Conference bulova::decw_jan-89_to_nov-90

843.0. "Can't create bitmap on VS3500" by 32423::SCHNEIDER (New lamps for old) Wed May 24 1989 20:10

DECwindows seems to be illuminating a hardware difference between the
VS2000 and the VS3500 and unfortunately the VS3500 comes out looking like
the loser.  I'm hoping someone can comment on the difference in the way
identical code is running on the two workstations.

The code implements zooming of images by a factor of 2.  It starts with
image data, then calls:

XCreateBitmapFromData to create the bitmap,
XCopyPlane to draw to the display.  It is set to zoom.

The Zoom_in function allocates (malloc) another buffer 4 times as big
as the first.  It then duplicates the bits of the image data appropriately
to effect zooming and calls:

XCreateBitmapFromData again.  On a VS2000, this works fine.  On a VS3500
it returns null if the original image isn't "very small".  On a VS2000,
it will even work again, but not on the VS3500.

Is there a hardware reason for this behavior, such as a lack of frame buffer
memory in the 3500?

Dan

XCreateBitmapFromData creates a pixmap of depth 1.  One of the properties of
pixmaps is that there's a limited amount of room for them.  If there isn't
enough room for a pixmap of the size you requested, the pixmap create routine
will return null.

What I'd do instead is use XCreateImage to create an image structure of depth
1 and the appropriate width and height.  Use XYBitmap as the image type.
Just point the data field of the call to the newly-malloc'd buffer.  Then fill
in the zoomed data and do a XCopyPlane specifying the image structure as the
source drawable.

--PSW