annotate docs/man3/SDL_LockSurface.3 @ 1544:ab1e4c41ab71

Fixed bug #33 Mike Frysinger wrote: > with libsdl-1.2.9, some games (like bomberclone) started > segfaulting in Gentoo [...snip...] > the last change in the last hunk: [...snip...] > if i change the statement to read: > (table[which].blit_features & GetBlitFeatures()) == GetBlitFeatures() > bomberclone no longer segfaults on my box Alex Volkov wrote: > The test "(table[which].blit_features & GetBlitFeatures()) == > table[which].blit_features)" is correct, and the previous > "(table[which].cpu_mmx == SDL_HasMMX())" was actually broken. I think there is potentially a slightly different cause of the above problem. During the introduction of the Altivec code, the blit_table struct field 'alpha' got changed from a straightforward enum to a bitmask, which makes perfect sense by itself. However, now the table driven blitter selection code in SDL_CalculateBlitN() can choose the wrong blitters when searching for a NO_ALPHA blitter because of the following code: int a_need = 0; ... (a_need & table[which].alpha) == a_need && When searching through the normal_blit_2[] table, a SET_ALPHA blitter (like Blit_RGB565_ARGB8888) can now be selected instead of a NO_ALPHA one, causing alpha channel bits to appear in a non-alpha destination surface. I suppose this could theoretically be an indirect cause of the segfault mentioned above. I *think* this can be fixed by changing to int a_need = NO_ALPHA;
author Sam Lantinga <slouken@libsdl.org>
date Wed, 15 Mar 2006 15:47:49 +0000
parents e5bc29de3f0a
children 546f7c1eb755
rev   line source
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1 .TH "SDL_LockSurface" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference"
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2 .SH "NAME"
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3 SDL_LockSurface\- Lock a surface for directly access\&.
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4 .SH "SYNOPSIS"
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5 .PP
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6 \fB#include "SDL\&.h"
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7 .sp
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8 \fBint \fBSDL_LockSurface\fP\fR(\fBSDL_Surface *surface\fR);
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9 .SH "DESCRIPTION"
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10 .PP
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11 \fBSDL_LockSurface\fP sets up a surface for directly accessing the pixels\&. Between calls to \fBSDL_LockSurface\fP and \fBSDL_UnlockSurface\fP, you can write to and read from \fBsurface->\fBpixels\fR\fR, using the pixel format stored in \fBsurface->\fBformat\fR\fR\&. Once you are done accessing the surface, you should use \fBSDL_UnlockSurface\fP to release it\&.
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12 .PP
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13 Not all surfaces require locking\&. If \fBSDL_MUSTLOCK\fP(\fBsurface\fR) evaluates to \fB0\fR, then you can read and write to the surface at any time, and the pixel format of the surface will not change\&.
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14 .PP
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15 No operating system or library calls should be made between lock/unlock pairs, as critical system locks may be held during this time\&.
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16 .PP
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17 It should be noted, that since SDL 1\&.1\&.8 surface locks are recursive\&. This means that you can lock a surface multiple times, but each lock must have a match unlock\&.
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18 .PP
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19 .nf
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20 \f(CW \&.
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21 \&.
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22 SDL_LockSurface( surface );
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23 \&.
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24 /* Surface is locked */
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25 /* Direct pixel access on surface here */
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26 \&.
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27 SDL_LockSurface( surface );
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28 \&.
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29 /* More direct pixel access on surface */
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30 \&.
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31 SDL_UnlockSurface( surface );
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32 /* Surface is still locked */
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33 /* Note: Is versions < 1\&.1\&.8, the surface would have been */
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34 /* no longer locked at this stage */
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35 \&.
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36 SDL_UnlockSurface( surface );
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37 /* Surface is now unlocked */
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38 \&.
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39 \&.\fR
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40 .fi
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41 .PP
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42 .SH "RETURN VALUE"
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43 .PP
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44 \fBSDL_LockSurface\fP returns \fB0\fR, or \fB-1\fR if the surface couldn\&'t be locked\&.
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45 .SH "SEE ALSO"
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46 .PP
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47 \fI\fBSDL_UnlockSurface\fP\fR
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48 ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01