# OpenGL Terrain Realism

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I have created a terrain program which basically uses various terrain techniques such as Hill Algorithm and Fault Formation and I wish to texture the terrain more realistically. For Example: Current Screenshot http://img441.imageshack.us/my.php?image=screenshot2je3.jpg I want to be able to create a realistic beach, water and underwater terrain effects. I tried to do this artistically by using gradient filtering through Photoshop between two tiles however this didn't work too well with various artefacts being present. Is there a way to use a Color Key or combine textures to produce an effect such as http://shiny3d.host.sk/images/galeria/0.2/screen2.jpg I don't have pixel shader support until I get my GC, but I have combiner and extension support for multitexturing from what i can see. I've looked everywhere for ideas and tried using slopes to determine which texture to fade or use but I've come to a stump at the moment, so am trying to get billboarding working for various objects. Or any example code/tutorial of how to implement such a system in OpenGL Any help is greatly appreciated Neutrinohunter

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An article on Delphi3D.net shows one way to multi-texture a terrain using texture combiners and vertex colours. Naturally the code is Delphi, but it should at least give some pointers on how you may want to go about it in your own renderer.

Regards,
ViLiO

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I just replied to a similar post.

You may also find this document (PDF) on our old terrain engine usefull.

Regards,

Serge van keulen

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Linear Interpolation between Three Textures? I'm running a GeForce 4 MX, I'm not sure that could be done with something like this. Isn't there a way to say determine a percentage of each texture say using vertex heights?

For Example:

Say the min height was 0.0 and the max height was 15. From 0-5 would be water, 4-9 would be beach, 8-12 would be grass and 11-15 would be rock or something like that

Thanks
Jamie

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I guess you read the PDF document?
Blending three texels per pixel on a GForce MX (actually a TNT2) is possible. In fact, I was using a TNT2 when I was developing the technique. And it was fast enough too.

Sure you can just select what texture to use using elevation values. However, at least two issues rise:

1. Since you don't want to (or can't) use shaders, you can only switch textures at a vertex. This means that texture transitions will follow triangle edges. Unless you use a very high vertex density (which you probably shouldn't), this will not look good (jaggy).

2. To make it look natural, you probably want to make a nice blended transition when switching textures. This means blending at least two textures for some overlapping area. If you use blending factors per vertex, you will need several triangles to make any kind of gradual transition. And again, triangle density determines quality.

(Unless you use only use elevation for texture selection (only vertical transitions), you will need more transition possibilities. The moment more then 2 materials (for example; grass, rock and sand) meet at one vertex, you need more blending possibilities.)

To get rid of the vertex density dependency and to have more freedom in applying textures and making transitions I developed the technique described in the PDF.

My first attempt was based on vertex based blend-factors. And it is a good place to start.
I would recommend you to try the vertex approach too. Maybe after that you may feel up to the challenge to try the blend-factor per texel approach. (The blend map could be generated automatically based on anything you want including elevation)

For the blend-factors per vertex approach, the Delphi3D article as suggested by "ViLiO" is very good.

Regards,

Serge van Keulen

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Hi,
at first you can take a look at UT2003/4 map editor to see how it renders terrains and make use of issue of layers.
Layer is a representative material and a cover factor which specifies where the layer material is visible(an alpha map, simply). UT2003 paints layers in multiple passes but it doesn't use any LOD alghoritm so it can afford for drawing only these layers that are actually visible which speeds drawing up. I've been working on terrain rendering engine using LOD(rottgers alg) and layers for a while and i can say its best to render using shaders. Havying 16 texture images you can draw up to 12 layers in a single pass, of course with smooth transitions:
12 units - materials
3 units - cover maps(textures with alpha factor for layers encoded in rgba components).
Believe me, looks great, works great and fast :)
Screen:
http://www.fotosik.pl/pokaz_obrazek/2133e101f38672ff.html

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Well I only have two texture units available to me, so I was thinking I would require a multipass approach.

Yes, I reviewed the PDF and the code from Delphi.Net. Having not studied Pascal it took me a while to find out what was going on where but I figured that the author was using a bmp to determine alpha values I think.

I'm guessing it would be a good idea to move to vertex arrays and VBOs at this point?

How would I go about making a rendering solution based on only two texture units? And or make a dynamic blend map for my terrain (my terrain is created using a parabolic hill technique).

if (MaxTexUnits > 3){//*** Unit 3glActiveTexture(GL_TEXTURE3);glEnable(GL_TEXTURE_2D);glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_PRIMARY_COLOR);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 1);//*** Unit 2glActiveTexture(GL_TEXTURE2);glEnable(GL_TEXTURE_2D);glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE2);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE2_RGB, GL_TEXTURE3);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB, GL_SRC_ALPHA);glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 1);//*** Unit 1glActiveTexture(GL_TEXTURE1);glEnable(GL_TEXTURE_2D);glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE1);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE2_RGB, GL_TEXTURE3);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB, GL_SRC_COLOR);glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 1);//*** Unit0glActiveTexture(GL_TEXTURE0);glEnable(GL_TEXTURE_2D); //Then Draw Stuff}else {            pglActiveTexture(GL_TEXTURE0_ARB);            glEnable(GL_TEXTURE_2D);                        glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);            glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE);            glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS);            glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);            glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_PRIMARY_COLOR);            glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);            glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 1);            pglActiveTexture(GL_TEXTURE1_ARB);            glEnable(GL_TEXTURE_2D);            //glBindTexture(GL_TEXTURE_2D, ids[1]);            glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);            glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE);            glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS);            glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);            glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE1);            glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);            glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE2_RGB, GL_TEXTURE0);            glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB, GL_SRC_COLOR);            glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 1);           //draw stuff          //bind new texture          pglActiveTexture(GL_TEXTURE1_ARB);          glEnable(GL_TEXTURE_2D);          glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);          glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE);          glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS);          glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);          glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE1);          glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE2_RGB, GL_TEXTURE3);glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB, GL_SRC_COLOR);glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 1);}

Something like that?

Jamie

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Mmm, ok I am thinking this is a bit far out of league atm. I can't seem to figure out what exactly is being done in either bit of code or your pdf.

My Vertex Density atm is a 1x1 quad in World Space but I could almost guarantee that the density of the example shown by ViLiO is much greater, yet that only runs at 13fps for me, so I don't think it would work at such a large scale example as mine.

Are there any other methods to consider?

Jamie

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I havn't read too much of the above posts.

My suggestions, 3D textures (or some above mentioned blending) + LIGHTING!

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I've only glossed over the other replies, but maybe you'll find this helpful. This technique can work on a geforce1 (though it will be slow), and the texturing looks very high res. That link uses Direct3D, but the ideas are applicable to OpenGL.

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