Android View — Paint 详解

2019年5月26日 141次阅读 来源: 赤兔欢

Android View — Paint 详解

在Android View 的概念中，Paint 如名字所代表的含义，是画笔的意思。像我们平时画图一样，Paint就是相当于笔，而Canvas就是纸，这里叫画布。Paint 可以设置的多种属性。

PaintCanvasView

定义一个最简单的自定义View来展示Paint 的多种属性。

  1. 重写onDraw 方法，在onDrasw 方法中调用子类的onChildDraw 方法，
  2. 所有的子类都要事先抽象的onChildDraw 方法，在onChildDraw真正的绘制图形
  3. onSizeChanged 确定View的宽和高。作为绘制View的宽和高的依据。
public abstract class PaintCanvasView extends View {
    protected Paint mPaint = new Paint();
    protected int mWidth;
    protected int mHeigth;
    protected RectF mRectF;

    public PaintCanvasView(Context context) {
        super(context);
        mRectF = new RectF();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        onChildDraw(canvas);
    }

    protected abstract void onChildDraw(Canvas canvas);

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mWidth = w;
        mHeigth = h;

        mRectF.left = 0;
        mRectF.top = 0;
        mRectF.right = w;
        mRectF.bottom = h;
    }

绘制文字

Paint 最基本的功能就是绘制文字。基本属性有:

  1. setTextSize 设置文字的大小
  2. setColor 设置文字的颜色
  3. setTextScaleX 水平方向上的缩放
  4. setTextSkewX 水平方向上的倾斜度
  5. setTypeface(Typeface typeface) 设置字体

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_text.png

    static public class TextPaintCanvasView extends PaintCanvasView{

        public TextPaintCanvasView(Context context) {
            super(context);
        }

        @Override
        protected void onChildDraw(Canvas canvas) {
            mPaint.setTextSize(mWidth/20);
            mPaint.setColor(Color.BLUE);
            mPaint.setTypeface(Typeface.SERIF);
            canvas.drawText("View Hello World", mWidth/10, mHeigth*1/4, mPaint);

            mPaint.setTextScaleX(2);
            canvas.drawText("View Hello World", mWidth/10, mHeigth*2/4, mPaint);

            mPaint.setTextScaleX(1);
            mPaint.setTextSkewX(-1);
            canvas.drawText("View Hello World", mWidth/10, mHeigth*3/4, mPaint);
        }
    }

setShadowLayer

绘制文字的阴影

/**
 * This draws a shadow layer below the main layer, with the specified
 * offset and color, and blur radius. If radius is 0, then the shadow
 * layer is removed.
 * <p>
 * Can be used to create a blurred shadow underneath text. Support for use
 * with other drawing operations is constrained to the software rendering
 * pipeline.
 * <p>
 * The alpha of the shadow will be the paint's alpha if the shadow color is
 * opaque, or the alpha from the shadow color if not.
 */
public void setShadowLayer(float radius, float dx, float dy, int shadowColor);

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_shadowLayer.png

    public static class ShadowLayerPaintView extends PaintCanvasView {
        public ShadowLayerPaintView(Context context) {
            super(context);
        }

        @Override
        protected void onChildDraw(Canvas canvas) {
            mPaint.setTextSize(mWidth/10);
            mPaint.setColor(Color.BLUE);
            mPaint.setShadowLayer(20, 0, 20, Color.GREEN);
            canvas.drawText("View Hello World", mWidth/10, mHeigth/2, mPaint);
        }
    }

setStrokeWidth

设置描边的宽度，在绘制 线条，各种几何图形时使用。
需要配合设置 style is Stroke or StrokeAndFill

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_StrokeWidth.png

    static public class LinePaintCanvasView extends PaintCanvasView{

        public LinePaintCanvasView(Context context) {
            super(context);
        }

        @Override
        protected void onChildDraw(Canvas canvas) {
            mPaint.setColor(Color.BLUE);
            mPaint.setStrokeWidth(10);
            canvas.drawLine(mWidth/10, mHeigth/2, mWidth - mWidth/10, mHeigth/2, mPaint);
        }
    }

Cap

Cap 表示表示画笔在离开画板时候留下的最后一点图形，比如矩形，圆形等。有三种:

