android shader 用法

 转自 http://blog.csdn.net/abcdef314159

http://blog.csdn.net/aigestudio/article/details/41799811

Shader渲染Android提供了5个子类，有BitmapShader，ComposeShader，LinearGradient，RadialGradient，SweepGradient。Shader中有一个TileMode，共有3种模式，

CLAMP：当图片小于绘制尺寸时要进行边界拉伸来填充

REPEAT：当图片小于绘制尺寸时重复平铺

MIRROR：当图片小于绘制尺寸时镜像平铺

我们先来看一下BitmapShader，

public class ShaderView extends View {
    private Bitmap mBitmap;
    private Shader mBitmapShader = null;
    private Paint mPaint;

    public ShaderView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.icon);
        mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.REPEAT,
                Shader.TileMode.MIRROR);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setShader(mBitmapShader);
        canvas.drawRect(0, 0, mBitmap.getWidth() * 4, mBitmap.getHeight() * 4,
                mPaint);
    }

}

运行结果为

我们看到左右平铺，上下镜像，在来改一下，只需要把上面的mBitmapShader改一下就可

mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP,
        Shader.TileMode.MIRROR);

看到上下镜像，左右拉伸，再来看一下LinearGradient

public LinearGradient(float x0, float y0, float x1, float y1, int colors[], float positions[],
           TileMode tile)

float x0 ：渐变的x坐标起点
float y0 ：渐变的y坐标起点
float x1 ：渐变的x坐标终点
float y1 ：渐变的y坐标终点
int colors[]：渐变的颜色数组
float positions[]：颜色的相对位置
TileMode tile：上面的3种模式

public class ShaderView extends View {
    private Shader mLinearGradient = null;
    private Paint mPaint;

    public ShaderView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mLinearGradient = new LinearGradient(0, 0, 100, 100, new int[] {
                Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE },
                new float[] { 0, .1F, .8F, .9F }, Shader.TileMode.REPEAT);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setShader(mLinearGradient);
        canvas.drawRect(0, 0, 900, 1000, mPaint);
    }
}

我们看到上面的小数数组是渐变的相对位置，如果positions为空，这均匀分布，修改一下

mLinearGradient = new LinearGradient(0, 0, 100, 100, new int[] {
        Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE }, null,
        Shader.TileMode.REPEAT);

再来修改一下模式，因为最后一个是白色容易和手机屏幕混淆，所以添加了一个绿色

mLinearGradient = new LinearGradient(0, 0, 100, 100,
        new int[] { Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE,
                Color.GREEN }, null, Shader.TileMode.CLAMP);

我们看到最后一个颜色是拉伸，再修改一下

mLinearGradient = new LinearGradient(0, 0, 100, 100,
        new int[] { Color.RED, Color.YELLOW, Color.BLACK, Color.WHITE,
                Color.GREEN }, null, Shader.TileMode.MIRROR);

镜像模式，所以感觉有点对称。在看一下LinearGradient的另一个构造方法，

LinearGradient(float x0, float y0, float x1, float y1, int color0, int color1,
            TileMode tile)

其中color0是颜色的起始点，color1是颜色的终止点，我们就演示一个看看

mLinearGradient = new LinearGradient(0, 0, 100, 100, Color.RED,
        Color.YELLOW, Shader.TileMode.MIRROR);

再来看一下RadialGradient

RadialGradient(float x, float y, float radius,
                          int colors[], float positions[], TileMode tile)

它实现的是环形渐变，
x：渐变的中心x坐标

y：渐变的中心y坐标

radius：渐变的半径

colors：梯度渐变的颜色数组

positions：和LinearGradient类似，用来指定颜色数组的相对位置

public class ShaderView extends View {
    private Shader mRadialGradient = null;
    private Paint mPaint;

    public ShaderView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mRadialGradient = new RadialGradient(200, 400, 100, new int[] {
                Color.YELLOW, Color.RED, Color.BLUE, Color.GREEN }, null,
                Shader.TileMode.REPEAT);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setShader(mRadialGradient);
        canvas.drawRect(0, 0, 900, 1000, mPaint);
    }
}

运行结果如上，再来修改一下

mRadialGradient = new RadialGradient(200, 400, 100, new int[] {
        Color.YELLOW, Color.RED, Color.BLUE, Color.GREEN }, null,
        Shader.TileMode.CLAMP);

再来修改一下

mRadialGradient = new RadialGradient(200, 400, 100, new int[] {
        Color.YELLOW, Color.RED, Color.BLUE, Color.GREEN }, null,
        Shader.TileMode.MIRROR);

还有个构造方法，这里就不在演示

RadialGradient(float x, float y, float radius,
                          int color0, int color1, TileMode tile)

下面看一下SweepGradient

SweepGradient(float cx, float cy,
                         int colors[], float positions[])

cx，cy：扫描中心的x，y坐标

colors：渐变的数组颜色
positions：渐变的相对位置

public class ShaderView extends View {
    private Shader mSweepGradient = null;
    private Paint mPaint;

    public ShaderView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mSweepGradient = new SweepGradient(400, 400, new int[] { Color.YELLOW,
                Color.RED, Color.BLUE, Color.GREEN }, new float[] { 0, .2F,
                .6F, .9F });
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setShader(mSweepGradient);
        canvas.drawCircle(400, 400, 300, mPaint);
    }
}

还有最后一个ComposeShader，这个是组合的Shader

public class ShaderView extends View {
    private Shader mSweepGradient = null;
    private Shader mBitmapShader = null;
    private Shader mComposeShader = null;
    private Paint mPaint;
    private Bitmap mBitmap;

    public ShaderView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.icon);
        mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.REPEAT,
                Shader.TileMode.MIRROR);
        mSweepGradient = new SweepGradient(mBitmap.getWidth() * 2,
                mBitmap.getWidth() * 2, new int[] { Color.YELLOW,
                Color.RED, Color.BLUE, Color.GREEN }, new float[] { 0, .2F,
                .6F, .9F });
        mComposeShader = new ComposeShader(mBitmapShader, mSweepGradient,
                PorterDuff.Mode.DARKEN);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setShader(mComposeShader);
        canvas.drawRect(0, 0, mBitmap.getWidth() * 4, mBitmap.getHeight() * 4,
                mPaint);
    }
}