all: Replace tagged unions with a more traditional object model

This rewrites the bulk of Waffle's code.

When I first began writing Waffle, I wanted to experiment with
a non-traditional object model that used tagged unions. Very soon I began
to abhor the "innovative" decision. This patch replaces the tagged-union
model with a more traditional object model (as found in the Linux kernel
[1], Google's NaCl, libdrm, and many other places) that uses vtables and
embedded structures.

[1] Neil Brown. LWN, 2011 June 1. Object-oriented design patterns in the kernel.
    (Part 1: http://lwn.net/Articles/444910/).
    (Part 2: http://lwn.net/Articles/446317/).

As an example of the new object model, below is an outline of how
waffle_window_swap_buffers() is now implemeneted.

// file: waffle_window.c

bool
waffle_window_swap_buffers(struct waffle_window *self)
{
    struct wcore_window *wc_self = wcore_window(self); // safe cast
    // Check preconditions ...
    return wc_self->vtbl->swap_buffers(wc_self);
}

// file: wcore_window.h

struct wcore_window_vtbl {
    bool
    (*swap_buffers)(struct wcore_window *self);
    // More member functions ...
};

struct wcore_window {
    const struct wcore_window_vtbl *vtbl;
    struct waffle_window {} wfl;
    // More members ...
};

// file: glx_window.h

struct glx_window {
    struct wcore_window wcore;
    // More members ...
};

// file: glx_window.c

static bool
glx_window_swap_buffers(struct wcore_window *wc_self)
{
    struct glx_window *self = glx_window(wc_self); // safe cast
    // Call glXSwapBuffers ...
    return true;
}

static const struct wcore_window_vtbl glx_window_wcore_vtbl = {
    .swap_buffers = glx_window_swap_buffers,
    // More members ...
};

