view docs/man3/SDL_BlitSurface.3 @ 1212:7663bb0f52c7

To: sdl@libsdl.org From: Christian Walther <cwalther@gmx.ch> Date: Thu, 15 Dec 2005 21:19:53 +0100 Subject: [SDL] More mouse enhancements for Mac OS X The attached patch brings two more enhancements to mouse handling on Mac OS X (Quartz): 1. Currently, after launching an SDL application, SDL's notion of the mouse position is stuck in the top left corner (0,0) until the first time the mouse is moved. That's because the UpdateMouse() function isn't implemented in the Quartz driver. This patch adds it. 2. When grabbing input while the mouse cursor is hidden, the function CGAssociateMouseAndMouseCursorPosition(0) is called, which prevents the system's notion of the mouse location from moving (and therefore leaving the SDL window) even when the mouse is moved. However, apparently the Wacom tablet driver (and maybe other special pointing device drivers) doesn't care about that setting and still allows the mouse location to go outside of the window. Interestingly, the system cursor, which is made visible by the existing code in SDL in that case, does not follow the mouse location, but appears in the middle of the SDL window. The mouse location being outside of the window however means that mouse button events go to background applications (or the dock or whatever is there), which is very confusing to the user who sees no cursor outside of the SDL window. I have not found any way of intercepting these events (and that's probably by design, as "normal" applications shouldn't prevent the user from bringing other applications' windows to the front by clicking on them). An idea would be placing a fully transparent, screen-filling window in front of everything, but I fear that this might affect rendering performance (by doing unnecessary compositing, using up memory, or whatever). The deluxe solution to the problem would be talking to the tablet driver using AppleEvents to tell it to constrain its mapped area to the window (see Wacom's "TabletEventDemo" sample app, http://www.wacomeng.com/devsupport/mac/downloads.html), but I think that the bloat that solution would add to SDL would outweigh its usefulness. What I did instead in my patch is reassociating mouse and cursor when the mouse leaves the window while an invisible grab is in effect, and restoring the grab when the window is entered. That way, the grab can still be effectively broken by a tablet, but at least it's obvious to the user that it is broken. That change is minimal - it doesn't affect operation with a mouse (or a trackpad), and the code that it adds is not executed on every PumpEvents() call, only when entering and leaving the window. Unless there are any concerns about the patch, please apply. Feel free to shorten the lengthy comment in SDL_QuartzEvents.m if you think it's too verbose. Thanks -Christian
author Ryan C. Gordon <icculus@icculus.org>
date Mon, 02 Jan 2006 00:31:00 +0000
parents e5bc29de3f0a
children 546f7c1eb755
line wrap: on
line source

.TH "SDL_BlitSurface" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference" 
.SH "NAME"
SDL_BlitSurface\- This performs a fast blit from the source surface to the destination surface\&.
.SH "SYNOPSIS"
.PP
\fB#include "SDL\&.h"
.sp
\fBint \fBSDL_BlitSurface\fP\fR(\fBSDL_Surface *src, SDL_Rect *srcrect, SDL_Surface *dst, SDL_Rect *dstrect\fR);
.SH "DESCRIPTION"
.PP
This performs a fast blit from the source surface to the destination surface\&.
.PP
Only the position is used in the \fBdstrect\fR (the width and height are ignored)\&.
.PP
If either \fBsrcrect\fR or \fBdstrect\fR are \fBNULL\fP, the entire surface (\fBsrc\fR or \fBdst\fR) is copied\&.
.PP
The final blit rectangle is saved in \fBdstrect\fR after all clipping is performed (\fBsrcrect\fR is not modified)\&.
.PP
The blit function should not be called on a locked surface\&.
.PP
The results of blitting operations vary greatly depending on whether \fBSDL_SRCAPLHA\fP is set or not\&. See \fISDL_SetAlpha\fR for an explaination of how this affects your results\&. Colorkeying and alpha attributes also interact with surface blitting, as the following pseudo-code should hopefully explain\&. 
.PP
.nf
\f(CWif (source surface has SDL_SRCALPHA set) {
    if (source surface has alpha channel (that is, format->Amask != 0))
        blit using per-pixel alpha, ignoring any colour key
    else {
        if (source surface has SDL_SRCCOLORKEY set)
            blit using the colour key AND the per-surface alpha value
        else
            blit using the per-surface alpha value
    }
} else {
    if (source surface has SDL_SRCCOLORKEY set)
        blit using the colour key
    else
        ordinary opaque rectangular blit
}\fR
.fi
.PP
.SH "RETURN VALUE"
.PP
If the blit is successful, it returns \fB0\fR, otherwise it returns \fB-1\fR\&.
.PP
If either of the surfaces were in video memory, and the blit returns \fB-2\fR, the video memory was lost, so it should be reloaded with artwork and re-blitted: 
.PP
.nf
\f(CW        while ( SDL_BlitSurface(image, imgrect, screen, dstrect) == -2 ) {
                while ( SDL_LockSurface(image)) < 0 )
                        Sleep(10);
                -- Write image pixels to image->pixels --
                SDL_UnlockSurface(image);
        }\fR
.fi
.PP
 This happens under DirectX 5\&.0 when the system switches away from your fullscreen application\&. Locking the surface will also fail until you have access to the video memory again\&.
.SH "SEE ALSO"
.PP
\fI\fBSDL_LockSurface\fP\fR, \fI\fBSDL_FillRect\fP\fR, \fI\fBSDL_Surface\fR\fR, \fI\fBSDL_Rect\fR\fR
...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01