SDL_PixelFormat(3)

💖 SDL_PixelFormat 💖

okay bestie, welcome to SDL_PixelFormat(3) from the SDL API Reference — the lil struct that holds all the tea about how a surface's pixels are actually colored. no cap, this one's lowkey the blueprint. let's get into it 🫶

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✨ NAME ✨

SDL_PixelFormat — stores surface format information

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🎀 STRUCTURE DEFINITION 🎀

here's the whole vibe, character for character:

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;

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🦋 STRUCTURE DATA 🦋

every field, no skips, we're thorough in this house:

• palette — pointer to the palette, or NULL if the BitsPerPixel>8
• BitsPerPixel — how many bits it takes to represent each pixel in a surface. usually 8, 16, 24 or 32.
• BytesPerPixel — how many bytes it takes 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

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🌸 DESCRIPTION 🌸

so a SDL_PixelFormat describes the format of the pixel data stored at the pixels field of a SDL_Surface. every single surface keeps a SDL_PixelFormat in the format field. it's giving... universal. 👑

if you wanna do pixel-level modifications on a surface, then understanding how SDL stores its color information is essential. like, not optional. periodt.

🍓 the 8-bit girlies

8-bit pixel formats are the easiest to understand, fr. since it's 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->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);
.
.

🌈 the TrueColor era

pixel formats above 8-bit are an entirely different experience. they're considered to be "TrueColor" formats and the color information is stored in the pixels themselves, not in a palette. iconic behaviour honestly. 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);
.
.
.

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👑 SEE ALSO 👑

SDL_Surface, SDL_MapRGB

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that's the whole page bestie, you ate it 💅✨

courtesy of SDL, dated Tue 11 Sep 2001, 23:01 — yes she's an elder but she's still mother 🎀 go lock a surface and slay some pixels for me, mwah 💖