Cube's edges in OpenGL - c++

Question

I have drawn a cube in OpenGl to use it as skybox.
I'm using a single texture image and I use the UV coordinates to locate the 6 faces in the right positions.
I send the texture with the following code:
//------------------------------------Luminance--------------------------------------------------------------
glPixelStorei(GL_UNPACK_ROW_LENGTH, m_width);
glBindTexture(GL_TEXTURE_2D, texturePointer[0]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, m_width, m_height, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, m_uYdata);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
//--------------------------------------U component------------------------------------------------------------
glPixelStorei(GL_UNPACK_ROW_LENGTH, m_uvWidth);
glBindTexture(GL_TEXTURE_2D, texturePointer[1]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, m_uvWidth, m_uvHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, m_uUdata);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
//------------------------------------- V component-------------------------------------------------------------
glBindTexture(GL_TEXTURE_2D, texturePointer[2]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, m_uvWidth, m_uvHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, m_uVdata);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
I can't remove the white edges between the faces of the cube, see the picture below:
GL_NEAREST remove the problem but the quality of the image is lower,
how can I use GL_LINEAR and remove this effect?
Edit:
The cube is created using the following Tutorial:
Model loading
Considering that the texture is made by six faces stitched in columns.
The actual Blender object is:
# Blender v2.77 (sub 0) OBJ File: 'demo_cube.blend'
# www.blender.org
o Cube
v 1.000000 -1.000000 -1.000000
v 1.0000000 -1.000000 1.000000
v -1.000000 -1.000000 1.000000
v -1.000000 -1.000000 -1.000000
v 1.000000 1.000000 -1.000000
v 1.0000000 1.000000 1.000000
v -1.000000 1.000000 1.000000
v -1.000000 1.000000 -1.000000
vt 0.833333333 0.0000
vt 0.666666666 1.0000
vt 0.833333333 1.0000
vt 0.833333333 0.0000
vt 1.000000000 1.0000
vt 1.000000000 0.0000
vt 0.333333333 1.0000
vt 0.500000000 0.0000
vt 0.333333333 0.0000
vt 0.500000000 1.0000
vt 0.666666666 0.0000
vt 0.500000000 0.0000
vt 0.000000000 0.0000
vt 0.166666666 1.0000
vt 0.166666666 0.0000
vt 0.333333333 0.0000
vt 0.166666666 1.0000
vt 0.333333333 1.0000
vt 0.666666666 0.0000
vt 0.833333333 1.0000
vt 0.500000000 1.0000
vt 0.666666666 1.0000
vt 0.000000000 1.0000
vt 0.166666666 0.0000
s off
f 2/1 4/2 1/3
f 8/4 6/5 5/6
f 5/7 2/8 1/9
f 6/10 3/11 2/12
f 3/13 8/14 4/15
f 1/16 8/17 5/18
f 2/1 3/19 4/2
f 8/4 7/20 6/5
f 5/7 6/21 2/8
f 6/10 7/22 3/11
f 3/13 7/23 8/14
f 1/16 4/24 8/17
//44 and 47
The fragment shader is:
#version 330 core
in vec2 oTexCoord;
uniform sampler2D yChannel;
uniform sampler2D uChannel;
uniform sampler2D vChannel;
out vec4 color;
const vec3 offset = vec3(0.0625, 0.5, 0.5);
const mat3 coef = mat3(
1.164, 0.0, 1.793,
1.164, -0.213, -0.533,
1.164, 2.112, 0.0
);
void main()
{
vec2 nTexCoord = vec2(oTexCoord.x, 1.0 - oTexCoord.y);
vec4 Tcolor = vec4(1.0);
if(oTexCoord.y <1 && oTexCoord.y > 0.0) {
if(oTexCoord.x < 1 && oTexCoord.x > 0.0) {
vec3 yuv = vec3(
texture(yChannel, nTexCoord).r,
texture(uChannel, nTexCoord).r,
texture(vChannel, nTexCoord).r
) - offset;
vec3 rgb = yuv * coef;
Tcolor = vec4(rgb, 1.0);
}
}
color = Tcolor;
}

Answer 1

I think you want to use cubemaps and GL_ARB_seamless_cube_map:
Although it is unlikely that the generated ( s t ) coordinate lies significantly outside the determined cube map face, it is often the case that the locations of the individual elements required during a linear sampling do not lie within the determined face, and their coordinates will therefore be modified by the selected clamping and wrapping rules. This often has the effect of producing seams or other discontinuities in the sampled texture.
This extension allows implementations to take samples from adjacent cube map faces, providing the ability to create seamless cube maps.
(emph. mine).
To use it, first check that you indeed have that extension (this depends on your platform and on which toolkit is eventually helping you into accessing OpenGL), then just write
glEnable(GL_TEXTURE_CUBE_MAP_SEAMLESS);
to enable it (globally).