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Skybox cubemap not showing properly


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#1 Wilds   Members   -  Reputation: 128

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Posted 08 August 2012 - 01:16 PM

I have used a cubemap to render my skybox, I am using openGL 3.3, GLSL 330.
The problem is that it's only showing a a blue skybox.
I can see inside gDEBugger that my cubemap is created properly.

Loading of my image files and creating the cubemap
[source lang="cpp"]void TextureCube::LoadTGA(std::string filename, bool mipmap){ // used vars TGAFile tga[6]; memset(tga, 0, sizeof(TGAFile) * 6); GLenum internForm; GLenum externForm; if(mTextureID != 0) Dispose(); // fill in texture names mTextures[0] = filename + "_lf.tga"; mTextures[1] = filename + "_rt.tga"; mTextures[2] = filename + "_bk.tga"; mTextures[3] = filename + "_ft.tga"; mTextures[4] = filename + "_dn.tga"; mTextures[5] = filename + "_up.tga"; // load each file for(int i = 0; i < 6; i++) { if( !LoadImageTGA(mTextures[i], &tga[i])) { printf("Could not load %s\n", mTextures[i].c_str()); // delete previous loaded tga for(int j = 0; j < i;j++) { delete []tga[i].data; } return; } } // set data mWidth = tga[0].width; mHeight = tga[0].height; // create texture and bind it glGenTextures(1, &mTextureID); glBindTexture(GL_TEXTURE_CUBE_MAP, mTextureID); // check which formats to use if(tga[0].bytesperpixel == 1) { internForm = GL_LUMINANCE; externForm = GL_LUMINANCE; } else if(tga[0].bytesperpixel == 3) { internForm = GL_RGB; externForm = GL_BGR; } else if(tga[0].bytesperpixel == 4) { internForm = GL_RGBA; externForm = GL_BGRA; } // set texture state glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE); glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // check if we want to generate mipmaps if(mipmap) { glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR); glEnable(GL_TEXTURE_CUBE_MAP_SEAMLESS); glGenerateMipmap(GL_TEXTURE_CUBE_MAP); } else { glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR); } // put the data inside //glPixelStorei(GL_UNPACK_ALIGNMENT, 1); glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X, 0, internForm, mWidth, mHeight, 0, externForm, GL_UNSIGNED_BYTE, tga[1].data); glTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_X, 0, internForm, mWidth, mHeight, 0, externForm, GL_UNSIGNED_BYTE, tga[0].data); glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_Y, 0, internForm, mWidth, mHeight, 0, externForm, GL_UNSIGNED_BYTE, tga[5].data); glTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, 0, internForm, mWidth, mHeight, 0, externForm, GL_UNSIGNED_BYTE, tga[4].data); glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_Z, 0, internForm, mWidth, mHeight, 0, externForm, GL_UNSIGNED_BYTE, tga[3].data); glTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_Z, 0, internForm, mWidth, mHeight, 0, externForm, GL_UNSIGNED_BYTE, tga[2].data); // unbind glBindTexture(GL_TEXTURE_CUBE_MAP, 0); //free memory for(int i = 0; i < 6; i++) { delete []tga[i].data; }}[/source]

The rest:
[source lang="cpp"]class TextureCube{private: std::string mTextures[6]; GLuint mTextureID; GLuint mWidth; GLuint mHeight;public: TextureCube() {} ~TextureCube() { Dispose(); } // Create texture GLvoid LoadTGA(std::string fileName, bool mipmap = false); // methods inline GLuint GetID() { return mTextureID; } inline GLuint GetWidth() { return mWidth; } inline GLuint GetHeight() { return mHeight; } inline GLvoid Bind() { if(glIsTexture(mTextureID)) { glBindTexture(GL_TEXTURE_CUBE_MAP, mTextureID); } else { printf("Not a valid texture name"); } } inline GLvoid Unbind() { glBindTexture(GL_TEXTURE_CUBE_MAP, 0); } inline GLvoid Dispose() { if(mTextureID) { Unbind(); glDeleteTextures(1, &mTextureID); } }};[/source]
Vertex shader:
[source lang="cpp"]#version 330layout(location = 0) in vec3 inPos;out vec3 outUV;uniform mat4 mvpMatrix;void main(){ outUV = inPos; gl_Position = mvpMatrix * vec4(inPos, 1.0);}[/source]

Fragment shader:
[source lang="cpp"]#version 330in vec3 UV;out vec4 fragcolor;uniform samplerCube cubeMap;void main(){ fragcolor = texture(cubeMap, UV);}[/source]

