sky/sdk/lib/rendering/README.md - Issue 1190123003: Decouple Canvas from DisplayList and map Picture and PictureRecorder more directly to their Skia co…

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Issue 1190123003: Decouple Canvas from DisplayList and map Picture and PictureRecorder more directly to their Skia co… (Closed) Base URL: git@github.com:domokit/mojo.git@master

Patch Set: Rebased version of previous patch Created 5 years, 6 months ago

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1 Sky Rendering	1 Sky Rendering

2 =============	2 =============

3	3

4 The Sky render tree is a low-level layout and painting system based on a	4 The Sky render tree is a low-level layout and painting system based on a

5 retained tree of objects that inherit from [`RenderObject`](object.dart). Most	5 retained tree of objects that inherit from [`RenderObject`](object.dart). Most

6 developers using Sky will not need to interact directly with the rendering tree.	6 developers using Sky will not need to interact directly with the rendering tree.

7 Instead, most developers should use [Sky widgets](../widgets/README.md), which	7 Instead, most developers should use [Sky widgets](../widgets/README.md), which

8 are built using the render tree.	8 are built using the render tree.

9	9

10 Overview	10 Overview

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37	37

38 * Implementations of `performLayout` are expected to call `layout` on their	38 * Implementations of `performLayout` are expected to call `layout` on their

39 children. When calling `layout`, a `RenderObject` must use the	39 children. When calling `layout`, a `RenderObject` must use the

40 `parentUsesSize` parameter to declare whether its `performLayout` function	40 `parentUsesSize` parameter to declare whether its `performLayout` function

41 depends on information read from the child. If the parent doesn't declare	41 depends on information read from the child. If the parent doesn't declare

42 that it uses the child's size, the edge from the parent to the child becomes	42 that it uses the child's size, the edge from the parent to the child becomes

43 a _relayout boundary_, which means the child (and its subtree) might undergo	43 a _relayout boundary_, which means the child (and its subtree) might undergo

44 layout without the parent undergoing layout.	44 layout without the parent undergoing layout.

45	45

46 * Subclasses of `RenderObject` must implement a `paint` function that draws a	46 * Subclasses of `RenderObject` must implement a `paint` function that draws a

47 visual representation of the object onto an `RenderObjectDisplayList`. If	47 visual representation of the object onto a `RenderCanvas`. If

48 the `RenderObject` has children, the `RenderObject` is responsible for	48 the `RenderObject` has children, the `RenderObject` is responsible for

49 painting its children using the `paintChild` function.	49 painting its children using the `paintChild` function on the `RenderCanvas`.

50	50

51 * Subclasses of `RenderObject` must call `adoptChild` whenever they add a	51 * Subclasses of `RenderObject` must call `adoptChild` whenever they add a

52 child. Similarly, they must call `dropChild` whenever they remove a child.	52 child. Similarly, they must call `dropChild` whenever they remove a child.

53	53

54 * Most subclasses of `RenderObject` will implement a `hitTest` function that	54 * Most subclasses of `RenderObject` will implement a `hitTest` function that

55 lets clients query the render tree for objects that intersect with a given	55 lets clients query the render tree for objects that intersect with a given

56 user input location. `RenderObject` itself does not impose a particular	56 user input location. `RenderObject` itself does not impose a particular

57 type signature on `hitTest`, but most implementations will take an argument	57 type signature on `hitTest`, but most implementations will take an argument

58 of type `HitTestResult` (or, more likely, a model-specific subclass of	58 of type `HitTestResult` (or, more likely, a model-specific subclass of

59 `HitTestResult`) as well as an object that describes the location at which	59 `HitTestResult`) as well as an object that describes the location at which

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136 * Avoid using save/restore on canvases.	136 * Avoid using save/restore on canvases.

137	137

138	138

139 Dependencies	139 Dependencies

140 ------------	140 ------------

141	141

142 * [`package:sky/base`](../base)	142 * [`package:sky/base`](../base)

143 * [`package:sky/mojo`](../mojo)	143 * [`package:sky/mojo`](../mojo)

144 * [`package:sky/animation`](../mojo)	144 * [`package:sky/animation`](../mojo)

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