OpenGL C++ Depth buffer not working - c++

Question

I've been testing with OpenGL for a while and have not been able to get the depth buffer to work, despite using GLUT_DEPTH as a parameter in glutInitDisplayMode and doing glClear(GL_DEPTH_BUFFER_BIT) at the start of the display function. I don't know what else I'm missing.
Below is a minimum working example and Figure 1 and 2. Comment out the parameters under Figure 1 and 2 when you want to view the other one.
Figure 1 (above blue):
Figure 2 (below red):
Example:
#include <vector>
#include <gl\glut.h>
typedef std::vector<float> floatvec;
// Figure 1 (above blue)
float posX = 8.00f;
float posY = 7.54f;
float posZ = -0.89f;
float angleX = 300.50f;
float angleY = 45.33f;
// Figure 2 (below red)
float posX = 4.12f;
float posY = -4.87f;
float posZ = -3.84f;
float angleX = 343.25f;
float angleY = -45.00f;
int screenW = 720;
int screenH = 540;
float fMin = 0.5;
float fMax = 100.0;
float alpha = 60.0;
// Draws a rectangle in 3D
void DrawQuad(floatvec c) {
glBegin(GL_QUADS);
glVertex3f(-c[0], -c[1], -c[2]);
glVertex3f(-c[3], -c[4], -c[5]);
glVertex3f(-c[6], -c[7], -c[8]);
glVertex3f(-c[9], -c[10], -c[11]);
glEnd();
}
void Display() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glPushMatrix();
glRotatef(angleY, 1.0f, 0.0f, 0.0f);
glRotatef(angleX, 0.0f, 1.0f, 0.0f);
glRotatef(180.0, 0.0f, 0.0f, 1.0f);
glTranslatef(posX, posY, posZ);
// Draws the tiles
glColor3f(1.0, 0.0, 0.0); // Red
DrawQuad({ 0, 0, 0,
5, 0, 0,
5, 0, 5,
0, 0, 5 });
glColor3f(0.0, 0.0, 1.0); // Blue
DrawQuad({ 0, 3, 0,
5, 3, 0,
5, 3, 5,
0, 3, 5 });
glPopMatrix();
glutSwapBuffers();
}
void Reshape(int width, int height) {
glViewport(0, 0, (GLsizei)width, (GLsizei)height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(alpha, (GLfloat)width / (GLfloat)height, fMin, fMax);
glMatrixMode(GL_MODELVIEW);
}
int main(int iArgc, char** cppArgv) {
glutInit(&iArgc, cppArgv);
glEnable(GL_DEPTH_TEST);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(screenW, screenH);
glutCreateWindow("Example");
glutDisplayFunc(Display);
glutIdleFunc(Display);
glutReshapeFunc(Reshape);
glutMainLoop();
return 0;
}

Answer 1

You just need to change where you call glEnable(GL_DEPTH_TEST);
Put it after glutCreateWindow and it will work fine.
Something like this:
int main(int iArgc, char** cppArgv) {
glutInit(&iArgc, cppArgv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(screenW, screenH);
glutCreateWindow("Example");
glEnable(GL_DEPTH_TEST);
glutDisplayFunc(Display);
glutIdleFunc(Display);
glutReshapeFunc(Reshape);
glutMainLoop();
return 0;
}
Just tested here and it worked.

Answer 2

I am a little bit rusty in OpenGL, but, putting the glEnable line in the Display function will make the trick.
#include <vector>
#include <GL/glut.h>
typedef std::vector<float> floatvec;
//Figure 1 (above blue)
//float posX = 8.00f;
//float posY = 7.54f;
//float posZ = -0.89f;
//float angleX = 300.50f;
//float angleY = 45.33f;
// Figure 2 (below red)
float posX = 4.12f;
float posY = -4.87f;
float posZ = -3.84f;
float angleX = 343.25f;
float angleY = -45.00f;
int screenW = 720;
int screenH = 540;
float fMin = 0.5;
float fMax = 100.0;
float alpha = 60.0;
// Draws a rectangle in 3D
void DrawQuad(floatvec c) {
glBegin(GL_QUADS);
glVertex3f(-c[0], -c[1], -c[2]);
glVertex3f(-c[3], -c[4], -c[5]);
glVertex3f(-c[6], -c[7], -c[8]);
glVertex3f(-c[9], -c[10], -c[11]);
glEnd();
}
void Display() {
glEnable(GL_DEPTH_TEST);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glPushMatrix();
glRotatef(angleY, 1.0f, 0.0f, 0.0f);
glRotatef(angleX, 0.0f, 1.0f, 0.0f);
glRotatef(180.0, 0.0f, 0.0f, 1.0f);
glTranslatef(posX, posY, posZ);
// Draws the tiles
glColor3f(1.0, 0.0, 0.0); // Red
DrawQuad({ 0, 0, 0,
5, 0, 0,
5, 0, 5,
0, 0, 5 });
glColor3f(0.0, 0.0, 1.0); // Blue
DrawQuad({ 0, 3, 0,
5, 3, 0,
5, 3, 5,
0, 3, 5 });
glPopMatrix();
glutSwapBuffers();
}
void Reshape(int width, int height) {
glViewport(0, 0, (GLsizei)width, (GLsizei)height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(alpha, (GLfloat)width / (GLfloat)height, fMin, fMax);
glMatrixMode(GL_MODELVIEW);
}
int main(int iArgc, char** cppArgv) {
glutInit(&iArgc, cppArgv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(screenW, screenH);
glutCreateWindow("Example");
glutDisplayFunc(Display);
glutIdleFunc(Display);
glutReshapeFunc(Reshape);
glutMainLoop();
return 0;
}