Skybox class:
[source lang="cpp"]#ifndef SKYBOX_H_#define SKYBOX_H_#include <string>#include "../System/CAbstractSystem.h"#include "../Graphics/Buffers/VertexBuffer.h"#include "../Graphics/TextureCube.h"#include "../Graphics/Shader.h"#include "Camera.h"class Skybox{private: // features Camera* mCamera; TextureCube mTexCube; ShaderProgram mShader; // buffers VertexBuffer mVertices; GLuint mElementsID; GLuint vaoID;public: Skybox() {} void Init(std::string fileName, Camera* camera) { mCamera = camera; // vertex position in object space GLfloat verticeAttrib[] = { // front -1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, -1.0, // top -1.0, 1.0, -1.0, 1.0, 1.0, -1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0, // back 1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, 1.0, 1.0, 1.0, // bottom -1.0, -1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, -1.0, -1.0, -1.0, // left -1.0, -1.0, 1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0, // right 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, -1.0, }; GLushort elements[] = { // front 0, 1, 2, 2, 3, 0, // top 4, 5, 6, 6, 7, 4, // back 8, 9, 10, 10, 11, 8, // bottom 12, 13, 14, 14, 15, 12, // left 16, 17, 18, 18, 19, 16, // right 20, 21, 22, 22, 23, 20, }; // generate vertex array object to melt all buffer objects glGenVertexArrays(1,&vaoID); glBindVertexArray(vaoID); // create vertex buffer object mVertices.Create(verticeAttrib, sizeof(verticeAttrib) / sizeof(GLfloat), GL_STATIC_DRAW); // indices glGenBuffers(1, &mElementsID); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mElementsID); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW); // load texture mTexCube.LoadTGA(fileName); // shader data std::string vertex; std::string fragment; // creating shaders CAbstractSystem::LoadTextFile("Data\\shaders\\skybox.vert", vertex); CAbstractSystem::LoadTextFile("Data\\shaders\\skybox.frag", fragment); // load shaders mShader.CreateProgram(vertex, fragment); } void Dispose() { mTexCube.Dispose(); mShader.Dispose(); mVertices.Dispose(); glDeleteBuffers(1, &mElementsID); glBindVertexArray(0); glDeleteVertexArrays(1, &vaoID); } ~Skybox() { Dispose(); } void Draw() { GLint OldCullFaceMode; glGetIntegerv(GL_CULL_FACE_MODE, &OldCullFaceMode); GLint OldDepthFuncMode; glGetIntegerv(GL_DEPTH_FUNC, &OldDepthFuncMode); glCullFace(GL_FRONT); glDepthFunc(GL_LEQUAL); Mat4 trans = Mat4::Translate(mCamera->GetWorld().GetPosition()) * Mat4::ScaleUniform(85); Mat4 combined = mCamera->GetProjection() * mCamera->GetView() * trans; //get matrix uniform mShader.Bind(); int mLoc = glGetUniformLocation(mShader.GetID(), "mvpMatrix"); glUniformMatrix4fv(mLoc, 1, GL_FALSE, (GLfloat*)&combined); //enable vertex position mVertices.Bind(); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0); glEnableVertexAttribArray(0); mTexCube.Bind(); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mElementsID); glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_SHORT, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); glDisableVertexAttribArray(0); // vertex positions glCullFace(OldCullFaceMode); glDepthFunc(OldDepthFuncMode); mVertices.Unbind(); mTexCube.Unbind(); mShader.Unbind(); }};#endif[/source]

Edited by Wilds, 08 August 2012 - 01:19 PM.


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#2 dpadam450   Members   -  Reputation: 934

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Posted 08 August 2012 - 02:28 PM

If you temporarily make the cubemap all red, do you see red? If so the texture is applied.

Could be your uv value being wrong.

#3 Wilds   Members   -  Reputation: 128

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Posted 08 August 2012 - 02:45 PM

Yes, that is the case!
What could i be doing wrong then?

#4 Ignifex   Members   -  Reputation: 507

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Posted 09 August 2012 - 05:56 AM

I would say the problem is in your mvpMatrix. From your code, it seems you add translation, which shouldn't be there.

Edited by Ignifex, 09 August 2012 - 06:02 AM.


#5 Wilds   Members   -  Reputation: 128

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Posted 09 August 2012 - 09:59 AM

The cube coordinates are not affected by the transformation as the shader gets the untransformed object space vertices from the VBO.

