Как glOrtho и glVertex3f работают вместе ⇐ C++

[Anonymous]

У меня есть код, который должен рисовать плоский прямоугольник позади вращающегося куба.
Однако прямоугольник продолжает появляться перед кубом, независимо от того, что я изменяю в glOrtho и glVertex3f для обеих фигур. Пожалуйста, объясните математические принципы работы glOrtho в сочетании с glVertex3f, чтобы прямоугольник отображался позади куба.
//-lglut -lGLEW -lGL -lGLU -lm

#include // Include the GLEW header file
#include // Include the GLUT header file
#include
#include
#include
#include
#include
#include
#include

GLuint texture;
GLfloat angle = 0.0;

const float zNNear=0.5;
const float zFar=-0.5;

// Rotate X
double rX=0;
// Rotate Y
double rY=0;

bool running = true;
bool inc = false;
bool inc2 = false;
bool inc3 = false;
bool inc4 = false;

bool* keyStates = new bool[256];

float yVal = 0.0f;
float yVal2 = 0.1f;
float yVal3 = 0.0f;
float yVal4 = 0.1f;

GLuint LoadBMP(const char *fileName)
{
FILE *file=fopen(fileName,"rb");
if (!file)
{
printf("Image could not be loaded\n");
return 0;
}

unsigned char header[54];
fread(header,1,54,file);

unsigned int dataPos=*(int*)&(header[0x0A]);
unsigned int imageSize=*(int*)&(header[0x22]);
unsigned int width=*(int*)&(header[0x12]);
unsigned int height=*(int*)&(header[0x16]);

if(imageSize == 0)
{
imageSize = width*height*3;
}
if(dataPos == 0)
{
dataPos = 54;
}

unsigned char *data = new unsigned char[imageSize];
fread(data,1,imageSize,file);
fclose(file);

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D,0,GL_RGB,width,height,0,GL_BGR,
GL_UNSIGNED_BYTE,data);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
delete(data);

return texture;
}

void FreeTexture(GLuint texture)
{
glDeleteTextures(1, &texture);
}

void keyOperations(void)
{
if(keyStates['a'])
{
}
}

void drawCube(void)
{
glBindTexture(GL_TEXTURE_2D, texture);
glOrtho(0.0,0.0,0.0,0.0,4.0,4.0);
glBegin(GL_QUADS);

//front
glTexCoord2f(0.0f,0.0f);glVertex3f(-0.5f,-0.5f,zNNear);
glTexCoord2f(0.5f,0.0f) ;glVertex3f(0.5f,-0.5f,zNNear);
glTexCoord2f(0.5f,0.5f) ;glVertex3f(0.5f,0.5f,zNNear);
glTexCoord2f(0.0f,0.5f) ;glVertex3f(-0.5f,0.5f,zNNear);

//back
glTexCoord2f(0.0f,0.0f);glVertex3f(-0.5f,-0.5f,zFar);
glTexCoord2f(0.5f,0.0f) ;glVertex3f(0.5f,-0.5f,zFar);
glTexCoord2f(0.5f,0.5f) ;glVertex3f(0.5f,0.5f,zFar);
glTexCoord2f(0.0f,0.5f) ;glVertex3f(-0.5f,0.5f,zFar);

//top
glTexCoord2f(0.0f,0.0f);glVertex3f(-0.5f,0.5f,zFar);
glTexCoord2f(0.5f,0.0f) ;glVertex3f(0.5f,0.5f,zFar);
glTexCoord2f(0.5f,0.5f) ;glVertex3f(0.5f,0.5f,zNNear);
glTexCoord2f(0.0f,0.5f) ;glVertex3f(-0.5f,0.5f,zNNear);

//bottom
glTexCoord2f(0.0f,0.0f);glVertex3f(-0.5f,-0.5f,zFar);
glTexCoord2f(0.5f,0.0f) ;glVertex3f(0.5f,-0.5f,zFar);
glTexCoord2f(0.5f,0.5f) ;glVertex3f(0.5f,-0.5f,zNNear);
glTexCoord2f(0.0f,0.5f) ;glVertex3f(-0.5f,-0.5f,zNNear);

