SDL入门(转,方便自己)

Posted on 2010-06-11 17:00 莫失莫忘 阅读(482) 评论(0)  编辑 收藏 引用

第一章 基础

初始化

SDL由八个子系统组成——音频、CDROM、事件处理、文件I/O、游戏杆、线程、记时器和视频。使用前必须调用SDL_Init或 SDL_InitSubSystem初始化。SDL_Init必须早于其他所有SDL调用,它将自动初始化事件处理、文件I/O和线程子系统,并根据参数 选择启动其他子系统。例如,初始化缺省和视频子系统:

SDL_Init(SDL_INIT_VIDEO);初始化缺省、视频和记时器子系统:

SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER);SDL_Init对应SDL_Quit(和SDL_QuitSubSystem)。SDL_Quit关闭所有子系统,必须在程序关闭前调用。

除此之外,我们还必须进行错误处理。很多SDL函数返回一个值指示成功与否。例如SDL_Init失败时返回-1。每当SDL出错时,错误信息被保存,并可用SDL_GetError取得。

例1-1 初始化SDL

#include "SDL.h" /* All SDL App's need this */

#include <stdio.h>

int main() {

printf("Initializing SDL.\n");

/* Initialize defaults, Video and Audio */

if((SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO)==-1)) {

printf("Could not initialize SDL: %s.\n", SDL_GetError());

exit(-1);

}

printf("SDL initialized.\n");

printf("Quiting SDL.\n");

/* Shutdown all subsystems */

SDL_Quit();

printf("Quiting....\n");

exit(0);

}

第二章 图像和视频

SDL Vidow显示

初始化SDL Video显示

视频是最常用的部分,也是SDL最完整的子系统。下面的初始化过程是每个SDL程序都要做的,即使可能有些不同。

例2-1 初始化视频

SDL_Surface *screen;

/* Initialize the SDL library */

if( SDL_Init(SDL_INIT_VIDEO) < 0 ) {

fprintf(stderr,

"Couldn't initialize SDL: %s\n", SDL_GetError());

exit(1);

}

/* Clean up on exit */

atexit(SDL_Quit);

/*

* Initialize the display in a 640x480 8-bit palettized mode,

* requesting a software surface

*/

screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE);

if ( screen == NULL ) {

fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",

SDL_GetError());

exit(1);

}

初始化最佳视频模式

如果你希望某种色深(颜色数)但如果用户的显示器不支持也可以接受其他色深,使用加SDL_ANYFORMAT参数的SDL_SetVideoMode。您还可以用SDL_VideoModeOK来找到与请求模式最接近的模式。

例2-2 初始化最佳视频模式

/* Have a preference for 8-bit, but accept any depth */

screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_ANYFORMAT);

if ( screen == NULL ) {

fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",

SDL_GetError());

exit(1);

}

printf("Set 640x480 at %d bits-per-pixel mode\n",

screen->format->BitsPerPixel);

读取并显示BMP文件

当SDL已经初始化,视频模式已经选择,下面的函数将读取并显示指定的BMP文件。

例2-3 读取并显示BMP文件

void display_bmp(char *file_name)

{

SDL_Surface *image;

/* Load the BMP file into a surface */

image = SDL_LoadBMP(file_name);

if (image == NULL) {

fprintf(stderr, "Couldn't load %s: %s\n", file_name, SDL_GetError());

return;

}

/*

* Palettized screen modes will have a default palette (a standard

* 8*8*4 colour cube), but if the image is palettized as well we can

* use that palette for a nicer colour matching

*/

if (image->format->palette && screen->format->palette) {

SDL_SetColors(screen, image->format->palette->colors, 0,

image->format->palette->ncolors);

}

/* Blit onto the screen surface */

if(SDL_BlitSurface(image, NULL, screen, NULL) < 0)

fprintf(stderr, "BlitSurface error: %s\n", SDL_GetError());

SDL_UpdateRect(screen, 0, 0, image->w, image->h);

/* Free the allocated BMP surface */

SDL_FreeSurface(image);

}

直接在显示上绘图

下面两个函数实现在图像平面的像素读写。它们被细心设计成可以用于所有色深。记住在使用前要先锁定图像平面,之后要解锁。

在像素值和其红、绿、蓝值间转换,使用SDL_GetRGB()和SDL_MapRGB()。

例2-4 getpixel()

/*

* Return the pixel value at (x, y)

* NOTE: The surface must be locked before calling this!

*/

Uint32 getpixel(SDL_Surface *surface, int x, int y)

{

int bpp = surface->format->BytesPerPixel;

/* Here p is the address to the pixel we want to retrieve */

Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;

switch(bpp) {

case 1:

return *p;

case 2:

return *(Uint16 *)p;

case 3:

if(SDL_BYTEORDER == SDL_BIG_ENDIAN)

return p[0] << 16 | p[1] << 8 | p[2];

else

return p[0] | p[1] << 8 | p[2] << 16;

case 4:

return *(Uint32 *)p;

default:

return 0; /* shouldn't happen, but avoids warnings */

}

}

例2-5 putpixel()

/*

* Set the pixel at (x, y) to the given value

* NOTE: The surface must be locked before calling this!