  1. BUTT 正常模式
  2. ROUND
  3. SQUARE
  4. 默认是BUTT, 但是从图上可以看出设置与不设置在长度上有一些差异。

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_cap.png

 public enum Cap {
        BUTT    (0),
        ROUND   (1),
        SQUARE  (2);
    }

    static public class CapPaintCanvasView extends PaintCanvasView{

        @Override
        protected void onChildDraw(Canvas canvas) {

            mPaint.setColor(Color.DKGRAY);
            mPaint.setStrokeWidth(50);
            canvas.drawLine(mWidth/10, mHeigth/5, mWidth - mWidth/10, mHeigth/5, mPaint);

            mPaint.setStrokeCap(Paint.Cap.BUTT);
            canvas.drawLine(mWidth/10, mHeigth*2/5, mWidth - mWidth/10, mHeigth*2/5, mPaint);

            mPaint.setStrokeCap(Paint.Cap.ROUND);
            canvas.drawLine(mWidth/10, mHeigth*3/5, mWidth - mWidth/10, mHeigth*3/5, mPaint);

            mPaint.setStrokeCap(Paint.Cap.SQUARE);
            canvas.drawLine(mWidth/10, mHeigth*4/5, mWidth - mWidth/10, mHeigth*4/5, mPaint);
        }
    }

Jonin

Jonin 表示图形连接处的样式.有锐角，圆形，斜面三种。

    public enum Join {
        MITER   (0),
        ROUND   (1),
        BEVEL   (2);
    }

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_join.png

static public class JoinPaintCanvasView extends PaintCanvasView{

        @Override
        protected void onChildDraw(Canvas canvas) {

            mPaint.setColor(Color.CYAN);
            mPaint.setStrokeWidth(50);
            mPaint.setStyle(Paint.Style.STROKE);

            Path  path = new Path();
            path.moveTo(mWidth/8, mHeigth/10);
            path.lineTo(mWidth/4, mHeigth - mHeigth/8);

            mPaint.setStrokeJoin(Paint.Join.MITER);
            path.lineTo(mWidth/2, mHeigth/8);
            canvas.drawPath(path, mPaint);

            mPaint.setStrokeJoin(Paint.Join.ROUND);
            path.lineTo(mWidth*3/4, mHeigth - mHeigth/8);
            canvas.drawPath(path, mPaint);

            mPaint.setStrokeJoin(Paint.Join.BEVEL);
            path.lineTo(mWidth*7/8, mHeigth/8);
            canvas.drawPath(path, mPaint);
        }
    }

Align

Align 用于在绘制文本时表示的对齐方式：

    public enum Align {
        LEFT    (0),
        CENTER  (1),
        RIGHT   (2);
    }

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_align.png

    static public class AlignPaintCanvasView extends PaintCanvasView{

        @Override
        protected void onChildDraw(Canvas canvas) {

            mPaint.setTextSize(mWidth/10);
            mPaint.setColor(Color.BLUE);
            mPaint.setTextAlign(Paint.Align.LEFT);
            canvas.drawText("Align View", mWidth/2, mHeigth*1/4, mPaint);

            mPaint.setTextAlign(Paint.Align.CENTER);
            canvas.drawText("Align View", mWidth/2, mHeigth*2/4, mPaint);

            mPaint.setTextAlign(Paint.Align.RIGHT);
            canvas.drawText("Align View", mWidth/2, mHeigth*3/4, mPaint);
        }
    }

ColorFilter

ColorMatrixColorFilter

颜色ColorMatrix 是一个5*4的矩阵. 默认的ColorMatrix为：【
1, 0, 0, 0, 0, // R
0, 1, 0, 0, 0, // G
0, 0, 1, 0, 0, // B
0, 0, 0, 1, 0, // A
】

最后一列表示偏移。通过函数
public void setScale(float rScale, float gScale, float bScale,float aScale) 来控制各个颜色分量的比重。

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_ColorMatrix.png

/**
 * 4x5 matrix for transforming the color and alpha components of a Bitmap.
 * The matrix can be passed as single array, and is treated as follows:
 *
 *  [ a, b, c, d, e,
 *    f, g, h, i, j,
 *    k, l, m, n, o,
 *    p, q, r, s, t ]
 *
 * When applied to a color [R, G, B, A] the resulting color
 * is computed as:
 *   R = a*R + b*G + c*B + d*A + e;
 *   G = f*R + g*G + h*B + i*A + j;
 *   B = k*R + l*G + m*B + n*A + o;
 *   A = p*R + q*G + r*B + s*A + t;
 *   

    static public class ColorMatrixColorFilterView extends PaintCanvasView{

        @Override
        protected void onChildDraw(Canvas canvas) {

            ColorMatrix colorMatrix = new ColorMatrix(new float[]{
                    1, 0, 0, 0, 0,
                    0, 1, 0, 0, 0,
                    0, 0, 1, 0, 0,
                    0, 0, 0, 1, 0,
            });

            int strokeWidth = 20;
            int min = Math.min(mWidth, mHeigth);
            int radius = min/3;

