1.實驗目的:
- 通過示範代碼1,理解簡單光照明模型的基本原理與實現;
- 通過示範代碼2和太陽系示範代碼,學習與掌握OpenGL光照與材質設置與使用方法。
2.實驗內容:
在示範代碼1基礎上,按以下要求修改:
(1) 閱讀和修改示範代碼中的有關參數,產生不同光照效果,觀察顯示效果。挑選兩張修改的效果圖保存爲圖1-2,與對應修改的代碼一起保存至word實驗文檔中(15分鐘);
(2) 將代碼中的球面改爲圓錐面,將圓錐面的光照效果圖存爲圖3,與對應修改的代碼一起保存至word實驗文檔中(25分鐘);
在示範代碼2的基礎上,按以下要求完成任務:
(3) 閱讀和修改示範代碼2中的有關參數,產生不同光照效果,觀察顯示效果。挑選兩張修改的效果圖保存爲圖4-5,與對應修改的代碼一起保存至word實驗文檔中(15分鐘);
(4)參考太陽系示範代碼,該代碼顯示一個簡單的太陽系模型,嘗試爲其增加光照與材質效果,挑選兩張修改的效果圖保存爲圖6-7,與對應修改的代碼一起保存至word實驗文檔中(25分鐘);
(5) 整理word實驗文檔,將其命名爲“序號-姓名-Prj6.doc”,電子版提交至雨課堂,A4打印稿下一次課前或實驗課前提交。
3.實驗原理:
Phong光照明模型是由物體表面上一點P反射到視點的光強I爲環境光的反射光強Ie、理想漫反射光強Id、和鏡面反射光Is的總和,即
其中R,V,N爲單位矢量;爲點光源發出的入射光強;爲環境光的漫反射光強;環境光的漫反射係數;漫反射係數( )取決於表面的材料;鏡面反射係數( );n冪次,用以模擬反射光的空間分佈,表面越光滑,n越大。
在用Phong模型進行真實感圖形計算時,對物體表面上的每個點P,均需計算光線的反射方向R,再由V計算 。爲減少計算量,我們可以作如下假設:a)光源在無窮遠處,即光線方向L爲常數;b)視點在無窮遠處,即視線方向V爲常數;c)用 近似 。這裏H爲L和V的角平分向量, 。在這種簡化下,由於對所有的點總共只需計算一次H的值,節省了計算時間。結合RGB顏色模型,Phong光照明模型的最終形式詳見教材公式(8.21)。
示範代碼1中,光源在無窮遠處,光線方向爲單位向量L(0.5, 0.5, 0.707),視點在無窮遠處,視線方向V爲(0, 0, 1)。
4.示範代碼:
(1) 示範代碼1-球面簡單光照模型效果圖
#include <GL/glut.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
struct Vector
{
float fx, fy, fz;
};
struct Color
{
float Ir, Ig, Ib;
};
float KaIa;//環境光強度
float Kd, n;
Vector H,light;
Color mLight, mColor;//mLight表示漫反射光與鏡面反射光強度
GLboolean bLight = false;
void CirclePt(int x0, int y0, int x, int y, Color mColor)
{
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib);
glBegin(GL_POINTS);
glVertex2i ( x+x0, y+y0);//x,y
glVertex2i ( -x+x0, y+y0);//-x,y
glVertex2i ( x+x0, -y+y0);//x, -y
glVertex2i ( -x+x0, -y+y0);//-x, -y
glVertex2i ( y+x0, x+y0);//y, x
glVertex2i ( y+x0, -x+y0);//y, -x
glVertex2i ( -y+x0, x+y0);//-y, x
glVertex2i ( -y+x0,-x+y0);//-y, -x
glEnd();
}
//中點圓生成算法
void MidCircle(int x0, int y0, int r, Color mColor)
{
int x,y,deltax,deltay,d;
x = 0;
y = r;
deltax = 3;
deltay = 5-r-r;
d = 1-r;
CirclePt( x0, y0, x, y, mColor);
while(x<y)
{
if(d<0)
{
d += deltax;
deltax += 2;
deltay += 2;
x++;
}
else
{
d += deltay;
deltax += 2;
deltay += 4;
x++;
y--;
}
CirclePt( x0, y0, x, y, mColor);
}
}
//填充圓域爲圓餅
void FlatCircle(int x0, int y0, int r, Color mColor)
{
int x,y,deltax,deltay,d;
x = 0;
y = r;
deltax = 3;
deltay = 5-r-r;
d = 1-r;
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib);
glBegin(GL_POINTS);
{
for(int i=-x;i<=x;i++)
{
glVertex2i (i+x0,y+y0);
glVertex2i (i+x0,-y+y0);
}
for(int i=-y;i<=y;i++)
{
glVertex2i (i+x0,x+y0);
glVertex2i (i+x0,-x+y0);
}
while(x<y)
{
if(d<0)
{
d += deltax;
deltax += 2;
deltay += 2;
x++;
}
else
{
d += deltay;
deltax += 2;
deltay += 4;
x++;
y--;
}
for(int i=-x;i<=x;i++)
{
glVertex2i (i+x0,y+y0);
glVertex2i (i+x0,-y+y0);
}
for(int i=-y;i<=y;i++)
{
glVertex2i (i+x0,x+y0);
glVertex2i (i+x0,-x+y0);
}
}
}
glEnd();
}
//初始化設定
void Init()
{
float mo;
Vector eye;
mLight.Ir = 0;
mLight.Ig = 175;
mLight.Ib = 0;
KaIa=80;
Kd = 1;
n = 10;
light.fx=0.50;light.fy=0.50;
light.fz = sqrt(1-(light.fx*light.fx)-(light.fy*light.fy));
eye.fx=0;eye.fy=0;eye.fz=1;
H.fx=light.fx+eye.fx;
H.fy=light.fy+eye.fy;
H.fz=light.fz+eye.fz;
mo=sqrt(H.fx*H.fx+H.fy*H.fy+H.fz*H.fz);
H.fx=(H.fx/mo);H.fy=(H.fy/mo);H.fz=(H.fz/mo);
H.fx=(H.fx/mo);H.fy=(H.fy/mo);H.fz=(H.fz/mo);
glClearColor(0.0, 0.0, 0.0, 0.0);
glShadeModel(GL_SMOOTH);
}
//根據Phong模型計算光強
Color Phong(int x0, int y0, int r, int x, int y)
{
Vector N;
float z,alpha,theta,Ks;
