C# 奇怪的拉绳行为

我正在用

g.DrawString

在图像上绘制字符串。在我这样做之前，我还在源图像上绘制图像

这就是我的代码的样子：

Bitmap sourceBitmap = Image.FromFile(myBitmap) as Bitmap;
Graphics g = Graphics.FromImage(sourceBitmap);

// drawing some other images on sourceBitmap with g.DrawImage

int positionx = 100;
Font ftemp = cvt.ConvertFromString(myfont) as Font; // predefined font
SizeF mysize = TextRenderer.MeasureText(mytext, ftemp); 
PointF myposition = new PointF(positionx - mysize.Width, positiony) // align right
g.DrawString(mytext, ftemp, new SolidBrush(mycolor), myposition);

这就是我得到的：

如果我现在在前面提到的代码之前添加这两行代码，如下所示：

Bitmap sourceBitmap = Image.FromFile(myBitmap) as Bitmap;
Graphics g = Graphics.FromImage(sourceBitmap);

// drawing some other images on sourceBitmap with g.DrawImage

sourceBitmap = new Bitmap(sourceBitmap); // sourceBitmap is the bitmap (png) I'm drawing on from the very beginning.
g = Graphics.FromImage((Image)sourceBitmap);

int positionx = 100;
Font ftemp = cvt.ConvertFromString(myfont) as Font; // predefined font
SizeF mysize = TextRenderer.MeasureText(mytext, ftemp); 
PointF myposition = new PointF(positionx - mysize.Width, positiony) // align right
g.DrawString(mytext, ftemp, new SolidBrush(mycolor), myposition);

Font f = new Font("Arial", 10.0f, GraphicsUnit.Pixel);

我明白了：

---

除了这两行，我什么也没改。所以我的问题是这是怎么发生的

检查源PNG的DPI。从文件加载位图时，它将加载文件中记录的DPI。基于内存中已存在的另一位图创建新位图时，会将其重置为屏幕DPI。它不携带原始的DPI设置

您可以指定用GraphicsUnit表示字体。像素如下：

Bitmap sourceBitmap = Image.FromFile(myBitmap) as Bitmap;
Graphics g = Graphics.FromImage(sourceBitmap);

// drawing some other images on sourceBitmap with g.DrawImage

sourceBitmap = new Bitmap(sourceBitmap); // sourceBitmap is the bitmap (png) I'm drawing on from the very beginning.
g = Graphics.FromImage((Image)sourceBitmap);

int positionx = 100;
Font ftemp = cvt.ConvertFromString(myfont) as Font; // predefined font
SizeF mysize = TextRenderer.MeasureText(mytext, ftemp); 
PointF myposition = new PointF(positionx - mysize.Width, positiony) // align right
g.DrawString(mytext, ftemp, new SolidBrush(mycolor), myposition);

Font f = new Font("Arial", 10.0f, GraphicsUnit.Pixel);

---

否则，字体将随图像的DPI进行缩放。图像DPI仅用于定义图像的实际单位（英寸）大小。缩放文本时，您可能希望也可能不希望使用该信息，这取决于您是否缩放文本以进行打印。

检查源PNG的DPI。从文件加载位图时，它将加载文件中记录的DPI。基于内存中已存在的另一位图创建新位图时，会将其重置为屏幕DPI。它不携带原始的DPI设置

您可以指定用GraphicsUnit表示字体。像素如下：

Bitmap sourceBitmap = Image.FromFile(myBitmap) as Bitmap;
Graphics g = Graphics.FromImage(sourceBitmap);

// drawing some other images on sourceBitmap with g.DrawImage

sourceBitmap = new Bitmap(sourceBitmap); // sourceBitmap is the bitmap (png) I'm drawing on from the very beginning.
g = Graphics.FromImage((Image)sourceBitmap);

int positionx = 100;
Font ftemp = cvt.ConvertFromString(myfont) as Font; // predefined font
SizeF mysize = TextRenderer.MeasureText(mytext, ftemp); 
PointF myposition = new PointF(positionx - mysize.Width, positiony) // align right
g.DrawString(mytext, ftemp, new SolidBrush(mycolor), myposition);

Font f = new Font("Arial", 10.0f, GraphicsUnit.Pixel);

---

否则，字体将随图像的DPI进行缩放。图像DPI仅用于定义图像的实际单位（英寸）大小。缩放文本时，您可能希望也可能不希望使用该信息，这取决于您是否缩放文本以进行打印。

那么，第一个版本中的

g

来自何方？第一个版本中的

g

来自何方？