OpenGL Bresenham Line

Question

У меня есть базовый код для рисования линии Bresenham с использованием opengl. Проблема в том, что в конце она не показывает результаты. Открывается и закрывается только окно без каких-либо других ошибок. Кто-нибудь может мне помочь?

#include <math.h> 
#include <iostream> 
#include <algorithm> 
#include <GL\glew.h> 
#include <GL\freeglut.h> 

int ww = 600, wh = 400; 
int xi, yi, xf, yf; 
bool firstClick = true; 

using namespace std; 

void setPixel(int x, int y) 
{ 
    glColor3f(0.0, 0.0, 0.0); //Set pixel to black 
    glBegin(GL_POINTS); 
    glVertex2i(x, y); //Set pixel coordinates 
    glEnd(); 
    glFlush(); //Render pixel 
} 

//Draw line if X distance is greater than Y 
void bresenhamX(int x0, int y0, int x1, int y1, int dx, int dy) 
{ 
    int i, j, k; 

    i = 2 * dy - dx; 
    j = 2 * dy; 
    k = 2 * (dy - dx); 
    if (!(x0 < x1)) { 
     swap(x0, x1); 
     swap(y0, y1); 
    } 
    setPixel(x0, y0); 
    while (x0 < x1) { 
     if (i < 0) 
      i += j; 
     else { 
      if (y0 < y1) 
       ++y0; 
      else 
       --y0; 
      i += k; 
     } 
     ++x0; 
     setPixel(x0, y0); 
    } 
} 

//Draw line if X distance is lesser than Y 
void bresenhamY(int x0, int y0, int x1, int y1, int dx, int dy) 
{ 
    int i, j, k; 

    i = 2 * dx - dy; 
    j = 2 * dx; 
    k = 2 * (dx - dy); 
    if (!(y0 < y1)) { 
     swap(x0, x1); 
     swap(y0, y1); 
    } 
    setPixel(x0, y0); 
    while (y0 < y1) { 
     if (i < 0) 
      i += j; 
     else { 
      if (x0 > x1) 
       --x0; 
      else 
       ++x0; 
      i += k; 
     } 
     ++y0; 
     setPixel(x0, y0); 
    } 
} 

//Called by mouse(), will call the appropriate function depending on the length of the X and Y axis 
void bresenham(int x0, int y0, int x1, int y1) 
{ 
    int dx = abs(x1 - x0); 
    int dy = abs(y1 - y0); 

    if (dx >= dy) 
     bresenhamX(x0, y0, x1, y1, dx, dy); 
    else 
     bresenhamY(x0, y0, x1, y1, dx, dy); 
} 

//Calls Bresenham function when the mouse has traced a line 
void mouse(int btn, int state, int x, int y) 
{ 
    if (btn == GLUT_LEFT_BUTTON) { 
     if (firstClick) { 
      xi = x; 
      yi = (wh - y); 
      firstClick = false; 
     } 
     else { 
       xf = x; 
       yf = (wh - y); 
       bresenham(xi, yi, xf, yf); 
       firstClick = true; 
     } 
    } 
} 

// Keyboard input processing routine. 
void keyInput(unsigned char key, int x, int y) 
{ 
    switch (key) 
    { 
    case 27: // Press escape to exit. 
     exit(0); 
     break; 
    default: 
     break; 
    } 
} 

// Drawing (display) routine. 
void drawScene(void) 
{ 
    glClearColor(0.4, 0.7, 0.5, 1.0); // Set foreground color 
    glColor3f(0.2, 0.3, 0.3); // Clear screen to background color. 
    glClear(GL_COLOR_BUFFER_BIT); //Flush created objects to the screen, i.e., force rendering. 
    glFlush(); 
} 

// OpenGL window reshape routine. 
void setup() 
{ 
    glViewport(0, 0, ww, wh); // Set viewport size to be entire OpenGL window. 
    glMatrixMode(GL_PROJECTION); // Set matrix mode to projection. 
    glLoadIdentity(); // Clear current projection matrix to identity. 
    gluOrtho2D(0.0, (GLdouble)ww, 0.0, (GLdouble)wh); // Specify the orthographic (or perpendicular) projection, i.e., define the viewing box. 
    glMatrixMode(GL_MODELVIEW); // Set matrix mode to modelview. 
} 

// Main routine: defines window properties, creates window, registers callback routines and begins processing. 
int main(int argc, char **argv) 
{ 
    glutInit(&argc, argv); // Initialize GLUT. 
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); // Set display mode as single-buffered and RGB color. 
    glutInitWindowSize(ww, wh); // Set OpenGL window size. 
    glutInitWindowPosition(100, 100); // Set position of OpenGL window upper-left corner. 
    glutCreateWindow("Bresenham"); // Create OpenGL window with title. 
    glutDisplayFunc(drawScene); // Register display routine. 
    setup(); // Register reshape routine. 
    glutKeyboardFunc(keyInput); // Register keyboard routine. 
    glutMouseFunc(mouse); // Begin processing. 
    glutMainLoop(); 
    return 0; 
} 

