我正在使用Bresenham的中点算法作为作业在OpenGL上运行类似于MS Paint的应用程序。到目前为止，我可以画线和椭圆。调整窗口大小时，我会全部丢失。我怎样才能画出它们？
完整代码:
#include "GL/glut.h"
#include <stdio.h>
#include <math.h>
int i;
//int mainWindow, subWindow;
int X1, Y1, X2, Y2;
int modoDeDibujo;
int W = 1000, H = 1000;
/*void menuApp (int value)
{
if (value == 1) printf("Linea\n");
if (value == 2) printf("Circulo\n");
if (value == 3) printf("Elipsis\n");
if (value == 4) exit(0);
}
void crearMenu()
{
//inicio Creando el menu
int submenu;
submenu = glutCreateMenu(menuApp);
glutAddMenuEntry("Linea", 1);
glutAddMenuEntry("Elipse",3);
glutAddMenuEntry("Salir",4);
glutCreateMenu(menuApp);
glutAddSubMenu("SubMenu", submenu);
glutAttachMenu(GLUT_RIGHT_BUTTON);
//fin Creando el menu
}*/
void renderPoint(void) /*REVISAR ESTO*/
{
glClear (GL_COLOR_BUFFER_BIT);
glBegin (GL_POINTS);
glVertex2f (-0.98, 0.98);
glEnd ();
glFlush ();
}
void renderPoint(double x, double y)
{
//printf("BEFORE TRANSFORM %f\t%f\t# renderPoint\n", x, y);
W = glutGet(GLUT_WINDOW_WIDTH);
H = glutGet(GLUT_WINDOW_HEIGHT);
float X;
float Y;
glBegin (GL_POINTS);
X = (2*x/W) - 1;
Y = (-2*y/H) + 1;
glVertex2f (X, Y);
//printf("TRANSFORMED POINT %f\t%f\t# renderPoint\n", X, Y);
glEnd ();
glFlush ();
}
/*wiki pseudo:
function line(x0, x1, y0, y1) //x1
boolean steep := abs(y1 - y0) > abs(x1 - x0)//x2
if steep then//x3
swap(x0, y0) //x4
swap(x1, y1) //x5
if x0 > x1 then //x6
swap(x0, x1) //x7
swap(y0, y1) //x8
int deltax := x1 - x0 //x9
int deltay := abs(y1 - y0) //x10
int error := deltax / 2 //x11
int ystep //x12
int y := y0 //x13
if y0 < y1 then ystep := 1 else ystep := -1 //x14
for x from x0 to x1 //x15
if steep then plot(y,x) else plot(x,y) //x16
error := error - deltay //x17
if error < 0 then //x18
y := y + ystep //x19
error := error + deltax //x20
*/
void bresenham1(GLint x0, GLint x1, GLint y0, GLint y1) //function line(x0, x1, y0, y1)
{
//double result1 = fabs((double)y1 - y0); //abs(y1 - y0)
//double result2 = fabs((double)x1 - x0); //abs(x1 - x0)
int result1 = abs(y1-y0);
int result2 = abs(x1-x0);
bool steep = (result1 > result2); //boolean steep := abs(y1 - y0) > abs(x1 - x0)
if (steep){ //if steep then
GLint aux1 = x0; //swap(x0, y0)
x0=y0;
y0 = aux1;
GLint aux2 = x1; // swap (x1,y1)
x1=y1;
y1=aux2;
}
if(x0>x1){ // if (x0>x1)
GLint aux3=x0; //swap(x0,x1)
x0=x1;
x1=aux3;
GLint aux4=y0;//swap(y0,y1)
y0=y1;
y1=aux4;
}
int deltax = x1-x0; // deltax = x1-x0
int deltay = abs(y1-y0); // int deltay := abs(y1 - y0) - revisar
int error = (deltax / 2); //int error := deltax / 2
int ystep; // int ystep
int y = y0; //int y := y0
if (y0<y1){ //if y0 < y1 then ystep := 1 else ystep := -1
ystep=1;
}
else {ystep=-1;}
for (int x=x0; x<=x1; x++){ //for x from x0 to x1