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>

8 files changed, 479 insertions, 169 deletions

diff --git a/src/waffle/core/wcore_config.h b/src/waffle/core/wcore_config.h
new file mode 100644
index 0000000..abccdf8
--- /dev/null
+++ b/src/waffle/core/wcore_config.h
@@ -0,0 +1,76 @@
+// Copyright 2012 Intel Corporation
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice, this
+//   list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include <waffle/api/api_object.h>
+
+#include "wcore_display.h"
+#include "wcore_util.h"
+
+struct wcore_config;
+
+struct wcore_config_vtbl {
+    bool
+    (*destroy)(struct wcore_config *self);
+};
+
+struct wcore_config {
+    const struct wcore_config_vtbl *vtbl;
+
+    struct waffle_config {} wfl;
+    struct api_object api;
+
+    struct wcore_display *display;
+};
+
+DEFINE_CONTAINER_CAST_FUNC(wcore_config,
+                           struct wcore_config,
+                           struct waffle_config,
+                           wfl)
+
+static inline bool
+wcore_config_init(struct wcore_config *self,
+                  struct wcore_display *display)
+{
+    assert(self);
+    assert(display);
+
+    self->api.display_id = display->api.display_id;
+    self->display = display;
+
+    return true;
+}
+
+static inline bool
+wcore_config_teardown(struct wcore_config *self)
+{
+    assert(self);
+    return true;
+}
diff --git a/src/waffle/core/wcore_context.h b/src/waffle/core/wcore_context.h
new file mode 100644
index 0000000..7d1163d
--- /dev/null
+++ b/src/waffle/core/wcore_context.h
@@ -0,0 +1,77 @@
+// Copyright 2012 Intel Corporation
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice, this
+//   list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include <waffle/api/api_object.h>
+
+#include "wcore_config.h"
+#include "wcore_util.h"
+
+struct wcore_context;
+struct wcore_display;
+
+struct wcore_context_vtbl {
+    bool
+    (*destroy)(struct wcore_context *self);
+};
+
+struct wcore_context {
+    const struct wcore_context_vtbl *vtbl;
+
+    struct waffle_context {} wfl;
+    struct api_object api;
+
+    struct wcore_display *display;
+};
+
+DEFINE_CONTAINER_CAST_FUNC(wcore_context,
+                           struct wcore_context,
+                           struct waffle_context,
+                           wfl)
+
+static inline bool
+wcore_context_init(struct wcore_context *self,
+                   struct wcore_config *config)
+{
+    assert(self);
+    assert(config);
+
+    self->api.display_id = config->display->api.display_id;
+    self->display = config->display;
+
+    return true;
+}
+
+static inline bool
+wcore_context_teardown(struct wcore_context *self)
+{
+    assert(self);
+    return true;
+}
diff --git a/src/waffle/core/wcore_display.c b/src/waffle/core/wcore_display.c
new file mode 100644
index 0000000..0e42c96
--- /dev/null
+++ b/src/waffle/core/wcore_display.c
@@ -0,0 +1,57 @@
+// Copyright 2012 Intel Corporation
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice, this
+//   list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "wcore_display.h"
+
+#include <assert.h>
+#include <stdio.h>
+
+bool
+wcore_display_init(struct wcore_display *self,
+                   struct wcore_platform *platform)
+{
+    static size_t id_counter = 0;
+
+    assert(self);
+    assert(platform);
+
+    // FIXME: Not thread safe.
+    self->api.display_id = ++id_counter;
+    self->platform = platform;
+
+    if (self->api.display_id == 0) {
+        fprintf(stderr, "waffle: error: internal counter wrapped to 0\n");
+        abort();
+    }
+
+    return true;
+}
+
+bool
+wcore_display_teardown(struct wcore_display *self)
+{
+    assert(self);
+    return true;
+}
diff --git a/src/waffle/core/wcore_display.h b/src/waffle/core/wcore_display.h
new file mode 100644
index 0000000..d01a81a
--- /dev/null
+++ b/src/waffle/core/wcore_display.h
@@ -0,0 +1,69 @@
+// Copyright 2012 Intel Corporation
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice, this
+//   list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include <waffle/api/api_object.h>
+
+#include "wcore_util.h"
+
+struct wcore_display;
+struct wcore_platform;
+
+struct wcore_display_vtbl {
+    bool
+    (*destroy)(struct wcore_display *self);
+
+    bool
+    (*supports_context_api)(
+            struct wcore_display *self,
+            int32_t context_api);
+};
+
+struct wcore_display {
+    const struct wcore_display_vtbl *vtbl;
+
+    struct waffle_display {} wfl;
+    struct api_object api;
+
+    struct wcore_platform *platform;
+};
+
