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>SDL Library Documentation</TH |
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><DIV |
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><H1 |
><A |
NAME="GUIDEVIDEO" |
>Chapter 2. Graphics and Video</A |
></H1 |
><DIV |
CLASS="TOC" |
><DL |
><DT |
><B |
>Table of Contents</B |
></DT |
><DT |
><A |
HREF="guidevideo.html#GUIDEVIDEOINTRO" |
>Introduction to SDL Video</A |
></DT |
><DT |
><A |
HREF="guidevideoopengl.html" |
>Using OpenGL With SDL</A |
></DT |
></DL |
></DIV |
><DIV |
CLASS="SECT1" |
><H1 |
CLASS="SECT1" |
><A |
NAME="GUIDEVIDEOINTRO" |
>Introduction to SDL Video</A |
></H1 |
><P |
>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 |
><DIV |
CLASS="SECT2" |
><H2 |
CLASS="SECT2" |
><A |
NAME="AEN68" |
>Initializing the Video Display</A |
></H2 |
><P |
>This is what almost all SDL programs have to do in one way or |
another.</P |
><DIV |
CLASS="EXAMPLE" |
><A |
NAME="AEN71" |
></A |
><P |
><B |
>Example 2-1. Initializing the Video Display</B |
></P |
><PRE |
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); |
}</PRE |
></DIV |
></DIV |
><DIV |
CLASS="SECT2" |
><H2 |
CLASS="SECT2" |
><A |
NAME="AEN74" |
>Initializing the Best Video Mode</A |
></H2 |
><P |
>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.</P |
><DIV |
CLASS="EXAMPLE" |
><A |
NAME="AEN77" |
></A |
><P |
><B |
>Example 2-2. Initializing the Best Video Mode</B |
></P |
><PRE |
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);</PRE |
></DIV |
></DIV |
><DIV |
CLASS="SECT2" |
><H2 |
CLASS="SECT2" |
><A |
NAME="AEN80" |
>Loading and Displaying a BMP File</A |
></H2 |
><P |
>The following function loads and displays a BMP file given as |
argument, once SDL is initialised and a video mode has been set.</P |
><DIV |
CLASS="EXAMPLE" |
><A |
NAME="AEN83" |
></A |
><P |
><B |
>Example 2-3. Loading and Displaying a BMP File</B |
></P |
><PRE |
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); |
}</PRE |
></DIV |
></DIV |
><DIV |
CLASS="SECT2" |
><H2 |
CLASS="SECT2" |
><A |
NAME="AEN86" |
>Drawing Directly to the Display</A |
></H2 |
><P |
>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.</P |
><P |
>To convert between pixel values and their red, green, blue |
components, use SDL_GetRGB() and SDL_MapRGB().</P |
><DIV |
CLASS="EXAMPLE" |
><A |
NAME="AEN90" |
></A |
><P |
><B |
>Example 2-4. getpixel()</B |
></P |
><PRE |
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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