c++openglglut
OpenGL/GLUT lighting does not make sense
I have some serious problem in my lighting, I think my math is correct and I positioned every vertex correctly (counter clockwise) but still the result is not correct.
The are 4 triangle and there is a light source on top of them, everything is good when triangles are closed but as soon as they open then lighting inside the triangles would become incorrect.
Any help or hint?
#include <GL/glut.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#define PI 3.14159265
static int step = 0, step1, step2, step3, step4, step5, step6, step7, step8;
/* camera location in longitude and latitude */
static float alpha = 0.0;
static float beta = PI / 6.0;
/* position of camera */
static GLdouble cpos[3];
/* position of light source */
static GLfloat lpos[] = { 0,3,0, 0.001 };
/* vectors to specify material properties */
static GLfloat black[] = { 0.0, 0.0, 0.0, 1.0 };
static GLfloat white[] = { 1.0, 1.0, 1.0, 1.0 };
static GLfloat gray[] = { 0.5, 0.5, 0.5, 1.0 };
static GLfloat red[] = { 1.0, 0.0, 0.0, 1.0 };
static GLfloat green[] = { 0.0, 1.0, 0.0, 1.0 };
static GLfloat blue[] = { 0.0, 0.0, 1.0, 1.0 };
static GLfloat yellow[] = { 1.0, 1.0, 0.0, 1.0 };
static GLfloat magenta[] = { 1.0, 0.0, 1.0, 1.0 };
static GLfloat cyan[] = { 0.0, 1.0, 1.0, 1.0 };
static GLfloat darkcyan[] = { 0.0, 0.4, 0.4, 1.0 };
static GLfloat gold[] = { 255.0 / 255.0, 215.0 / 255.0, 0 / 255.0 };
static GLfloat silver[] = { 204.0 / 255.0, 204.0 / 255.0, 204.0 / 255.0 };
static bool trianglesExist = false;
static float stepBefore = step;
static float zoom = 10.0;
void writemessage()
{
printf("HW-1");
}
void init(void)
{
writemessage();
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_SMOOTH);
/* initially GL_FILL mode (default), later GL_LINE to show wireframe */
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glEnable(GL_LIGHTING);
glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE);
glEnable(GL_LIGHT0);
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei)w, (GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(75.0, (GLfloat)w / (GLfloat)h, 1.0, 20.0);
glMatrixMode(GL_MODELVIEW);
}
void display(void)
{
static int i;
static double angle1, angle2, angle3, angle4, Y1, Z1, Y2, Z2, X3, Y3, X4, Y4;
static double angle5, angle6, angle7, angle8, X5, Y5, X6, Y6, X7, Y7, X8, Y8;
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
/* initialize (modelview) matrix */
glLoadIdentity();
/* update camera position */
cpos[0] = zoom * cos(beta) * sin(alpha);
cpos[1] = zoom * sin(beta);
cpos[2] = zoom * cos(beta) * cos(alpha);
gluLookAt(cpos[0], cpos[1], cpos[2], 0.0, 1.0, 0.0, 0.0, 1.0, 0.0);
/* set current light source position */
glLightfv(GL_LIGHT0, GL_POSITION, lpos);
/* draw sphere to show light source */
glMaterialfv(GL_FRONT, GL_EMISSION, white);
glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 128);
glPushMatrix();
glTranslatef(lpos[0], lpos[1], lpos[2]);
glutSolidSphere(0.1, 10, 8);
glPopMatrix();
/* remaining objects do not look as if they emit light */
glMaterialfv(GL_FRONT, GL_EMISSION, black);
/* draw a tabletop */
glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE, darkcyan);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, white);
glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 64);
glNormal3f(0.0, 1.0, 0.0);
glBegin(GL_POLYGON);
glVertex3f(-5.0, -0.001, -3.0);
glVertex3f(-5.0, -0.001, 5.0);
glVertex3f(5.0, -0.001, 5.0);
