我尝试使用OpenGL绘制Bezier曲面。我的程序读取一个输入文件，其中包含用于曲面着色的绘图，控制点和调色板的多个采样点。它必须输出一个带有曲面图的新窗口，我可以在其中操作曲面和控制点的属性。
根据Bernstein多项式生成的点进行三角测量，并通过从三角形的最小和最大高度映射来为调色板指定颜色。
当我执行它时，为一行三角形分配了错误的颜色。我认为我的一个循环中有一个错误，但改变的值没有证明什么。
以下是代码：
#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
#include <cmath>
using namespace std;
struct vertex
{
float x;
float y;
float z;
};
struct RGB
{
float r;
float g;
float b;
};
int main_window;
bool TM = true;
vertex surfaceTranslate;
float surfaceRotate = 0;
vertex camera;
vertex up;
int currentPointX = 0, currentPointY = 0;
vertex toY;
int SampleR, SampleC;
int M, N;
int K;
vector < vector <vertex> > points;
vector <RGB> palette;
vector < vector <vertex> > control;
float minH, maxH;
int fact (int n)
{
if (!n || n == 1)
{
return 1;
}
return n * fact (n - 1);
}
int C (int n, int i)
{
return fact (n) / (fact (i) * fact (n - i));
}
void initialDisplay(void)
{
glClearColor (1.0, 1.0, 1.0, 1.0);
glDisable (GL_LIGHTING);
glEnable (GL_RESCALE_NORMAL);
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
gluPerspective (60, 1, 1, 1000000);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity();
}
void updateControl()
{
control.clear();
for (int i = 0; i < SampleR; ++i)
{
vector <vertex> temp;
for (int j = 0; j < SampleC; ++j)
{
float u = (float)(i) / (SampleR - 1);
float v = (float)(j) / (SampleC - 1);
vertex p;
p.x = p.y = p.z = 0;
for (int k = 0; k < M; ++k)
{
for (int m = 0; m < N; ++m)
{
float B_u = C (M - 1, k) * pow (u, k) * pow (1 - u, M - 1 - k);
float B_v = C (N - 1, m) * pow (v, m) * pow (1 - v, N - 1 - m);
p.x += B_u * B_v * points[k][m].x;
p.y += B_u * B_v * points[k][m].y;
p.z += B_u * B_v * points[k][m].z;
}
}
temp.push_back (p);
}
control.push_back (temp);
}
maxH = 1 << ((sizeof(float) * 8) - 1);
minH = -maxH;
for (int i = 0; i < SampleR - 1; ++i)
{
for (int j = 0; j < SampleC - 1; ++j)
{
float h = (control[i][j].y + control[i + 1][j].y + control[i][j + 1].y) / 3;
if (h > maxH)
{
maxH = h;
}
if (h < minH)
{
minH = h;
}
h = (control[i + 1][j].y + control[i][j + 1].y + control[i + 1][j + 1].y) / 3;
if (h > maxH)
{
maxH = h;
}
if (h < minH)
{
minH = h;
}
}
}
for (int i = 0; i < SampleR; ++i)
{
for (int j = 0; j < SampleC; ++j)
{
toY.x += control[i][j].x;
toY.z += control[i][j].z;
}
toY.x /= SampleR * SampleC;
toY.z /= SampleR * SampleC;
}
}
void display(void)
{
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
gluLookAt (camera.x, camera.y, camera.z, 0, 0, 0, up.x, up.y, up.z);
glTranslatef (surfaceTranslate.x, surfaceTranslate.y, surfaceTranslate.z);
glTranslatef (toY.x, toY.y, toY.z);
glRotatef (surfaceRotate, 0, 1, 0);
glTranslatef (- toY.x, -toY.y, -toY.z);
if (!TM)
{
glPointSize (10);
glBegin (GL_POINTS);
for (int i = 0; i < M; ++i)
{
for (int j = 0; j < N; ++j)
{
if (i == currentPointX && j == currentPointY)
{
glColor3f (1.0, 0.0, 0.0);
}
else
{
glColor3f (0.0, 0.0, 1.0);
}
glVertex3f (points[i][j].x, points[i][j].y, points[i][j].z);
}
}
glEnd();
}
glBegin (GL_TRIANGLES);
for (int i = 0; i < SampleR - 1; ++i)
{
for (int j = 0; j < SampleC - 1; ++j)
{
glVertex3f (control[i][j].x, control[i][j].y, control[i][j].z);
glVertex3f (control[i + 1][j].x, control[i + 1][j].y, control[i + 1][j].z);
glVertex3f (control[i][j + 1].x, control[i][j + 1].y, control[i][j + 1].z);
float h = (control[i][j].y + control[i + 1][j].y + control[i][j + 1].y) / 3;
int index = K * (h - minH) / (maxH - minH);
glColor3f (palette[index].r / 255, palette[index].g / 255, palette[index].b / 255);
glVertex3f (control[i + 1][j].x, control[i + 1][j].y, control[i + 1][j].z);
glVertex3f (control[i][j + 1].x, control[i][j + 1].y, control[i][j + 1].z);
glVertex3f (control[i + 1][j + 1].x, control[i + 1][j + 1].y, control[i + 1][j + 1].z);
h = (control[i + 1][j].y + control[i][j + 1].y + control[i + 1][j + 1].y) / 3;
index = K * (h - minH) / (maxH - minH);