if (steep){ // if steep then plot(y,x) else plot(x,y)
renderPoint(y,x);
}
else {
renderPoint(x,y);
}
error = error - deltay; //error := error - deltay
if (error<0) { //if error < 0 then
y = y + ystep; // y := y + ystep
error = error + deltax; //error := error + deltax
} // end if (error<0)
}// end for from x0 to x1
}// end bresenham
void Plot4EllipsePoints(int X, int Y,int CX,int CY){
renderPoint(CX+X, CY+Y); //point in quadrant 1
renderPoint(CX-X, CY+Y); // point in quadrant 2
renderPoint(CX-X, CY-Y); // point in quadrant 3
renderPoint(CX+X, CY-Y); // point in quadrant 4
}
void PlotEllipse (int CX, int CY, int XRadius, int YRadius) {
int X, Y;
int XChange, YChange;
int EllipseError;
int TwoASquare, TwoBSquare;
int StoppingX, StoppingY;
TwoASquare = 2 * XRadius * XRadius;
TwoBSquare = 2 * YRadius * YRadius;
X = XRadius;
Y =0;
XChange = YRadius*YRadius*(1-(2*XRadius));
YChange = XRadius * XRadius;
EllipseError =0;
StoppingX = TwoBSquare*XRadius;
StoppingY = 0;
while(StoppingX >= StoppingY){
Plot4EllipsePoints(X,Y,CX,CY);
Y++;
StoppingY=StoppingY + TwoASquare;
EllipseError= EllipseError+ YChange;
YChange= YChange+ TwoASquare;
if( ((2*EllipseError) + XChange)>0)
{
X--;
StoppingX = StoppingX - TwoBSquare;
EllipseError= EllipseError + XChange;
XChange = XChange + TwoBSquare;
}
}
//1st set of points done, start second set
X=0;
Y= YRadius;
XChange= YRadius*YRadius;
YChange = XRadius*XRadius*(1-2*YRadius);
EllipseError=0;
StoppingX =0;
StoppingY= TwoASquare * YRadius;
while(StoppingX <= StoppingY){ // 2nd set of points, y'<-1
Plot4EllipsePoints(X,Y, CX,CY);
X++;
StoppingX = StoppingX + TwoBSquare;
EllipseError = EllipseError + XChange;
XChange = XChange + TwoBSquare;
if (((2*EllipseError) + YChange)>0){
Y--;
StoppingY = StoppingY - TwoASquare;
EllipseError = EllipseError + YChange;
YChange = YChange + TwoASquare;
}
}
}
void renderAll (void)
{
/*glutSetWindow(mainWindow);
glutPostRedisplay();
glutSetWindow(subWindow);
glutPostRedisplay();*/
}
void movimiento(int boton, int estado, int x, int y)
{
if((estado == GLUT_DOWN) && (boton == GLUT_LEFT_BUTTON))//mouse down
{
X1 = x; Y1 = y;
PlotEllipse (x, y, 200, 100);
renderPoint(x,y);
}
if((estado == GLUT_UP) && (boton == GLUT_LEFT_BUTTON))//mouse up
{
//printf(" Up|x:%d, y:%d\n",x,y);
X2 = x; Y2 = y;
//renderLine();
bresenham1(X1,X2,Y1,Y2);
//PRUEBA USANDO LA PRIMITIVA DE OPENGL
glBegin( GL_LINES );
glEnd();
//renderPoint(x, y);
}
}
void MouseMove(int x, int y)
{
//printf("x:%d | y:%d\n", x,y);
X2 = x; Y2 = y;
//renderLine();
//bresenham1(X1, Y1, X2, Y2);
}
void teclado(unsigned char key, int x, int y)
{
if(key==1){
modoDeDibujo=1; // dibuja lineas
printf("Modo de dibujo: linea");
