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OpenGL Skybox cubemap not showing properly

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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, &tga))
{
printf("Could not load %s\n", mTextures.c_str());

// delete previous loaded tga
for(int j = 0; j < i;j++)
{
delete []tga.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.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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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.

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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:

[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

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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.

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 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.

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