>Graphics and Video<
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>SDL Library Documentation<
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CLASS="CHAPTER"
NAME="GUIDEVIDEO"
>Chapter
2. Graphics and Video<
/A
CLASS="TOC"
HREF="guidevideo.html#GUIDEVIDEOINTRO"
>Introduction to SDL Video<
/A
HREF="guidevideoopengl.html"
>Using OpenGL With SDL<
/A
CLASS="SECT1"
CLASS="SECT1"
NAME="GUIDEVIDEOINTRO"
>Introduction to SDL Video<
/A
>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.<
/P
CLASS="SECT2"
CLASS="SECT2"
NAME="AEN68"
>Initializing the Video Display<
/A
>This is what almost all SDL programs have to do in one way or
CLASS="EXAMPLE"
NAME="AEN71"
>Example
2-
1. Initializing the Video Display<
/B
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<
/A
>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
CLASS="EXAMPLE"
NAME="AEN77"
>Example
2-
2. Initializing the Best Video Mode<
/B
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-&#
62;format-&#
62;BitsPerPixel
);<
/PRE
CLASS="SECT2"
CLASS="SECT2"
NAME="AEN80"
>Loading and Displaying a BMP File<
/A
>The following function loads and displays a BMP file given as
argument, once SDL is initialised and a video mode has been set.<
/P
CLASS="EXAMPLE"
NAME="AEN83"
>Example
2-
3. Loading and Displaying a BMP File<
/B
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<
/A
>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
>To convert between pixel values and their red, green, blue
components, use SDL_GetRGB
() and SDL_MapRGB
().<
/P
CLASS="EXAMPLE"
NAME="AEN90"
>Example
2-
4. getpixel
()<
/B
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 */
}
}</PRE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN93"
></A
><P
><B
>Example 2-5. putpixel()</B
></P
><PRE
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;
}
}</PRE
></DIV
><P
>The following code uses the putpixel() function above to set a
yellow pixel in the middle of the screen.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN97"
></A
><P
><B
>Example 2-6. Using putpixel()</B
></P
><PRE
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; </PRE
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