天空盒纹理未显示在opengl中

Question

I have a simple skybox .

#include <GL/glew.h>
#include <GL/freeglut.h>
#include <vector>
#include <iostream>

#include "texture.h"
#include "deviLoader.h"

using namespace std;

static std::vector<GLuint> textures;

class Skybox
{
private:
float x, y, z;
float width, height, length;
bool isBottomRequired;
void rearrange();
void loadTextures();
public:
Skybox() {};
Skybox(float x, 
        float y, 
        float z, 
        float width, 
        float height, 
        float length);
void renderSkybox();
void setBottom(bool required);
~Skybox() {};
};

I load textures using devIL lib in method loadTextures .

void Skybox::loadTextures()
{
cout<<"SKYBOX: texture loading...";

Texture t;
LoadTexture(IL_BMP, "Back.bmp", &t);
textures.push_back(t.texID);

LoadTexture(IL_BMP, "Front.bmp", &t);
textures.push_back(t.texID);

LoadTexture(IL_BMP, "Bottom.bmp", &t);
textures.push_back(t.texID);

LoadTexture(IL_BMP, "Top.bmp", &t);
textures.push_back(t.texID);

LoadTexture(IL_BMP, "Left.bmp", &t);
textures.push_back(t.texID);

LoadTexture(IL_BMP, "Right.bmp", &t);
textures.push_back(t.texID);

/*
LoadTexture(IL_BMP, "Back.bmp", &t);
textures[0] = t.texID;
*/

cout<<"SUCCESS"<<endl;
}

where function loadTexture

void LoadTexture(ILenum FileType, char *filename, Texture *texture)
{
ilInit();
iluInit();

ilLoad(FileType, filename);

int err = ilGetError();
if (err != IL_NO_ERROR)
{
    const char* strError = iluErrorString(err);
    cout<<strError<<" - error during loading!"<<endl;
    return;
}

texture->width = ilGetInteger(IL_IMAGE_WIDTH);
texture->height = ilGetInteger(IL_IMAGE_HEIGHT);
texture->bpp = ilGetInteger(IL_IMAGE_BYTES_PER_PIXEL);

texture->imageData = ilGetData();

ilEnable(IL_CONV_PAL);

unsigned int type = ilGetInteger(IL_IMAGE_FORMAT);

glGenTextures(1, &texture->texID);
glBindTexture(GL_TEXTURE_2D, texture->texID);

gluBuild2DMipmaps(GL_TEXTURE_2D, texture->bpp, texture->width, texture->height,
    type, GL_UNSIGNED_BYTE, texture->imageData);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
}

In my main.cpp I declare skybox object as a global variable and render it in method draw

Skybox skyBox;
.....
//part of method draw
if (selected[7] == 1) {
    glDisable(GL_FOG);
    glEnable(GL_TEXTURE_2D);
    glPushMatrix();
        glTranslatef(-0.2, 4, 2.3);
        glScalef(0.15, 0.2, 0.19);
        skyBox.renderSkybox();
    glPopMatrix();
    glDisable(GL_TEXTURE_2D);
    if (selected[6] == 1)
        glEnable(GL_FOG);
}

renderSkybox method

void Skybox::renderSkybox()
{
glBindTexture(GL_TEXTURE_2D, textures[0]);
glBegin(GL_QUADS);
    glTexCoord2f(1.0, 0.0); glVertex3f(x + width, y, z);
    glTexCoord2f(1.0, 1.0); glVertex3f(x + width, y + height, z);
    glTexCoord2f(0.0, 1.0); glVertex3f(x, y + height, z);
    glTexCoord2f(0.0, 0.0); glVertex3f(x, y, z);
glEnd();

glBindTexture(GL_TEXTURE_2D, textures[1]);
glBegin(GL_QUADS);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(x, y, z + length);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(x, y + height, z + length);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(x + width, y + height, z + length);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(x + width, y,z + length);
glEnd();

if (isBottomRequired)
{
    glBindTexture(GL_TEXTURE_2D, textures[2]);
    glBegin(GL_QUADS);
        glTexCoord2f(1.0f, 0.0f); glVertex3f(x, y,z);
        glTexCoord2f(1.0f, 1.0f); glVertex3f(x, y,z + length);
        glTexCoord2f(0.0f, 1.0f); glVertex3f(x + width, y,z + length);
        glTexCoord2f(0.0f, 0.0f); glVertex3f(x + width, y,z);
    glEnd();
}

glBindTexture(GL_TEXTURE_2D, textures[3]);
glBegin(GL_QUADS);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(x + width, y + height, z);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(x + width, y + height, z + length);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(x, y + height,z + length);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(x, y + height,z);
glEnd();

glBindTexture(GL_TEXTURE_2D, textures[4]);
glBegin(GL_QUADS);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(x, y + height,z);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(x, y + height,z + length);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(x, y,z + length);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(x, y,z);
glEnd();

glBindTexture(GL_TEXTURE_2D, textures[5]);
glBegin(GL_QUADS);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(x + width, y,z);
    glTexCoord2f(1.0f, 0.0f); glVertex3f(x + width, y,z + length);
    glTexCoord2f(1.0f, 1.0f); glVertex3f(x + width, y + height,z + length);
    glTexCoord2f(0.0f, 1.0f); glVertex3f(x + width, y + height,z);
glEnd();
};

When I draw other objects - It is seen that skybox appears to be black What is the problem? Why it is black?

edit I've added project in case if somebody decides to look into problem with more details. There project and glm, assimp, devil, freeglut libs. Project is not finished but it should work.

http://www.filedropper.com/task

Answer 1

There are two strategies on drawing a skybox:

• use the skybox for "clearing": You draw the skybox as the first thing in your scene. Before drawing the skybox call glDisable(GL_DEPTH_TEST); glDepthMask(GL_FALSE); glDisable(GL_DEPTH_TEST); glDepthMask(GL_FALSE); , then draw the skybox and reenable depth testing ( glEnable(GL_DEPTH_TEST) ) and depth writes ( glDepthMask(GL_FALSE) ) as needed

• draw the skybox after the last opaque, but before blended geometry (requires support for depth clamping). Clear the scene with the depth buffer cleared to (pow(2, b)-1.)/pow(2, b) where b is the bit depth of the depth buffer. Draw the opaque scene as usual. Enable depth clamping and depth test set the depth test function to greater or equal ( glDepthFunc(GL_GEQUAL) ) and setup a projection, or scale up the skybox, so that the skybox quads will always stay behind the far clipping plane. Due to depth clamping the generated fragment depths with all be 1.0 passing the depth test rendering the skybox only at those areas of the screen, not covered by other geometry.