glColor3f (palette[index].r / 255, palette[index].g / 255, palette[index].b / 255);
}
}
glEnd();
glutSwapBuffers();
}
void keyboardEvent (unsigned char key, int x, int y)
{
if (TM)
{
switch (key)
{
case ('2'):
TM = false;
glutSetWindowTitle ("Surface Editing Mode");
break;
case ('q'):
--surfaceTranslate.x;
break;
case ('w'):
++surfaceTranslate.x;
break;
case ('a'):
--surfaceTranslate.y;
break;
case ('s'):
++surfaceTranslate.y;
break;
case ('z'):
--surfaceTranslate.z;
break;
case ('x'):
++surfaceTranslate.z;
break;
case ('r'):
++surfaceRotate;
break;
case ('t'):
--surfaceRotate;
break;
}
}
else
{
switch (key)
{
case ('1'):
TM = true;
glutSetWindowTitle ("Transformation Mode");
break;
case ('q'):
--points[currentPointX][currentPointY].x;
updateControl();
break;
case ('w'):
++points[currentPointX][currentPointY].x;
updateControl();
break;
case ('a'):
--points[currentPointX][currentPointY].y;
updateControl();
break;
case ('s'):
++points[currentPointX][currentPointY].y;
updateControl();
break;
case ('z'):
--points[currentPointX][currentPointY].z;
updateControl();
break;
case ('x'):
++points[currentPointX][currentPointY].z;
updateControl();
break;
case ('i'):
if (!(SampleR % 2))
{
SampleR /= 2;
updateControl();
}
break;
case ('o'):
SampleR *= 2;
updateControl();
break;
case ('k'):
if (!(SampleC % 2))
{
SampleC /= 2;
updateControl();
}
break;
case ('l'):
SampleC *= 2;
updateControl();
break;
}
}
glutPostRedisplay();
}
void arrowKeys (int key, int x, int y)
{
if (!TM)
{
switch (key)
{
case (GLUT_KEY_UP):
if (currentPointY < N - 1)
{
++currentPointY;
}
break;
case (GLUT_KEY_DOWN):
if (currentPointY)
{
--currentPointY;
}
break;
case (GLUT_KEY_LEFT):
if (currentPointX)
{
--currentPointX;
}
break;
case (GLUT_KEY_RIGHT):
if (currentPointX < M - 1)
{
++currentPointX;
}
break;
}
glutPostRedisplay();
}
}
void changeDirection (int x, int y)
{
float dist = sqrt (pow (camera.x, 2) + pow (camera.y, 2) + pow (camera.z, 2));
camera.x = dist * sin (360.0 / 800 * x * 0.0174532) * sin (360.0 / 800 * y * 0.0174532);
camera.y = dist * cos (360.0 / 800 * y * 0.0174532);
camera.z = dist * cos (360.0 / 800 * x * 0.0174532) * sin (360.0 / 800 * y * 0.0174532);
up.x = dist * sin (360.0 / 800 * x * 0.0174532) * sin (360.0 / 800 * y * 0.0174532 - 1) - camera.x;
up.y = dist * cos (360.0 / 800 * y * 0.0174532 - 1) - camera.y;
up.z = dist * cos (360.0 / 800 * x * 0.0174532) * sin (360.0 / 800 * y * 0.0174532 - 1) - camera.z;
glutPostRedisplay();
}
void mouseEvent (int key, int state, int x, int y)
{
if (key == GLUT_KEY_LEFT)
{
changeDirection (x, y);
}
}
void readFile (char *fname)
{
ifstream file (fname);
if (file.is_open())
{
file >> SampleR >> SampleC;
file >> M >> N;
for (int i = 0; i < M; ++i)
{
vector <vertex> tempv;
for (int j = 0; j < N; ++j)
{
vertex temp;
file >> temp.x >> temp.y >> temp.z;
tempv.push_back (temp);
}
points.push_back (tempv);
}
file >> K;
for (int i = 0; i < K; ++i)
{
RGB temp;
file >> temp.r >> temp.g >> temp.b;
palette.push_back (temp);
}
}
file.close();
}
int main (int argc, char *argv[])
{
surfaceTranslate.x = surfaceTranslate.y = surfaceTranslate.z = toY.x = toY.y = toY.z = up.x = up.z = 0;
up.y = 1;
camera.x = camera.y = camera.z = 100;
readFile (argv[1]);
updateControl();
glutInit (&argc,argv);
glutInitDisplayMode (GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutInitWindowPosition (50, 50);
glutInitWindowSize (800, 800);
main_window = glutCreateWindow ("Transformation Mode");
glutDisplayFunc (display);
glutKeyboardFunc (keyboardEvent);
glutSpecialFunc (arrowKeys);
glutMouseFunc (mouseEvent);
glutMotionFunc (changeDirection);
initialDisplay();
glutMainLoop();
}
答案 0 :(得分：1)
display（）中有两件事有问题：
当h == maxH时，（h - minH）/（maxH - minH）等于1.0f，这意味着该行：
index = K * (h - minH) / (maxH - minH);
简化为：
index = K;
和K是调色板的大小。一个简单的解决方法是添加对min（）的调用，如：
index = min(K-1, K * (h - minH) / (maxH - minH));