glVertex3f(5.0, -0.001, -3.0);
glEnd();
printf("%d", step);
printf("\n");
if (step <= 360)
trianglesExist = true;
else
trianglesExist = false;
if (step > 630 && step < 720){
step1 = 90;
step2 = 90;
step3 = 90;
step4 = 90;
step5 = 90;
step6 = 90;
step7 = 90;
step8 = step - 630;
}
else if (step > 540 && step < 720){
step1 = 90;
step2 = 90;
step3 = 90;
step4 = 90;
step5 = 90;
step6 = 90;
step7 = step - 540;
step8 = 0;
}
else if (step > 450 && step < 720){
step1 = 90;
step2 = 90;
step3 = 90;
step4 = 90;
step5 = 90;
step6 = step - 450;
step7 = 0;
step8 = 0;
}
else if (step > 360 && step < 720){
step1 = 90;
step2 = 90;
step3 = 90;
step4 = 90;
step5 = step - 360;
step6 = 0;
step7 = 0;
step8 = 0;
}
else if (step > 270 && step <= 360)
{
step1 = 90;
step2 = 90;
step3 = 90;
step4 = step - 270;
step5 = 0;
step6 = 0;
step7 = 0;
step8 = 0;
}
else if (step > 180 && step <= 360)
{
step1 = 90;
step2 = 90;
step3 = step - 180;
step4 = 0;
step5 = 0;
step6 = 0;
step7 = 0;
step8 = 0;
}
else if (step > 90 && step <= 360)
{
step1 = 90;
step2 = step - 90;
step3 = 0;
step4 = 0;
step5 = 0;
step6 = 0;
step7 = 0;
step8 = 0;
}
else if (step >= 0 && step <= 360)
{
step1 = step;
step2 = 0;
step3 = 0;
step4 = 0;
step5 = 0;
step6 = 0;
step7 = 0;
step8 = 0;
}
else;
// top back - first
glMaterialfv(GL_FRONT, GL_EMISSION, black);
glMaterialfv(GL_BACK, GL_EMISSION, black);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, gold);
glMaterialfv(GL_BACK, GL_AMBIENT_AND_DIFFUSE, silver);
glMaterialf(GL_BACK, GL_SHININESS, 128);
glMaterialf(GL_FRONT, GL_SHININESS, 128);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, white);
angle1 = ((float)step1 / 180) * PI;
glNormal3f(0, cos(angle1), -sin(angle1));
glBegin(GL_POLYGON);
glVertex3f(-3.0, 2.0, -1.0);
glVertex3f(0, 2.0 + 2.0 * sin(angle1), -1.0 + 2.0 * cos(angle1));
glVertex3f(3.0, 2.0, -1.0);
glEnd();
// top front - second
glMaterialfv(GL_FRONT, GL_EMISSION, black);
glMaterialfv(GL_BACK, GL_EMISSION, black);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, gold);
glMaterialfv(GL_BACK, GL_AMBIENT_AND_DIFFUSE, silver);
glMaterialf(GL_BACK, GL_SHININESS, 128);
glMaterialf(GL_FRONT, GL_SHININESS, 128);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, white);
angle2 = ((float)step2 / 180) * PI;
glNormal3f(0, cos(angle2), sin(angle2));
glBegin(GL_POLYGON);
glVertex3f(3.0, 2.0, 3.0);
glVertex3f(0, 2.0 + 2.0 * sin(angle2), 3.0 + -2.0 * cos(angle2));
glVertex3f(-3.0, 2.0, 3.0);
glEnd();
// top right - third
glMaterialfv(GL_FRONT, GL_EMISSION, black);
glMaterialfv(GL_BACK, GL_EMISSION, black);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, gold);
glMaterialfv(GL_BACK, GL_AMBIENT_AND_DIFFUSE, silver);
glMaterialf(GL_BACK, GL_SHININESS, 128);
glMaterialf(GL_FRONT, GL_SHININESS, 128);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, white);
angle3 = ((float)step3 / 180) * PI;
glNormal3f(sin(angle3), cos(angle3), 0);
glBegin(GL_POLYGON);
glVertex3f(3.0, 2.0, -1.0);
glVertex3f(3.0 - 3.0 * cos(angle3), 2.0 + 2.0 * sin(angle3), 1);
glVertex3f(3.0, 2.0, 3.0);
glEnd();
// top left - fourth
glMaterialfv(GL_FRONT, GL_EMISSION, black);
glMaterialfv(GL_BACK, GL_EMISSION, black);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, gold);
glMaterialfv(GL_BACK, GL_AMBIENT_AND_DIFFUSE, silver);
glMaterialf(GL_BACK, GL_SHININESS, 128);
glMaterialf(GL_FRONT, GL_SHININESS, 128);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, white);
angle4 = ((float)step4 / 180) * PI;
