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annotate docs/man3/SDL_SetAlpha.3 @ 1192:54aa9aa32327
To: sdl@libsdl.org
From: Christian Walther <cwalther@gmx.ch>
Date: Fri, 18 Nov 2005 23:39:02 +0100
Subject: [SDL] Mouse position bugs on Mac OS X
The attached patch fixes a few bugs in SDL related to the mouse position
in windowed mode on Mac OS X, reproduced using the attached minimal test
program - at least here on 10.3.9, with SDL CVS from today. Could anyone
test whether the bugs exist and are fixed by the patch on 10.2 and 10.4?
1. When using OpenGL, the vertical mouse positions obtained through
events or SDL_GetMouseState() are off by one.
2. When using OpenGL, SDL_WarpMouse() inverts the y coordinate.
3. Clicks on the topmost pixel row of the window are not recognized.
1 and 2 do not occur in non-OpenGL mode, while 3 does. All three only
occur in windowed mode, not in fullscreen.
The cause for 1 and 3 is that in Cocoa, "the location of the mouse"
seems to be defined as "the location of the top left corner of the mouse
pointer's hot pixel" (this is not documented, it's just what I found out
here), which together with the fact that Cocoa's usual y coordinates
start at the bottom and increase upwards means that the y coordinate of
the mouse runs from 1 to h, not from 0 to h-1, in a window of height h.
If it does work on 10.2 and 10.4 (I'll try to test it as soon as I can,
but at the moment all I have at hand is 10.3.9), can this be applied to
the CVS?
-Christian
To: sdl@libsdl.org
From: Christian Walther <cwalther@gmx.ch>
Date: Mon, 28 Nov 2005 10:41:51 +0100
Subject: [SDL] Re: Mouse position bugs on Mac OS X
I wrote:
> I'll try to test it as soon as I can, but at the moment all I have at hand is 10.3.9
So, here are the results of my tests (with patched and unpatched
frameworks compiled with Xcode 1.5 (gcc 3.3) on 10.3.9):
On 10.1.5, my test program doesn't run because of "Undefined symbols:
SDL undefined reference to _CGMainDisplayID expected to be defined in
Carbon". I guess not supporting 10.1 was a deliberate decision then and
that's OK with me.
On 10.2.8, 10.3.9, and 10.4.0, the bugs exist as described in my
original post and are fixed by my patch. That is, there is no difference
between pre/post 10.3 and the patched version works correctly in all
combinations of GL/non-GL and windowed/fullscreen.
I therefore recommend the patch for inclusion.
-Christian
author | Ryan C. Gordon <icculus@icculus.org> |
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date | Mon, 28 Nov 2005 13:58:26 +0000 |
parents | e5bc29de3f0a |
children | 546f7c1eb755 |
rev | line source |
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1 .TH "SDL_SetAlpha" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference" |
0 | 2 .SH "NAME" |
3 SDL_SetAlpha\- Adjust the alpha properties of a surface | |
4 .SH "SYNOPSIS" | |
5 .PP | |
6 \fB#include "SDL\&.h" | |
7 .sp | |
8 \fBint \fBSDL_SetAlpha\fP\fR(\fBSDL_Surface *surface, Uint32 flag, Uint8 alpha\fR); | |
9 .SH "DESCRIPTION" | |
10 .PP | |
11 .RS | |
12 \fBNote: | |
13 .PP | |
14 This function and the semantics of SDL alpha blending have changed since version 1\&.1\&.4\&. Up until version 1\&.1\&.5, an alpha value of 0 was considered opaque and a value of 255 was considered transparent\&. This has now been inverted: 0 (\fBSDL_ALPHA_TRANSPARENT\fP) is now considered transparent and 255 (\fBSDL_ALPHA_OPAQUE\fP) is now considered opaque\&. | |
15 .RE | |
16 .PP | |
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17 \fBSDL_SetAlpha\fP is used for setting the per-surface alpha value and/or enabling and disabling alpha blending\&. |
0 | 18 .PP |
