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Wilds

OpenGL
Skybox cubemap not showing properly

17 posts in this topic

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 330

layout(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 330

in 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
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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
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The cube coordinates are not affected by the transformation as the shader gets the untransformed object space vertices from the VBO.
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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?
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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:
[CODE]
[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
}
[/CODE]

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
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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.

[quote]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[/quote]
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.
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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 [u]last[/u], 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.
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Is anyone looking at my code? I am already doing the thing mhagain is doing (sorta). Edited by Wilds
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[quote name='dpadam450' timestamp='1344550038' post='4967928']
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.

[quote]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[/quote]
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.
[/quote]
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 :) )
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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: [url="http://www.wildrune.com/files/Gaian.rar"]download[/url] Edited by Wilds
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[quote name='Wilds' timestamp='1344527994' post='4967826']
The cube coordinates are not affected by the transformation as the shader gets the untransformed object space vertices from the VBO.
[/quote]

gl_Position shouldn't be translated either to keep the cube centered on the camera. Try Ignifex' suggestion and use [b]Mat4 combined = mCamera->GetProjection() * mCamera->GetView();[/b] without the translation part.
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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.
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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?
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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.
[b]It handles rotation as it is the inverse of the camera's world matrice.[/b]

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

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?
[b]Could you tell me how I do this, as just putting 0 behind [i][u]uniform samplerCube[/u] tex[/i] is not working.[/b]
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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!

[b]The problem:[/b]
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
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      For a game project I am working on, I would like to implement a 2D starfield as a background.
      I do not want to deal with static tiles, since I plan to slowly animate the starfield. So, I am trying to figure out how to generate a random starfield for the entire map.
      I feel that using a uniform distribution for the stars will not do the trick. Instead I would like something similar to the screenshot below, taken from the game Star Wars: Empire At War (all credits to Lucasfilm, Disney, and so on...).

      Is there someone who could have an idea of a distribution which could result in such a starfield?
      Any insight would be appreciated
    • By afraidofdark
      I have just noticed that, in quake 3 and half - life, dynamic models are effected from light map. For example in dark areas, gun that player holds seems darker. How did they achieve this effect ? I can use image based lighting techniques however (Like placing an environment probe and using it for reflections and ambient lighting), this tech wasn't used in games back then, so there must be a simpler method to do this.
      Here is a link that shows how modern engines does it. Indirect Lighting Cache It would be nice if you know a paper that explains this technique. Can I apply this to quake 3' s light map generator and bsp format ?
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