Re: [PyOpenGL-Users] More difficulties with framebuffers

[Derakon <de...@gm...>]

Er, my mistake: the megatiles render too *big* and I have to scale
them down. Each one renders in the right location (the lower-left
corner of the megatile is the same location in "canvas space" and
"megatile space") but is too large, so other pixels don't map
properly.

-Chris

On Thu, Dec 16, 2010 at 3:15 PM, Derakon <de...@gm...> wrote:
> After my previous success in getting framebuffers to run at all in my
> program, I spent some time getting them to work *properly*...and I'm
> stumped. To recap:
>
> I have a program that uses a camera to take images of the contents of
> a microscope slide. These images are tiled in a mosaic viewer, and the
> user can pan and zoom about in the viewer. Once we get a few thousand
> tiles, the viewer starts bogging down because it has to try to draw
> all of those tiles when the user is zoomed out. I want to modify the
> viewer to pre-render the tiles using framebuffers at a low level of
> detail (packing many tiles onto each pre-rendered megatile); then,
> when the user zooms out, I can switch from rendering each tile
> individually to using the pre-rendered megatiles with no apparent loss
> of detail but a reduction in orders of magnitude of the number of
> textures that OpenGL has to deal with.
>
> Unfortunately, I'm running into some scaling and offsetting issues --
> the megatiles render too small; I need to scale them up by a factor of
> about 1.958 to get them close to the right size. Obviously they should
> be rendering in exactly the right spot, but since I don't know why
> their scale is off I don't know what the proper fix is (the 1.958 is
> just a hack to get them approximately right).
>
> I've uploaded a standalone app that shows off the problem here:
>
> http://derakon.dyndns.org/~chriswei/temp/mosaicapp.tgz
>
> It depends on PyOpenGL, wx, and numpy. I'm using the framebuffers in
> GL.EXT here (old version of OpenGL).
>
> Controls:
> Left-click: prints out location of click in canvas space.
> Alt-left-click: pan
> Shift-alt-left-click: zoom
> Right-click: spawn a new tile
>
> The megatiles include some debugging rendering; every 400 units of
> canvas space, they render some text marking the location, as well as a
> single pixel marking the exact location. If you zoom in on some text
> you should see the point to the left of the left parenthesis; you can
> click on that to compare what the megatile thinks the location is to
> what the canvas knows the location is.
>
> As far as code is concerned, mosaicViewer.GLViewer.OnPaint(),
> mosaicTile.MegaTile.prerenderTiles(), and mosaicTile.MegaTile.render()
> should have everything; the rest is just infrastructure. I've uploaded
> just those three functions to a pastebin here:
>
> http://paste.ubuntu.com/544652/
>
> This is a mishmash of very old code and code I've written myself;
> sorry about the style clash. I'm doing my best to clean things up as I
> come to understand what they are.
>
> If any of you have any ideas about what could be going wrong, I'd love
> to hear them.
>
> -Chris
>