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<HTML><HEAD><TITLE>Graphics and Video</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="SDL Library Documentation"HREF="index.html"><LINKREL="UP"TITLE="SDL Guide"HREF="guide.html"><LINKREL="PREVIOUS"TITLE="Initializing SDL"HREF="guidebasicsinit.html"><LINKREL="NEXT"TITLE="Using OpenGL With SDL"HREF="guidevideoopengl.html"></HEAD><BODYCLASS="CHAPTER"BGCOLOR="#FFF8DC"TEXT="#000000"LINK="#0000ee"VLINK="#551a8b"ALINK="#ff0000"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">SDL Library Documentation</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="guidebasicsinit.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom"></TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="guidevideoopengl.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="CHAPTER"><H1><ANAME="GUIDEVIDEO"></A>Chapter 2. Graphics and Video</H1><DIVCLASS="TOC"><DL><DT><B>Table of Contents</B></DT><DT><AHREF="guidevideo.html#GUIDEVIDEOINTRO">Introduction to SDL Video</A></DT><DT><AHREF="guidevideoopengl.html">Using OpenGL With SDL</A></DT></DL></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="GUIDEVIDEOINTRO"></A>Introduction to SDL Video</H1><P>Video is probably the most common thing that SDL is used for, andso it has the most complete subsystem. Here are a fewexamples to demonstrate the basics.</P><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN68"></A>Initializing the Video Display</H2><P>This is what almost all SDL programs have to do in one way oranother.</P><DIVCLASS="EXAMPLE"><ANAME="AEN71"></A><P><B>Example 2-1. Initializing the Video Display</B></P><PRECLASS="PROGRAMLISTING"> 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); }</PRE></DIV></DIV><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN74"></A>Initializing the Best Video Mode</H2><P>If you have a preference for a certain pixel depth but will accept anyother, use SDL_SetVideoMode with SDL_ANYFORMAT as below. You can alsouse SDL_VideoModeOK() to find the native video mode that is closest tothe mode you request.</P><DIVCLASS="EXAMPLE"><ANAME="AEN77"></A><P><B>Example 2-2. Initializing the Best Video Mode</B></P><PRECLASS="PROGRAMLISTING"> /* 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);</PRE></DIV></DIV><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN80"></A>Loading and Displaying a BMP File</H2><P>The following function loads and displays a BMP file given asargument, once SDL is initialised and a video mode has been set.</P><DIVCLASS="EXAMPLE"><ANAME="AEN83"></A><P><B>Example 2-3. Loading and Displaying a BMP File</B></P><PRECLASS="PROGRAMLISTING">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);}</PRE></DIV></DIV><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN86"></A>Drawing Directly to the Display</H2><P>The following two functions can be used to get and set singlepixels of a surface. They are carefully written to work with any depthcurrently supported by SDL. Remember to lock the surface beforecalling them, and to unlock it before calling any other SDLfunctions.</P><P>To convert between pixel values and their red, green, bluecomponents, use SDL_GetRGB() and SDL_MapRGB().</P><DIVCLASS="EXAMPLE"><ANAME="AEN90"></A><P><B>Example 2-4. getpixel()</B></P><PRECLASS="PROGRAMLISTING">/* * 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 */ }}</PRE></DIV><DIVCLASS="EXAMPLE"><ANAME="AEN93"></A><P><B>Example 2-5. putpixel()</B></P><PRECLASS="PROGRAMLISTING">/* * 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; }}</PRE></DIV><P>The following code uses the putpixel() function above to set ayellow pixel in the middle of the screen.</P><DIVCLASS="EXAMPLE"><ANAME="AEN97"></A><P><B>Example 2-6. Using putpixel()</B></P><PRECLASS="PROGRAMLISTING"> /* 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; </PRE></DIV></DIV></DIV></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="guidebasicsinit.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="index.html"ACCESSKEY="H">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="guidevideoopengl.html"ACCESSKEY="N">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Initializing SDL</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="guide.html"ACCESSKEY="U">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Using OpenGL With SDL</TD></TR></TABLE></DIV></BODY></HTML>⌨️ 快捷键说明
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