Mercurial > sdl-ios-xcode
view docs/man3/SDL_PixelFormat.3 @ 563:04dcaf3da918
Massive Quartz input enhancements from Darrell Walisser. His email:
Enclosed is a patch that addresses the following:
--Various minor cleanups.
Removed dead/obsolete code, made some style cleanups
--Mouse Events
Now keep track of what button(s) were pressed so we know when to send
the mouse up event. This fixes the case where the mouse is dragged
outside of the game window and released (in which case we want to send
the mouse up event even though the mouse is outside the game window).
--Input Grabbing
Here is my take on the grabbing situation, which is the basis for the
new implementation.
There are 3 grab states, ungrabbed (UG), visible (VG), and invisible
(IG). Both VG and IG keep the mouse constrained to the window and
produce relative motion events. In VG the cursor is visible (duh), in
IG it is not. In VG, absolute motion events also work.
There are 6 actions that can affect grabbing:
1. Set Fullscreen/Window (F/W). In fullscreen, a visible grab should do
nothing. However, a fullscreen visible grab can be treated just like a
windowed visible grab, which is what I have done to help simplify
things.
2. Cursor hide/show (H/S). If the cursor is hidden when grabbing, the
grab is an invisible grab. If the cursor is visible, the grab should
just constrain the mouse to the window.
3. Input grab/ungrab(G/U). If grabbed, the cursor should be confined to
the window as should the keyboard input. On Mac OS X, the keyboard
input is implicitly grabbed by confining the cursor, except for
command-tab which can switch away from the application. Should the
window come to the foreground if the application is deactivated and
grab input is called? This isn't necessary in this implementation
because the grab state will be asserted upon activation.
Using my notation, these are all the cases that need to be handled
(state + action = new state).
UG+U = UG
UG+G = VG or IG, if cursor is visible or not
UG+H = UG
UG+S = UG
VG+U = UG
VG+G = VG
VG+H = IG
VG+S = VG
IG+U = UG
IG+G = IG
IG+H = IG
IG+S = VG
The cases that result in the same state can be ignored in the code,
which cuts it down to just 5 cases.
Another issue is what happens when the app loses/gains input focus from
deactivate/activate or iconify/deiconify. I think that if input focus
is ever lost (outside of SDL's control), the grab state should be
suspended and the cursor should become visible and active again. When
regained, the cursor should reappear in its original location and/or
grab state. This way, when reactivating the cursor is still in the same
position as before so apps shouldn't get confused when the next motion
event comes in. This is what I've done in this patch.
| author | Ryan C. Gordon <icculus@icculus.org> |
|---|---|
| date | Fri, 27 Dec 2002 20:52:41 +0000 |
| parents | e5bc29de3f0a |
| children | e867f327aa54 |
line wrap: on
line source
.TH "SDL_PixelFormat" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference" .SH "NAME" SDL_PixelFormat\- Stores surface format information .SH "STRUCTURE DEFINITION" .PP .nf \f(CWtypedef 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;\fR .fi .PP .SH "STRUCTURE DATA" .TP 20 \fBpalette\fR Pointer to the \fIpalette\fR, or \fBNULL\fP if the \fBBitsPerPixel\fR>8 .TP 20 \fBBitsPerPixel\fR The number of bits used to represent each pixel in a surface\&. Usually 8, 16, 24 or 32\&. .TP 20 \fBBytesPerPixel\fR The number of bytes used to represent each pixel in a surface\&. Usually one to four\&. .TP 20 \fB[RGBA]mask\fR Binary mask used to retrieve individual color values .TP 20 \fB[RGBA]loss\fR Precision loss of each color component (2^[RGBA]loss) .TP 20 \fB[RGBA]shift\fR Binary left shift of each color component in the pixel value .TP 20 \fBcolorkey\fR Pixel value of transparent pixels .TP 20 \fBalpha\fR Overall surface alpha value .SH "DESCRIPTION" .PP 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\&. .PP If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential\&. .PP 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: .PP .nf \f(CWSDL_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); \&. \&.\fR .fi .PP .PP 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\&. .PP .nf \f(CW/* 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); \&. \&. \&.\fR .fi .PP .SH "SEE ALSO" .PP \fI\fBSDL_Surface\fR\fR, \fI\fBSDL_MapRGB\fP\fR ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01