glNormal3f(-sin(angle4), cos(angle4), 0);
glBegin(GL_POLYGON);
glVertex3f(-3.0, 2.0, 3.0);
glVertex3f(-3.0 + 3.0 * cos(angle4), 2.0 + 2.0 * sin(angle4), 1);
glVertex3f(-3.0, 2.0, -1.0);
glEnd();
// buttom
glMaterialfv(GL_FRONT, GL_EMISSION, black);
glMaterialfv(GL_BACK, GL_EMISSION, black);
glMaterialfv(GL_BACK, GL_AMBIENT_AND_DIFFUSE, gold);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, silver);
glMaterialf(GL_BACK, GL_SHININESS, 128);
glMaterialf(GL_FRONT, GL_SHININESS, 128);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, white);
glBegin(GL_POLYGON);
glNormal3f(0, 1, 0);
glVertex3f(-3.0, 0.0, -1.0);
glVertex3f(-3.0, 0.0, 3.0);
glVertex3f(3.0, 0.0, 3.0);
glVertex3f(3.0, 0.0, -1.0);
glEnd();
glFlush();
glutSwapBuffers();
}
void keyboard(unsigned char key, int x, int y)
{
static int polygonmode[2];
switch (key) {
case 27:
exit(0);
break;
/* open and close the top */
case 'o':
if (step < 720) { stepBefore = step*1.0; step = step + 2; }
glutPostRedisplay();
break;
case 'c':
if (step > 0) {
stepBefore = step*1.0; step = step - 2;
}
glutPostRedisplay();
break;
/* w for switching between GL_FILL and GL_LINE
* Using a query command glGetIntegerv() we obtain two integers
* indicating the current GL_POLYGON_MODE for FRONT and BACK faces.
* Look up glIsEnabled() that may be found useful. */
case 'w':
glGetIntegerv(GL_POLYGON_MODE, polygonmode);
if (polygonmode[0] == GL_FILL)
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
else glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glutPostRedisplay();
break;
/* control lpos */
case 'x':
lpos[0] = lpos[0] + 0.2;
glutPostRedisplay();
break;
case 'X':
lpos[0] = lpos[0] - 0.2;
glutPostRedisplay();
break;
case 'y':
lpos[1] = lpos[1] + 0.2;
glutPostRedisplay();
break;
case 'Y':
lpos[1] = lpos[1] - 0.2;
glutPostRedisplay();
break;
case 'z':
lpos[2] = lpos[2] + 0.2;
glutPostRedisplay();
break;
case 'Z':
lpos[2] = lpos[2] - 0.2;
glutPostRedisplay();
break;
case '+':
if (zoom != 1.5)zoom = zoom - 0.5;
glutPostRedisplay();
break;
case '-':
zoom = zoom + 0.5;
glutPostRedisplay();
break;
default:
break;
}
}
void specialkey(GLint key, int x, int y)
{
switch (key) {
case GLUT_KEY_RIGHT:
alpha = alpha + PI / 180;
if (alpha > 2 * PI) alpha = alpha - 2 * PI;
glutPostRedisplay();
break;
case GLUT_KEY_LEFT:
alpha = alpha - PI / 180;
if (alpha < 0) alpha = alpha + 2 * PI;
glutPostRedisplay();
break;
case GLUT_KEY_UP:
if (beta < 0.45*PI) beta = beta + PI / 180;
glutPostRedisplay();
break;
case GLUT_KEY_DOWN:
if (beta > 0.05*PI) beta = beta - PI / 180;
glutPostRedisplay();
break;
default:
break;
}
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glLightModeli(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_TRUE);
glutInitWindowSize(800, 800);
glutInitWindowPosition(100, 100);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutSpecialFunc(specialkey);
glutMainLoop();
return 0;
}
Solution
The problem is with your light position array lpos. I'm assuming you want a positional light that emits light in all directions instead of a directional light which emits light in one direction only. For a positional light the 4th component of lpos should be set to 1 and for a directional light the value should be set to 0. For any value > 0, the x, y, and z values are actually divided by that 4th component so when it is set to 0.001, the light position is not really where you expect it to be.
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