[SOLVED] OpenGL lighting doesn't follow viewpoint

Snark1994 · 10-11-2011, 04:47 PM

I'm trying to use OpenGL in a programme, but I'm running into problems with lighting. What I would like is for the models to be lit from the direction of the viewpoint (ie. as if there were a torch strapped to the viewer's head, or a light on the camera or something).

The code I have works for some facings, but when I rotate by 180 degrees the light seems to "go out". I'm not entirely sure if it's not actually following my viewpoint, or whether something isn't configured correctly. This is a compilable code example showing the problem:

Code:

#include <GL/freeglut.h>
#include <math.h>
#define WIDTH 11
#define HEIGHT 11
#define BLOCKSIZE 5.0
const static float fdspeed = BLOCKSIZE*(0.002/1.5), rotspeed = 0.05;
const static double deg_to_rad = 3.141592653589793/180;
static float x = WIDTH*BLOCKSIZE/2, z= HEIGHT*BLOCKSIZE/2, facing = 0.0;
static int fd = 0, rt = 0, strafe = 0;

void drawWalls(int width, int height){
        glPolygonMode( GL_FRONT_AND_BACK, GL_FILL );
        glColor3f(1.0,1.0,1.0);
        glBegin(GL_POLYGON);
                glVertex3f(0.0,0.0,0.0);
                glVertex3f(0.0,-BLOCKSIZE,0.0);
                glVertex3f(width*BLOCKSIZE,-BLOCKSIZE,0.0);
                glVertex3f(width*BLOCKSIZE,0.0,0.0);
        glEnd();
        glBegin(GL_POLYGON);
                glVertex3f(0.0,0.0,0.0);
                glVertex3f(0.0,-BLOCKSIZE,0.0);
                glVertex3f(0.0,-BLOCKSIZE,height*BLOCKSIZE);
                glVertex3f(0.0,0.0,height*BLOCKSIZE);
        glEnd();
        glBegin(GL_POLYGON);
                glVertex3f(0.0,0.0,height*BLOCKSIZE);
                glVertex3f(0.0,-BLOCKSIZE,height*BLOCKSIZE);
                glVertex3f(width*BLOCKSIZE,-BLOCKSIZE,height*BLOCKSIZE);
                glVertex3f(width*BLOCKSIZE,0.0,height*BLOCKSIZE);
        glEnd();
        glBegin(GL_POLYGON);
                glVertex3f(height*BLOCKSIZE,0.0,0.0);
                glVertex3f(height*BLOCKSIZE,-BLOCKSIZE,0.0);
                glVertex3f(height*BLOCKSIZE,-BLOCKSIZE,height*BLOCKSIZE);
                glVertex3f(height*BLOCKSIZE,0.0,height*BLOCKSIZE);
        glEnd();
}
void display(void){
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glPushMatrix();
        glRotatef(facing, 0.0, 1.0, 0.0); // Rotate to the correct facing
        glTranslatef(-x, 0.5*BLOCKSIZE, -z); // Move the models to the correct x and z co-ordinates
        drawWalls(WIDTH,HEIGHT);
        glPopMatrix();
        glutSwapBuffers();
}
void reshape(int w, int h){
        glViewport(0, 0, (GLsizei) w, (GLsizei) h);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective(60.0, (GLfloat) w / (GLfloat) h, 0.45, (WIDTH>HEIGHT)?1.42*WIDTH*BLOCKSIZE:1.42*HEIGHT*BLOCKSIZE);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        gluLookAt(0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, -1.0, 0.0); // y is 'up', we begin looking up the -ve z axis.
}
void movePlayer(void){
        z += cos(facing*deg_to_rad)*fd*fdspeed;
        x -= sin(facing*deg_to_rad)*fd*fdspeed;
        z -= cos((facing+90)*deg_to_rad)*strafe*fdspeed;
        x += sin((facing+90)*deg_to_rad)*strafe*fdspeed;
        facing -= rt * rotspeed;
        while(facing < 0) facing += 360.0;
        while(facing >= 360) facing -= 360.0;
        glutPostRedisplay();
}
void skeyboard(int key, int x, int y){
        switch(key){
                case GLUT_KEY_RIGHT:
                        rt = 1;
                        break;
                case GLUT_KEY_LEFT:
                        rt = -1;
                        break;
                default:
                        break;
        }
        if(fd == 0 && rt == 0 && strafe == 0) glutIdleFunc(NULL);
        else glutIdleFunc(movePlayer);
}
void keyboard(unsigned char key, int x, int y){
        switch(key){
                case 'a':
                        strafe = -1;
                        break;
                case 'd':
                        strafe = 1;
                        break;
                case 'w':
                        fd = 1;
                        break;
                case 's':
                        fd = -1;
                        break;
                default:
                        break;
        }
        if(fd == 0 && rt == 0 && strafe == 0) glutIdleFunc(NULL);
        else glutIdleFunc(movePlayer);
}
void skeyboardUp(int key, int x, int y){
        switch(key){
                case GLUT_KEY_RIGHT:
                case GLUT_KEY_LEFT:
                        rt = 0;
                        break;
                default:
                        break;
        }
        if(fd == 0 && rt == 0 && strafe == 0) glutIdleFunc(NULL);
        else glutIdleFunc(movePlayer);
}
void keyboardUp(unsigned char key, int x, int y){
        switch(key){
                case 'a':
                case 'd':
                        strafe = 0;
                        break;
                case 'w':
                case 's':
                        fd = 0;
                        break;
                default:
                        break;
        }
        if(fd == 0 && rt == 0 && strafe == 0) glutIdleFunc(NULL);
        else glutIdleFunc(movePlayer);
}
void init(void){
        GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
        GLfloat mat_shininess[] = { 50.0 };
        GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