//right
glTexCoord2f(0.0f,0.0f);glVertex3f(0.5f,-0.5f,-zFar);
glTexCoord2f(0.5f,0.0f) ;glVertex3f(0.5f,0.5f,zFar);
glTexCoord2f(0.5f,0.5f) ;glVertex3f(0.5f,0.5f,zNNear);
glTexCoord2f(0.0f,0.5f) ;glVertex3f(0.5f,-0.5f,zNNear);

//left
glTexCoord2f(0.0f,0.0f);glVertex3f(-0.5f,-0.5f,zFar);
glTexCoord2f(0.5f,0.0f) ;glVertex3f(-0.5f,0.5f,zFar);
glTexCoord2f(0.5f,0.5f) ;glVertex3f(-0.5f,0.5f,zNNear);
glTexCoord2f(0.0f,0.5f) ;glVertex3f(-0.5f,-0.5f,zNNear);

glEnd();
}

void display(void)
{
keyOperations();

glClearColor(0.0f,0.0f,0.0f,1.0f);//set background color
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glOrtho(0.0,1.0,0.0,1.0,10.0,10.0);
glutPostRedisplay();

if(inc)
yVal -= 0.005f;
else
yVal += 0.005f;

if(yVal1.0f)
inc=true;

if(inc2)
yVal2 -= 0.005f;
else
yVal2 += 0.005f;

if(yVal21.0f)
inc2=true;

if(inc3)
yVal3 -= 0.005f;
else
yVal3 += 0.005f;

if(yVal31.0f)
inc3=true;

if(inc4)
yVal4 -= 0.005f;
else
yVal4 += 0.005f;

if(yVal41.0f)
inc4=true;

glColor3f(yVal, 0.0, 0.0); // Red
//glRectf(-1.0,1.0,1.0,0.5);
glBegin(GL_QUADS);
glVertex3f(0.25,0.25,-1.0);
glVertex3f(0.75,0.25,-1.0);
glVertex3f(0.75,0.75,-1.0);
glVertex3f(0.25,0.75,-1.0);

//glVertex3f(-1.0,1.0,2.0);
//glVertex3f(1.0,0.5,2.0);

glEnd();

//glColor3f(0.0, yVal2, 0.0); // Green
//glRectf(-1.0,0.5,1.0,0.0);

//glColor3f(yVal3, 0.25, 0.0); // Orange
//glRectf(-1.0,0.0,1.0,-0.5);

//glColor3f(0.0, yVal4, 0.25); // Orange
//glRectf(-1.0,-0.5,1.0,-1.0);

glRotatef( rX, 1.0, 0.0, 0.0 );

glRotatef( rY, 0.0, 1.0, 0.0 );

rX+=0.1;
rY+=0.1;

drawCube();

glutSwapBuffers();
}

void reShape(int w, int h)
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60,(GLfloat)w/(GLfloat)h, 1.0,100.0);
glMatrixMode(GL_MODELVIEW);
}

void init()
{
glEnable(GL_TEXTURE_2D);
texture=LoadBMP("Me8.bmp");
}

void reshape(int width, int height)
{
glViewport(0,0,(GLsizei)width, (GLsizei)height);

glMatrixMode(GL_PROJECTION); //glMatrixMode
glLoadIdentity();//replace the current matrix with the identity matrix

glMatrixMode(GL_MODELVIEW);
}

void keyPressed(unsigned char key, int x, int y)
{
keyStates[key]=true;
}

void keyUp(unsigned char key, int x, int y)
{
keyStates[key]=false;
}

int main(int argc, char **argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB|GLUT_DEPTH);
glutInitWindowSize(250,250);
glutInitWindowPosition(100,100);
glutCreateWindow("OpenGL Photo Example With Coloured Background");

init();

glEnable(GL_DEPTH_TEST);

glutDisplayFunc(display);//glutDisplayFunc

glutReshapeFunc(reshape);//sets the reshape callback for the current window.

glutKeyboardFunc(keyPressed);//sets the keyboard callback for the current window

glutKeyboardUpFunc(keyUp);//glutKeyboardUpFunc

glutMainLoop();//enters the GLUT event processing loop.

return 0;
}


Подробнее здесь: https://stackoverflow.com/questions/797 ... k-together