gui: implement container

Containers, somewhat inspired by GtkBox, allow to packed other GUI
elements into a single row or column.

src/gui/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_library(gui
     "src/bar.c"
     "src/button.c"
+    "src/container.c"
     "src/gui.c"
     "src/label.c"
     "src/progress_bar.c"

src/gui/inc/gui/container.h

@@ -0,0 +1,34 @@
+#ifndef GUI_CONTAINER_H
+#define GUI_CONTAINER_H
+
+#include <gui.h>
+#include <util.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+struct gui_container
+{
+    struct gui_common common;
+    short w, h;
+
+    enum
+    {
+        GUI_CONTAINER_MODE_H,
+        GUI_CONTAINER_MODE_V
+    } mode;
+};
+
+UTIL_STATIC_ASSERT(!offsetof(struct gui_container, common),
+    "unexpected offset for struct gui_container");
+
+void gui_container_init(struct gui_container *c);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* GUI_CONTAINER_H */

src/gui/src/container.c

@@ -0,0 +1,56 @@
+#include <gui/container.h>
+#include <gui.h>
+
+static void add_child(struct gui_common *const parent,
+    struct gui_common *const child)
+{
+    if (!child->get_dim)
+        return;
+
+    struct gui_container *const c = (struct gui_container *)parent;
+    short w, h;
+
+    child->get_dim(child, &w, &h);
+
+    switch (c->mode)
+    {
+        case GUI_CONTAINER_MODE_H:
+            child->x += c->w;
+            c->w += w;
+
+            if (h > c->h)
+                c->h = h;
+
+            break;
+
+        case GUI_CONTAINER_MODE_V:
+            child->y += c->h;
+            c->h += h;
+
+            if (w > c->w)
+                c->w = w;
+
+            break;
+    }
+}
+
+static void get_dim(const struct gui_common *const g,
+    short *const w, short *const h)
+{
+    struct gui_container *const c = (struct gui_container *)g;
+
+    *w = c->w;
+    *h = c->h;
+}
+
+void gui_container_init(struct gui_container *const c)
+{
+    *c = (const struct gui_container)
+    {
+        .common =
+        {
+            .add_child = add_child,
+            .get_dim = get_dim
+        }
+    };
+}