#6 dpadam450   Members   -  Reputation: 934

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Posted 09 August 2012 - 11:51 AM

I have no other good ideas other than make each side a different color. And see if at least the left is all red, right is all blue. If so, it could be doing something completely wrong. I would post a pic. Are you drawing any of the scene with it? Is your glClearColor blue? Maybe you aren't pointing the normals inward and its not drawing the skybox at all just using the clear color?

#7 Yours3!f   Members   -  Reputation: 1385

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Posted 09 August 2012 - 01:58 PM

hi, the proper way to do skyboxes is the following:
obviously create a 1x1x1 box in blender or whatever editor you prefer. you can just export the default cube to the obj format. (make sure you set normals to smooth!)
Load the 6 faces of your cubemap into a cubemap texture, and when you render it bind it to the GL_TEXTURE_CUBE_MAP target.
When rendering the skybox make sure you disable depth testing. this way you can make sure that the skybox is rendered properly behind everything.
then you have to pass a matrix to your shader: the inverse of your modelview matrix.
then use these shaders:
[vertex shader]
//set version to your target version
#version 420 core

uniform mat4 modelview_inv; //here comes the inverse modelview matrix

in vec4 in_vertex; //here comes the vertex data (ie. the cube)

out cross_shader_data
{
  vec3 tex_coord; //this gets passed to the pixel shader to sample the cubemap
} o;

void main()
{
  o.tex_coord = mat3(modelview_inv) * in_vertex.xyz; //calculate the texture coordinate, then interpolate along the cube faces
  gl_Position = in_vertex; //here's a trick: since we don't transform the cube it will always stay at (0, 0, 0) therefore wherever you go, it stays with you
}

[pixel shader]
//again set the version
#version 420 core

uniform samplerCube texture0; //you need to use a samplerCube for cubemapping

in cross_shader_data
{
  vec3 tex_coord; //incoming texture coordinates
} i;

out vec4 color; //this gets drawn into the framebuffer

void main()
{
  color = texture(texture0, i.tex_coord); //sample the cubemap along the coordinates
}

it is important to note that you either need to draw the cubemap before rendering anything (so that it doesn't cover any other objects), or you can use stenciling for optimizing the whole thing, and this way you'll need to draw the skybox last.
to add you'll probably need to adjust (rotate) the incoming cubemap faces (textures), because they may be in other coordinate system, and therefore they may not be in their place when rendered.

Edited by Yours3!f, 09 August 2012 - 02:11 PM.


#8 Yours3!f   Members   -  Reputation: 1385

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Posted 09 August 2012 - 01:59 PM

oh i duplicated my post :(

Edited by Yours3!f, 09 August 2012 - 02:00 PM.


#9 dpadam450   Members   -  Reputation: 934

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Posted 09 August 2012 - 04:07 PM

For your method: you aren't using a skybox, you are using a backdrop. Because of the fact you never rotate the box. That is the only reason you need to pass the modelview inverse and what not.

Secondly: Why use a stencil map in your method? Since you are using only 1 face of the cubemap (a backdrop plane). Why don't u just translate it to the end of the farplane and get rid of stencil operations completely and just use depth testing?

I wouldn't say that is the proper way. You are doing extra work to generate the same texture coordinates as this guy is with a static cube that gets rotated. And needing to pass extra data and perform extra operations with the inverse. Typically that method is more for a cube mapped object in the world.

here's a trick: since we don't transform the cube it will always stay at (0, 0, 0) therefore wherever you go, it stays with you

All you need to do to get that trick without using the inverse is just don't pass the translation portion of the camera matrix and just the rotation.

#10 mhagain   Crossbones+   -  Reputation: 8147

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Posted 09 August 2012 - 04:40 PM

Nope.

Draw as a 10x10x10 cube centered on the camera origin (I'm using 10 here because it's going to be comfortably above your near clipping plane distance; adjust as required) but otherwise untransformed. Draw it last, after everything else. Use glDepthRange (1, 1). Disable depth writing but leave depth test enabled.

This way you get correct positioning, early-Z, skybox behind all objects and minimal fillrate overhead.

It appears that the gentleman thought C++ was extremely difficult and he was overjoyed that the machine was absorbing it; he understood that good C++ is difficult but the best C++ is well-nigh unintelligible.


#11 Wilds   Members   -  Reputation: 128

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Posted 10 August 2012 - 01:16 AM

Is anyone looking at my code? I am already doing the thing mhagain is doing (sorta).

