windows phone 7 - Write text on image in WP7

Question

I am new to WP7 development and I would like to know how can I write text to image?

First is it possible to do so?

As in GDI we can write text to image as shown below:

Dim pth As New GraphicsPath()
pth.AddString(txtSample.Text, New FontFamily(DropFont.SelectedValue), 0, Integer.Parse(DropFontSize.SelectedValue), New Point(left, top), StringFormat.GenericTypographic)

But in WP7 as I came to know that GDI is not supported.So how Can I do this?

Edit:

I need to select an image from the pictures hub or take a picture using camera and display it in an image control and write some text and save back with a different name.

Any suggestions are most welcome.

Answer 1

You need to get hold of a WriteableBitmap, which can then be manipulated.

This can be done by either adding a UIElement using the Render method or you can manipulate the pixels directly using the Pixels array.

You probably only need to add TextBlock elements to the bitmap, but if you are curious about pixel manipulation here is how that is done:

I have only experience with pixel manipulation. This is not entirely straight forward, but you access pixel (x, y) in the one-dimensional array by translating y * width + x.

The value is in a format called argb32, ie values for alpha-channel (opacity), red, green and blue. Translation between regular Color and argb32 below:

    int ColorToInt(Color c)
    {
        var argb32 = c.A << 24 | c.R << 16 | c.G << 8 | c.B;
        return argb32;
    }

    Color IntToColor(int argb32)
    {
        const int mask = 0x000000FF;
        byte a, r, g, b;
        a = (byte)((argb32 >> 24) & mask);
        r = (byte)((argb32 >> 16) & mask);
        g = (byte)((argb32 >> 8) & mask);
        b = (byte)(argb32 & mask);
        return Color.FromArgb(a, r, g, b);
    }