+DEFINE_CONTAINER_CAST_FUNC(wcore_display,
+                           struct wcore_display,
+                           struct waffle_display,
+                           wfl)
+
+bool
+wcore_display_init(struct wcore_display *self,
+                   struct wcore_platform *platform);
+
+
+bool
+wcore_display_teardown(struct wcore_display *self);
diff --git a/src/waffle/core/wcore_platform.c b/src/waffle/core/wcore_platform.c
deleted file mode 100644
index 22cd914..0000000
--- a/src/waffle/core/wcore_platform.c
+++ /dev/null
@@ -1,147 +0,0 @@
-// Copyright 2012 Intel Corporation
-//
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are met:
-//
-// - Redistributions of source code must retain the above copyright notice, this
-//   list of conditions and the following disclaimer.
-//
-// - Redistributions in binary form must reproduce the above copyright notice,
-//   this list of conditions and the following disclaimer in the documentation
-//   and/or other materials provided with the distribution.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
-// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
-// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
-// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-/// @addtogroup wcore_platform
-/// @{
-
-/// @file
-
-#include "wcore_platform.h"
-
-#include <stdbool.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-
-#include <waffle/waffle_enum.h>
-#include <waffle/cgl/cgl_platform.h>
-#include <waffle/glx/glx_platform.h>
-#include <waffle/wayland/wayland_platform.h>
-#include <waffle/x11_egl/xegl_platform.h>
-
-#include "wcore_error.h"
-
-static uint64_t id_counter = 0;
-
-struct wcore_platform*
-wcore_platform_create(int platform)
-{
-    struct wcore_platform *self;
-
-    self = calloc(1, sizeof(*self));
-    if (!self) {
-        wcore_error(WAFFLE_OUT_OF_MEMORY);
-        return NULL;
-    }
-
-    self->id = ++id_counter;
-    if (self->id == 0) {
-        fprintf(stderr, "waffle: error: internal counter wrapped around to 0");
-        abort();
-    }
-
-    switch (platform) {
-#ifdef WAFFLE_HAS_CGL
-        case WAFFLE_PLATFORM_CGL:
-            self->native = cgl_platform_create(&self->dispatch);
-            if (!self->native)
-                goto error;
-            break;
-#endif
-#ifdef WAFFLE_HAS_GLX
-        case WAFFLE_PLATFORM_GLX:
-            self->native = glx_platform_create(&self->dispatch);
-            if (!self->native)
-                goto error;
-            break;
-#endif
-#ifdef WAFFLE_HAS_WAYLAND
-        case WAFFLE_PLATFORM_WAYLAND:
-            self->native = wayland_platform_create(&self->dispatch);
-            if (!self->native)
-                goto error;
-            break;
-#endif
-#ifdef WAFFLE_HAS_X11_EGL
-        case WAFFLE_PLATFORM_X11_EGL:
-            self->native = xegl_platform_create(&self->dispatch);
-            if (!self->native)
-                goto error;
-            break;
-#endif
-        default:
-            wcore_error_internal("bad value for platform (0x%x)", platform);
-            goto error;
-    }
-
-    self->native_tag = platform;
-
-    return self;
-
-error:
-    wcore_platform_destroy(self);
-    return NULL;
-}
-
-bool
-wcore_platform_destroy(struct wcore_platform *self)
-{
-    bool ok = true;
-
-    if (!self)
-        return true;
-
-    switch (self->native_tag) {
-#ifdef WAFFLE_HAS_CGL
-        case WAFFLE_PLATFORM_CGL:
-            ok &= cgl_platform_destroy(self->native);
-            break;
-#endif
-#ifdef WAFFLE_HAS_GLX
-        case WAFFLE_PLATFORM_GLX:
-            ok &= glx_platform_destroy(self->native);
-            break;
-#endif
-#ifdef WAFFLE_HAS_WAYLAND
-        case WAFFLE_PLATFORM_WAYLAND:
-            ok &= wayland_platform_destroy(self->native);
-            break;
-#endif
-#ifdef WAFFLE_HAS_X11_EGL
-        case WAFFLE_PLATFORM_X11_EGL:
-            ok &= xegl_platform_destroy(self->native);
-            break;
-#endif
-        default:
-            ok = false;
-            wcore_error_internal("bad value for wcore_platform._native_tag "
-                                 "(0x%x)", self->native_tag);
-            break;
-    }
-
-    return ok;
-}
-
-/// @}
diff --git a/src/waffle/core/wcore_platform.h b/src/waffle/core/wcore_platform.h
index dbb9237..587b280 100644
--- a/src/waffle/core/wcore_platform.h
+++ b/src/waffle/core/wcore_platform.h
@@ -23,37 +23,85 @@
 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-/// @defgroup wcore_platform wcore_platform
-/// @ingroup wcore
-///
-/// @brief Abstract native platform.
-/// @{
-
-/// @file
-
 #pragma once
 
