Jason, I was able to figure out the technique to accomplish this on Thursday before I went out of town. Here are the steps I went through:
* Create a polygon of the lake * Create an osg::Texture2D * Create an osg::Camera o Set to pre-render mode o Set to render in the frame buffer o Set to an orthographic view o Attach the lake polygon to the camera, it seems to me that this is how the geometry is used to populate the newly created texture and that this is referred to and render to texture (RTT or RTT camera) * Apply the newly created texture to the osg::Heightfield I got this working using a simple test application to figure out how to do it. I will add it to the real application today, but I expect it will work out as nicely as it did in the test application. I will let you know how it goes and at that time I will also post the source code for my test application in case anyone else wants to see how this works. Thanks, James From: [email protected] [mailto:[email protected]] On Behalf Of Jason Jerald Sent: Thursday, October 22, 2009 4:41 PM To: 'OpenSceneGraph Users' Subject: Re: [osg-users] z-fighting issue with coplanar polygons James, I am fairly new to OSG so I do not know what specific classes or API calls might be used. In non-OSG terms I think a way to do it would be to: 1. Create your lake geometry placed in relation to the terrain 2. Set up an orthographic camera looking from above, down towards the lake 3. Render the lake to texture 4. Set the uv texture coordinates of your terrain geometry to be equal to x,y (i.e., ignore the height) 5. Apply the lake texture to the terrain geometry I am sure there are more specific steps to think about as you implement it. Let us know if it works or if you think of something better. Jason From: [email protected] [mailto:[email protected]] On Behalf Of James Adkison ARA/CFD Sent: Thursday, October 22, 2009 4:02 AM To: OpenSceneGraph Users Subject: Re: [osg-users] z-fighting issue with coplanar polygons Jason, I'm going to try the 'project textures onto the terrain via UV mapping' solution today. I searching how to do this right now and I'm not sure if I finding relevant information. Can you provide a brief/high-level description of the steps I would need to go through to perform the UV mapping, specifically what classes and/or API calls would be involved, or a tutorial? I found some information on a RTT camera but I'm not sure if this is what I'm looking for. James From: [email protected] [mailto:[email protected]] On Behalf Of Jason Jerald Sent: Wednesday, October 21, 2009 9:09 PM To: 'OpenSceneGraph Users' Subject: Re: [osg-users] z-fighting issue with coplanar polygons I don't see much for performance implications as long as you are not dynamically changing the texture every frame. Jason From: [email protected] [mailto:[email protected]] On Behalf Of James Adkison ARA/CFD Sent: Wednesday, October 21, 2009 11:56 AM To: OpenSceneGraph Users Subject: Re: [osg-users] z-fighting issue with coplanar polygons I'm not very experienced in OSG and I spoke to a co-worker about this approach. The thought is that there might be some performance implications with this approach. This is because there may be multiple surface feature types and they can be enabled/disabled separately. For example, if there are lakes and forests they will be created in the texture but each time one of them is enabled disabled this process has to be repeated and each texture would be approx 1k x 1k. I'm going to give it a shot and see how it performs. Any other thoughts in the mean time? James From: [email protected] [mailto:[email protected]] On Behalf Of Jason Jerald Sent: Wednesday, October 21, 2009 2:16 PM To: 'OpenSceneGraph Users' Subject: Re: [osg-users] z-fighting issue with coplanar polygons Can you project onto a texture and then apply the texture to the geometry? Either in a modeling package or algorithmically by rendering to a texture and then project that texture onto the terrain by planar uv mapping? Jason From: [email protected] [mailto:[email protected]] On Behalf Of James Adkison ARA/CFD Sent: Wednesday, October 21, 2009 10:25 AM To: [email protected] Subject: [osg-users] z-fighting issue with coplanar polygons I'm using an Heightfield to represent my terrain and parts of the terrain could have a surface feature (e.g. a lake). The lake is being drawn as a polygon directly on the surface of the terrain. This, of course, is causing z-fighting to occur between the terrain and the surface feature. I have been trying to solve this problem and have run across a couple solutions but they aren't working for me. I have tried using polygon offset with the GL_OFFSET_POLYGON_FILL mode, which works when zoomed out far but up close z-fighting still occurs. I have tried using a stencil buffer approach but I can't get it to work properly. I can get the surface feature to stencil out the area of terrain but if you rotate the scene so that the surface feature is behind a mountain the stencil is still in place and the feature is rendered through the mountain. Hopefully, I am doing something wrong and someone can explain how I can make this work. James
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