图一到图四是我反推的一个过程，因为要去旋转水印画布，所以需要找到那个最大的边，也就是我们屏幕对角线的长度，以这个长度为边长画一个正方形，就是我们想要的旋转画布边长。
算出边长我们画出图一中红色的正方形，向上平移到黑色正方形的位置，无论画布如何旋转，我们蓝色的屏幕都不会留白。
代码：
package com.material.myview
import android.content.Context
import android.graphics.*
import android.graphics.drawable.Drawable
import kotlin.math.sqrt
/**
* @author Che
* @description: 水印控件
* @date :2021/11/10 17:31
*/
class WaterMarkView(
private val context: Context,
private val text: String,
private val angle: Int,
private val fontSize: Int
) : Drawable() {
private var mPaint: Paint = Paint()
private var bitmapWaterMark: Bitmap? =null
private var markWaterCanvas: Canvas? =null
//文字得宽高
private var textH: Float =0F
private var textW: Float =0F
//图片得宽高
private var bitmapW: Float =0F
private var bitmapH: Float =0F
//水印得位置
private var watermarkW: Int =0
private var watermarkH: Int =0
init {
mPaint.style = Paint.Style.FILL_AND_STROKE
mPaint.color = Color.parseColor("#AB78B1")
}
override fun draw(canvas: Canvas) {
mPaint.textSize = sp2px(context, fontSize.toFloat()).toFloat()
//文字宽高
textW =mPaint.measureText(text)
textH =mPaint.fontMetrics.bottom -mPaint.fontMetrics.top
//底层图片宽高
bitmapW =bounds.width().toFloat()
bitmapH =bounds.height().toFloat()
//算出水印的宽高
val sqr =sqrt((bitmapW *bitmapW +bitmapH *bitmapH))
watermarkW = sqr.toInt()
watermarkH = sqr.toInt()
//水印画布
bitmapWaterMark = Bitmap.createBitmap(
watermarkW, watermarkH, Bitmap.Config.ARGB_8888
)
markWaterCanvas = Canvas(bitmapWaterMark!!)
var ss =sqrt(2.toFloat()) /2
markWaterCanvas?.translate(-((sqrt(2 *watermarkH *watermarkH.toFloat())) /2 -watermarkH /2)*ss,
-((sqrt(2 *watermarkH *watermarkH.toFloat())) /2 -watermarkH /2)*ss)
//旋转
markWaterCanvas?.rotate(
angle.toFloat(), (watermarkW /2).toFloat(),
(watermarkW /2).toFloat()
)
//根据画布大小添加水印文字
val textLength =textW +80
val textColumn =textH +120
val row: Int = (watermarkW / textLength).toInt()
val column: Int = (watermarkH / textColumn).toInt()
for (iin 0..row +1) {
var count =0
for (jin 0..column +2) {
count++
if (count %2 ==0) {
markWaterCanvas?.drawText(
text,
textLength * i,
textColumn * j,
mPaint,
)
}else {
//偶数行进行错开
markWaterCanvas?.drawText(
text,
textLength * i + (textW /2),
textColumn * j,
mPaint,
)
}
}
}
if (bitmapWaterMark !=null) {
canvas?.drawBitmap(bitmapWaterMark!!, 0f, 0f, mPaint)
}
}
override fun setAlpha(alpha: Int) {
}
override fun setColorFilter(colorFilter: ColorFilter?) {
}
override fun getOpacity(): Int {
return PixelFormat.UNKNOWN
}
companion object {
fun sp2px(context: Context, spValue: Float): Int {
val fontScale = context.resources.displayMetrics.scaledDensity
return (spValue * fontScale +0.5f).toInt()
}
}
}