Textures and glsl

[Gabba123XXL]

Hello,
I try to use a simple 2D texture with OpenGL 3.1 and by using a shader program. I tried to map on a sphere but it does not work. The Sphere is black.

My steps were.

1) To initialize the texture

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 
glTexImage2D(GL_TEXTURE_2D,
	0,
	GL_RGB,
	128,
	128,
	0,
	GL_RGB,
	GL_UNSIGNED_BYTE,
	pointer);

2) Using a shader program with input attribute for the texels.

// vertex shader
#version 140
 
in vec3 MCVertex;
in vec3 MCNormal;
in vec2 TexCoord0;
...
 
// fragment shader
#version 140
 
in float LightIntensity;
in vec2 TexCoord;
 
out vec4 FragColor;
 
uniform sampler2D SampleTexture;
 
void main()
{
vec3 lightColor = vec3(texture(SampleTexture, TexCoord));
FragColor = vec4(lightColor * LightIntensity, 1.0);
}

3) before I start to render the geometry, I bound the texture

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, _id);

What I have forgotten? Or maybe the order of the commands are wrong?

Thanks in advance!

[Alfonse Reinheart]

Have you tried texturing something simpler first, like a quad? That way, we can rule out whether it's the texture coordinate or the texture itself.

[Gabba123XXL]

Sorry no! But I could try. In OpenGL there are no Quads!

[Alfonse Reinheart]

In OpenGL there are no Quads!

There are no spheres either, but you managed to render one of those, didn't you? Just make a mesh that's a quad instead of a sphere.

[Gabba123XXL]

So far I used simple boxes and generated texels.
I used triangle strip to draw to draw each face of the box. (Quads are depricated.)

[Gabba123XXL]

Sorry... I did not say... the result is the same... it is black...

The texel coordinates are 2D and in the interval [0,1]

[Gabba123XXL]

For example I used for the front face of the box the following vertices and texels:

vertices: (-1,1,1),(-1,-1,1),(1,-1,1),(1,1,1)
texels: (0,1), (0,0), (1,0), (1,1)

The imagedata is rgb and the values are in the range [0,255].

[BionicBytes]

There are two obvious reasons why the output may be black (I'm not saying this is the cause, however).

// fragment shader
#version 140

in float LightIntensity;
in vec2 TexCoord;

out vec4 FragColor;

uniform sampler2D SampleTexture;

void main()
{
vec3 lightColor = vec3(texture(SampleTexture, TexCoord));
FragColor = vec4(lightColor * LightIntensity, 1.0);

First, remove the "LightIntensity" uniform from the shader and just output the texture colour.
eg, FragColor = vec4(lightColor, 1.0);

If that fails too, emit a Red colour eg vec4 (1.0);

Secondly, what have you sent to GL as the uniform value to link the ActiveTexture Unit to the shader's uniform "SampleTexture"?
In other words, have you set up the uniform parameter containing the value 0 and sent it to Opengl using glUniform1i (locationofUniform, 0)? How did you determine the location of the uniform "SampleTexture" - did you query for it, or set it explicitely?

[Gabba123XXL]

Hello,
the LightIntensity is not the problem, for sure... I had not listed the complete code of the vertex shader, there is a LightIntensity as an output variable.

So far... I assume there could be a configuration problem. To the question about "SampleTexture";
I determined the location of the uniform variable "SampleTexture" and then I used "glUniform1iv(texLoc, 1, data)". The data is GLint and has one element.

Ahh... How I have to handle the texels input into attribute "TexCoord0"? I did like with the vertices in a buffer object and with STATIC_DRAW.

[BionicBytes]

LightIntensity is not the problem, for sure... I had not listed the complete code of the vertex shader, there is a LightIntensity as an output variable.

I realize there is an output variable, but I wanted you to eliminate the possibility that it has a value other than 0.
Perhaps emit vec4(LightIntensity) as FragData to test that part of the code.
There is only two possible ways FragData is emitting black
1. The lightIntensity value is 0
2. The Texture is black, or not bound correctly to the shader.

These are the reasons why you need to eliminate each possibility one at a time. If all fails emit a solid red colour to check you actually getting some valid output.