Why doesn't my OpenGL Radar implementation render on screen? - c++

Question

I want to implement radar for my 3D game using openGL. I have been trying to accomplish it in many ways, but none of them approved to be correct. Here is the snippet of my code below:
int xi, yi;
GLfloat x,z;
glPushMatrix();
{
glTranslatef(-0.8f, 0.2f, -3.0f);
glColor3f(0.0f, 0.0f, 1.0f);
x = playerTank->givePosX();
z = playerTank->givePosZ();
xi = (int)((x + 1000) / 20) + 5;
yi = (int)(((z + 1000) / 20) + screenHeight - 105);
glPushMatrix();
{
glScalef(xi,yi,1.0f);
glBegin(GL_QUADS);
glVertex2i(xi-5, yi-5);
glVertex2i(xi+5, yi-5);
glVertex2i(xi+5, yi+5);
glVertex2i(xi-5, yi+5);
glEnd();
}
glPopMatrix();
glColor3f(1.0f, 0.0f, 0.0f);
glPushMatrix();
{
glScalef(xi,yi,1.0f);
for (int i = 0; i < tanks.size(); i++)
{
x = tanks[i]->givePosX();
z = tanks[i]->givePosZ();
xi = (int)((x + 1000) / 20) + 5;
yi = (int)(((z + 1000) / 20) + screenHeight - 105);
if (xi > 0 && xi < 110 && yi > (screenHeight - 110) && yi < screenHeight)
{
if (tanks[i] != playerTank)
{
glBegin(GL_TRIANGLES);
glVertex2i(xi, yi-5);
glVertex2i(xi+5, yi+5);
glVertex2i(xi-5, yi+5);
glEnd();
}
}
}
}
glPopMatrix();
glColor3f(0.0f, 1.0f, 0.0f);
glPushMatrix();
{
glScalef(xi,yi,1.0f);
for (int i = 0; i < obstacles.size(); i++)
{
x = obstacles[i]->givePosX();
z = obstacles[i]->givePosZ();
xi = (int)((x + 1000) / 20) + 5;
yi = (int)(((z + 1000) / 20) + screenHeight - 105);
glBegin(GL_LINE_LOOP);
glVertex2i(xi-3, yi-3);
glVertex2i(xi+3, yi-3);
glVertex2i(xi+3, yi+3);
glVertex2i(xi-3, yi+3);
glEnd();
}
}
glPopMatrix();
}
glPopMatrix();
Why doesn't anything appear on the screen?

Answer 1

Some things to try:
Make sure you've set up the renderer correctly - what calls are you making to set up the scene? Take a look at some of the lessons on nehe for some hints.
Make a simple square the size of the screen. You're doing something along those lines in the top section (blue quad right?) but make sure it's centred - looks like you might be pushing it up and right by 1000 units.
Check you're winding the correct way. Looks like you are from my somewhat rusty OGL memories.
Try translating in different directions. Looks to me like you might be translating the wrong way with your first translatef.