View Full Version : Text disappears in the off-screen rendering bitmap

05-27-2002, 05:12 PM

Now i am working on off-screen rendering of an OpenGL view (under MS-Windows) so that I can generate an AVI file from the bitmaps.
My approach is similar to the approach in OpenGL SuperBible--a memory device context is first created and binded, then draw the model to a buffer, and save the buffer as bitmap file.

Everything is OK except i cannot show the text on the screen to the generated bitmap. I use the bitmap fonts in above book (2/e, p.245), bascially based on MS-Win 32 API wglUseFontBitmap().

The text display is OK on screen but disappear in the bitmap. i cannot figure out it's the problem of pixel format setting or font library. I use the same rendering function for on-screen and off-screen rendering.

Any idea?

Thank you in advance for your kind reply.

05-27-2002, 10:30 PM
Hi !

I don't have a clue, make sure that you don't have any small difference between the onscreen/offscreen rendering code, check wglUse... for error codes (GetLastError) and also check for errors when you render the text (glGetError).


05-28-2002, 03:25 AM
Thank you for your kind reply.

Now I adopt another approach to capture the screen image for making AVI.
I use ::glReadPixels() to capture image into an image buffer and it works for either text and OpenGL model.

The only problem is if there is an overlapped window over the drawing window, ::glReadPixels() will loss data
in the area of overlap (this is in fact OpenGL-implement dependent, see http://www.frii.com/~martz/oglfaq/rasterization.htm
about the discussion of overlapping problem of ::glReadPixels() )

Any idea to the new problem ?