+#include <assert.h>
 #include <stdbool.h>
 #include <stdint.h>
 
-struct native_dispatch;
-union native_platform;
+struct wcore_config;
+struct wcore_config_attrs;
+struct wcore_context;
+struct wcore_display;
+struct wcore_platform;
+struct wcore_window;
 
-struct wcore_platform {
-    /// @brief Each instance has a unique id.
-    uint64_t id;
+struct wcore_platform_vtbl {
+    bool
+    (*destroy)(struct wcore_platform *self);
+
+    struct wcore_display*
+    (*connect_to_display)(
+            struct wcore_platform *self,
+            const char *name);
+
+    struct wcore_config*
+    (*choose_config)(
+            struct wcore_platform *self,
+            struct wcore_display *dpy,
+            const struct wcore_config_attrs *attrs);
+
+    struct wcore_context*
+    (*create_context)(
+            struct wcore_platform *self,
+            struct wcore_config *config,
+            struct wcore_context *share_ctx);
 
-    /// @brief One of WAFFLE_PLATFORM_*. Denotes type of `native`.
-    int native_tag;
+    struct wcore_window*
+    (*create_window)(
+            struct wcore_platform *self,
+            struct wcore_config *config,
+            int width,
+            int height);
 
-    union native_platform *native;
-    const struct native_dispatch *dispatch;
+    bool
+    (*make_current)(
+            struct wcore_platform *self,
+            struct wcore_display *dpy,
+            struct wcore_window *window,
+            struct wcore_context *ctx);
+
+    void*
+    (*get_proc_address)(
+            struct wcore_platform *self,
+            const char *proc);
+
+    bool
+    (*dl_can_open)(
+            struct wcore_platform *self,
+            int32_t waffle_dl);
+
+    void*
+    (*dl_sym)(
+            struct wcore_platform *self,
+            int32_t waffle_dl,
+            const char *symbol);
 };
 
-struct wcore_platform*
-wcore_platform_create(int platform);
+struct wcore_platform {
+    const struct wcore_platform_vtbl *vtbl;
+};
 
-bool
-wcore_platform_destroy(struct wcore_platform *self);
+static inline bool
+wcore_platform_init(struct wcore_platform *self)
+{
+    assert(self);
+    return true;
+}
 
-/// @}
+static inline bool
+wcore_platform_teardown(struct wcore_platform *self)
+{
+    assert(self);
+    return true;
+}
diff --git a/src/waffle/core/wcore_util.h b/src/waffle/core/wcore_util.h
new file mode 100644
index 0000000..ad5921e
--- /dev/null
+++ b/src/waffle/core/wcore_util.h
@@ -0,0 +1,50 @@
+// Copyright 2012 Intel Corporation
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice, this
+//   list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <stddef.h>
+
+#define container_of(ptr, type, member) ({                              \
+        const __typeof__(((type *)0)->member ) *__mptr = (ptr);         \
+        (type*)((void*)__mptr - offsetof(type, member));                \
+     })
+
+/// @brief Safe downcast using container_of().
+///
+/// If given a null pointer, return null.
+#define DEFINE_CONTAINER_CAST_FUNC(func_name,                           \
+                                   container_type,                      \
+                                   member_type,                         \
+                                   member)                              \
+                                                                        \
+    static inline container_type*                                       \
+    func_name(member_type *member##_self)                               \
+    {                                                                   \
+        if (member##_self)                                              \
+            return container_of(member##_self, container_type, member); \
+        else                                                            \
+            return 0;                                                   \
+    }
diff --git a/src/waffle/core/wcore_window.h b/src/waffle/core/wcore_window.h
new file mode 100644
index 0000000..c642e80
--- /dev/null
+++ b/src/waffle/core/wcore_window.h
@@ -0,0 +1,80 @@
+// Copyright 2012 Intel Corporation
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice, this
+//   list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include "wcore_config.h"
+#include "wcore_util.h"
+
+struct wcore_window;
+
+struct wcore_window_vtbl {
+    bool
+    (*destroy)(struct wcore_window *self);
+
+    bool
+    (*show)(struct wcore_window *self);
+
+    bool
+    (*swap_buffers)(struct wcore_window *self);
+};
+
+struct wcore_window {
+    const struct wcore_window_vtbl *vtbl;
+
+    struct waffle_window {} wfl;
+    struct api_object api;
+
+    struct wcore_display *display;
+};
+
+DEFINE_CONTAINER_CAST_FUNC(wcore_window,
+                           struct wcore_window,
+                           struct waffle_window,
+                           wfl)
+
+
+static inline bool
+wcore_window_init(struct wcore_window *self,
+                  struct wcore_config *config)
+{
+    assert(self);
+    assert(config);
+
+    self->api.display_id = config->display->api.display_id;
+    self->display = config->display;
+
+    return true;
+}
+
+static inline bool
+wcore_window_teardown(struct wcore_window *self)
+{
+    assert(self);
+    return true;
+}