Ks=1.0-Kd;
z=sqrt((float)(r*r-(x-x0)*(x-x0)-(y-y0)*(y-y0)));
N.fx=(x-x0)*1.0/r;
N.fy=(y-y0)*1.0/r;
N.fz = z*1.0/r;
theta = N.fx * light.fx + N.fy * light.fy + N.fz * light.fz;
if(theta<0)
theta=0;
alpha=H.fx*N.fx+H.fy*N.fy+H.fx*N.fz;
if(alpha<0)
alpha=0;
mColor.Ir=KaIa+mLight.Ir*Kd*theta+mLight.Ir*Ks*pow(alpha,n);
mColor.Ig=KaIa+mLight.Ig*Kd*theta+mLight.Ig*Ks*pow(alpha,n);
mColor.Ib=KaIa+mLight.Ib*Kd*theta+mLight.Ib*Ks*pow(alpha,n);
return mColor;
}
//根據計算的光強按球體的結果着色
void Sphere(int x0, int y0, int r)
{
int x,y,deltax,deltay,d;
x = 0;
y = r;
deltax = 3;
deltay = 5-r-r;
d = 1-r;
glBegin(GL_POINTS);
{
for(int i=-x;i<=x;i++)
{
mColor=Phong(x0,y0,r,i+x0,y+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,y+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,-y+y0);
}
for(int i=-y;i<=y;i++)
{
mColor=Phong(x0,y0,r,i+x0,x+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,x+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,-x+y0);
}
while(x<y)
{
if(d<0)
{
d += deltax;
deltax += 2;
deltay += 2;
x++;
}
else
{
d += deltay;
deltax += 2;
deltay += 4;
x++;
y--;
}
for(int i=-x;i<=x;i++)
{
mColor=Phong(x0,y0,r,i+x0,y+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,y+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,-y+y0);
}
for(int i=-y;i<=y;i++)
{
mColor=Phong(x0,y0,r,i+x0,x+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,x+y0);
glColor3ub (mColor.Ir, mColor.Ig, mColor.Ib); glVertex2i (i+x0,-x+y0);
}
}
}
glEnd();
}
void myDisplay()
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f (1.0f, 1.0f, 1.0f);
Color clr;
clr.Ir = 180, clr.Ig = 180, clr.Ib = 180;
MidCircle(100, 200, 50, clr);
FlatCircle(250, 200, 50, clr);
Sphere(400, 200, 50);
glFlush();
}
void Reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLdouble) w, 0.0, (GLdouble) h);
}
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
glutInitWindowPosition(100, 100);
glutInitWindowSize(500, 400);
glutCreateWindow("Hello Light!");
Init();
glutDisplayFunc(myDisplay);
glutReshapeFunc(Reshape);
glutMainLoop();
return 0;
}
程序運行結果:
圖1
(2) 示範代碼2-OpenGL光照與材質下球體效果圖
#include <GL/glut.h>
#include <stdlib.h>
// Initialize material property, light source, lighting model, and depth buffer.
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 };
GLfloat white_light[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat Light_Model_Ambient[] = { 0.2 , 0.2 , 0.2 , 1.0 }; //
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);
glLightfv(GL_LIGHT0, GL_DIFFUSE, white_light);
glLightfv(GL_LIGHT0, GL_SPECULAR, white_light);
glLightModelfv(GL_LIGHT_MODEL_AMBIENT, Light_Model_Ambient); //
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_DEPTH_TEST);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glutSolidSphere (0.5, 20, 16);
//glutSolidTeapot(0.5);
glFlush();
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei)w, (GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if (w <= h)
glOrtho(-1.5, 1.5, -1.5*(GLfloat)h / (GLfloat)w,
1.5*(GLfloat)h / (GLfloat)w, -10.0, 10.0);
else
glOrtho(-1.5*(GLfloat)w / (GLfloat)h,
1.5*(GLfloat)w / (GLfloat)h, -1.5, 1.5, -10.0, 10.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(500, 500);
glutInitWindowPosition(100, 100);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}
程序運行結果:
圖2