            mPaint.setColorFilter(new ColorMatrixColorFilter(colorMatrix));
            mPaint.setColor(Color.argb(255, 255, 128, 103));
            canvas.drawCircle(mRectF.centerX(), mRectF.centerY(), min/2, mPaint);

            colorMatrix.setScale(0, 1f, 1f, 1f);
            mPaint.setColorFilter(new ColorMatrixColorFilter(colorMatrix));
            canvas.drawCircle(mWidth/3/2,   mHeigth/2, radius - strokeWidth, mPaint);

            mPaint.setColor(Color.argb(255, 255, 128, 103));
            colorMatrix.setScale(1, 0f, 0f, 1f);
            mPaint.setColorFilter(new ColorMatrixColorFilter(colorMatrix));
            canvas.drawCircle(mWidth*5/6, mHeigth/2, radius - strokeWidth, mPaint);
        }
    }

LightingColorFilter

LightingColorFilter 和 ColorMatrixColorFilter 道理上上一样的，都是通过控制RGBA 的数值实现滤镜的效果。在参数上有一些差异，ColorMatrixColorFilter 是分别操作颜色的各个通道。LightingColorFilter 则是直接传入两个RGBA的色彩参数。

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_LightingColorFilter.png

/**
 *
 * Given a source color RGB, the resulting R'G'B' color is computed thusly:
 * R' = R * colorMultiply.R + colorAdd.R
 * G' = G * colorMultiply.G + colorAdd.G
 * B' = B * colorMultiply.B + colorAdd.B
 */
 

    static public class LightingColorFilterView extends PaintCanvasView{
        Context mContext;
        public LightingColorFilterView(Context context) {
            super(context);
            mContext = context;
            setLayerType(LAYER_TYPE_SOFTWARE, null);
        }

        @Override
        protected void onChildDraw(Canvas canvas) {
            Bitmap bitmap = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.colorfilter);
            Rect srcRect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
            int min = Math.min(mWidth, mHeigth)/3;

            canvas.drawBitmap(bitmap, srcRect, new Rect(mWidth/2 - min, mHeigth/2 - min, mWidth/2 + min, mHeigth/2 + min), mPaint);
            mPaint.setColorFilter(new LightingColorFilter(0xFF00FFFF, 0x00FF0000));
            canvas.drawBitmap(bitmap, srcRect, new Rect(mWidth/6 - min, mHeigth/2 - min, mWidth/6 + min, mHeigth/2 + min), mPaint);
            mPaint.setColorFilter(new LightingColorFilter(0xFF00FFFF, 0x00000000));
            canvas.drawBitmap(bitmap, srcRect, new Rect(mWidth*5/6 - min, mHeigth/2 - min, mWidth*5/6 + min, mHeigth/2 + min), mPaint);
        }
    }

PorterDuffColorFilter

PorterDuffColorFilter 构造参数需要传入两个参数。第一个为颜色值，第二个为混合模式。
然后Paint 在draw Bitmap 的时候Bitmap 和颜色值 按照第二个参数的进行混合。

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_PorterDuffColorFilter.png

    static public class PorterDuffColorFilterView extends PaintCanvasView{
        Context mContext;

        public PorterDuffColorFilterView(Context context) {
            super(context);
            mContext = context;
            setLayerType(LAYER_TYPE_SOFTWARE, null);
        }

        @Override
        protected void onChildDraw(Canvas canvas) {
            Bitmap bitmap = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.androidicon);
            Rect srcRect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
            int min = Math.min(mWidth, mHeigth)/3;

            canvas.drawBitmap(bitmap, srcRect, new Rect(mWidth/2 - min, mHeigth/2 - min, mWidth/2 + min, mHeigth/2 + min), mPaint);

            mPaint.setColorFilter(new PorterDuffColorFilter(Color.DKGRAY, PorterDuff.Mode.DST));
            canvas.drawBitmap(bitmap, srcRect, new Rect(mWidth/6 - min, mHeigth/2 - min, mWidth/6 + min, mHeigth/2 + min), mPaint);

            mPaint.setColorFilter(new PorterDuffColorFilter( Color.argb(255, 255, 128, 103), PorterDuff.Mode.SRC));
            canvas.drawBitmap(bitmap, srcRect, new Rect(mWidth*5/6 - min, mHeigth/2 - min, mWidth*5/6 + min, mHeigth/2 + min), mPaint);
        }
    }

MaskFilter

BlurMaskFilterView

BlurMaskFilter为模糊面罩，可以在图形边缘添加一些毛玻璃效果。
BlurMaskFilter 构造函数两个参数，第一个参数为阴影的模糊半径，第二个参数为模糊模式 枚举类型 Blur。

public BlurMaskFilter(float radius, Blur style)

