Display cube in OpenGL

Question

I am trying to display a cube with 6 bitmaps in order to achieve the skybox effect. My problem is that one texture is displayed on each face of the cube. I checked gDEBugger, in cubic texture memory I only have one image (since I am trying to load six images).

Code coded texture:

bool Texture::LoadCubicTexture(vector<string> filenameTable) { glGenTextures(1,&texID); glBindTexture(GL_TEXTURE_CUBE_MAP,texID); glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_MAG_FILTER,GL_LINEAR); glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_MIN_FILTER,GL_LINEAR); glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_WRAP_T,GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_WRAP_R,GL_CLAMP_TO_EDGE); int i = 0; vector<string>::iterator vsit; // There is always six filenames for(vsit=filenameTable.begin();vsit!=filenameTable.end();++vsit) { string filename = *vsit; BMPData* bmpData = LoadTextureBMPData_custom(filename); glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X+i,0,GL_RGB,bmpData->width,bmpData->height,0,GL_BGR,GL_UNSIGNED_BYTE,&(bmpData->data[0])); i++; delete daneObrazu; } glGenerateMipmap(GL_TEXTURE_CUBE_MAP); return true; } 

VS:

 #version 330 core in vec3 vVertexPos; in vec3 vertexUV; out vec3 vCoords; uniform mat4 MVP; void main() { vCoords = normalize(vertexUV); gl_Position = MVP * vec4(vVertexPos,1.0); } 

FS:

 #version 330 core in vec3 vCoords; uniform samplerCube cube; out vec4 vFragColor; void main() { vFragColor = texture(cube, vCoords); } 

Obj file:

 # Blender v2.62 (sub 0) OBJ File: 'skybox.blend' # www.blender.org mtllib skybox.mtl o Cube v 10.487665 -10.487666 -10.487665 v 10.487665 -10.487666 10.487665 v -10.487667 -10.487666 10.487664 v -10.487662 -10.487666 -10.487670 v 10.487671 10.487666 -10.487660 v 10.487659 10.487666 10.487673 v -10.487670 10.487666 10.487662 v -10.487665 10.487666 -10.487666 vt 0.990480 0.014286 vt 0.993478 0.991259 vt 0.016505 0.994256 vt 0.013507 0.017283 vt 0.988479 0.008111 vt 0.985457 0.993412 vt 0.000157 0.990390 vt 0.003179 0.005089 vt 0.002693 1.001082 vt -0.000347 0.009939 vt 0.990796 0.006898 vt 0.993837 0.998041 vt 0.004581 0.999210 vt 0.001535 0.006444 vt 0.994302 0.003398 vt 0.997347 0.996165 vt 0.004172 -0.000587 vt 0.996320 -0.003630 vt 0.999364 0.988517 vt 0.007216 0.991561 vt 0.000632 0.000140 vt 0.983846 -0.002921 vt 0.986862 0.995017 vt 0.003648 0.998078 vn 0.000000 -1.000000 0.000000 vn 0.000000 1.000000 0.000000 vn 1.000000 0.000000 0.000000 vn -0.000000 -0.000000 1.000000 vn -1.000000 -0.000000 -0.000000 vn 0.000000 0.000000 -1.000000 usemtl Skybox s off f 1/1/1 2/2/1 3/3/1 f 1/1/1 3/3/1 4/4/1 f 5/5/2 8/6/2 7/7/2 f 5/5/2 7/7/2 6/8/2 f 1/9/3 5/10/3 6/11/3 f 1/9/3 6/11/3 2/12/3 f 2/13/4 6/14/4 7/15/4 f 2/13/4 7/15/4 3/16/4 f 3/17/5 7/18/5 8/19/5 f 3/17/5 8/19/5 4/20/5 f 5/21/6 1/22/6 4/23/6 f 5/21/6 4/23/6 8/24/6 

My questions:

• Are the methods that I use in this code look normal?
• How do textures compare for a cube (in GL_TEXTURE_CUBE_MAP texture) when there are only 2 UVs? (I mean overall.)
• Is it possible to use automatic UV generation in this situation (I have to make a lot of changes in the shader)?
• Can anyone suggest me where I can find the problem? (with some probability; buffers, shaders, grids, just a suggestion)?

