pods::SDL::PixelFormat(3pm) User Contributed Perl Documentation pods::SDL::PixelFormat(3pm)NAME
SDL::PixelFormat - Stores surface format information
CATEGORY
Core, Video, Structure
SYNOPSIS
my $surface = SDL::Surface->new( ...
$surface->format; #this returns the PixelFormat object attached to this surface
PixelFormat is only created in a "SDL::Surface". This module only provides getters to the surface's pixelformat. Later on we will provide
setting capability.
DESCRIPTION
An "SDL::PixelFormat " stores surface format information
METHODS
palette
$surface->format->palette;
Returns the "SDL_Palette" and SDL::Palette of the format of the surface.
BitsPerPixel
$surface->format->BitsPerPixel;
The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32. (1 to 7 are not allowed when creating a surface or
open a video mode
BytesPerPixel
$surface->format->BytesPerPixel;
The number of bytes used to represent each pixel in a surface. Usually one to four.
[RGBA]loss
$surface->format->Rloss; #red loss
$surface->format->Bloss; #blue loss
$surface->format->Gloss; #green loss
$surface->format->Aloss; #alpha loss
Precision loss of each color component (2[RGBA]loss)
[RGBA]shift
$surface->format->Rshift; #red shift
$surface->format->Bshift; #blue shift
$surface->format->Gshift; #green shift
$surface->format->Ashift; #alpha shift
Binary left shift of each color component in the pixel value
[RGBA]mask
$surface->format->Rmask; #red mask
$surface->format->Bmask; #blue mask
$surface->format->Gmask; #green mask
$surface->format->Amask; #alpha mask
Binary left shift of each color component in the pixel value
colorkey
$surface->format->colorkey;
Pixel value of transparent pixels.
alpha
$surface->format->alpha;
Overall surface alpha value
SEE ALSO
SDL::Surface
AUTHORS
See "AUTHORS" in SDL.
perl v5.14.2 2012-05-28 pods::SDL::PixelFormat(3pm)
Check Out this Related Man Page
SDL_PixelFormat(3) SDL API Reference SDL_PixelFormat(3)NAME
SDL_PixelFormat - Stores surface format information
STRUCTURE DEFINITION
typedef struct SDL_PixelFormat {
SDL_Palette *palette;
Uint8 BitsPerPixel;
Uint8 BytesPerPixel;
Uint8 Rloss, Gloss, Bloss, Aloss;
Uint8 Rshift, Gshift, Bshift, Ashift;
Uint32 Rmask, Gmask, Bmask, Amask;
Uint32 colorkey;
Uint8 alpha;
} SDL_PixelFormat;
STRUCTURE DATA
palette Pointer to the palette, or NULL if the BitsPerPixel>8
BitsPerPixel The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32.
BytesPerPixel The number of bytes used to represent each pixel in a surface. Usually one to four.
[RGBA]mask Binary mask used to retrieve individual color values
[RGBA]loss Precision loss of each color component (2^[RGBA]loss)
[RGBA]shift Binary left shift of each color component in the pixel value
colorkey Pixel value of transparent pixels
alpha Overall surface alpha value
DESCRIPTION
A SDL_PixelFormat describes the format of the pixel data stored at the pixels field of a SDL_Surface. Every surface stores a SDL_PixelFor-
mat in the format field.
If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential.
8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 BitsPerPixel and 1 BytesPerPixel. Since BytesPer-
Pixel is 1, all pixels are represented by a Uint8 which contains an index into palette->colors. So, to determine the color of a pixel in a
8-bit surface: we read the color index from surface->pixels and we use that index to read the SDL_Color structure from surface->for-
mat->palette->colors. Like so:
SDL_Surface *surface;
SDL_PixelFormat *fmt;
SDL_Color *color;
Uint8 index;
.
.
/* Create surface */
.
.
fmt=surface->format;
/* Check the bitdepth of the surface */
if(fmt->BitsPerPixel!=8){
fprintf(stderr, "Not an 8-bit surface.
");
return(-1);
}
/* Lock the surface */
SDL_LockSurface(surface);
/* Get the topleft pixel */
index=*(Uint8 *)surface->pixels;
color=fmt->palette->colors[index];
/* Unlock the surface */
SDL_UnlockSurface(surface);
printf("Pixel Color-> Red: %d, Green: %d, Blue: %d. Index: %d
",
color->r, color->g, color->b, index);
.
.
Pixel formats above 8-bit are an entirely different experience. They are considered to be "TrueColor" formats and the color information is
stored in the pixels themselves, not in a palette. The mask, shift and loss fields tell us how the color information is encoded. The mask
fields allow us to isolate each color component, the shift fields tell us the number of bits to the right of each component in the pixel
value and the loss fields tell us the number of bits lost from each component when packing 8-bit color component in a pixel.
/* Extracting color components from a 32-bit color value */
SDL_PixelFormat *fmt;
SDL_Surface *surface;
Uint32 temp, pixel;
Uint8 red, green, blue, alpha;
.
.
.
fmt=surface->format;
SDL_LockSurface(surface);
pixel=*((Uint32*)surface->pixels);
SDL_UnlockSurface(surface);
/* Get Red component */
temp=pixel&fmt->Rmask; /* Isolate red component */
temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */
temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */
red=(Uint8)temp;
/* Get Green component */
temp=pixel&fmt->Gmask; /* Isolate green component */
temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */
temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */
green=(Uint8)temp;
/* Get Blue component */
temp=pixel&fmt->Bmask; /* Isolate blue component */
temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */
temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */
blue=(Uint8)temp;
/* Get Alpha component */
temp=pixel&fmt->Amask; /* Isolate alpha component */
temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */
temp=temp<<fmt->Aloss; /* Expand to a full 8-bit number */
alpha=(Uint8)temp;
printf("Pixel Color -> R: %d, G: %d, B: %d, A: %d
", red, green, blue, alpha);
.
.
.
SEE ALSO
SDL_Surface, SDL_MapRGB
SDL Tue 11 Sep 2001, 23:01 SDL_PixelFormat(3)