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>

1 files changed, 70 insertions, 22 deletions

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;
+}