Re: [PyOpenGL-Users] More difficulties with framebuffers

[Christopher B. <Chr...@no...>]

Sorry for the slow response -- lots going on here.

Derakon wrote:
> I took a look at your code, but it looks like you're doing this all
> "manually" while I'm trying to leverage OpenGL to do the work for me.

I'm not sure that's true. We do break the process down into two stages:

1) generate the tiles at different zoom levels.

2) render them.

1) is done without using OpenGL at all. Perhaps we should have used it, 
  but we've had in mind being able to use different rendering back-ends, 
for instance for PDF generation or printing, so we wanted to b able to 
have the tiles without any OpenGL.

We've also separated the generation of tiles from rendering because we 
may well want to use tiles that are pre-generated, such as from 
OpenStreetMap and the like.

2) The rendering stage is using OpenGL as much as I know how. For a 
given zoom level, we need to determine which scale of tiles to use, 
which specific tiles to use, how they are scaled to OpenGL coords, then 
pass them in. Isn't that what you are doing?


> The basic flow of my code is:
> 
> Main render function:
>   if zoomed far out:
>     render each megatile in view
>   else:
>     render each individual tile in view

That's pretty much what we do, except we have many levels of zoom -- it 
looks like you have only two.

> Add new tile function:
>   find megatile(s) that this tile overlaps
>     render tile to megatiles

ahh -- that is a bit different. rather than renderintg each tile each 
time, you render to a megatile, then just render that. What is the 
advantage of that, why not just render the tiles directly? I suppose 
that does take a Python loop, but I don't think that's very slow in this 
case. Our tiles are 256X256, so for a 1000X1000 screen, that's 16 tiles 
--not many at all.

> Something is going wrong in the "render to megatile" code, since when
> I render the megatile later in the main render function, its scale is
> off. But I can't figure out why.

It is a real pain to get the math right for that kind of thing. All I 
can suggest is some really tedious debugging/print statements, and check 
the math at each  step.

good luck,

-Chris



> -Chris
> 
> On Thu, Dec 16, 2010 at 4:31 PM, Christopher Barker
> <Chr...@no...> wrote:
>> On 12/16/10 4:26 PM, Christopher Barker wrote:
>>> Sorry, no time to try to take a look at your code, but we have a similar
>>> system in maproom, for rending tiles at different zoom levels, maybe it
>>> will help you figure out your issue:
>>>
>>> https://bitbucket.org/dhelfman/maproom/wiki/Home
>> I think this is the relevant file:
>>
>> https://bitbucket.org/dhelfman/maproom/src/668ea464624e/maproomlib/plugin/Tile_set_layer.py


-- 
Christopher Barker, Ph.D.
Oceanographer

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