app: confine the eglWindow indirection to the Wayland backend

Only the Wayland backend needs an wl_egl_window between the wl_surface
and EGL. Move code dealing with the indirection to Wayland specific
code.

Then, introduce the eglDriver interface instead of referencing the
native window type directly. This will help when multiple backends are
supported at runtime (e.g. Wayland+X11).

Finally, move the eglDriver implementation methods from GOOS-specific
code to separate EGL-specific files, allowing EGL types to be used
directly instead of unsafe.Pointer and uinptr.

The result is simpler generic EGL code, and easier path towards X11
support.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/egl_wayland.go

@@ -6,7 +6,7 @@ package app
 
 import (
 	"errors"
-	"unsafe"
+	"sync"
 )
 
 /*
@@ -24,29 +24,48 @@ type (
 	_EGLNativeWindowType  = C.EGLNativeWindowType
 )
 
-type eglWindow struct {
-	w *C.struct_wl_egl_window
+var eglWindows struct {
+	mu      sync.Mutex
+	windows map[*C.struct_wl_surface]*C.struct_wl_egl_window
 }
 
-func newEGLWindow(w _EGLNativeWindowType, width, height int) (*eglWindow, error) {
-	surf := (*C.struct_wl_surface)(unsafe.Pointer(w))
-	win := C.wl_egl_window_create(surf, C.int(width), C.int(height))
-	if win == nil {
-		return nil, errors.New("wl_egl_create_window failed")
+func (w *window) eglDestroy() {
+	surf, _, _ := w.surface()
+	if surf == nil {
+		return
+	}
+	eglWindows.mu.Lock()
+	defer eglWindows.mu.Unlock()
+	if eglWin, ok := eglWindows.windows[surf]; ok {
+		C.wl_egl_window_destroy(eglWin)
+		delete(eglWindows.windows, surf)
 	}
-	return &eglWindow{win}, nil
 }
 
-func (w *eglWindow) window() _EGLNativeWindowType {
-	return w.w
+func (w *window) eglDisplay() _EGLNativeDisplayType {
+	return w.display()
 }
 
-func (w *eglWindow) resize(width, height int) {
-	C.wl_egl_window_resize(w.w, C.int(width), C.int(height), 0, 0)
-}
-
-func (w *eglWindow) destroy() {
-	C.wl_egl_window_destroy(w.w)
+func (w *window) eglWindow(visID int) (_EGLNativeWindowType, int, int, error) {
+	surf, width, height := w.surface()
+	if surf == nil {
+		return nilEGLNativeWindowType, 0, 0, errors.New("wayland: no surface")
+	}
+	eglWindows.mu.Lock()
+	defer eglWindows.mu.Unlock()
+	eglWin, ok := eglWindows.windows[surf]
+	if !ok {
+		if eglWindows.windows == nil {
+			eglWindows.windows = make(map[*C.struct_wl_surface]*C.struct_wl_egl_window)
+		}
+		eglWin = C.wl_egl_window_create(surf, C.int(width), C.int(height))
+		if eglWin == nil {
+			return nilEGLNativeWindowType, 0, 0, errors.New("wayland: wl_egl_create_window failed")
+		}
+		eglWindows.windows[surf] = eglWin
+	}
+	C.wl_egl_window_resize(eglWin, C.int(width), C.int(height), 0, 0)
+	return eglWin, width, height, nil
 }
 
 func eglGetDisplay(disp _EGLNativeDisplayType) _EGLDisplay {