gpu: reset to the default framebuffer on reset

The macOS backend doesn't re-create contexts, holding on to the first
created instead. Make sure the GPU leaves the default framebuffer bound,
in case the context is re-used.

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

app/internal/window/gl_macos.go

@@ -50,6 +50,11 @@ func (c *context) Release() {
 	c.Lock()
 	defer c.Unlock()
 	C.gio_clearCurrentContext()
+	// We could release the context with [view clearGLContext]
+	// and rely on [view openGLContext] auto-creating a new context.
+	// However that second context is not properly set up by
+	// OpenGLContextView, so we'll stay on the safe side and keep
+	// the first context around.
 }
 
 func (c *context) Present() error {

gpu/gpu.go

@@ -354,6 +354,7 @@ func (g *GPU) BeginFrame() {
 	g.ctx.SetBlend(false)
 	g.renderer.pather.stenciler.invalidateFBO()
 	g.coverTimer.end()
+	g.ctx.BindFramebuffer(g.defFBO)
 }
 
 func (g *GPU) EndFrame() {