Add “custom-widgets” example

This small example demonstrates defining and
binding to your own subclass of a QT widget.

examples/custom-widgets/README.md

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+# “Goodbye” example
+
+This is a bare-minimum example egg that shows how one can define their own
+custom QT widgets and bind to their methods in a way compatible with qt-light.
+
+It defines an `OurButton` C++ class that is derived from 
+[`QPushButton`](https://doc.qt.io/qt-6/qpushbutton.html) with one change:  
+It adds a `SayGoodbye()` method that changes the button’s label to “Goodbye”.
+
+We write a wrapper C-function `gb_saygoodbye()` and bind this function into
+our `goodbye-widgets` module under the name `gb:saygoodbye`. It is run on the
+button (originally labelled “Quit” in the `goodbye.ui` file), so changing its
+text to “Goodbye”.

examples/custom-widgets/goodbye-widgets.h

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+#include <QPushButton>
+
+class OurButton : public QPushButton {
+public:
+	OurButton(QWidget* parent);
+
+	void SayGoodbye();
+};

examples/custom-widgets/goodbye-widgets.scm

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+;;;; qt-light.scm
+
+
+(module goodbye-widgets (gb:saygoodbye)
+
+(import
+  scheme
+  (chicken base)
+  (chicken bitwise)
+  (chicken foreign)
+  (chicken format)
+  (chicken fixnum)
+  (chicken string)
+  bind
+  miscmacros
+  qt-light
+  srfi-4 srfi-1 protobj matchable
+  )
+
+
+(define <gb-button> (% <qt-widget> (class 'gb-button)))
+
+(define (qt:->pointer i) (and i (? i pointer)))
+(define (qt:pointer->button p) (and p (% <gb-button> (pointer p))))
+
+(bind-rename/pattern "gb_" "gb:")
+(bind-type gbbutton c-pointer gb:->pointer gb:pointer->button)
+
+#>
+#define ___safe
+#define ___bool         int
+#define ___out
+<#
+
+#>
+extern "C" {
+	    #include "prototypes.h"
+	    }
+<#
+
+(bind-file*  "prototypes.h")
+
+)

examples/custom-widgets/goodbye.egg

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+((synopsis "An example program that uses a subclassed QT widget.")
+ (category ui)
+ (license "BSD")
+ (dependencies bind protobj qt-light matchable miscmacros shell)
+ (author "Jaidyn Ann")
+ (components
+   (extension
+     goodbye-widgets
+       (custom-build "../../chicken-compile-qt-extension.scm")
+       (csc-options                     ;
+       "-O3" "-d1" "-X" "bind" "-s" "-k" "-emit-link-file" "goodbye-widgets.link" "-o" "goodbye-widgets.o")
+       )
+   (program goodbye)))

examples/custom-widgets/goodbye.scm

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+(import qt-light goodbye-widgets protobj
+        (chicken io))
+
+(define a (qt:init))
+(define w (qt:widget (call-with-input-file "goodbye.ui" (lambda (p) (read-string #f p)))))
+(print (? w pointer))
+(define b (qt:find w "goodbyeButton"))
+(print b)
+(qt:connect b "clicked()" a "quit()")
+(qt:show w)
+(gb:saygoodbye b)
+(qt:run)

examples/custom-widgets/goodbye.ui

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+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>Form</class>
+ <widget class="QWidget" name="Form">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>295</width>
+    <height>144</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string/>
+  </property>
+  <widget class="QLabel" name="label">
+   <property name="geometry">
+    <rect>
+     <x>40</x>
+     <y>30</y>
+     <width>201</width>
+     <height>31</height>
+    </rect>
+   </property>
+   <property name="font">
+    <font>
+     <pointsize>15</pointsize>
+     <bold>true</bold>
+    </font>
+   </property>
+   <property name="text">
+    <string>Adieu, monsieur!</string>
+   </property>
+   <property name="alignment">
+    <set>Qt::AlignCenter</set>
+   </property>
+  </widget>
+  <widget class="OurButton" name="goodbyeButton">
+   <property name="geometry">
+    <rect>
+     <x>180</x>
+     <y>90</y>
+     <width>75</width>
+     <height>31</height>
+    </rect>
+   </property>
+   <property name="text">
+    <string>Quit</string>
+   </property>
+  </widget>
+ </widget>
+ <customwidgets>
+  <customwidget>
+   <class>OurButton</class>
+   <extends>QPushButton</extends>
+   <header>custom_widget.h</header>
+  </customwidget>
+ </customwidgets>
+ <resources/>
+ <connections/>
+</ui>

examples/custom-widgets/main.cpp

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+#include "goodbye-widgets.h"
+
+#define gbbutton          OurButton *
+
+OurButton::OurButton(QWidget* parent)
+	: QPushButton(parent)
+{
+}
+
+
+void
+OurButton::SayGoodbye()
+{
+	setText("Goodbye");
+}
+
+
+#define cwbutton          OurButton *
+
+extern "C" {
+#include "prototypes.h"
+}
+
+
+void
+gb_saygoodbye(cwbutton button)
+{
+	button->SayGoodbye();
+}

examples/custom-widgets/prototypes.h

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+/* prototypes.h */
+
+
+void gb_saygoodbye(gbbutton button);