[Edit]: I tried hard-coded vertices and uv in a separate source file, and I have the same problem - one texture for all faces of the cube. Hard-coded data seems correct:

 #include "TestCube.h" vector<vec3> GetTestCubeVertices() { vector<vec3> vrtx; const float xd = 1.0f; const float yd = 1.0f; const float zd = 1.0f; const float testCubeVertices[] = { -xd, -yd, zd, xd, -yd, zd, -xd, yd, zd, // ABE xd, -yd, zd, -xd, yd, zd, xd, yd, zd, // BEF xd, -yd, zd, xd, -yd, -zd, xd, yd, zd, // BCF xd, -yd, -zd, xd, yd, zd, xd, yd, -zd, // CFG xd, -yd, -zd, -xd, -yd, -zd, xd, yd, -zd, // CDG -xd, -yd, -zd, xd, yd, -zd, -xd, yd, -zd, // DGH -xd, -yd, -zd, -xd, -yd, zd, -xd, yd, -zd, // DAH -xd, -yd, zd, -xd, yd, -zd, -xd, yd, zd, // AHE -xd, yd, zd, xd, yd, zd, -xd, yd, -zd, // EFH xd, yd, zd, -xd, yd, -zd, xd, yd, -zd, // FHG xd, -yd, zd, -xd, -yd, zd, xd, -yd, -zd, // BAC -xd, -yd, zd, xd, -yd, -zd, -xd, -yd, -zd, // ACD }; for(int i=0;i<108;i=i+3) vrtx.push_back(vec3(testCubeVertices[i],testCubeVertices[i+1],testCubeVertices[i+2])); return vrtx; } vector<vec2> GetTestCubeUVs() { vector<vec2> uv; const float testCubeUV[] = { 0,0, 1,0, 0,1, // ABE 1,0, 0,1, 1,1, // BEF 0,0, 1,0, 0,1, // BCF 1,0, 0,1, 1,1, // CFG 0,0, 1,0, 0,1, // CDG 1,0, 0,1, 1,1, // DGH 0,0, 1,0, 0,1, // DAH 1,0, 0,1, 1,1, // AHE 0,0, 1,0, 0,1, // EFH 1,0, 0,1, 1,1, // FHG 0,0, 1,0, 0,1, // BAC 1,0, 0,1, 1,1, // ACD }; for(int i=0;i<72;i=i+2) uv.push_back(vec2(testCubeUV[i],testCubeUV[i+1])); return uv; } 

Two more elementary questions, I have an OpenGL call:

 glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_WRAP_R,GL_CLAMP_TO_EDGE); 

• I understand that OpenGL automatically processes the r coordinate, because to have information in the constant GL_TEXTURE_CUBE_MAP_POSITIVE_X for glTexImage2D ()?
• Is there any modification of the r coordinate in Vertex Shader?

The results screen below will appear (writing to the depth buffer is disabled and no settings are specified, but this is not my problem now):

I noticed that the duplicated texture is the fifth loaded texture (GL_TEXTURE_CUBE_MAP_POSITIVE_Z).

[LAST EDIT.]: There was a problem with the UV coordinates in Skybox VS (the r coordinate has one value), Skybox VS should be as shown below:

 void main() { vCoords = normalize(vVertexPos); gl_Position = MVP * vec4(vVertexPos,1.0); } 

There were several issues with Skybox technology, but they were not the subject of this stream. Solvable.

Answer 1

Texture cube maps are displayed using a three-dimensional texture coordinate: it is used to determine which piece of the face is actually selected, and then get the actual two-dimensional texture coordinate used to access the face text of the cube map.

Your texture coordinates are 2D (wrong), and indeed, the vertexUV texture coordinate (and therefore vCoords ) the Z coordinate is always 0, displaying an undefined texture (missing components are copied by the default attribute value, i.e. vec4 (0,0,0 ,1)).

To get the desired result, change the vertex shader to use the middle coordinate:

 vCoords = normalize(vVertexPos);