Android之Canvas

一、概述
The Canvas class holds the "draw" calls. To draw something, you need 4 basic components: A Bitmap to hold the pixels, a Canvas to host the draw calls (writing into the bitmap), a drawing primitive (e.g. Rect, Path, text, Bitmap), and a paint (to describe the colors and styles for the drawing).
Canvas类支持“draw”的调用，可以去绘制别的事物。你需要四种基本的组成成分：
(1)Bitmap(图像)
(2)Canvas(画布，主办描绘调用等，即等待绘制到bitmap中)
(3)primitive(绘制的原始事物（例如矩形、路径、文本、图像）)
(4)paint（颜料,描述描绘的颜色和风格）
二、嵌套类
Nested Classes

enum
Canvas.EdgeType

enum
Canvas.VertexMode

三、常量
Constans

int
ALL_SAVE_FLAG
当restore()方法被调用时，恢复全部东西

int
CLIP_SAVE_FLAG
当restore()方法被调用时，恢复当前剪辑

int
CLIP_TO_LAYER_SAVE_FLAG
clip against the layer's bounds

剪辑对立层的边界

int
FULL_COLOR_LAYER_SAVE_FLAG
the layer needs to 8-bits per color component

int
HAS_ALPHA_LAYER_SAVE_FLAG
the layer needs to per-pixel alpha

int
MATRIX_SAVE_FLAG
restore the current matrix when restore() is called

当调用restore()方法时，恢复现有矩阵

四、公共构造函数
Public Constructors

Canvas()

Construct an empty raster canvas

Canvas(Bitmap bitmap)

Construct a canvas with the specified bitmap to draw into

Canvas(GL gl)

Construct a canvas with the specified gl context

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