1 /*
2  * Copyright 2020 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package androidx.compose.ui.graphics.drawscope
18 
19 import androidx.compose.ui.geometry.Size
20 import androidx.compose.ui.graphics.Canvas
21 import androidx.compose.ui.graphics.layer.GraphicsLayer
22 import androidx.compose.ui.unit.Density
23 import androidx.compose.ui.unit.LayoutDirection
24 
25 /**
26  * Default density value that is used as a stub to provide a non-null density parameter within
27  * CanvasDrawScope. Density is provided as a parameter as part of the draw call to issue drawing
28  * commands into a target canvas so this Density value is never consumed
29  */
30 internal val DefaultDensity = Density(1.0f, 1.0f)
31 
32 /**
33  * Object that provides the dependencies to support a [DrawScope] drawing environment. Namely this
34  * provides the drawing bounds represented as a size as well as the target [Canvas] to issue drawing
35  * commands into. Additionally the [DrawContext] handles updating [Canvas] state during
36  * transformations and updating the size of the drawing bounds that may occur during these
37  * transformations.
38  *
39  * This exposes necessary internal state to the implementation of the [DrawScope] in order to
40  * support inline scoped transformation calls without allowing consumers of [DrawScope] to modify
41  * state directly thus maintaining the stateless API surface
42  */
43 interface DrawContext {
44 
45     /** The current size of the drawing environment */
46     var size: Size
47 
48     /** The target canvas to issue drawing commands */
49     var canvas: Canvas
50         get() = EmptyCanvas
51         set(_) {}
52 
53     /** The controller for issuing transformations to the drawing environment */
54     val transform: DrawTransform
55 
56     /** [LayoutDirection] of the layout being drawn in. */
57     var layoutDirection: LayoutDirection
58         get() = LayoutDirection.Ltr
59         set(_) {}
60 
61     /**
62      * [Density] used to assist in conversions of density independent pixels to raw pixels to draw
63      */
64     var density: Density
65         get() = DefaultDensity
66         set(_) {}
67 
68     /**
69      * Current [GraphicsLayer] we are drawing into. Might be null if the [canvas] is not provided by
70      * a [GraphicsLayer], for example in the case of a software-accelerated drawing.
71      */
72     var graphicsLayer: GraphicsLayer?
73         get() = null
74         set(_) {}
75 }
76