drawable的定义如下：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <!--size的比例控制在16：9，对于纯色渐变图，在转换为bitmap时候，内存占用最小，
    但是不影响bitmap的绘制效果。-->
    <size
        android:width="9dp"
        android:height="16dp" />

    <gradient
        android:angle="0"
        android:endColor="#FF192F40"
        android:startColor="#FF320707" />
</shape>

使用代码将其读取并转换为bitmap绘制在ImageView上面

@JvmStatic
    fun drawableToBitmap(drawable: Drawable): Bitmap? {
        if (drawable is BitmapDrawable) {
            return drawable.bitmap
        }
        MLog.warn(TAG, "drawableToBitmap called " +
                "drawable.intrinsicWidth width :${drawable.intrinsicWidth} ," +
                " drawable.intrinsicHeight :${drawable.intrinsicHeight} ")

        val bitmap = Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight,
                Bitmap.Config.ARGB_8888)
        val canvas = Canvas(bitmap)
        drawable.setBounds(0, 0, canvas.width, canvas.height)
        drawable.draw(canvas)
        MLog.warn(TAG, "drawableToBitmap called return " +
                "bitmap width :${bitmap.width} , height :${bitmap.height} " +
                "size : ${bitmap.allocationByteCount / 1024} kb")
        return bitmap
    }

1、

size设置如下：

    <size
        android:width="1125dp"
        android:height="1995dp" />
日志输出：

2020-11-18 20:24:41.607 7225-7225/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called drawable.intrinsicWidth width :3375 , drawable.intrinsicHeight :5985 
2020-11-18 20:24:41.695 7225-7225/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called return bitmap width :3375 , height :5985 size : 78903 kb

78903 kb = 77MB

2、

size设置如下：

    <size
        android:width="720dp"
        android:height="1280dp" />
日志输出：
2020-11-18 20:18:54.169 3864-3864/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called drawable.intrinsicWidth width :2160 , drawable.intrinsicHeight :3840 
2020-11-18 20:18:54.207 3864-3864/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called return bitmap width :2160 , height :3840 size : 31744 kb

 31744 kb = 31MB

3、

size设置如下：

    <size
        android:width="72dp"
        android:height="128dp" />
日志输出：
2020-11-18 20:22:46.559 6132-6132/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called drawable.intrinsicWidth width :216 , drawable.intrinsicHeight :384 
2020-11-18 20:22:46.561 6132-6132/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called return bitmap width :216 , height :384 size : 324 kb

324 kb = 0.31MB

4、

size设置如下：

    <size
        android:width="9dp"
        android:height="16dp" />
日志输出：

2020-11-18 20:27:16.450 8343-8343/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called drawable.intrinsicWidth width :27 , drawable.intrinsicHeight :48 
2020-11-18 20:27:16.451 8343-8343/com.yy.dreamer W/EnhanceDrawableResourceParse: drawableToBitmap called return bitmap width :27 , height :48 size : 5 kb

5kb = 0.0048MB

绘制出来的效果

结论：

在Android xml文件定义的shape Drawable ，可以尽量小的定义size，这样在转换为bitmap时候，可以最大限度的节省内存，但是不影响绘制效果。