Multitexturing
Author
Hi,
I would like to know if it is possible, using ARB extension, to blend 2 textures "following" a mask being a third texture. For example using texture C (greyscale), Opengl should blend texture A and B, using texture A for black values of C, texture B for white values and 50% of A and B for grey values.
And if it is possible, how to do it ?
Yes, you can do it using ARB_texture_env_combine and ARB_texture_env_crossbar or NV_texture_env_combine4 extension:
With ARB_texture_env_combine you have the following operation GL_INTERPOLATE_ARB available. You can use it the following way:
The Interpolation here is done with:
result_color = color_of_texture_A * greyscale + color_of_texture_B * (1 - greyscale)
For more information see
http://oss.sgi.com/projects/ogl-sample/registry/ARB/texture_env_combine.txt
Hope this will help!
--------------------------------------------------------
"If it looks good, it is good computer graphics"
"If it looks like computer graphics, it is bad computer graphics"
Corrail
corrail@gmx.at
ICQ#59184081
With ARB_texture_env_combine you have the following operation GL_INTERPOLATE_ARB available. You can use it the following way:
glActiveTextureARB(GL_TEXTURE0_ARB);glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, your_texture_A);glActiveTextureARB(GL_TEXTURE1_ARB);glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, your_texture_B);glActiveTextureARB(GL_TEXTURE1_ARB);glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, your_greyscale_texture);glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COMBINE);glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COMBINE, GL_INTERPOLATE_ARB);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_TEXTURE0_ARB);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_TEXTURE1_ARB);glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB_ARB, GL_TEXTURE2_ARB);The Interpolation here is done with:
result_color = color_of_texture_A * greyscale + color_of_texture_B * (1 - greyscale)
For more information see
http://oss.sgi.com/projects/ogl-sample/registry/ARB/texture_env_combine.txt
Hope this will help!
--------------------------------------------------------
"If it looks good, it is good computer graphics"
"If it looks like computer graphics, it is bad computer graphics"
Corrail
corrail@gmx.at
ICQ#59184081
Gheez, Corrail, you got me by the time I used the search feature. Gotta wait for the next forums which have much faster search functions 
Author
Great ! Thx you 2 !!!
I was thinking using this technique for terrain transitions.
What do you think about this ?
I was thinking using this technique for terrain transitions.
What do you think about this ?
That is certainly a bad idea, because that''s exactly what we''re doing for our terrain engine 
In fact, it''s very good as long as you have to blend between two textures (grass<->rock), but when it comes to blend three textures (grass<->rock<->sand<->grass) this isn''t enough.
jm2c
In fact, it''s very good as long as you have to blend between two textures (grass<->rock), but when it comes to blend three textures (grass<->rock<->sand<->grass) this isn''t enough.
jm2c
Heis ppl...
First of All: Corrail, you have a little bug in your code:
But thats ok....
Ok, this is using 3 textures and 3 slots! But I thinck that is possible using the same efect when the slot2 texture is 32 bits! How to do alpha blend between textures?
First of All: Corrail, you have a little bug in your code:
glActiveTextureARB(GL_TEXTURE0_ARB);glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, your_texture_A);glActiveTextureARB(GL_TEXTURE1_ARB);glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, your_texture_B);glActiveTextureARB(GL_TEXTURE1_ARB); => should be GL_TEXTURE2_ARBglEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, your_greyscale_texture); But thats ok....
Ok, this is using 3 textures and 3 slots! But I thinck that is possible using the same efect when the slot2 texture is 32 bits! How to do alpha blend between textures?
Author
My last question, but I think Vincoof has answered : how many textures can be used for multitexturing ?
Should 3 textures be used with rgb chanels of a 4th texture indicating the percentage of the blending ?
r -> % of 1st texture
g -> % of 2nd texture
b -> % of 3rd texture
Should 3 textures be used with rgb chanels of a 4th texture indicating the percentage of the blending ?
r -> % of 1st texture
g -> % of 2nd texture
b -> % of 3rd texture
@vincoof :-P
@Filami
*damn* My codes never will be perfect... :-)
I think you can realize this with only 2 textures using GL_OPERAND_RGB_ARB:
texture_A: 32 Bit RGBA texture where the RGB values represent the 24 Bit texture and the 8 Bit Alpha represents your grayscale texture
texture_B: normal 24 Bit RGB texture
// Texture Stage 0
glActiveTextureARB(GL_TEXTURE0_ARB);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture_A);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COMBINE);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COMBINE, GL_REPLACE_ARB);
// copying the alpha value in the first texture environment
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_TEXTURE0_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERANT0_RGB_ARB, GL_SRC_ALPHA);
// Texture Stage 1
glActiveTextureARB(GL_TEXTURE1_ARB);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture_B);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COMBINE);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COMBINE, GL_INTERPOLATE_ARB);
// Using Alpha value from previous texture environment
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_TEXTURE0_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_TEXTURE1_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB_ARB, GL_PREVIOUS_ARB);
Hope this will work!
--------------------------------------------------------
"If it looks good, it is good computer graphics"
"If it looks like computer graphics, it is bad computer graphics"
Corrail
corrail@gmx.at
ICQ#59184081
[edited by - Corrail on October 23, 2003 10:39:29 AM]
[edited by - Corrail on October 23, 2003 10:40:38 AM]
@Filami
*damn* My codes never will be perfect... :-)
I think you can realize this with only 2 textures using GL_OPERAND_RGB_ARB:
texture_A: 32 Bit RGBA texture where the RGB values represent the 24 Bit texture and the 8 Bit Alpha represents your grayscale texture
texture_B: normal 24 Bit RGB texture
// Texture Stage 0
glActiveTextureARB(GL_TEXTURE0_ARB);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture_A);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COMBINE);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COMBINE, GL_REPLACE_ARB);
// copying the alpha value in the first texture environment
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_TEXTURE0_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERANT0_RGB_ARB, GL_SRC_ALPHA);
// Texture Stage 1
glActiveTextureARB(GL_TEXTURE1_ARB);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture_B);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COMBINE);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COMBINE, GL_INTERPOLATE_ARB);
// Using Alpha value from previous texture environment
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_TEXTURE0_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_TEXTURE1_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB_ARB, GL_PREVIOUS_ARB);
Hope this will work!
--------------------------------------------------------
"If it looks good, it is good computer graphics"
"If it looks like computer graphics, it is bad computer graphics"
Corrail
corrail@gmx.at
ICQ#59184081
[edited by - Corrail on October 23, 2003 10:39:29 AM]
[edited by - Corrail on October 23, 2003 10:40:38 AM]
Thanck you Corrail...It''s pretty damn complicated that expressions...but I thinck I can figure it out! At least I''m hightlighted!
This topic is closed to new replies.
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