这个API不支持硬件加速，需要设置：

setLayerType(LAYER_TYPE_SOFTWARE, null);

public enum Blur {
        /**
         * Blur inside and outside the original border.
         */
        NORMAL(0),
        
        /**
         * Draw solid inside the border, blur outside.
         */
        SOLID(1),

        /**
         * Draw nothing inside the border, blur outside.
         */
        OUTER(2),

        /**
         * Blur inside the border, draw nothing outside.
         */
        INNER(3);
        
        Blur(int value) {
            native_int = value;
        }
        final int native_int;
    }

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_BlurMaskFilter.png

    static public class BlurMaskFilterView extends PaintCanvasView{

        @Override
        protected void onChildDraw(Canvas canvas) {

            int strokeWidth = 20;
            int min = Math.min(mWidth, mHeigth);
            int radius = mWidth/8;
            mPaint.setStrokeWidth(strokeWidth);
            mPaint.setColor(Color.RED);

            mPaint.setMaskFilter(new BlurMaskFilter(strokeWidth, BlurMaskFilter.Blur.NORMAL));
            canvas.drawCircle(mWidth/4/2,   mHeigth/2, radius - strokeWidth, mPaint);

            mPaint.setMaskFilter(new BlurMaskFilter(strokeWidth, BlurMaskFilter.Blur.SOLID));
            canvas.drawCircle(mWidth*3/4/2, mHeigth/2, radius - strokeWidth, mPaint);

            mPaint.setMaskFilter(new BlurMaskFilter(strokeWidth, BlurMaskFilter.Blur.OUTER));
            canvas.drawCircle(mWidth*5/4/2, mHeigth/2, radius - strokeWidth, mPaint);

            mPaint.setMaskFilter(new BlurMaskFilter(strokeWidth, BlurMaskFilter.Blur.INNER));
            canvas.drawCircle(mWidth*7/8, mHeigth/2, radius - strokeWidth, mPaint);
        }
    }

EmbossMaskFilterView

EmbossMaskFilter 用来设置浮雕效果，其原理是模拟光照效果，靠近光的一面显得亮一点，远离光的一面显得暗一点，这样就通过颜色的亮暗营造出浮雕的3D立体效果。
构造函数：

public EmbossMaskFilter(float[] direction, float ambient, float specular, float blurRadius)

direction 是float数组，定义长度为3的数组[x,y,z]，来指定光源的方向
ambient 取值在0到1之间，定义背景光 或者说是周围光
specular 定义镜面反射系数
blurRadius 模糊半径

direction 代表光源的坐标系，可以这样想想，如果所绘制的物体在原点，direction代表光源的左标，根据光源的位置不同，可以显示不同的效果。如果Z轴为负，就是在物体的后边，显示要暗一些，如果在原点，就和物体重叠，显示为黑色。显示的效果还要和环境光ambient和镜面反射specular有关系。环境光的强弱同样会影响效果。镜面反射specular的含义是根据我们学习的光的反射定律，理性情况下所有的光先都被反射回去，实际情况下光的反射要有一定的损失，镜子算是镜面反射比较强的例子。

这个API同样不支持硬件加速，需要设置：

setLayerType(LAYER_TYPE_SOFTWARE, null);

《Android View — Paint 详解》
《Android View — Paint 详解》 paint_EmbossMaskFilter.png

    static public class EmbossMaskFilterView extends PaintCanvasView{

        @Override
        protected void onChildDraw(Canvas canvas) {

            int strokeWidth = 20;
            int radius = mWidth/8;
            mPaint.setStrokeWidth(strokeWidth);
            mPaint.setColor(Color.RED);

            mPaint.setMaskFilter(new EmbossMaskFilter(new float[] { 1, 1, 1F }, 0.1F, 8, 3));
            canvas.drawCircle(mWidth/3/2,   mHeigth/2, radius - strokeWidth, mPaint);

            mPaint.setMaskFilter(new EmbossMaskFilter(new float[] { 1, 1, -1F }, 0.1F, 8, 3));
            canvas.drawCircle(mWidth*3/3/2, mHeigth/2, radius - strokeWidth, mPaint);

            mPaint.setMaskFilter(new EmbossMaskFilter(new float[] { 0, 0, 1F }, 0.1F, 8, 3));
            canvas.drawCircle(mWidth*5/3/2, mHeigth/2, radius - strokeWidth, mPaint);
        }
    }
    原文作者：赤兔欢
    原文地址: https://www.jianshu.com/p/5ef2e63a7bb8
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