[OpenJDK 2D-Dev] Optimizing pixmap reads and write

[Roman Kennke]

I'm currently implementing a SurfaceData for VxWorks/WindML.
Unfortunately, this graphics library (WindML) doesn't provide me direct
framebuffer access. Therefore I have to perform read and write
operations for rendering operations (at least, for images and likewise
non-primitives). I was thinking that in many cases I can avoid reading
the surface data (i.e. for rendering opaque images) or in some cases
writing (when transferring the surface data to another incompatible
surface). So I implemented my GetRasInfo like this (pseudocode):

malloc(pixels, size);
if (lockFlags & SD_LOCK_READ) {
  readPixelsFromSurface();
}

and the Release function:

if (lockFlags & SD_LOCK_WRITE) {
  writePixelsToSurface();
}
free(pixels);

Unfortunately, this doesn't work well. When rendering translucent or
bitmask images, it does NOT set the the SD_LOCK_READ flag, and therefore
I don't read the surface pixels here, resulting in uninitialized
background for these images. This means, it only renders correctly if I
ignore the SD_LOCK_READ flag and read every time, even if I wouldn't
need to.

My question is, did I get something wrong in my understanding of the
flags? Or is this a bug? Or just something that hasn't been
implemented/optimized yet, because it isn't needed on OpenJDKs primary
platforms? (Although, I would think, that at least for non-DGA surfaces
it would be a nice little optimization at least on X11).

/Roman

-- 
Dipl.-Inform. (FH) Roman Kennke, Software Engineer, http://kennke.org
aicas Allerton Interworks Computer Automated Systems GmbH
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