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19 The\fBsurface\fR parameter specifies which surface whose alpha attributes you wish to adjust\&. \fBflags\fR is used to specify whether alpha blending should be used (\fBSDL_SRCALPHA\fP) and whether the surface should use RLE acceleration for blitting (\fBSDL_RLEACCEL\fP)\&. \fBflags\fR can be an OR\&'d combination of these two options, one of these options or 0\&. If \fBSDL_SRCALPHA\fP is not passed as a flag then all alpha information is ignored when blitting the surface\&. The \fBalpha\fR parameter is the per-surface alpha value; a surface need not have an alpha channel to use per-surface alpha and blitting can still be accelerated with \fBSDL_RLEACCEL\fP\&. |
0 | 20 .PP |
21 .RS | |
22 \fBNote: | |
23 .PP | |
24 The per-surface alpha value of 128 is considered a special case and is optimised, so it\&'s much faster than other per-surface values\&. | |
25 .RE | |
26 .PP | |
27 Alpha effects surface blitting in the following ways: | |
28 .TP 20 | |
29 RGBA->RGB with \fBSDL_SRCALPHA\fP | |
30 The source is alpha-blended with the destination, using the alpha channel\&. \fBSDL_SRCCOLORKEY\fP and the per-surface alpha are ignored\&. | |
31 .TP 20 | |
32 RGBA->RGB without \fBSDL_SRCALPHA\fP | |
33 The RGB data is copied from the source\&. The source alpha channel and the per-surface alpha value are ignored\&. | |
34 .TP 20 | |
35 RGB->RGBA with \fBSDL_SRCALPHA\fP | |
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36 The source is alpha-blended with the destination using the per-surface alpha value\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. The alpha channel of the copied pixels is set to opaque\&. |
0 | 37 .TP 20 |
38 RGB->RGBA without \fBSDL_SRCALPHA\fP | |
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39 The RGB data is copied from the source and the alpha value of the copied pixels is set to opaque\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. |
0 | 40 .TP 20 |
41 RGBA->RGBA with \fBSDL_SRCALPHA\fP | |
42 The source is alpha-blended with the destination using the source alpha channel\&. The alpha channel in the destination surface is left untouched\&. \fBSDL_SRCCOLORKEY\fP is ignored\&. | |
43 .TP 20 | |
44 RGBA->RGBA without \fBSDL_SRCALPHA\fP | |
45 The RGBA data is copied to the destination surface\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. | |
46 .TP 20 | |
47 RGB->RGB with \fBSDL_SRCALPHA\fP | |
48 The source is alpha-blended with the destination using the per-surface alpha value\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. | |
49 .TP 20 | |
50 RGB->RGB without \fBSDL_SRCALPHA\fP | |
51 The RGB data is copied from the source\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. | |
55
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52 .PP |
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53 .RS |
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54 \fBNote: |
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55 .PP |
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56 Note that RGBA->RGBA blits (with SDL_SRCALPHA set) keep the alpha of the destination surface\&. This means that you cannot compose two arbitrary RGBA surfaces this way and get the result you would expect from "overlaying" them; the destination alpha will work as a mask\&. |
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57 .PP |
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58 Also note that per-pixel and per-surface alpha cannot be combined; the per-pixel alpha is always used if available |
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59 .RE |
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60 .SH "RETURN VALUE" |
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61 .PP |
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62 This function returns \fB0\fR, or \fB-1\fR if there was an error\&. |
0 | 63 .SH "SEE ALSO" |
64 .PP | |
65 \fI\fBSDL_MapRGBA\fP\fR, \fI\fBSDL_GetRGBA\fP\fR, \fI\fBSDL_DisplayFormatAlpha\fP\fR, \fI\fBSDL_BlitSurface\fP\fR | |
181
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66 ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01 |