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//设置着色器

public Shader setShader(Shader shader) {

    // If mShader changes, cached value of native shader aren't valid, since

    // old shader's pointer may be reused by another shader allocation later

    if (mShader != shader) {

        mNativeShader = -1;

        // Release any native references to the old shader content

        nSetShader(mNativePaint, 0);

    }

    // Defer setting the shader natively until getNativeInstance() is called

    mShader = shader;

    return shader;

}

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//设置着色器

paint.shader = BitmapShader(

    bitmap,

    Shader.TileMode.REPEAT,

    Shader.TileMode.REPEAT

)

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//通过反正切得到角度

val first = allPoints[0] //第一个点

val last = allPoints[allPoints.size-1] //最后一个点

val angle = atan2((last.y - first.y).toDouble(),(last.x - first.x).toDouble()) * (180 / Math.PI)

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//旋转+缩放

val dstbmp = Bitmap.createBitmap(

    bmp, 0, 0, bmp.width, bmp.height,

    Matrix().apply {

        // 缩放原图

        postScale(0.5f, 0.5f)

        // 向左旋转45度，参数为正则向右旋转

        postRotate(defaultDegrees, bmp.width / 2f, bmp.height / 2f)

    }, true

)

//设置着色器

paint.shader = BitmapShader(

    dstbmp,

    Shader.TileMode.REPEAT,

    Shader.TileMode.REPEAT

)