Drawing to an existing image with X-window

Question

I am using X-window (X11) to render 2D graphics (lines, circles, text...). But rather than drawing to a window, I need to draw to an existing bitmap image. Is there a way to achieve this? If yes, are there restrictions on the bitmap format?

(Notice: I am not trying to render an image to a window.)

Answer 1

Yes, it is possible to draw to an existing bitmap image using X-window (X11). You can do this by using the Xlib library, which provides functions for creating and manipulating windows, as well as for drawing graphics.

To draw to an existing bitmap image, you will need to create a bitmap using the XCreateBitmapFromData function. This function takes a pointer to the data for the bitmap, the width and height of the bitmap, and the depth of the bitmap (in bits per pixel). You can then create a Pixmap object using the XCreatePixmap function and specify the bitmap as the data for the Pixmap.

Once you have created the Pixmap, you can use the standard Xlib functions, such as XDrawLine and XDrawString, to draw graphics to the Pixmap. When you are finished drawing, you can use the XGetImage function to retrieve the data for the Pixmap as an XImage object. You can then use the XGetPixel function to access the pixel data for the XImage and copy it to your own data structure or save it to a file.

As for the bitmap format, Xlib supports a variety of bitmap formats, including 1-bit monochrome, 8-bit pseudocolor, and 24-bit truecolor. You can choose the format that best suits your needs, depending on the requirements of your application.

I hope this helps. Let me know if you have any questions or need further assistance.

Answer 2

• Create a pixmap via: XCreatePixmap
• Create a context via XCreateGC , specifying the pixmap as the drawable.
• Transfer the contents of your existing image via XPutImage (see also Transferring Images between Client and Server ), specifying the pixmap as the drawable and the related context.
• do your renderings via GC Convenience Routines and Graphics Functions
• Get the contents from the pixmap via: XGetImage , see also Transferring Images between Client and Server
• Save the image data.