# OpenGL engine repair

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I was wondering if I could get some help fixing some bugs and glitches within my engine. I am new to the whole opengl language so if I am doing anything wrong please let me know. My main problem is setting up the projection direction system. Some help could be really um helpful...
#include <gl/gl.h>
#include <gl/glu.h>
#include <gl/glut.h>
using namespace std;

float cord_x=50.0;
float cord_y=0.0;
float cord_z=50.0;

float yaw=0.0;  //direction
float pitch=0.0;  //zdirection
float roll=0.0;  //spin

float pi=3.141592654;

void keypress(unsigned char key, int x, int y)
{
switch(key)
{
case 27:

case 'a':
yaw-=2.0;
break;

case 'd':
yaw+=2.0;
break;

case 'w':
pitch+=2.0;
break;

case 's':
pitch-=2.0;
break;
}
glutPostRedisplay();
}

void init()
{
glClearColor(0,0,0,0);
glEnable(GL_DEPTH_TEST);
}

void projection(int width, int height)
{
//glViewport(0,0,width,height);
glMatrixMode(GL_PROJECTION);
gluPerspective(45.0f,width/height,1.0f,10000.0f);
}

void display()
{
float room_width=255;
float room_height=255;

glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);

gluLookAt(cord_x,cord_y+5,cord_z,yaw,pitch,0.0,0.0,1.0,0.0);

glBegin(GL_POLYGON);
glColor3d(.25,.25,.25);
glVertex3f(0,0,0); glVertex3f(room_width,0,0);
glVertex3f(room_width,0,room_height); glVertex3f(0,0,room_height);
glEnd();

glBegin(GL_POLYGON);
glColor3d(0,0,1);
glVertex3f(-2,0,0); glVertex3f(2,0,0);
glVertex3f(2,3,0); glVertex3f(-2,3,0);
glEnd();

glBegin(GL_POLYGON);
glColor3d(0,1,0);
glVertex3f(room_width-2,0,0); glVertex3f(room_width+2,0,0);
glVertex3f(room_width+2,3,0); glVertex3f(room_width-2,3,0);
glEnd();

glBegin(GL_POLYGON);
glColor3d(1,0,0);
glVertex3f(room_width-2,0,room_height); glVertex3f(room_width+2,0,room_height);
glVertex3f(room_width+2,3,room_height); glVertex3f(room_width-2,3,room_height);
glEnd();

glBegin(GL_POLYGON);
glColor3d(.5,.5,0);
glVertex3f(-2,0,room_height); glVertex3f(2,0,room_height);
glVertex3f(2,3,room_height); glVertex3f(-2,3,room_height);
glEnd();

glutSwapBuffers();
glutPostRedisplay();
}

void step()
{
//step loop
}

//last fuction
int main(int argc,char**argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);
glutInitWindowSize(480,480);
glutInitWindowPosition(25,25);
glutCreateWindow("alpha engine");
init();

glutDisplayFunc(display);
glutIdleFunc(step);
glutReshapeFunc(projection);
glutKeyboardFunc(keypress);

glutMainLoop();
return 0;
}


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Do you understand the meaning of the different sets of parameters of gluLookAt?

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What do you mean by that, because I might know? I have been doing some research on gluLookAt and found very little info for what I am looking at doing. From what I read the first three digits are the cameras location, the next 6 digits are uncertain to me.

I am sure this looks and sounds like a large task, and I am sorry about that. I have reached a roadblock and the only way to pass it is with a little professional revision.

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The first three parameters are the Eye vector (where your looking from), the next three are the LookAt vector (where you're looking at), and the final three parameters are the up vector (which way points up). The values (yaw & pitch) you are passing in are wrong.

As a side note, before writing an "engine", I would suggest reading and fully understanding how the OpenGL API works. It will definitely shed some light as to how things work. Have you tried searching through OpenGL.org for information?

RANT: Why make an engine, and not a game instead? Or at least a few demos to fully understand how it all works? In it's current state, your code is like a Ford Fiesta or a Pinto. Far from being a fully featured commercial (or Open Source) engine. All too often, people use this magical term of "engine" to describe everything from a text-based adventure game to their "industry breaking MMO" idea.

When will we see people just write a game and not see the in-experienced trying to be like Carmack or Sweeney or Abrash or any of the well-experienced game/engine programmers. I'm NOT directing this at you specifically, but a more broad comment about so many posts here. It seems like almost every post heading has either MMO or Engine in the title. More people should focus on making games, gaining experience and having fun than trying to design the next Unreal Engine and ultimately fail because they do not have enough experience to know all of the pitfalls and design complexities associated with such a task.

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Man you got me all wrong, your definition and mine of engine must be different. This is meant for a game but I can't really call it that while its in this really early state of development. Listen I have 4 years of game making experience, I am not that retarded to think that I am making the next Doom or Half-Life game. I have just started learning opengl and its more complex than what I was previously using, its alot harder to learn and master. I currently know many game makering concepts(I am alot less of a noob than you give credit for) but am having some issues learning all the commands and learning about how opengl runs. I know what I currently have isn't worth crap, and that is why I am trying to work out all the kinks now.

