// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.ui.sketchy;

using fuchsia.images;

// A Canvas allows clients to draw strokes, which are dynamically tessellated
// and inserted into the global Scenic scene-graph.
[Discoverable]
protocol Canvas {
    // Init() must be called once, before invoking any other operations.
    Init(CanvasListener? listener);

    // Enqueue a list of operations, which will not take effect until Present() is
    // called.  It is allowable to call Enqueue() several times before calling
    // Present(); the effect is the same as if all operations had been
    // concatenated into a single Enqueue() call.
    //
    // Akin to fuchsia::ui::gfx::Session.Enqueue(); see scenic/session.fidl for details.
    Enqueue(vector<Command> commands);

    // Present all previously enqueued operations.  In order to pipeline the
    // preparation of the resources required to render the scene, two lists of
    // fences (implemented as events) are passed.
    //
    // Akin to fuchsia::ui::gfx::Session.Present(); see scenic/session.fidl for details.
    Present(uint64 presentation_time)
        -> (fuchsia.images.PresentationInfo presentation_info);
};

// Allows clients to observe canvas events.
protocol CanvasListener {
    OnError(string description);
    OnStrokeFinished(uint32 stroke_id, StrokePath path);
    OnPageViewerInvalidated(uint32 viewer_id);
};