is the filename, with a customization that if the file is an icon, then this icon is displayed next to the file name, otherwise the name appears in red italic without an icon. For illustration, we’ll use Matlab’s builtin icons folder: %matlabroot%/toolbox/matlab/icons/:

Custom listbox cell-renderer    Custom combobox cell-renderer

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Categories: GUI, Java, Medium risk of breaking in future versions, UI controls
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CheckboxList

Several years ago I blogged about using a checkbox-tree in Matlab. A few days ago there was a question on the Matlab Answers forum asking whether something similar can be done with Matlab listboxes, i.e. add checkboxes next to each list item. There are actually several alternatives for this and I thought this could be a good opportunity to discuss them:

MathWorks CheckBoxList

MathWorks CheckBoxList


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Categories: GUI, Java, Medium risk of breaking in future versions, UI controls, Undocumented feature
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8 Comments