Add sample for type Form

build.gradle

@@ -39,6 +39,18 @@ konanArtifacts {
             linkerOpts "build/samples.res"
         }
     }
+
+    program('sampleForm') {
+        srcFiles 'samples/form/main.kt'
+        srcFiles fileTree('src/main/kotlin')
+        libraries {
+            artifact 'libui'
+        }
+        target 'mingw', {
+            dependsOn 'windres'
+            linkerOpts "build/samples.res"
+        }
+    }
 }
 
 task windres(type: Exec) {

samples/form/README.md

@@ -0,0 +1,7 @@
+# Form
+
+The sample shows a window with a basic login form. It has a field for username with plain text and another field for  password with masked text that hides its content. Also there is a button with `Login` text.
+
+| Platform | Preview |
+| :--: | :--: |
+| Linux | ![Screenshot on Ubuntu](form-ubuntu.png)

samples/form/main.kt

@@ -0,0 +1,38 @@
+import kotlinx.cinterop.*
+import libui.*
+
+fun main(args: Array<String>) = memScoped {
+    val options = alloc<uiInitOptions>()
+    val error = uiInit(options.ptr)
+    if (error != null) throw Error("Error: '${error.toKString()}'")
+
+    val window = Window(
+        title = "Authentication required",
+        width = 320,
+        height = 200,
+        hasMenubar = false)
+    window.margined = true
+
+    val box = VerticalBox().apply { padded = true }
+
+    val (username, password) = Entry() to PasswordEntry()
+
+    val button = Button(text = "Login")
+    uiButtonOnClicked(
+         button,
+         staticCFunction { _, _ -> /* TODO: Get text from username and password */ },
+         button)
+
+    val form = Form().apply { padded = true }
+    uiFormAppend(form, "Username", username.reinterpret(), 0)
+    uiFormAppend(form, "Password", password.reinterpret(), 0)
+
+    uiBoxAppend(box, form.reinterpret(), 0)
+    uiBoxAppend(box, button.reinterpret(), 0)
+
+    uiWindowSetChild(window, box.reinterpret())
+    uiWindowOnClosing(window, staticCFunction { _, _ -> uiQuit(); 1 }, null)
+    uiControlShow(window.reinterpret())
+    uiMain()
+    uiUninit()
+}