Edited by Wilds, 10 August 2012 - 04:52 AM.


#12 Yours3!f   Members   -  Reputation: 1385

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Posted 10 August 2012 - 02:57 AM

For your method: you aren't using a skybox, you are using a backdrop. Because of the fact you never rotate the box. That is the only reason you need to pass the modelview inverse and what not.

Secondly: Why use a stencil map in your method? Since you are using only 1 face of the cubemap (a backdrop plane). Why don't u just translate it to the end of the farplane and get rid of stencil operations completely and just use depth testing?

I wouldn't say that is the proper way. You are doing extra work to generate the same texture coordinates as this guy is with a static cube that gets rotated. And needing to pass extra data and perform extra operations with the inverse. Typically that method is more for a cube mapped object in the world.

here's a trick: since we don't transform the cube it will always stay at (0, 0, 0) therefore wherever you go, it stays with you

All you need to do to get that trick without using the inverse is just don't pass the translation portion of the camera matrix and just the rotation.

well you'd do stenciling anyways for lighting, so it may come handy. you'd use more than one face of the cube, because of perspectivity, but it's true that if you render it to the back of your frustum than it's the same. I don't think that's extra work. it's 1 matrix mul vs 1 matrix mul... (plus only 1 matrix gets passed, vs 1 matrix passed, that is the same amount of data passed :) )

#13 Wilds   Members   -  Reputation: 128

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Posted 10 August 2012 - 03:35 AM

what i can conclude is that it only picks the front texture, the +Z, I concluded this by making each part of the cubemap a different color.

I have added a link to my executable! please tell me the results.
Windows only: download

Edited by Wilds, 10 August 2012 - 03:37 AM.


#14 Erik Rufelt   Crossbones+   -  Reputation: 3532

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Posted 10 August 2012 - 04:12 AM

The cube coordinates are not affected by the transformation as the shader gets the untransformed object space vertices from the VBO.


gl_Position shouldn't be translated either to keep the cube centered on the camera. Try Ignifex' suggestion and use Mat4 combined = mCamera->GetProjection() * mCamera->GetView(); without the translation part.

#15 Wilds   Members   -  Reputation: 128

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Posted 10 August 2012 - 04:41 AM

I translate the cube's position to the camera's to keep it's position at the center of the camera.
I tried what you suggested, the translation of the position shouldn't affect texture coords, only which textures I am seeing based on the cube's orientation.

#16 Ignifex   Members   -  Reputation: 507

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Posted 10 August 2012 - 09:05 AM

Ah, that clears up your idea behind the code there and your method should work.
Honestly though, there are only a few things that can still go wrong:
- mCamera->getView() does not handle rotation, although I am sure you use it in other parts of your code as well.
- The translation you apply to move the cube toward the camera is wrong. Why the scale 85?
For the above two, the obvious thing to try is to render your texture coordinates as RGB and see what you get.
Although unlikely:
- Your binding of the cube map faces is still wrong. Could you set your uniform samplerCube cubeMap to 0, just to be safe?

#17 Wilds   Members   -  Reputation: 128

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Posted 10 August 2012 - 10:15 AM

Thanks for your comment I tried visually debugging the skybox, it seems the texture coordinate passed is 0,0,0 the faces are all black!

- mCamera->getView() does not handle rotation, although I am sure you use it in other parts of your code as well.
It handles rotation as it is the inverse of the camera's world matrice.

- The translation you apply to move the cube toward the camera is wrong. Why the scale 85?
This one is also correct, the 85 scale is just a test value.

For the above two, the obvious thing to try is to render your texture coordinates as RGB and see what you get.
Although unlikely:
- Your binding of the cube map faces is still wrong. Could you set your uniform samplerCube cubeMap to 0, just to be safe?
Could you tell me how I do this, as just putting 0 behind uniform samplerCube tex is not working.

#18 Wilds   Members   -  Reputation: 128

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Posted 10 August 2012 - 10:21 AM

Oke I solved it! thanks everyone, especially Ignifex, your tip about visually debugging helped me alot!
Good learning lesson, always name the input of the fragment shader the same as the output of the vertex shader!

The problem:
In the shaders i named the linking output and input of the vertex to fragment shaders differently.

Wrong
out vec3 outUV; // inside vertex shader
in vec3 UV; // inside fragment shader

Good:
out vec3 UV; // inside vertex shader
in Vec3 UV; // inside fragment shader

Edited by Wilds, 10 August 2012 - 10:22 AM.





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