Linux and UNIX Man Pages

Test Your Knowledge in Computers #371
Difficulty: Medium
PHP opcodes are generated each time the program is launched and are always interpreted and not just-in-time compiled.
True or False?
Linux & Unix Commands - Search Man Pages

sdl_maprgb(3) [redhat man page]

SDL_MapRGB(3)							 SDL API Reference						     SDL_MapRGB(3)

SDL_MapRGB- Map a RGB color value to a pixel format. SYNOPSIS
#include "SDL.h" Uint32 SDL_MapRGB(SDL_PixelFormat *fmt, Uint8 r, Uint8 g, Uint8 b); DESCRIPTION
Maps the RGB color value to the specified pixel format and returns the pixel value as a 32-bit int. If the format has a palette (8-bit) the index of the closest matching color in the palette will be returned. If the specified pixel format has an alpha component it will be returned as all 1 bits (fully opaque). RETURN VALUE
A pixel value best approximating the given RGB color value for a given pixel format. If the pixel format bpp (color depth) is less than 32-bpp then the unused upper bits of the return value can safely be ignored (e.g., with a 16-bpp format the return value can be assigned to a Uint16, and similarly a Uint8 for an 8-bpp format). SEE ALSO
Tue 11 Sep 2001, 23:01 SDL_MapRGB(3)

Check Out this Related Man Page

SDL_PixelFormat(3)						 SDL API Reference						SDL_PixelFormat(3)

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
Tue 11 Sep 2001, 23:01 SDL_PixelFormat(3)

Featured Tech Videos