        glClearColor (0.0, 0.0, 0.0, 0.0);
        glShadeModel (GL_SMOOTH);
        glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
        glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);
        glLightfv(GL_LIGHT0, GL_POSITION, light_position);

        glEnable(GL_NORMALIZE);
        glEnable(GL_LIGHTING);
        glEnable(GL_LIGHT0);
        glEnable(GL_DEPTH_TEST);

        glutDisplayFunc(display);
        glutReshapeFunc(reshape);
        glutKeyboardFunc(keyboard);
        glutKeyboardUpFunc(keyboardUp);
        glutSpecialFunc(skeyboard);
        glutSpecialUpFunc(skeyboardUp);
        glutIdleFunc(movePlayer);
}
int main(int argc, char** argv){
        glutInit(&argc, argv);
        glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
        glutInitWindowSize(500, 500);
        glutInitWindowPosition(100, 100);
        glutCreateWindow(argv[0]);
        init();
        glutMainLoop();
        return 0;
}

Compile with

Code:

gcc file.c -o file -lglut -lGL -lGLU -Wall

The OpenGL-y stuff is in "main", "reshape", "display" and "init". The other functions are for handling input, plus a function to draw the walls.

Controls are WASD to move forward/left/back/right, left/right arrow keys to turn around. Expected behaviour is that you can always see the walls which are around you, actual behaviour is that the screen is almost black until you turn around to face the other direction.

Thanks in advance for any help

millgates · 10-11-2011, 05:51 PM

Hi,
I don't know if it is the problem here, but I don't see any calls to glNormalXX in your code. You need to set normals to each surface you render so the OpenGL can determine the angle between the normal to the face and the direction to the source of the light. I don't know how Opengl treats normals if not specified, but it probably uses some default value such as 0.0, 0.0, 1.0 or so. If all normals are the same for all vertices in the scene, then if you look at the wall in one direction it is light because the normals are pointing towards you. If you then turn around 180 degrees the normals on the other wall will point away from you and the walls will be dark.

so for example the code to draw one of the walls could be

Code:

        glBegin(GL_POLYGON);
                glNormal3f(0.0, 0.0, 1.0);
                glVertex3f(0.0,0.0,0.0);
                glVertex3f(0.0,-BLOCKSIZE,0.0);
                glVertex3f(width*BLOCKSIZE,-BLOCKSIZE,0.0);
                glVertex3f(width*BLOCKSIZE,0.0,0.0);
        glEnd();

Note: Since the walls are rectangles, you could probably render them as GL_QUAD (or, even better, GL_TRIANGLE_STRIP) and draw all four walls within a single glBegin() / glEnd() pair, which should result in better performance.

Snark1994 · 10-12-2011, 12:49 PM

Ah brilliant!

That fixed it

Thank you very much.

resetreset · 10-14-2011, 02:44 PM

Sorry, since we're on the topic, can anyone tell me how to actually INSTALL OpenGL on a Ubuntu system? Snark?

dugan · 10-14-2011, 04:22 PM

This was at the top of my first Google search:

http://ubuntuforums.org/showpost.php...00&postcount=2

Seriously, stop wasting people's time by asking questions that you can easily find the answers to yourself.

As this had been pointed out to you dozens of times, and your post was a threadjack, I have punished you by rating your post "not helpful".