how can we make spot lights - c++

Question

i need to draw street lights, but it is illuminating the entire environment, i couldnt make it seem like a spot light. The code below is the one i tried
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0) ;
GLfloat color[4] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat position[4] = {SCREEN_W/2,SCREEN_H/2,0.0,0.0};
float LightDir[3] = {0.0f, 0.0f, -1.0f}; // towards the viewer
glLighti(GL_LIGHT0, GL_SPOT_CUTOFF, 30);
glLightfv(GL_LIGHT0, GL_POSITION, position);
glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, LightDir);
glLightfv(GL_LIGHT0, GL_DIFFUSE, color);

Answer 1

Like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <GL/glut.h>
/* Some <math.h> files do not define M_PI... */
#ifndef M_PI
#define M_PI 3.14159265
#endif
#define TWO_PI (2*M_PI)
typedef struct lightRec {
float amb[4];
float diff[4];
float spec[4];
float pos[4];
float spotDir[3];
float spotExp;
float spotCutoff;
float atten[3];
float trans[3];
float rot[3];
float swing[3];
float arc[3];
float arcIncr[3];
} Light;
static int useSAME_AMB_SPEC = 1;
/* *INDENT-OFF* */
static float modelAmb[4] = {0.2, 0.2, 0.2, 1.0};
static float matAmb[4] = {0.2, 0.2, 0.2, 1.0};
static float matDiff[4] = {0.8, 0.8, 0.8, 1.0};
static float matSpec[4] = {0.4, 0.4, 0.4, 1.0};
static float matEmission[4] = {0.0, 0.0, 0.0, 1.0};
/* *INDENT-ON* */
#define NUM_LIGHTS 3
static Light spots[] =
{
{
{0.2, 0.0, 0.0, 1.0}, /* ambient */
{0.8, 0.0, 0.0, 1.0}, /* diffuse */
{0.4, 0.0, 0.0, 1.0}, /* specular */
{0.0, 0.0, 0.0, 1.0}, /* position */
{0.0, -1.0, 0.0}, /* direction */
{20.0},
{60.0}, /* exponent, cutoff */
{1.0, 0.0, 0.0}, /* attenuation */
{0.0, 1.25, 0.0}, /* translation */
{0.0, 0.0, 0.0}, /* rotation */
{20.0, 0.0, 40.0}, /* swing */
{0.0, 0.0, 0.0}, /* arc */
{TWO_PI / 70.0, 0.0, TWO_PI / 140.0} /* arc increment */
},
{
{0.0, 0.2, 0.0, 1.0}, /* ambient */
{0.0, 0.8, 0.0, 1.0}, /* diffuse */
{0.0, 0.4, 0.0, 1.0}, /* specular */
{0.0, 0.0, 0.0, 1.0}, /* position */
{0.0, -1.0, 0.0}, /* direction */
{20.0},
{60.0}, /* exponent, cutoff */
{1.0, 0.0, 0.0}, /* attenuation */
{0.0, 1.25, 0.0}, /* translation */
{0.0, 0.0, 0.0}, /* rotation */
{20.0, 0.0, 40.0}, /* swing */
{0.0, 0.0, 0.0}, /* arc */
{TWO_PI / 120.0, 0.0, TWO_PI / 60.0} /* arc increment */
},
{
{0.0, 0.0, 0.2, 1.0}, /* ambient */
{0.0, 0.0, 0.8, 1.0}, /* diffuse */
{0.0, 0.0, 0.4, 1.0}, /* specular */
{0.0, 0.0, 0.0, 1.0}, /* position */
{0.0, -1.0, 0.0}, /* direction */
{20.0},
{60.0}, /* exponent, cutoff */
{1.0, 0.0, 0.0}, /* attenuation */
{0.0, 1.25, 0.0}, /* translation */
{0.0, 0.0, 0.0}, /* rotation */
{20.0, 0.0, 40.0}, /* swing */
{0.0, 0.0, 0.0}, /* arc */
{TWO_PI / 50.0, 0.0, TWO_PI / 100.0} /* arc increment */
}
};
static void
usage(char *name)
{
printf("\n");
printf("usage: %s [options]\n", name);
printf("\n");
printf(" Options:\n");
printf(" -geometry Specify size and position WxH+X+Y\n");
printf(" -lm Toggle lighting(SPECULAR and AMBIENT are/not same\n");
printf("\n");
#ifndef EXIT_FAILURE /* should be defined by ANSI C <stdlib.h> */
#define EXIT_FAILURE 1
#endif
exit(EXIT_FAILURE);
}
static void
initLights(void)
{
int k;
for (k = 0; k < NUM_LIGHTS; ++k) {
int lt = GL_LIGHT0 + k;
Light *light = &spots[k];
glEnable(lt);
glLightfv(lt, GL_AMBIENT, light->amb);
glLightfv(lt, GL_DIFFUSE, light->diff);
if (useSAME_AMB_SPEC)
glLightfv(lt, GL_SPECULAR, light->amb);
else
glLightfv(lt, GL_SPECULAR, light->spec);
glLightf(lt, GL_SPOT_EXPONENT, light->spotExp);
