How to use glColorTable ?(attach code)

[LLM]

this is my code:

  GLubyte table[256][4];   
	int i;   

	for (i=0;i<256;i++) {      
		table[i][0] = 255;      
		table[i][1] = 0;      
		table[i][2] = 0;      
		table[i][3] = 255;   
	}


	glColorTable(GL_COLOR_TABLE,   
	             GL_RGBA8,
	             256,
		     GL_RGBA,			             GL_UNSIGNED_BYTE,
		     table);

	BYTE texture[8*8];
	for(i=0; i<8*8; i++)
	{
		texture[i] = i;
	} 

glBindTexture(GL_TEXTURE_2D, TextureIndex); 

glTexParameteri(GL_TEXTURE_3D,
GL_TEXTURE_WRAP_S, GL_REPEAT);
  
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_REPEAT); 
 
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, GL_REPEAT);  

glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);  

glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);  

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);  

glTexImage2D(GL_TEXTURE_2D,              
	     0,					
	     GL_COLOR_INDEX8_EXT,           
	     8, 8,		       
	     0,			               
	     GL_COLOR_INDEX,		
	     GL_UNSIGNED_BYTE,	           
	     texture);

Is anyting Wrong? If it was correct, the texture
color should be red. But it’s not red. why?

[Trahern]

Well, In fact I dont know anything about glColorTable as I have never used it however can I ask you why do you post this question in OpenGL Shading language forum? Maybe you would receive better answers in some other forum.

[Relic]

GL_COLOR_INDEX8_EXT requires the extension GL_EXT_paletted_texture.
http://oss.sgi.com/projects/ogl-sample/registry/EXT/paletted_texture.txt
Read the “Support” paragraph carefully.

[mabraham]

Support for GL_EXT_paletted_texture is very limited; it is supported on many NVIDIA chipsets EXCEPT the more recent NV4x. Thus, whether the author of the original post intended or not, the topic is somewhat relevant to this forum because a very simple fragment shader can achieve the same effect as GL_EXT_paletted_texture.

Compile and bind the following program, and set the values of ‘tex’ and ‘palette’ to the numbers of the texture units that hold your indexed texture (2-D) and colour table (1-D), respectively.

uniform sampler2D tex;
uniform sampler1D palette;

void main()
{
gl_FragColor = gl_Color * texture1D( palette, texture2D( tex, gl_TexCoord[ 0 ].st ).r );
}

[Komat]

Originally posted by mabraham:

gl_FragColor = gl_Color * texture1D( palette, texture2D( tex, gl_TexCoord[ 0 ].st ).r );

This will only work if point filtering is enabled for both textures. Unless I am mistaken the paletized textures have the lookup done before any filtering is applied.

[mabraham]

Komat, I’m sure you’re right (incidentally, I only ever used that shader with nearest neighbour filtering enabled for both units).

I guess one would have to do linear interpolation in the shader if that is desired?

[Komat]

I guess one would have to do linear interpolation in the shader if that is desired?
Yes

[LLM]

Thanks all. I’m confusing with the fast volume rendering. I thought using glColorTable should
be more effective.