windows滚动条

今天自己写了《windows程序设计》184页的用键盘控制滚动条显示程序，对滚动条显示有点感悟，留个纪念！

代码如下：

#include <Windows.h>#include <math.h>#include "SYSMETS.h"LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam);int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,PSTR szCmdLine,int iCmdShow){static TCHAR szAppName[]=TEXT("First Program");MSG msg;HWND hwnd;WNDCLASS wndclass;wndclass.style=CS_HREDRAW|CS_VREDRAW;wndclass.lpfnWndProc=WndProc;wndclass.cbClsExtra=0;wndclass.cbWndExtra=0;wndclass.hInstance=hInstance;wndclass.hIcon=LoadIcon(NULL,IDI_APPLICATION);wndclass.hCursor=LoadCursor(NULL,IDC_ARROW);wndclass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);wndclass.lpszMenuName=NULL;wndclass.lpszClassName=szAppName;if (!RegisterClass(&wndclass)){MessageBox(hwnd,TEXT("Error exists!"),TEXT("Error!"),MB_ICONERROR);return 0;}hwnd=CreateWindow(szAppName,TEXT("Hello World!"),WS_OVERLAPPEDWINDOW|WS_HSCROLL|WS_VSCROLL,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,NULL,NULL,hInstance,NULL);ShowWindow(hwnd,iCmdShow);UpdateWindow(hwnd);while (GetMessage(&msg,hwnd,0,0)){TranslateMessage(&msg);DispatchMessage(&msg);}return msg.wParam;}LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam){static int cxChar,cyChar,cxCaps,cxClient,cyClient;int iVertPos,x,y,i,iPaintBeg,iPaintEnd;TCHAR szBuffer[20];HDC hdc;PAINTSTRUCT ps;TEXTMETRIC tm;SCROLLINFO si;switch(message){case WM_CREATE:hdc=GetDC(hwnd);GetTextMetrics(hdc,&tm);cxChar=tm.tmAveCharWidth;cyChar=tm.tmHeight+tm.tmExternalLeading;cxCaps=(tm.tmPitchAndFamily&1?3:2)*cxChar/2;ReleaseDC(hwnd,hdc);return 0;case WM_SIZE:cxClient=LOWORD(lParam);cyClient=HIWORD(lParam);si.cbSize=sizeof(si);si.fMask=SIF_RANGE|SIF_PAGE;si.nMin=0;si.nMax=NUMLINES-1;si.nPage=cyClient/cyChar;SetScrollInfo(hwnd,SB_VERT,&si,TRUE);return 0;case WM_VSCROLL:si.cbSize=sizeof(si);si.fMask=SIF_ALL;GetScrollInfo(hwnd,SB_VERT,&si);iVertPos=si.nPos;switch(LOWORD(wParam)){case SB_TOP:si.nPos=si.nMin;break;case SB_BOTTOM:si.nPos=si.nMax;break;case SB_PAGEUP:si.nPos-=si.nPage;break;case SB_PAGEDOWN:si.nPos+=si.nPage;break;case SB_LINEUP:si.nPos-=1;break;case SB_LINEDOWN:si.nPos+=1;break;case SB_THUMBTRACK:si.nPos=si.nTrackPos;break;default:break;}si.cbSize=sizeof(si);si.fMask=SIF_POS;SetScrollInfo(hwnd,SB_VERT,&si,TRUE);GetScrollInfo(hwnd,SB_VERT,&si);if (si.nPos!=iVertPos){ScrollWindow(hwnd,0,cyChar*(iVertPos-si.nPos),NULL,NULL);UpdateWindow(hwnd);}return 0;case WM_KEYDOWN:switch(wParam){case VK_UP:SendMessage(hwnd,WM_VSCROLL,SB_LINEUP,0);break;case VK_DOWN:SendMessage(hwnd,WM_VSCROLL,SB_LINEDOWN,0);break;case VK_PRIOR:SendMessage(hwnd,WM_VSCROLL,SB_PAGEUP,0);break;case VK_NEXT:SendMessage(hwnd,WM_VSCROLL,SB_PAGEDOWN,0);break;default:break;}return 0;      //关键代码case WM_PAINT:si.cbSize=sizeof(si);si.fMask=SIF_ALL;GetScrollInfo(hwnd,SB_VERT,&si);iVertPos=si.nPos;   hdc=BeginPaint(hwnd,&ps);iPaintBeg=max(0,si.nPos+ps.rcPaint.top/cyChar);iPaintEnd=min(si.nMax,si.nPos+ps.rcPaint.bottom/cyChar);for (i=iPaintBeg;i<=iPaintEnd;i++){y=cyChar*(i-iVertPos);TextOut(hdc,0,y,sysmetrics[i].szLabel,lstrlen(sysmetrics[i].szLabel));TextOut(hdc,22*cxCaps,y,sysmetrics[i].szDesc,lstrlen(sysmetrics[i].szDesc));SetTextAlign(hdc,TA_TOP|TA_RIGHT);TextOut(hdc,60*cxCaps,y,szBuffer,wsprintf(szBuffer,TEXT("%5d"),GetSystemMetrics(sysmetrics[i].Index)));SetTextAlign(hdc,TA_LEFT|TA_TOP);}EndPaint(hwnd,&ps);return 0;case WM_DESTROY:PostQuitMessage(0);return 0;}return DefWindowProc(hwnd,message,wParam,lParam);}

原来我老是有个疑问：

1、iPaintBeg=max(0,si.nPos+ps.rcPaint.top/cyChar);
      iPaintEnd=min(si.nMax,si.nPos+ps.rcPaint.bottom/cyChar);

      这两句是干嘛用的？

2、为什么是for (i=iPaintBeg;i<=iPaintEnd;i++)这样循环？

3、y=cyChar*(i-iVertPos);

     为什么是i-iVertPos？

今天调试了一下，颇有感悟！

调试时滚动条下拉了一行！

首先给出调试时一些参数，是我写的一张图：

得出了一些结论：

1、下拉滚动条时，只更新时新出现的客户区，这个矩形的具体参数存数在ps.rcPaint中。

更新起点iPaintBeg是需更新矩形的顶部所在的行数，iPaintEnd是底部所在的行数。即图中新出现一行的顶部和底部。

2、for循环就是输出这些新出现的文本

3、i-iVerPos就是以新客户区的顶部为起点更新客户区