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Quote:
 Original post by snowfellMan you got me all wrong, your definition and mine of engine must be different. This is meant for a game but I can't really call it that while its in this really early state of development. Listen I have 4 years of game making experience, I am not that retarded to think that I am making the next Doom or Half-Life game. I have just started learning opengl and its more complex than what I was previously using, its alot harder to learn and master. I currently know many game makering concepts(I am alot less of a noob than you give credit for) but am having some issues learning all the commands and learning about how opengl runs. I know what I currently have isn't worth crap, and that is why I am trying to work out all the kinks now.

Sorry but I get irked pretty at times about the word "engine" being used so much...In either case, I have a few helpful suggestions for your code:

- IF you have to redefine PI, change your definition of pi to the maximum number of decimal places for the given platform (i.e. 4) and don't forget to add an 'f' at the end to re-enforce it's a float. Otherwise some compilers will make it a double and cast it to a float at compile time. This could be done everywhere. i.e. float pi=3.1415f;
- When using glBegin/glEnd pairs, put as many primitives in them as possible. This will speed things up when rendering in Immediate mode. Since your using GL_POLYGON for a wall, consider using GL_QUADS so each wall will be split after 4 vertices are added. If you don't change the type being created, all points you add will be connected into one fugly looking object. Keep in mind that usually Triangles (or Triangle Strips) give the best performance although this may not always be the case (depending on hardware)
- Unless your debugging something, it is not good to use Immediate mode rendering (glBegin/glEnd calls), instead consider using Vertex Arrays or Vertex Buffer Objects. You will see a considerable speed increase.
- Reduce or eliminate the use of Doubles in your code (speed), unless you need that extra precision which is highly unlikely.
- Change glColor3d to either glColor3f (float) or ideally glColor3ub (unsigned bytes) because you won't see that extra visual precision on 32-bit colour and it's faster.

[Edited by - shwasasin on May 28, 2008 5:05:20 PM]

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No problem, I know what you mean about poser game programmers.

Those tips all seem to make sense to me, but my main issues are revolving around the camera direction code. I am trying to set up motion for a simple fps camera but I am having some issues. What I currently have set is obviously wrong, and I was wondering what type of commands I would look into to get it fixed. All that code does right now is turn about 25 degrees in both ways then stops. Any suggestions?

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Quote:
 Original post by snowfellNo problem, I know what you mean about poser game programmers. Those tips all seem to make sense to me, but my main issues are revolving around the camera direction code. I am trying to set up motion for a simple fps camera but I am having some issues. What I currently have set is obviously wrong, and I was wondering what type of commands I would look into to get it fixed. All that code does right now is turn about 25 degrees in both ways then stops. Any suggestions?

The problem, as far as I can see in your code is that you're not actually rotating anything. To solve this, you'll need to dust off those old trigonometry books from high school. This is something I whipped up quickly and probably has compile errors but it will give you a quick idea as to what's going on. I should mention that the player_x/z are the Eye, and the lookat_x/z is, well, the lookat for use the with the gluLookAt function. :)

float player_x = 0.0f; // This is the players position in the worldfloat player_y = 0.0f;float player_z = 0.0f;float player_yaw = 0.0f; // What direction he's facing (I'm not worried about P/R)float player_speed = 64.0f;float lookat_x = 0.0f; // Current view posfloat lookat_z = 0.0f;float lookat_distance = 1000.0f;void player_forward(void){  // To turn, uncomment below, 1.0f = 1d  // player_yaw += 1.0f;   const float rad = M_PI / 180.0f * player_yaw;  const float s = sinf( rad );  const float c = cosf( rad );  // Move player  player_x += (s * player_speed);  player_z -= (c * player_speed);  // Update lookAt  lookat_x = player_x + (s * lookat_distance); // Update view once  lookat_z = player_z - (c * lookat_distance);}

[Edited by - shwasasin on May 28, 2008 6:48:09 PM]

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ah so that is why I couldn't figure it out. Never took trig yet, not till college. So this is a general way of getting the camera to move?

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Quote:
 Original post by snowfellah so that is why I couldn't figure it out. Never took trig yet, not till college. So this is a general way of getting the camera to move?

This is one of many ways to do it. I used the player_x/z position as the camera eye because generally in FPS's the player and the camera are linked (you see through the players eyes). Although in a real-world situation you would want to change the eye_y to be different than the player_y (depending on how you code things), because you could be potentially looking through their feet. With the code provided and a bit of tweaking you could easily make the camera/player go forward/backward, strafe left/right, and turn left/right.

Definitely read up on the trigonometry stuff (sin, cos, tan, etc...) to get a better idea on how it all works as these are important concepts for gaming. And let me know if you have questions, I won't bark (this time)!

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