}
if (key==2){
modoDeDibujo=2; //dibuja elipses
}
if(key == 27)exit(0);
}
void especiales(int key, int x, int y)
{
if(key == GLUT_KEY_F1) exit(0);
}
static void
key(unsigned char k, int x, int y)
{
switch (k) {
case 27: /* Escape */
exit(0);
break;
default:
return;
}
glutPostRedisplay();
}
int main (int argc, char *argv [])
{
i = 0;
//inicializa las operaciones de OpenGL/GLUT, db cr antes de usar funciones GLUT
glutInit (&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGBA);
glutInitWindowPosition (100, 100);
glutInitWindowSize (W, H);
//Crea una ventana de Opengl
glutCreateWindow ("tarea");
glutDisplayFunc (renderPoint);
glutMouseFunc(movimiento);
glutKeyboardFunc(teclado);//teclas ASCII
glutSpecialFunc(especiales);//captura las teclas [f1..f12]
//glutPassiveMotionFunc(pasivo);
glutKeyboardFunc(key);
glutMotionFunc(MouseMove);
//crearMenu();
glutMainLoop ();
}
最佳答案
首先，您需要安排代码。您必须只有一个显示功能，该功能可以清除缓冲区，调用其他绘制函数并将其刷新到屏幕(或者，如果您使用的是双缓冲区，则交换缓冲区)。
调整窗口大小时，GLUT将调用显示函数，即众所周知的renderPoint():
glutDisplayFunc (renderPoint);
renderPoint 在重绘“点”之前清除缓冲区，例如:
void renderPoint(void) /*REVISAR ESTO*/
{
glClear (GL_COLOR_BUFFER_BIT);
glBegin (GL_POINTS);
glVertex2f (-0.98, 0.98);
glEnd ();
glFlush ();
}
由于已清除缓冲区，因此在函数renderPoint之外绘制的所有点(圆点，线点..)都没有意义，因为您没有从“主显示函数renderPoint调用它们”。
如何在屏幕上保持这些点？
您必须将点(要绘制的任何点)存储在缓冲区中，例如数组，动态数组，std::vector或其他任何东西。在显示功能中，编写循环语句以访问每个点并提取x和y ..然后绘制它们。
例如，代替上述功能，将其替换为:
class MyPoint {
public:
float x;
float y;
MyPoint(float x, float y)
{
this->x = x;
this->y = y;
} };
#include <vector>
std::vector<MyPoint> testPoints;
void renderPoint(void) /*REVISAR ESTO*/ {
testPoints.push_back(MyPoint(-0.58,0.58));
testPoints.push_back(MyPoint(0.58,0.58));
testPoints.push_back(MyPoint(0.58,-0.58));
glClear (GL_COLOR_BUFFER_BIT);
glPointSize(2);
glBegin (GL_POINTS);
for(int i=0;i<testPoints.size();i++)
{
glVertex2f (testPoints[i].x, testPoints[i].y);
}
glEnd ();
glFlush ();
}
如您所见，通过使用诸如(std::vector)之类的动态数组来存储这些点并使用for循环语句，我们能够使这三个点保持可见。
还有什么？
mouse click”事件，您可以add or push_back的两个点代表数组或std::vector中称为lineArray的行端点。在display function中，使for循环语句在提取两个线点之后绘制每条线。 glutReshapeFunc和glViewport来确保调整大小事件后视口与窗口具有相同的变暗。而且我认为gluOrtho2d比尝试从Windows坐标空间映射到OpenGL坐标空间您的程序可能是这样的:
void drawTestPoints()
{
for(int i=0;i<length;i++)
{
renderPoint(pointsArray[i].x,pointsArray[i].y);// vector of points/(MyPoint)
}
}
void drawLines()
{
for(int i=0;i<length;)
{
MyPoint startPoint = linesArray[i];
MyPoint endPoint = linesArray[i+1];
bresenham1(startPoint.x,endPoint.x,startPoint.y,endPoint.y);
i+=2;
}
}
void drawAll()
{
glClear (GL_COLOR_BUFFER_BIT);
drawTestPoints();
drawLines();
drawOtherShapes();
glFlush();
}
.
.
.
// in the main func:
glutDisplayFunc (drawAll);
==