glLightf(lt, GL_SPOT_CUTOFF, light->spotCutoff);
glLightf(lt, GL_CONSTANT_ATTENUATION, light->atten[0]);
glLightf(lt, GL_LINEAR_ATTENUATION, light->atten[1]);
glLightf(lt, GL_QUADRATIC_ATTENUATION, light->atten[2]);
}
}
static void
aimLights(void)
{
int k;
for (k = 0; k < NUM_LIGHTS; ++k) {
Light *light = &spots[k];
light->rot[0] = light->swing[0] * sin(light->arc[0]);
light->arc[0] += light->arcIncr[0];
if (light->arc[0] > TWO_PI)
light->arc[0] -= TWO_PI;
light->rot[1] = light->swing[1] * sin(light->arc[1]);
light->arc[1] += light->arcIncr[1];
if (light->arc[1] > TWO_PI)
light->arc[1] -= TWO_PI;
light->rot[2] = light->swing[2] * sin(light->arc[2]);
light->arc[2] += light->arcIncr[2];
if (light->arc[2] > TWO_PI)
light->arc[2] -= TWO_PI;
}
}
static void
setLights(void)
{
int k;
for (k = 0; k < NUM_LIGHTS; ++k) {
int lt = GL_LIGHT0 + k;
Light *light = &spots[k];
glPushMatrix();
glTranslatef(light->trans[0], light->trans[1], light->trans[2]);
glRotatef(light->rot[0], 1, 0, 0);
glRotatef(light->rot[1], 0, 1, 0);
glRotatef(light->rot[2], 0, 0, 1);
glLightfv(lt, GL_POSITION, light->pos);
glLightfv(lt, GL_SPOT_DIRECTION, light->spotDir);
glPopMatrix();
}
}
static void
drawLights(void)
{
int k;
glDisable(GL_LIGHTING);
for (k = 0; k < NUM_LIGHTS; ++k) {
Light *light = &spots[k];
glColor4fv(light->diff);
glPushMatrix();
glTranslatef(light->trans[0], light->trans[1], light->trans[2]);
glRotatef(light->rot[0], 1, 0, 0);
glRotatef(light->rot[1], 0, 1, 0);
glRotatef(light->rot[2], 0, 0, 1);
glBegin(GL_LINES);
glVertex3f(light->pos[0], light->pos[1], light->pos[2]);
glVertex3f(light->spotDir[0], light->spotDir[1], light->spotDir[2]);
glEnd();
glPopMatrix();
}
glEnable(GL_LIGHTING);
}
static void
drawPlane(int w, int h)
{
int i, j;
float dw = 1.0 / w;
float dh = 1.0 / h;
glNormal3f(0.0, 0.0, 1.0);
for (j = 0; j < h; ++j) {
glBegin(GL_TRIANGLE_STRIP);
for (i = 0; i <= w; ++i) {
glVertex2f(dw * i, dh * (j + 1));
glVertex2f(dw * i, dh * j);
}
glEnd();
}
}
int spin = 0;
void
display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glPushMatrix();
glRotatef(spin, 0, 1, 0);
aimLights();
setLights();
glPushMatrix();
glRotatef(-90.0, 1, 0, 0);
glScalef(1.9, 1.9, 1.0);
glTranslatef(-0.5, -0.5, 0.0);
drawPlane(16, 16);
glPopMatrix();
drawLights();
glPopMatrix();
glutSwapBuffers();
}
void
animate(void)
{
spin += 0.5;
if (spin > 360.0)
spin -= 360.0;
glutPostRedisplay();
}
void
visibility(int state)
{
if (state == GLUT_VISIBLE) {
glutIdleFunc(animate);
} else {
glutIdleFunc(NULL);
}
}
int
main(int argc, char **argv)
{
int i;
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
/* process commmand line args */
for (i = 1; i < argc; ++i) {
if (!strcmp("-lm", argv[i])) {
useSAME_AMB_SPEC = !useSAME_AMB_SPEC;
} else {
usage(argv[0]);
}
}
glutCreateWindow("GLUT spotlight swing");
glutDisplayFunc(display);
glutVisibilityFunc(visibility);
glMatrixMode(GL_PROJECTION);
glFrustum(-1, 1, -1, 1, 2, 6);
glMatrixMode(GL_MODELVIEW);
glTranslatef(0.0, 0.0, -3.0);
glRotatef(45.0, 1, 0, 0);
glEnable(GL_LIGHTING);
glEnable(GL_NORMALIZE);
glLightModelfv(GL_LIGHT_MODEL_AMBIENT, modelAmb);
glLightModelf(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_TRUE);
glLightModelf(GL_LIGHT_MODEL_TWO_SIDE, GL_FALSE);
glMaterialfv(GL_FRONT, GL_AMBIENT, matAmb);
glMaterialfv(GL_FRONT, GL_DIFFUSE, matDiff);
glMaterialfv(GL_FRONT, GL_SPECULAR, matSpec);
glMaterialfv(GL_FRONT, GL_EMISSION, matEmission);
glMaterialf(GL_FRONT, GL_SHININESS, 10.0);
initLights();
glutMainLoop();
return 0;
}