Android images and text generate new images (Canvas)

1. Requirement description

The project has a requirement to display text on a full-screen image and generate a new image and share it. The image is full-screen and the text is centered.

So I thought of using Canvas to draw directly.

2. Implement the code

    private fun createImg(imageView: ImageView, textView: TextView): Bitmap {
        //返回具有指定宽度和高度的可变位图
        val imageViewBitmap =
            Bitmap.createBitmap(imageView.width, imageView.height, Bitmap.Config.ARGB_8888)
        //使用指定的位图构造一个画布以绘制到其中。位图必须是可变的。
        val imageViewCanvas = Canvas(imageViewBitmap)
        //手动将此视图（及其所有子视图）渲染到给定的Canvas。
        imageView.draw(imageViewCanvas)
        val textViewText = textView.text.toString()
        val textViewTextSize = textView.textSize
        val textViewTextColor = textView.currentTextColor
        val combinedBitmap =
            Bitmap.createBitmap(imageView.width, imageView.height, Bitmap.Config.ARGB_8888)
        val combinedCanvas = Canvas(combinedBitmap)
        //绘制指定的位图，其上角/左角位于（x，y），并由当前矩阵变换。
        combinedCanvas.drawBitmap(imageViewBitmap, 0f, 0f, null)
        val textPaint = TextPaint()
        textPaint.textSize = textViewTextSize
        textPaint.color = textViewTextColor
        val maxWidth = 300f * textView.context.resources.displayMetrics.density
        val textLayout = StaticLayout(
            textViewText,
            textPaint,
            maxWidth.toInt(),
            Layout.Alignment.ALIGN_CENTER,
            1.0f,
            0.0f,
            false
        )
        //文案居中
        val textY = (imageView.height - textLayout.height) / 2
        combinedCanvas.save()
        combinedCanvas.translate((imageView.width - maxWidth) / 2, textY.toFloat())
        //文本绘制到画布中去
        textLayout.draw(combinedCanvas)
        combinedCanvas.restore()
        return combinedBitmap

    }

The specific principles are commented in the code.

2023.11.06

I found that it is not necessary. Just generate a picture from the parent layout. The above method takes a lot of time and is not performance friendly.

 val width = mBinding.allContentCL.width
 val height = mBinding.allContentCL.height
 val bitmap: Bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
 val canvas = Canvas(bitmap)
 mBinding.allContentCL.draw(canvas)

That'll be fine. This bitmap object is the picture generated by this control