*/

void putpixel(SDL_Surface *surface, int x, int y, Uint32 pixel)

{

int bpp = surface->format->BytesPerPixel;

/* Here p is the address to the pixel we want to set */

Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;

switch(bpp) {

case 1:

*p = pixel;

break;

case 2:

*(Uint16 *)p = pixel;

break;

case 3:

if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {

p[0] = (pixel >> 16) & 0xff;

p[1] = (pixel >> 8) & 0xff;

p[2] = pixel & 0xff;

} else {

p[0] = pixel & 0xff;

p[1] = (pixel >> 8) & 0xff;

p[2] = (pixel >> 16) & 0xff;

}

break;

case 4:

*(Uint32 *)p = pixel;

break;

}

}

例2-6 使用上面的putpixel()在屏幕中心画一个黄点

/* Code to set a yellow pixel at the center of the screen */

int x, y;

Uint32 yellow;

/* Map the color yellow to this display (R=0xff, G=0xFF, B=0x00)

Note: If the display is palettized, you must set the palette first.

*/

yellow = SDL_MapRGB(screen->format, 0xff, 0xff, 0x00);

x = screen->w / 2;

y = screen->h / 2;

/* Lock the screen for direct access to the pixels */

if ( SDL_MUSTLOCK(screen) ) {

if ( SDL_LockSurface(screen) < 0 ) {

fprintf(stderr, "Can't lock screen: %s\n", SDL_GetError());

return;

}

}

putpixel(screen, x, y, yellow);

if ( SDL_MUSTLOCK(screen) ) {

SDL_UnlockSurface(screen);

}

/* Update just the part of the display that we've changed */

SDL_UpdateRect(screen, x, y, 1, 1);

return;


并用SDL和OpenGL

SDL可以在多种平台(Linux/X11, Win32, BeOS, MacOS Classic/Toolbox, MacOS X, FreeBSD/X11 and Solaris/X11)上创建和使用OpenGL上下文。这允许你在OpenGL程序中使用SDL的音频、事件、线程和记时器,而这些通常是GLUT的任务。

初始化

和普通的初始化类似,但有三点不同:必须传SDL_OPENGL参数给SDL_SetVideoMode;必须使用SDL_GL_SetAttribute指定一些GL属性(深度缓冲区位宽,帧缓冲位宽等);如果您想使用双缓冲,必须作为GL属性指定

例2-7 初始化SDL加OpenGL

/* Information about the current video settings. */

const SDL_VideoInfo* info = NULL;

/* Dimensions of our window. */

int width = 0;

int height = 0;

/* Color depth in bits of our window. */

int bpp = 0;

/* Flags we will pass into SDL_SetVideoMode. */

int flags = 0;

/* First, initialize SDL's video subsystem. */

if( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {

/* Failed, exit. */

fprintf( stderr, "Video initialization failed: %s\n",

SDL_GetError( ) );

quit_tutorial( 1 );

}

/* Let's get some video information. */

info = SDL_GetVideoInfo( );

if( !info ) {

/* This should probably never happen. */

fprintf( stderr, "Video query failed: %s\n",

SDL_GetError( ) );

quit_tutorial( 1 );

}

/*

* Set our width/height to 640/480 (you would

* of course let the user decide this in a normal

* app). We get the bpp we will request from

* the display. On X11, VidMode can't change

* resolution, so this is probably being overly

* safe. Under Win32, ChangeDisplaySettings

* can change the bpp.

*/

width = 640;

height = 480;

bpp = info->vfmt->BitsPerPixel;

/*

* Now, we want to setup our requested

* window attributes for our OpenGL window.

* We want *at least* 5 bits of red, green

* and blue. We also want at least a 16-bit

* depth buffer.

*

* The last thing we do is request a double

* buffered window. '1' turns on double

* buffering, '0' turns it off.

*

* Note that we do not use SDL_DOUBLEBUF in

* the flags to SDL_SetVideoMode. That does

* not affect the GL attribute state, only

* the standard 2D blitting setup.

*/

SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );

SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );

SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );

SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );

SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );

/*

* We want to request that SDL provide us

* with an OpenGL window, in a fullscreen

* video mode.

*

* EXERCISE:

* Make starting windowed an option, and

* handle the resize events properly with

* glViewport.

*/

flags = SDL_OPENGL | SDL_FULLSCREEN;

/*

* Set the video mode

*/

if( SDL_SetVideoMode( width, height, bpp, flags ) == 0 ) {

/*

* This could happen for a variety of reasons,

* including DISPLAY not being set, the specified

* resolution not being available, etc.

*/

fprintf( stderr, "Video mode set failed: %s\n",

SDL_GetError( ) );

quit_tutorial( 1 );

}


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