Question

用C++如何实现bresenham画线算法？计算机图形学上面有个drawpixel的函数。不知道怎么用。

不知道是不是要用MFC。。完全不懂。请高手赐教。邮箱396279682@qq.com

Answer 1

在MFC中可以这样实现：
//Bresenham算法画直线
void CMyView::OnDrawLineByBresenham()
{
// TODO: Add your command handler code here
CDC* pDC = GetDC();
CPoint PtBegin(80,130);//起始点
CPoint PtEnd(320,370);//终止点

int s1,s2,interchange;
double X = PtBegin.x;
double Y = PtBegin.y;
double deltax,deltay,f,Temp;
deltax=abs(PtEnd.x-PtBegin.x);
deltay=abs(PtEnd.y-PtBegin.y);

if(PtBegin.x-PtBegin.x>=0) s1=1; else s1=-1;
if(PtEnd.y-PtBegin.y>=0) s2=1; else s2=-1;
f=2*deltay-deltax;
if(deltay>deltax)
{
Temp=deltax;
deltax=deltay;
deltay=Temp;
interchange=1;
}
else interchange=0;
for(int i=1;i<=(deltax+deltay);i++)
{
if(f>=0)
{
if(interchange==1) X+=s1;
else Y+=s2;
pDC->SetPixel(int(X),int(Y),RGB(0,50,250));
f=f-2*deltax;
}
else
{
if(interchange==1) Y+=s2;
else X+=s1;
pDC->SetPixel(int(X),int(Y),RGB(200,0,0));
f=f+2*deltay;
}
}
}
编译环境:VC6.0

Answer 2

#include <windows.h>

void Bresenham(HDC hdc,int x1,int y1,int x2,int y2);

/* Declare Windows procedure */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

/* Make the class name into a global variable */
char szClassName[ ] = "WinClassName";

int WINAPI WinMain (HINSTANCE hThisInstance,
HINSTANCE hPrevInstance,
LPSTR lpszArgument,
int nCmdShow)
{
HWND hwnd; /* This is the handle for our window */
MSG msg; /* Here messages to the application are saved */
WNDCLASSEX wincl; /* Data structure for the windowclass */

/* The Window structure */
wincl.hInstance = hThisInstance;
wincl.lpszClassName = szClassName;
wincl.lpfnWndProc = WindowProcedure; /* This function is called by windows */
wincl.style = CS_DBLCLKS; /* Catch double-clicks */
wincl.cbSize = sizeof (WNDCLASSEX);

/* Use default icon and mouse-pointer */
wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
wincl.hCursor = LoadCursor (NULL, IDC_CROSS);
wincl.lpszMenuName = NULL; /* No menu */
wincl.cbClsExtra = 0; /* No extra bytes after the window class */
wincl.cbWndExtra = 0; /* structure or the window instance */
/* Use Windows's default colour as the background of the window */
wincl.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);

/* Register the window class, and if it fails quit the program */
if (!RegisterClassEx (&wincl))
return 0;

/* The class is registered, let's create the program*/
hwnd = CreateWindowEx (
0, /* Extended possibilites for variation */
szClassName, /* Classname */
"Bresenham", /* Title Text */
WS_OVERLAPPEDWINDOW, /* default window */
CW_USEDEFAULT, /* Windows decides the position */
CW_USEDEFAULT, /* where the window ends up on the screen */
544, /* The programs width */
375, /* and height in pixels */
HWND_DESKTOP, /* The window is a child-window to desktop */
NULL, /* No menu */
hThisInstance, /* Program Instance handler */
NULL /* No Window Creation data */
);

/* Make the window visible on the screen */
ShowWindow (hwnd, nCmdShow);

/* Run the message loop. It will run until GetMessage() returns 0 */
while (GetMessage (&msg, NULL, 0, 0))
{
/* Translate virtual-key messages into character messages */
TranslateMessage(&msg);
/* Send message to WindowProcedure */
DispatchMessage(&msg);
}

/* The program return-value is 0 - The value that PostQuitMessage() gave */
return msg.wParam;
}

/* This function is called by the Windows function DispatchMessage() */

LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
HDC hdc;
PAINTSTRUCT ps;
static int x1,x2,y1,y2;
switch (message) /* handle the messages */
{
case WM_LBUTTONDOWN:
x1=LOWORD(lParam);
y1=HIWORD(lParam);
break;
case WM_LBUTTONUP:
x2=LOWORD(lParam);
y2=HIWORD(lParam);
hdc=GetDC(hwnd);
Bresenham(hdc,x1,y1,x2,y2);
ReleaseDC(hwnd,hdc);
break;
case WM_PAINT:
hdc=BeginPaint(hwnd,&ps);

EndPaint(hwnd,&ps);
break;
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
}

return 0;
}

void Bresenham(HDC hdc,int x1,int y1,int x2,int y2)
{
int t,x,y,dx,dy,error;
bool flag = abs(y2-y1)>abs(x2-x1);
if( flag )
{
t=x1;x1=y1;y1=t;
t=x2;x2=y2;y2=t;
}
if( x1>x2 )
{
t=x1;x1=x2;x2=t;
t=y1;y1=y2;y2=t;
}
dx=x2-x1;
dy=abs(y2-y1);
error=dx/2;
for(x=x1,y=y1;x<=x2;++x)
{
if(flag) SetPixel(hdc,y,x,0);
else SetPixel(hdc,x,y,0);
error-=dy;
if(error<0)
{
y1<y2?++y:--y;
error+=dx;
}
}
}参考资料：win32 application

Answer 3

　　drawpixel()函数这就是VC画点的，不同的平台由不同的函数来画点，这个是API函数不管什么平台归结到底都是调用这个函数来画点。
　　COLORREF SetPixel(
　　HDC hdc, // handle to DC
　　int X, // x-coordinate of pixel
　　int Y, // y-coordinate of pixel
　　COLORREF crColor // pixel color
　　);