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[SDL] Bad math in SDL_RenderCopy Mason Wheeler to sdl When I tried to render an image using something other than NULL for srcrect, it got horribly distorted. I traced it down to the fact that the math in the rectangle adjustments performed just before the call to renderer->RenderCopy is written inside out. It should look like this: if (dstrect->w != real_dstrect.w) { int deltax = (dstrect->x - real_dstrect.x); int deltaw = (dstrect->w - real_dstrect.w); real_srcrect.x += (deltax * real_srcrect.w) / dstrect->w; real_srcrect.w += (deltaw * real_srcrect.w) / dstrect->w; } if (dstrect->h != real_dstrect.h) { int deltay = (dstrect->y - real_dstrect.y); int deltah = (dstrect->h - real_dstrect.h); real_srcrect.y += (deltay * real_srcrect.h) / dstrect->h; real_srcrect.h += (deltah * real_srcrect.h) / dstrect->h;
author Sam Lantinga <slouken@libsdl.org>
date Sat, 03 Oct 2009 16:23:16 +0000
parents 546f7c1eb755
children 1238da4a7112
line wrap: on
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.TH "SDL_LockSurface" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference" 
.SH "NAME"
SDL_LockSurface \- Lock a surface for directly access\&.
.SH "SYNOPSIS"
.PP
\fB#include "SDL\&.h"
.sp
\fBint \fBSDL_LockSurface\fP\fR(\fBSDL_Surface *surface\fR);
.SH "DESCRIPTION"
.PP
\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\&.
.PP
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\&. 
.PP
No operating system or library calls should be made between lock/unlock pairs, as critical system locks may be held during this time\&.
.PP
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\&. 
.PP
.nf
\f(CW    \&.
    \&.
    SDL_LockSurface( surface );
    \&.
    /* Surface is locked */
    /* Direct pixel access on surface here */
    \&.
    SDL_LockSurface( surface );
    \&.
    /* More direct pixel access on surface */
    \&.
    SDL_UnlockSurface( surface );
    /* Surface is still locked */
    /* Note: Is versions < 1\&.1\&.8, the surface would have been */
    /* no longer locked at this stage                         */
    \&.
    SDL_UnlockSurface( surface );
    /* Surface is now unlocked */
    \&.
    \&.\fR
.fi
.PP
.SH "RETURN VALUE"
.PP
\fBSDL_LockSurface\fP returns \fB0\fR, or \fB-1\fR if the surface couldn\&'t be locked\&.
.SH "SEE ALSO"
.PP
\fI\fBSDL_UnlockSurface\fP\fR
...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01