Canvas 源码

最新推荐文章于 2024-11-20 15:36:51 发布

mzxysxx

最新推荐文章于 2024-11-20 15:36:51 发布

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文章标签： android开发

本文链接：https://blog.youkuaiyun.com/mzxysxx/article/details/52929448

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本文探讨了Android开发中的自定义控件绘制，重点解析了Canvas的源码。Canvas作为绘制的基础，涉及bitmap、canvas、绘图材料和画笔四个关键组件。文章介绍了Canvas的构造方法，包括无参构造和基于bitmap的构造，以及如何设置和获取canvas的密度和viewport。此外，还讨论了剪辑边界、保存和恢复状态的功能，为Android图形绘制提供了深入的理解。

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最近在看自定义控件---绘制view

今天先上点Canvas的源码，持续更新中。。。

下面是一点Canvas源码

/**
 * 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).
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about how to use Canvas, read the
 * <a href="{@docRoot}guide/topics/graphics/2d-graphics.html">
 * Canvas and Drawables</a> developer guide.</p></div>
 */
public class Canvas {
    /** @hide */
    public static boolean sCompatibilityRestore = false;

    /**
     * Should only be assigned in constructors (or setBitmap if software canvas),
     * freed in finalizer.
     * @hide
     */
    protected long mNativeCanvasWrapper;

 /**
     * Construct an empty raster canvas. Use setBitmap() to specify a bitmap to
     * draw into.  The initial target density is {@link Bitmap#DENSITY_NONE};
     * this will typically be replaced when a target bitmap is set for the
     * canvas.
     */
    public Canvas() {
        if (!isHardwareAccelerated()) {
            // 0 means no native bitmap
            mNativeCanvasWrapper = initRaster(null);
            mFinalizer = new CanvasFinalizer(mNativeCanvasWrapper);
        } else {
            mFinalizer = null;
        }
    }

Canvas 类保存了draw 的调用，你需要四个基本的组件来绘制。1.bitmap保存像素的位图。2.canvas保存draw的调用。3一个原始绘画材料，4.一个画笔（color，style）

有两个构造方法，一个无参