Mercurial > sdl-ios-xcode
annotate docs/man3/SDL_PixelFormat.3 @ 1057:e9d23bb80140
Date: Mon, 02 May 2005 04:23:16 -0500
From: Jonathan Atkins
Subject: Re: [PATCH] *CRITICAL* 8bit direct RGB palette not being created
I think that SDL_AllocFormat should create the palette for all 8bit
surfaces. And when the RGBAmasks match the normal 3:3:2:0 we need to
apply the old behavior. If the mask doesn't match that, then we need
to make the right palette assuming the masks are valid (I don't think
we validate any masks for high color surfaces...so we wouldn't here)
Then there's always a palette available for the 8bit surfaces.
This restores the normal behavior and allows for masks to create
palettes automatically for odd masks even, which would be a neato
thing to have in there, as SDL never did this before.
| author | Sam Lantinga <slouken@libsdl.org> |
|---|---|
| date | Mon, 16 May 2005 05:34:58 +0000 |
| parents | e5bc29de3f0a |
| children | e867f327aa54 |
| rev | line source |
|---|---|
|
181
e5bc29de3f0a
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Sam Lantinga <slouken@libsdl.org>
parents:
55
diff
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1 .TH "SDL_PixelFormat" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference" |
| 0 | 2 .SH "NAME" |
| 3 SDL_PixelFormat\- Stores surface format information | |
| 4 .SH "STRUCTURE DEFINITION" | |
| 5 .PP | |
| 6 .nf | |
| 7 \f(CWtypedef struct{ | |
| 8 SDL_Palette *palette; | |
| 9 Uint8 BitsPerPixel; | |
| 10 Uint8 BytesPerPixel; | |
| 11 Uint32 Rmask, Gmask, Bmask, Amask; | |
| 12 Uint8 Rshift, Gshift, Bshift, Ashift; | |
| 13 Uint8 Rloss, Gloss, Bloss, Aloss; | |
| 14 Uint32 colorkey; | |
| 15 Uint8 alpha; | |
| 16 } SDL_PixelFormat;\fR | |
| 17 .fi | |
| 18 .PP | |
| 19 .SH "STRUCTURE DATA" | |
| 20 .TP 20 | |
| 21 \fBpalette\fR | |
| 22 Pointer to the \fIpalette\fR, or \fBNULL\fP if the \fBBitsPerPixel\fR>8 | |
| 23 .TP 20 | |
| 24 \fBBitsPerPixel\fR | |
| 25 The number of bits used to represent each pixel in a surface\&. Usually 8, 16, 24 or 32\&. | |
| 26 .TP 20 | |
| 27 \fBBytesPerPixel\fR | |
| 28 The number of bytes used to represent each pixel in a surface\&. Usually one to four\&. | |
| 29 .TP 20 | |
| 30 \fB[RGBA]mask\fR | |
| 31 Binary mask used to retrieve individual color values | |
| 32 .TP 20 | |
| 33 \fB[RGBA]loss\fR | |
| 34 Precision loss of each color component (2^[RGBA]loss) | |
| 35 .TP 20 | |
| 36 \fB[RGBA]shift\fR | |
| 37 Binary left shift of each color component in the pixel value | |
| 38 .TP 20 | |
| 39 \fBcolorkey\fR | |
| 40 Pixel value of transparent pixels | |
| 41 .TP 20 | |
| 42 \fBalpha\fR | |
| 43 Overall surface alpha value | |
| 44 .SH "DESCRIPTION" | |
| 45 .PP | |
| 46 A \fBSDL_PixelFormat\fR describes the format of the pixel data stored at the \fBpixels\fR field of a \fI\fBSDL_Surface\fR\fR\&. Every surface stores a \fBSDL_PixelFormat\fR in the \fBformat\fR field\&. | |
| 47 .PP | |
| 48 If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential\&. | |
| 49 .PP | |
| 50 8-bit pixel formats are the easiest to understand\&. Since its an 8-bit format, we have 8 \fBBitsPerPixel\fR and 1 \fBBytesPerPixel\fR\&. Since \fBBytesPerPixel\fR is 1, all pixels are represented by a Uint8 which contains an index into \fBpalette\fR->\fBcolors\fR\&. So, to determine the color of a pixel in a 8-bit surface: we read the color index from \fBsurface\fR->\fBpixels\fR and we use that index to read the \fI\fBSDL_Color\fR\fR structure from \fBsurface\fR->\fBformat\fR->\fBpalette\fR->\fBcolors\fR\&. Like so: | |
