Re: [gl4java-usergroup] Follow-up texture-mapping questions

[Kenneth B. R. <kbr...@al...>]

> From: Mark Montana <pat...@lm...>
> 
> (Q1) I am loading fairly large textures of satellite imagery of
> the Earth. Two of them are 1024x1024 (powers of two) in RGB
> format. These two images load and render just fine. The third
> texture is 2048x1024 (also powers of two) in RGB format. This
> one gets a GL error during my call to glTexImage2d(), and the
> error is "invalid value." I determined that value that makes it
> unhappy is the image width (2048).  If I lie to OpenGL and tell
> it that the width is only1024, the image loads and renders
> without an error (of course it looks screwed up, but I expect
> that since I lied about the true width). Any insight on why it
> cannot handle the 2048 width?

The 1024 width call is not just going to look wrong, it's also
going to use half the texture memory.

> I know that it is not related to the hardware, graphics card,
> graphics card driver, or machine configuration. I know this
> because our application is half GL4Java and half Java3D. The
> Java3D display loads the same exact textures and renders them
> with no problem. I also do not think it is related to the total
> amount of texture memory available; again because Java3D has no
> problem, and I can disable the Java3D display and disable to
> two 1024x1024 textures in the GL4Java display...and the GL4Java
> display still gets the same error on the 2048x1024 texture.

It sounds to me like you're running low on texture memory.
Splitting the texture into two sub-textures will allow the OpenGL
implementation to swap out one texture while rendering the
other. This won't be able to be done with the one large texture.

> Could it have something to do with the OpenGL context or
> configuration that I am requesting???
> Could it be related to the fact that I am using display-lists???

Don't know.

> (Q2) My textures are rendered in a 2D display, no lighting, no
> normals, no materials. The polygons underneath the texture are
> white. The texture comes out way to dark with GL_DECAL or
> GL_REPLACE. When I try GL_MODULATE or GL_BLEND, it gets really
> washed-out. We had this same exact problem in the Java3D
> display with these textures. We fixed it there by using some
> texture-environment settings that are unique to Java3D. (In
> other words, the Java3D people used some of the more advanced
> features of blending functions and/or filters to create a new
> blending equation that works well.) I was considering a
> decompile of the Java3D code to see how they did it, but I
> thought I would as for some advice on this problem first.

Altering the whiteness of the polygons should allow you to
control how washed-out the texture appears with GL_MODULATE. I've
found it was necessary to disable lighting while rendering
decal-style textures. See the sources to the Grand Canyon demo at
http://java.sun.com/products/jfc/tsc/articles/jcanyon/ , in
particular Sky.java (which turns on lighting only when rendering
the sky hemisphere) and MultiResTile.java, which sets up the
texture environment for the terrain.

-Ken