Subversion Repositories Kolibri OS

>

>

>Graphics and Video

>

NAME="GENERATOR"

CONTENT="Modular DocBook HTML Stylesheet Version 1.64

">

REL="HOME"

TITLE="SDL Library Documentation"

HREF="index.html">

REL="UP"

TITLE="SDL Guide"

HREF="guide.html">

REL="PREVIOUS"

TITLE="Initializing SDL"

HREF="guidebasicsinit.html">

REL="NEXT"

TITLE="Using OpenGL With SDL"

HREF="guidevideoopengl.html">

>

CLASS="CHAPTER"

BGCOLOR="#FFF8DC"

TEXT="#000000"

LINK="#0000ee"

VLINK="#551a8b"

ALINK="#ff0000"

>

CLASS="NAVHEADER"

>

WIDTH="100%"

BORDER="0"

CELLPADDING="0"

CELLSPACING="0"

>

>

COLSPAN="3"

ALIGN="center"

>SDL Library Documentation

>

>

>

WIDTH="10%"

ALIGN="left"

VALIGN="bottom"

>

HREF="guidebasicsinit.html"

>Prev

>

>

WIDTH="80%"

ALIGN="center"

VALIGN="bottom"

>

>

WIDTH="10%"

ALIGN="right"

VALIGN="bottom"

>

HREF="guidevideoopengl.html"

>Next

>

>

>

>

ALIGN="LEFT"

WIDTH="100%">

>

CLASS="CHAPTER"

>

>

NAME="GUIDEVIDEO"

>Chapter 2. Graphics and Video

>

>

CLASS="TOC"

>

>

>

>Table of Contents

>

>

>

HREF="guidevideo.html#GUIDEVIDEOINTRO"

>Introduction to SDL Video

>

>

>

HREF="guidevideoopengl.html"

>Using OpenGL With SDL

>

>

>

>

CLASS="SECT1"

>

CLASS="SECT1"

>

NAME="GUIDEVIDEOINTRO"

>Introduction to SDL Video

>

>

>Video is probably the most common thing that SDL is used for, and

so it has the most complete subsystem. Here are a few

examples to demonstrate the basics.

>

CLASS="SECT2"

>

CLASS="SECT2"

>

NAME="AEN68"

>Initializing the Video Display

>

>

>This is what almost all SDL programs have to do in one way or

another.

>

CLASS="EXAMPLE"

>

NAME="AEN71"

>

>

>

>Example 2-1. Initializing the Video Display

>

>

CLASS="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);

    }

>

>

>

CLASS="SECT2"

>

CLASS="SECT2"

>

NAME="AEN74"

>Initializing the Best Video Mode

>

>

>If you have a preference for a certain pixel depth but will accept any

other, use SDL_SetVideoMode with SDL_ANYFORMAT as below. You can also

use SDL_VideoModeOK() to find the native video mode that is closest to

the mode you request.

>

CLASS="EXAMPLE"

>

NAME="AEN77"

>

>

>

>Example 2-2. Initializing the Best Video Mode

>

>

CLASS="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);

>

>

>

CLASS="SECT2"

>

CLASS="SECT2"

>

NAME="AEN80"

>Loading and Displaying a BMP File

>

>

>The following function loads and displays a BMP file given as

argument, once SDL is initialised and a video mode has been set.

>

CLASS="EXAMPLE"

>

NAME="AEN83"

>

>

>

>Example 2-3. Loading and Displaying a BMP File

>

>

CLASS="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);

}

>

>

>

CLASS="SECT2"

>

CLASS="SECT2"

>

NAME="AEN86"

>Drawing Directly to the Display

>

>

>The following two functions can be used to get and set single

pixels of a surface. They are carefully written to work with any depth

currently supported by SDL. Remember to lock the surface before

calling them, and to unlock it before calling any other SDL

functions.

>

>To convert between pixel values and their red, green, blue

components, use SDL_GetRGB() and SDL_MapRGB().

>

CLASS="EXAMPLE"

>

NAME="AEN90"

>

>

>

>Example 2-4. getpixel()

>

>

CLASS="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 */

    }

}

>

>

CLASS="EXAMPLE"

>

NAME="AEN93"

>

>

>

>Example 2-5. putpixel()

>

>

CLASS="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;

    }

}

>

>

>The following code uses the putpixel() function above to set a

yellow pixel in the middle of the screen.

>

CLASS="EXAMPLE"

>

NAME="AEN97"

>

>

>

>Example 2-6. Using putpixel()

>

>

CLASS="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;

>

>

>

>

>

CLASS="NAVFOOTER"

>

ALIGN="LEFT"

WIDTH="100%">

WIDTH="100%"

BORDER="0"

CELLPADDING="0"

CELLSPACING="0"

>

>

WIDTH="33%"

ALIGN="left"

VALIGN="top"

>

HREF="guidebasicsinit.html"

>Prev

>

>

WIDTH="34%"

ALIGN="center"

VALIGN="top"

>

HREF="index.html"

>Home

>

>

WIDTH="33%"

ALIGN="right"

VALIGN="top"

>

HREF="guidevideoopengl.html"

>Next

>

>

>

>

WIDTH="33%"

ALIGN="left"

VALIGN="top"

>Initializing SDL

>

WIDTH="34%"

ALIGN="center"

VALIGN="top"

>

HREF="guide.html"

>Up

>

>

WIDTH="33%"

ALIGN="right"

VALIGN="top"

>Using OpenGL With SDL

>

>

>

>

>

>