Multitexture - Environment plus stencil texture

OpenGL OpenGL: Basic Coding
1

I need to apply a spherical mapped environment texture to an object followed by another texture that uses alpha blended texture. The result is an a shiny object apart from areas that were excluded by the second texture.

Now the problem is down to the fact that I can’t afford the performance hit caused by the multipass rendering and wondered how / whether I could use achieve the same result in a singlepass ?

I need to avoid many of the more advanced features now supported by cards - let’s say that it’s got to work on something like an NVidia Geforce 2.

Many thanks,

Andrew

2

Why not multitexture instead of multipass ?
search “Official Multitexture Extension” in following page :
http://www.opengl.org/resources/features/OGLextensions/

3

Thanks for the reply … I think that I am on my way now … lots to learn again, as I’ve no idea what half of this does yet ! Some good pointers to some docs would be good.

OK … I’ve found some code that I’ve modified and it works … but … issues of card compatibility are of concern … for example is GL_COMBINE4_NV which obviously originates from NVidia - is it available on most cards - ATI ?

Thanks

// Initialization
// Already tested for extensions …
glGenTextures(1, fTextureName1);
glActiveTextureARB(GL_TEXTURE0_ARB);
LoadBitmapFile(‘LogoMetal.bmp’, fTextureName1, GL_FALSE);

// The ‘true’ flag creates a texture with an alpha channel.
glGenTextures(1, fTextureName2);
glActiveTextureARB(GL_TEXTURE1_ARB);
LoadBitmapFile(‘Tile.bmp’, fTextureName2, GL_TRUE);

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE4_NV);
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB_EXT, GL_ADD);

glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_EXT, GL_PREVIOUS_EXT);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB_EXT, GL_SRC_COLOR);

glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB_EXT, GL_ZERO);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB_EXT, GL_ONE_MINUS_SRC_COLOR);

glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB_EXT, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB_EXT, GL_SRC_COLOR);

glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE3_RGB_EXT, GL_TEXTURE0_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND3_RGB_EXT, GL_SRC_ALPHA);

// Draw routine …
glActiveTextureARB(GL_TEXTURE1_ARB);
glEnable(GL_TEXTURE_2D);
glActiveTextureARB(GL_TEXTURE0_ARB);
glBindTexture(GL_TEXTURE_2D, fTextureName2);
glActiveTextureARB(GL_TEXTURE1_ARB);
glBindTexture(GL_TEXTURE_2D, fTextureName1);

glPushAttrib(GL_ENABLE_BIT);
glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP);
glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP);
glEnable(GL_TEXTURE_GEN_S);
glEnable(GL_TEXTURE_GEN_T);
glCallList(fGLList);
glPopAttrib;

glActiveTextureARB(GL_TEXTURE1_ARB);
glDisable(GL_TEXTURE_2D)

4

Yes it is NV only, i think the following extension looks more suitable :
http://oss.sgi.com/projects/ogl-sample/registry/ARB/texture_env_combine.txt
and is widely supported from geforce2/radeon7000 hardware :
http://delphi3d.net/hardware/extsupport.php?extension=GL_ARB_texture_env_combine

5

Many thanks for your help …

Andrew