From QB64.org wiki
- _SOURCE handle&
- The handle is a LONG integer value from the _SOURCE function or a handle created by _NEWIMAGE.
- If the handle is designated as 0, it refers to the current SCREEN image.
- A source image can only supply information to a program. POINT and GET might require a source other than the one currently active.
- Explanation: Create a new image with handle 'a', then use _DEST to define the image to draw on. Draw a pixel then set the source to 'a' and use POINT to show what color is in that position. White (15) and is the color set with PSET. Use _DEST 0 for the screen to display the results.
See the examples in: