View Source: SDL_PixelFormat(3) - Waikato Linux Users Group

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SDL_!PixelFormat
!!!SDL_!PixelFormat
NAME
STRUCTURE DEFINITION
STRUCTURE DATA
DESCRIPTION
SEE ALSO
----
!!NAME


SDL_!PixelFormat- Stores surface format information
!!STRUCTURE DEFINITION


typedef struct{
SDL_Palette *palette;
Uint8  !BitsPerPixel;
Uint8  !BytesPerPixel;
Uint32 Rmask, Gmask, Bmask, Amask;
Uint8  Rshift, Gshift, Bshift, Ashift;
Uint8  Rloss, Gloss, Bloss, Aloss;
Uint32 colorkey;
Uint8  alpha;
} SDL_!PixelFormat;
!!STRUCTURE DATA


__palette__ Pointer to the ''palette'', or __NULL__
if the __!BitsPerPixel____


__!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_!PixelFormat__ 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 __!BytesPerPixel__ 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__-__format__-__palette__-__colors__.
Like so:


SDL_Surface *surface;
SDL_!PixelFormat *fmt;
SDL_Color *color;
Uint8 index;
.
.
/* Create surface */
.
.
fmt=surface-


Pixel formats above 8-bit are an entirely different
experience. They are considered to be


/* 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-
!!SEE ALSO


__SDL_Surface__, __SDL_MapRGB__
----

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Last edited on Monday, June 3, 2002 6:53:47 pm by "perry"

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