[英]I am trying to create a skybox with openGL in C, but am only getting a black screen
我正在尝试使用C语言中的OpenGL创建一个Skybox。我看了很多教程,看了很多人的代码,但我不认为我会错过任何东西,但是却出现了黑屏。 我把整个事情弄错了吗?
#include <windows.h>
#include <GL/glut.h>
#include <GL/glu.h>
#include <GL/gl.h>
#include <stdio.h>
#include <math.h>
GLuint texture[6];
/**
* Init function initializing the background to black.
*/
void init()
{
glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW | GL_PROJECTION);
glEnable(GL_DEPTH_TEST);
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(-1.0, 1.0, -1.0, 1.0, 1.5, 20.0);
glMatrixMode(GL_MODELVIEW);
}
GLuint LoadTexture(const char * filename, int width, int height)
{
GLuint texture;
unsigned char * data;
FILE * file;
//Open the image file
file = fopen(filename, "rb");
//If it doesn't open just return 0
if(file == NULL)
{
return 0;
}
//Allocate space for data and read
data = (unsigned char *)malloc(width * height * 3);
fread(data, width * height * 3, 1, file);
//Close the file
fclose(file);
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
gluBuild2DMipmaps( GL_TEXTURE_2D, 3, width, height, GL_RGB, GL_UNSIGNED_BYTE, data );
free(data);
return texture;
}
void draw()
{
int width = 512;
int height = 512;
int length = 512;
//start in this coordinates
int x = 0;
int y = 0;
int z = 0;
//center the square
x = x - width / 2;
y = y - height / 2;
z = z - length / 2;
// Bind the BACK texture of the sky map to the BACK side of the cube
glBindTexture(GL_TEXTURE_2D, texture[0]);
glBegin(GL_QUADS);
glTexCoord2f(1.0f, 0.0f); glVertex3f(x + width, y, z);
glTexCoord2f(1.0f, 1.0f); glVertex3f(x + width, y + height, z);
glTexCoord2f(0.0f, 1.0f); glVertex3f(x, y + height, z);
glTexCoord2f(0.0f, 0.0f); glVertex3f(x, y, z);
glEnd();
//FRONT
glBindTexture(GL_TEXTURE_2D, texture[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();
//BOTTOM
glBindTexture(GL_TEXTURE_2D, texture[4]);
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();
//TOP
glBindTexture(GL_TEXTURE_2D, texture[5]);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f); glVertex3f(x + width, y + height, z);
glTexCoord2f(1.0f, 0.0f); glVertex3f(x + width, y + height, z + length);
glTexCoord2f(1.0f, 1.0f); glVertex3f(x, y + height, z + length);
glTexCoord2f(0.0f, 1.0f); glVertex3f(x, y + height, z);
glEnd();
//LEFT
glBindTexture(GL_TEXTURE_2D, texture[2]);
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();
//RIGHT
glBindTexture(GL_TEXTURE_2D, texture[3]);
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();
}
void display()
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
gluLookAt(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
texture[0] = LoadTexture("back.bmp", 512, 512);
/*texture[0] = SOIL_load_OGl_texture
{
"back.bmp",
SOIL_LOAD_AUTO,
SOIL_CREATE_NEW_ID,
SOIL_FLAG_INVERT_Y
};*/
texture[1] = LoadTexture("front.bmp", 512, 512);
texture[2] = LoadTexture("left.bmp", 512, 512);
texture[3] = LoadTexture("right.bmp", 512, 512);
texture[4] = LoadTexture("cesped.bmp", 512, 512);
texture[5] = LoadTexture("top.bmp", 512, 512);
glEnable(GL_TEXTURE_2D);
glEnable(GL_TEXTURE_GEN_S);
glEnable(GL_TEXTURE_GEN_T);
draw();
glutSwapBuffers();
}
int main(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH | GLUT_ALPHA);
glutInitWindowSize(1000, 1000);
glutInitWindowPosition(100, 100);
glutCreateWindow("blah");
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}
问题似乎是,天空盒不在可见区域内。 当看投影矩阵的定义时glFrustum(-1.0, 1.0, -1.0, 1.0, 1.5, 20.0);
,人们看到,沿z轴的可见值必须在1.5到20.0之间。 但是,天空盒从-256.0绘制到256.0,位于远平面/近平面的后面并被剪掉。
有两种可能的解决方案:一种可以画一个较小的天空盒或增加可见区域。 通常,在两种情况下,结果都是相同的(至少在渲染天空盒时不进行深度测试作为第一个对象时,通常这样做)。
根据评论:像素的纹理大小与几何图形的大小之间没有关系。 因此,无需绘制边长为512的立方体。
似乎有些事情会发生:
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