handbindings: explore how to bind connect() calls

.gitignore

@@ -3,9 +3,9 @@
 gen_*
 
 # binaries
-miqt
+cmd/handbindings/handbindings
-cmd/bindings_test/direct
+cmd/handbindings/bindings_test/direct
-cmd/bindings_test/testapp
+cmd/handbindings/bindings_test/testapp
 cmd/genbindings/genbindings
 
 

cmd/handbindings/binding.cpp

@@ -3,6 +3,10 @@
 #include <QWidget>
 #include <QPushButton>
 
+extern "C" {
+    extern void miqt_exec_callback(void* cb, int argc, void* argv);
+}
+
 PQApplication QApplication_new(int* argc, char** argv) {
     // QApplication takes these parameters byref, not by value
     return new QApplication(*argc, argv);
@@ -24,6 +28,12 @@ void QPushButton_show(PQPushButton self) {
     static_cast<QPushButton*>(self)->show();
 }
 
+void QPushButton_connect_pressed(PQPushButton self, void* cb) {
+    QPushButton::connect(static_cast<QPushButton*>(self), &QPushButton::pressed, [=]() {
+        miqt_exec_callback(cb, 0, nullptr);
+    });
+}
+
 int QApplication_exec(PQApplication self) {
     return static_cast<QApplication*>(self)->exec();
 }

cmd/handbindings/binding.go

@@ -10,6 +10,7 @@ package main
 import "C"
 
 import (
+	"runtime/cgo"
 	"unsafe"
 )
 
@@ -24,6 +25,21 @@ func CArray(data []string) (C.int, **C.char) {
 	return C.int(len(data)), (**C.char)(unsafe.Pointer(c_argv))
 }
 
+type CallbackFunc func(argc C.int, args *C.void)
+
+//export miqt_exec_callback
+func miqt_exec_callback(cb *C.void, argc C.int, args *C.void) {
+	// Our CABI for all callbacks is void(int, void*).
+	// Our Go ABI is CallbackFunc
+	// Then the Go bindings can unmarshal the arguments and C.free() them as necessary
+	cfunc, ok := (cgo.Handle(uintptr(unsafe.Pointer(cb))).Value()).(CallbackFunc)
+	if !ok {
+		panic("miqt: callback of non-callback type (heap corruption?)")
+	}
+
+	cfunc(argc, args)
+}
+
 //
 
 type QApplication struct {
@@ -81,3 +97,14 @@ func (this *QPushButton) Show() {
 func (this *QPushButton) AsQWidget() *QWidget {
 	return &QWidget{h: C.PQWidget(this.h)} // Type cast
 }
+
+func (this *QPushButton) OnPressed(cb func()) {
+	var cbWrapper CallbackFunc = func(argc C.int, args *C.void) {
+		// Unmarshal arguments
+		// Pressed() doesn't take any, though
+		cb()
+	}
+
+	C.QPushButton_connect_pressed(this.h, unsafe.Pointer(uintptr(cgo.NewHandle(cbWrapper))))
+	// TODO allow disconnect'ing, or tie lifespan for handle.Delete(), ...
+}

cmd/handbindings/binding.h

@@ -5,6 +5,8 @@
 extern "C" {
 #endif
 
+#include <stdint.h>
+
 typedef void* PQApplication;
 
 typedef void* PQPushButton;
@@ -21,6 +23,8 @@ PQPushButton QPushButton_new(const char* label, PQWidget parent);
 
 void QPushButton_show(PQPushButton self);
 
+void QPushButton_connect_pressed(PQPushButton self, void* cb);
+
 int QApplication_exec(PQApplication self);
 
 #ifdef __cplusplus

cmd/handbindings/main.go

@@ -23,6 +23,10 @@ func main() {
 	btn := NewQPushButton("Hello world!", wid)
 	_ = btn
 
+	btn.OnPressed(func() {
+		fmt.Println("Clicked!")
+	})
+
 	wid.Show()
 
 	app.Exec()