| 51 .PP | |
| 52 .nf | |
| 53 \f(CWSDL_Surface *surface; | |
| 54 SDL_PixelFormat *fmt; | |
| 55 SDL_Color *color; | |
| 56 Uint8 index; | |
| 57 | |
| 58 \&. | |
| 59 \&. | |
| 60 | |
| 61 /* Create surface */ | |
| 62 \&. | |
| 63 \&. | |
| 64 fmt=surface->format; | |
| 65 | |
| 66 /* Check the bitdepth of the surface */ | |
| 67 if(fmt->BitsPerPixel!=8){ | |
| 68 fprintf(stderr, "Not an 8-bit surface\&. | |
| 69 "); | |
| 70 return(-1); | |
| 71 } | |
| 72 | |
| 73 /* Lock the surface */ | |
| 74 SDL_LockSurface(surface); | |
| 75 | |
| 76 /* Get the topleft pixel */ | |
| 77 index=*(Uint8 *)surface->pixels; | |
| 78 color=fmt->palette->colors[index]; | |
| 79 | |
| 80 /* Unlock the surface */ | |
| 81 SDL_UnlockSurface(surface); | |
| 82 printf("Pixel Color-> Red: %d, Green: %d, Blue: %d\&. Index: %d | |
| 83 ", | |
| 84 color->r, color->g, color->b, index); | |
| 85 \&. | |
| 86 \&.\fR | |
| 87 .fi | |
| 88 .PP | |
| 89 .PP | |
|
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90 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\&. |
| 0 | 91 .PP |
| 92 .nf | |
| 93 \f(CW/* Extracting color components from a 32-bit color value */ | |
| 94 SDL_PixelFormat *fmt; | |
| 95 SDL_Surface *surface; | |
| 96 Uint32 temp, pixel; | |
| 97 Uint8 red, green, blue, alpha; | |
| 98 \&. | |
| 99 \&. | |
| 100 \&. | |
| 101 fmt=surface->format; | |
| 102 SDL_LockSurface(surface); | |
|
55
55f1f1b3e27d
Added new docs for SDL 1.2.1
Sam Lantinga <slouken@lokigames.com>
parents:
0
diff
changeset
|
103 pixel=*((Uint32*)surface->pixels); |
| 0 | 104 SDL_UnlockSurface(surface); |
| 105 | |
| 106 /* Get Red component */ | |
| 107 temp=pixel&fmt->Rmask; /* Isolate red component */ | |
| 108 temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */ | |
| 109 temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */ | |
| 110 red=(Uint8)temp; | |
| 111 | |
| 112 /* Get Green component */ | |
| 113 temp=pixel&fmt->Gmask; /* Isolate green component */ | |
| 114 temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */ | |
| 115 temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */ | |
| 116 green=(Uint8)temp; | |
| 117 | |
| 118 /* Get Blue component */ | |
| 119 temp=pixel&fmt->Bmask; /* Isolate blue component */ | |
| 120 temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */ | |
| 121 temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */ | |
| 122 blue=(Uint8)temp; | |
| 123 | |
| 124 /* Get Alpha component */ | |
| 125 temp=pixel&fmt->Amask; /* Isolate alpha component */ | |
| 126 temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */ | |
| 127 temp=temp<<fmt->Aloss; /* Expand to a full 8-bit number */ | |
| 128 alpha=(Uint8)temp; | |
| 129 | |
| 130 printf("Pixel Color -> R: %d, G: %d, B: %d, A: %d | |
| 131 ", red, green, blue, alpha); | |
| 132 \&. | |
| 133 \&. | |
| 134 \&.\fR | |
| 135 .fi | |
| 136 .PP | |
| 137 .SH "SEE ALSO" | |
| 138 .PP | |
| 139 \fI\fBSDL_Surface\fR\fR, \fI\fBSDL_MapRGB\fP\fR | |
|
181
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Updated from the SDL Documentation Project
Sam Lantinga <slouken@libsdl.org>
parents:
55
diff
changeset
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140 ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01 |