我正在使用Bresenham的中点算法作为家庭作业在OpenGL上使用类似MS的绘画应用程序。到目前为止，我可以绘制线条和椭圆。在调整窗口大小时，我失去了它们。我怎样才能把它们画出来？
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 ();
}
答案 0 :(得分：4)
首先，您需要安排代码。您必须只有一个显示功能，清除缓冲区，调用其他绘图功能并将它们刷新到屏幕上（如果使用双缓冲区，则交换缓冲区）。
在调整窗口大小时，GLUT将调用显示函数，即renderPoint（），如您所知：
glutDisplayFunc (renderPoint);
renderPoint 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 ();
}
由于缓冲区已被清除，因此在函数renderPoint之外绘制的所有点（圆点，线的点......）都没有意义，因为你没有从“主显示函数调用它们”是renderPoint。
如何在屏幕上保留点数？
您必须将点（您想要绘制的任何点）存储在缓冲区中，例如数组，动态数组，std :: vector或其他任何内容。在display函数中，编写一个循环语句来访问每个点并提取x和y ..然后绘制它们。
例如，代替上述函数，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 ();
}
正如您所看到的，通过使用动态数组（如（std :: vector）来存储点并使用for循环语句，我们可以保持三个点可见。
还有什么？
使用其他形状执行相同的方法，因此对于每个“mouse click”事件，您可以add or push_back两个点表示数组或std :: vector中的行结束点lineArray。在display function中，在提取两个线点后创建一个for循环语句来绘制每一行。
您应该使用glutReshapeFunc和glViewport来确保视口在调整大小事件后具有与窗口相同的尺寸。而且我认为gluOrtho2d比尝试从Windows坐标空间映射到OpenGL坐标空间更优雅
安排您的代码，以便您只使用一个显示功能。
您的计划可能是这样的：
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);
==
答案 1 :(得分：3)
不要认为它是“让他们画画”。请考虑事件和“我什么时候需要重绘我的对象”。
为此，您需要处理resize事件并重新运行绘图代码。我也猜测你的对象可能不会在另一个应用程序被移动到它们之后重绘，或者它被移出屏幕稍微然后被带回来。如果是这种情况，您需要确定要处理的事件，这也会导致重绘。
答案 2 :(得分：2)
以下是Windows的一个简单示例： http://www.falloutsoftware.com/tutorials/gl/gl2.htm