Add buildable_state() to commands lists

vulkano/src/command_buffer/std/dispatch.rs

@@ -116,6 +116,11 @@ unsafe impl<'a, L, Pl, S, Pc> StdCommandsList for DispatchCommand<'a, L, Pl, S,
         self.previous.extract_current_image_state(image)
     }
 
+    #[inline]
+    fn buildable_state(&self) -> bool {
+        true
+    }
+
     unsafe fn raw_build<I, F>(self, additional_elements: F, barriers: I,
                               mut final_barrier: PipelineBarrierBuilder) -> Self::Output
         where F: FnOnce(&mut UnsafeCommandBufferBuilder<L::Pool>),

vulkano/src/command_buffer/std/empty.rs

@@ -85,6 +85,11 @@ unsafe impl<P> StdCommandsList for PrimaryCbBuilder<P> where P: CommandPool {
         None
     }
 
+    #[inline]
+    fn buildable_state(&self) -> bool {
+        true
+    }
+
     unsafe fn raw_build<I, F>(self, additional_elements: F, barriers: I,
                               final_barrier: PipelineBarrierBuilder) -> Self::Output
         where F: FnOnce(&mut UnsafeCommandBufferBuilder<Self::Pool>),

vulkano/src/command_buffer/std/mod.rs

@@ -66,8 +66,14 @@ pub unsafe trait StdCommandsList {
         DispatchCommand::new(self, pipeline, sets, dimensions, push_constants)
     }
 
+    /// Returns true if the command buffer can be built. This function should always return true,
+    /// except when we're building a primary command buffer that is inside a render pass.
+    fn buildable_state(&self) -> bool;
+
     /// Turns the commands list into a command buffer that can be submitted.
     fn build(self) -> Self::Output where Self: Sized {
+        assert!(self.buildable_state());
+
         unsafe {
             self.raw_build(|_| {}, iter::empty(), PipelineBarrierBuilder::new())
         }
@@ -122,6 +128,8 @@ pub unsafe trait StdCommandsList {
     ///   the command numbers to be inferior to `num_commands`.
     /// - `final_barrier` is a pipeline barrier that must be added at the end of the
     ///   command buffer builder.
+    ///
+    /// This function doesn't check that `buildable_state` returns true.
     unsafe fn raw_build<I, F>(self, additional_elements: F, barriers: I,
                               final_barrier: PipelineBarrierBuilder) -> Self::Output
         where F: FnOnce(&mut UnsafeCommandBufferBuilder<Self::Pool>),

vulkano/src/command_buffer/std/update_buffer.rs

@@ -101,6 +101,11 @@ unsafe impl<'a, L, B, D: ?Sized> StdCommandsList for UpdateCommand<'a, L, B, D>
         self.previous.check_queue_validity(queue)
     }
 
+    #[inline]
+    fn buildable_state(&self) -> bool {
+        true
+    }
+
     unsafe fn extract_current_buffer_state<Ob>(&mut self, buffer: &Ob)
                                                -> Option<Ob::CommandListState>
         where Ob: TrackedBuffer