mojo/services/ui/views/interfaces/layouts.mojom

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

[DartPackage="mojo_services"]
module mojo.ui;

import "mojo/services/geometry/interfaces/geometry.mojom";
import "mojo/services/surfaces/interfaces/surface_id.mojom";

// Box constraints for layout.
//
// A box constraint allows a parent view to determine the size of its child
// by constraining its width and height.  Each dimension is considered
// independently.  If a constraint only admits a single value in one or both
// dimensions (because the minimum and maximum values are equal) then it is
// said to be "tight" in those dimension.
//
// A |Size| respects this constraint if, and only if, all of the following
// relations hold:
//
//   size.width >= constraints.min_width
//   size.width <= constraints.max_width
//   size.height >= constraints.min_height
//   size.height <= constraints.max_height
//
// The view manager validates all constraints before delivering them to a
// child view; it will close its connection if the parent view supplies
// constraints which are ill-formed.
struct BoxConstraints {
  // The minimum width of the view in device pixels.
  // Must be >= 0.
  int32 min_width;

  // The maximum width of the view in device pixels.
  // Must be >= |min_width|.
  int32 max_width;

  // The minimum height of the view in device pixels.
  // Must be >= 0.
  int32 min_height;

  // The maximum height of the view in device pixels.
  // Must be >= |min_height|.
  int32 max_height;
};

// Layout parameters provided by a parent view to one of its children.
//
// TODO(jeffbrown): We will eventually need to pass a bunch more information
// such as theme colors, virtual light sources for shadows, elevation, and
// more.  It is unclear whether we'll want to put that information here
// or somewhere else but it may be convenient to stash it here because we
// will already have an invalidation mechanism in place.
struct ViewLayoutParams {
  // The size constraints for the child.
  mojo.ui.BoxConstraints constraints;

  // The ratio between the size of one display device pixel to the size
  // of one logical pixel, assuming pixels are square.  This value changes
  // in relation to display density and zoom level.
  // Must be > 0.
  float device_pixel_ratio = 1.0;
};

// Layout information for a view.
struct ViewLayoutInfo {
  // The view's surface id for composition by the parent.
  mojo.SurfaceId surface_id;

  // The actual size of the view in device pixels.
  mojo.Size size;
};