C语言漫谈（二） 图像显示 Windows和Linux

　　关于图像显示有很多库可以用，Windows下有GDI，GDI+，D3D等，Linux下有X Window和Wayland，此外还有OpenGL ，SDL等图形库以及各种GUI库。

　　了解最原始的方式，对于加深理解依然是有帮助的。下面给Windows和Linux下显示位图的最简单例子：

　　Windows用GDI显示图像的例子：

 1 /*
 2 * FileName: Image_Win.c
 3 * Usage:    tcc -luser32 -lgdi32 -run Image_Win.c
 4 */
 5
 6 #include <windows.h>
 7 #include <stdlib.h>
 8 //
 9 typedef unsigned char byte;
10
11 typedef struct {
12     int Width;
13     int Height;
14     byte *Data;
15 } Image;
16
17 LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM w, LPARAM l)
18 {
19     HDC hdc;
20     RECT rect;
21     Image img;
22     BITMAPINFO bmi;
23     PAINTSTRUCT ps;
24     int iRowLength;
25     //
26     ZeroMemory(&bmi, sizeof(BITMAPINFO));
27     bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
28     bmi.bmiHeader.biPlanes = 1;
29     bmi.bmiHeader.biBitCount = 24;
30     bmi.bmiHeader.biCompression = BI_RGB;
31     //
32     switch (msg) {
33     case WM_DESTROY:
34         PostQuitMessage(1);
35         break;
36     case WM_PAINT:
37         hdc = BeginPaint (hwnd, &ps) ;
38         GetClientRect(hwnd,&rect);
39         img.Width = rect.right - rect.left;
40         iRowLength = ((img.Width*8 * 3 + 31) & ~31) >> 3;
41         img.Height = rect.bottom - rect.top;
42         img.Data =  (byte*)malloc(iRowLength*img.Height);
43         for(int i=0;i<iRowLength*img.Height;i++)
44             img.Data[i] = rand()%256;
45         bmi.bmiHeader.biWidth = img.Width;
46         bmi.bmiHeader.biHeight = img.Height;
47         SetDIBitsToDevice(hdc, 0, 0, img.Width, img.Height,
48                           0, 0, 0, img.Height, img.Data, &bmi, DIB_RGB_COLORS);
49         break;
50     default:
51         return DefWindowProc(hwnd, msg, w, l);
52     }
53     return 0;
54 }
55
56 int main(int argc, char* argv[])
57 {
58     static TCHAR szAppName[] = TEXT("RandColor");
59     HWND         hwnd;
60     MSG          msg;
61     WNDCLASS     wndclass;
62     int iCmdShow = 1;
63     HINSTANCE hInstance = NULL;
64     //
65     wndclass.style = CS_HREDRAW | CS_VREDRAW;
66     wndclass.lpfnWndProc = WndProc;
67     wndclass.cbClsExtra = 0;
68     wndclass.cbWndExtra = 0;
69     wndclass.hInstance = hInstance;
70     wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
71     wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
72     wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
73     wndclass.lpszMenuName = NULL;
74     wndclass.lpszClassName = szAppName;
75     if (!RegisterClass(&wndclass)) {
76         MessageBox(NULL, TEXT("This program requires Windows NT!"), szAppName, MB_ICONERROR);
77         return 0;
78     }
79     hwnd = CreateWindow(szAppName, TEXT("Image"), WS_OVERLAPPEDWINDOW^WS_THICKFRAME,
80                         CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
81                         NULL, NULL, hInstance, NULL);
82     //The message loop.
83     ShowWindow(hwnd, iCmdShow);
84     UpdateWindow(hwnd);
85
86     while (GetMessage(&msg, NULL, 0, 0)) {
87         TranslateMessage(&msg);
88         DispatchMessage(&msg);
89     }
90     return 0;
91 }

　　Linux下用X Window显示图像的例子：

 1 /*
 2 * FileName: Image_Linux.c
 3 * Usage:    tcc -lX11 -run Image_Linux.c
 4 */
 5 #include <X11/Xlib.h>
 6 #include <X11/Xutil.h>
 7
 8 #include <stdlib.h>
 9
10 #define WIDTH 640
11 #define HEIGHT 480
12
13 int main(int argc, char **argv)
14 {
15     int win_b_color;
16     int win_w_color;
17     XEvent xev;
18     Window window;
19     Visual *visual;
20     XImage *ximage;
21     GC gc;
22
23     char*buffer=(char*)malloc(WIDTH*HEIGHT*4*sizeof(char));
24
25     Display *display = XOpenDisplay(NULL);
26     win_b_color = BlackPixel(display, DefaultScreen(display));
27     win_w_color = BlackPixel(display, DefaultScreen(display));
28     window = XCreateSimpleWindow(display,DefaultRootWindow(display),0, 0, WIDTH, HEIGHT, 0,win_b_color, win_w_color);
29     visual = DefaultVisual(display, 0);
30     //XSelectInput(display, window, ExposureMask | KeyPressMask);
31     XMapWindow(display, window);
32     XFlush(display);
33     gc = XCreateGC(display, window, 0, NULL);
34     //XEvent event;
35     while (1) {
36         for (int i = 0; i < WIDTH*HEIGHT*4; i ++)
37             buffer[i] = rand()%256;
38         ximage=XCreateImage(display, visual, 24,ZPixmap, 0, buffer,WIDTH, HEIGHT, 32, 0);
39         XPutImage(display, window,gc, ximage, 0, 0, 0, 0,WIDTH, HEIGHT);
40     }
41     return 0;
42 }

　　下一次将介绍矢量图方面的知识，主要以EMF,SVG和PostScript进行说明。