Answer 1

1. магазин от линии начинаются/конечные точки в функции обратного вызова мыши & ВЫПУСКАЙТЕ glutPostRedisplay()
2. Рисовать линию отображения обратного вызова с использованием хранимой информации

Все вместе:

#include <algorithm> 
#include <GL/glut.h> 

int ww = 600, wh = 400; 
int xi, yi, xf, yf; 
bool firstClick = true; 

using namespace std; 

void setPixel(int x, int y) 
{ 
    glColor3f(0.0, 0.0, 0.0); //Set pixel to black 
    glBegin(GL_POINTS); 
    glVertex2i(x, y); //Set pixel coordinates 
    glEnd(); 
} 

//Draw line if X distance is greater than Y 
void bresenhamX(int x0, int y0, int x1, int y1, int dx, int dy) 
{ 
    int i, j, k; 

    i = 2 * dy - dx; 
    j = 2 * dy; 
    k = 2 * (dy - dx); 
    if (!(x0 < x1)) { 
     swap(x0, x1); 
     swap(y0, y1); 
    } 
    setPixel(x0, y0); 
    while (x0 < x1) { 
     if (i < 0) 
      i += j; 
     else { 
      if (y0 < y1) 
       ++y0; 
      else 
       --y0; 
      i += k; 
     } 
     ++x0; 
     setPixel(x0, y0); 
    } 
} 

//Draw line if X distance is lesser than Y 
void bresenhamY(int x0, int y0, int x1, int y1, int dx, int dy) 
{ 
    int i, j, k; 

    i = 2 * dx - dy; 
    j = 2 * dx; 
    k = 2 * (dx - dy); 
    if (!(y0 < y1)) { 
     swap(x0, x1); 
     swap(y0, y1); 
    } 
    setPixel(x0, y0); 
    while (y0 < y1) { 
     if (i < 0) 
      i += j; 
     else { 
      if (x0 > x1) 
       --x0; 
      else 
       ++x0; 
      i += k; 
     } 
     ++y0; 
     setPixel(x0, y0); 
    } 
} 

//Called by mouse(), will call the appropriate function depending on the length of the X and Y axis 
void bresenham(int x0, int y0, int x1, int y1) 
{ 
    int dx = abs(x1 - x0); 
    int dy = abs(y1 - y0); 

    if (dx >= dy) 
     bresenhamX(x0, y0, x1, y1, dx, dy); 
    else 
     bresenhamY(x0, y0, x1, y1, dx, dy); 
} 

//Calls Bresenham function when the mouse has traced a line 
bool drawLine = false; 
void mouse(int btn, int state, int x, int y) 
{ 
    if(btn == GLUT_LEFT_BUTTON && state == GLUT_UP) { 
     if (firstClick) { 
      xi = x; 
      yi = (wh - y); 
      firstClick = false; 
      drawLine = false; 
     } 
     else { 
      xf = x; 
      yf = (wh - y); 
      firstClick = true; 
      drawLine = true; 
     } 
    } 
    glutPostRedisplay(); 
} 

// Keyboard input processing routine. 
void keyInput(unsigned char key, int x, int y) 
{ 
    switch (key) 
    { 
    case 27: // Press escape to exit. 
     exit(0); 
     break; 
    default: 
     break; 
    } 
} 

// Drawing (display) routine. 
void drawScene(void) 
{ 
    glClearColor(0.4, 0.7, 0.5, 1.0); // Set foreground color 
    glColor3f(0.2, 0.3, 0.3); // Clear screen to background color. 
    glClear(GL_COLOR_BUFFER_BIT); //Flush created objects to the screen, i.e., force rendering. 
    if(drawLine) 
    { 
     bresenham(xi, yi, xf, yf); 
    } 
    glFlush(); 
} 

// OpenGL window reshape routine. 
void setup() 
{ 
    glViewport(0, 0, ww, wh); // Set viewport size to be entire OpenGL window. 
    glMatrixMode(GL_PROJECTION); // Set matrix mode to projection. 
    glLoadIdentity(); // Clear current projection matrix to identity. 
    gluOrtho2D(0.0, (GLdouble)ww, 0.0, (GLdouble)wh); // Specify the orthographic (or perpendicular) projection, i.e., define the viewing box. 
    glMatrixMode(GL_MODELVIEW); // Set matrix mode to modelview. 
} 

// Main routine: defines window properties, creates window, registers callback routines and begins processing. 
int main(int argc, char **argv) 
{ 
    glutInit(&argc, argv); // Initialize GLUT. 
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); // Set display mode as single-buffered and RGB color. 
    glutInitWindowSize(ww, wh); // Set OpenGL window size. 
    glutInitWindowPosition(100, 100); // Set position of OpenGL window upper-left corner. 
    glutCreateWindow("Bresenham"); // Create OpenGL window with title. 
    glutDisplayFunc(drawScene); // Register display routine. 
    setup(); // Register reshape routine. 
    glutKeyboardFunc(keyInput); // Register keyboard routine. 
    glutMouseFunc(mouse); // Begin processing. 
    glutMainLoop(); 
    return 0; 
}