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Initial revision
author Sam Lantinga <slouken@lokigames.com>
date Thu, 26 Apr 2001 16:45:43 +0000
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1 <HTML
2 ><HEAD
3 ><TITLE
4 >SDL_SetAlpha</TITLE
5 ><META
6 NAME="GENERATOR"
7 CONTENT="Modular DocBook HTML Stylesheet Version 1.61
8 "><LINK
9 REL="HOME"
10 TITLE="SDL Library Documentation"
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13 TITLE="Video"
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16 TITLE="SDL_SetColorKey"
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21 ><BODY
22 CLASS="REFENTRY"
23 BGCOLOR="#FFF8DC"
24 TEXT="#000000"
25 LINK="#0000ee"
26 VLINK="#551a8b"
27 ALINK="#ff0000"
28 ><DIV
29 CLASS="NAVHEADER"
30 ><TABLE
31 WIDTH="100%"
32 BORDER="0"
33 CELLPADDING="0"
34 CELLSPACING="0"
35 ><TR
36 ><TH
37 COLSPAN="3"
38 ALIGN="center"
39 >SDL Library Documentation</TH
40 ></TR
41 ><TR
42 ><TD
43 WIDTH="10%"
44 ALIGN="left"
45 VALIGN="bottom"
46 ><A
47 HREF="sdlsetcolorkey.html"
48 >Prev</A
49 ></TD
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51 WIDTH="80%"
52 ALIGN="center"
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56 WIDTH="10%"
57 ALIGN="right"
58 VALIGN="bottom"
59 ><A
60 HREF="sdlsetcliprect.html"
61 >Next</A
62 ></TD
63 ></TR
64 ></TABLE
65 ><HR
66 ALIGN="LEFT"
67 WIDTH="100%"></DIV
68 ><H1
69 ><A
70 NAME="SDLSETALPHA"
71 >SDL_SetAlpha</A
72 ></H1
73 ><DIV
74 CLASS="REFNAMEDIV"
75 ><A
76 NAME="AEN1612"
77 ></A
78 ><H2
79 >Name</H2
80 >SDL_SetAlpha&nbsp;--&nbsp;Adjust the alpha properties of a surface</DIV
81 ><DIV
82 CLASS="REFSYNOPSISDIV"
83 ><A
84 NAME="AEN1615"
85 ></A
86 ><H2
87 >Synopsis</H2
88 ><DIV
89 CLASS="FUNCSYNOPSIS"
90 ><A
91 NAME="AEN1616"
92 ></A
93 ><P
94 ></P
95 ><PRE
96 CLASS="FUNCSYNOPSISINFO"
97 >#include "SDL.h"</PRE
98 ><P
99 ><CODE
100 ><CODE
101 CLASS="FUNCDEF"
102 >int <B
103 CLASS="FSFUNC"
104 >SDL_SetAlpha</B
105 ></CODE
106 >(SDL_Surface *surface, Uint32 flag, Uint8 alpha);</CODE
107 ></P
108 ><P
109 ></P
110 ></DIV
111 ></DIV
112 ><DIV
113 CLASS="REFSECT1"
114 ><A
115 NAME="AEN1622"
116 ></A
117 ><H2
118 >Description</H2
119 ><DIV
120 CLASS="NOTE"
121 ><BLOCKQUOTE
122 CLASS="NOTE"
123 ><P
124 ><B
125 >Note: </B
126 >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 (<TT
127 CLASS="LITERAL"
128 >SDL_ALPHA_TRANSPARENT</TT
129 >) is now considered transparent and 255 (<TT
130 CLASS="LITERAL"
131 >SDL_ALPHA_OPAQUE</TT
132 >) is now considered opaque.</P
133 ></BLOCKQUOTE
134 ></DIV
135 ><P
136 ><TT
137 CLASS="FUNCTION"
138 >SDL_SetAlpha</TT
139 > is used for setting the per-surface alpha and/or enabling and disabling per-pixel alpha blending.</P
140 ><P
141 >The <TT
142 CLASS="PARAMETER"
143 ><I
144 >surface</I
145 ></TT
146 > parameter specifies which surface whose alpha attributes you wish to adjust. <TT
147 CLASS="PARAMETER"
148 ><I
149 >flags</I
150 ></TT
151 > is used to specify whether alpha blending should be used (<TT
152 CLASS="LITERAL"
153 >SDL_SRCALPHA</TT
154 >) and whether the surface should use RLE acceleration for blitting (<TT
155 CLASS="LITERAL"
156 >SDL_RLEACCEL</TT
157 >). <TT
158 CLASS="PARAMETER"
159 ><I
160 >flags</I
161 ></TT
162 > can be an OR'd combination of these two options, one of these options or 0. If <TT
163 CLASS="LITERAL"
164 >SDL_SRCALPHA</TT
165 > is not passed as a flag then all alpha information is ignored when blitting the surface. The <TT
166 CLASS="PARAMETER"
167 ><I
168 >alpha</I
169 ></TT
170 > 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 <TT
171 CLASS="LITERAL"
172 >SDL_RLEACCEL</TT
173 >. Setting the per-surface alpha value to 0 disables per-surface alpha blending.</P
174 ><DIV
175 CLASS="NOTE"
176 ><BLOCKQUOTE
177 CLASS="NOTE"
178 ><P
179 ><B
180 >Note: </B
181 >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.</P
182 ></BLOCKQUOTE
183 ></DIV
184 ><P
185 >Alpha effects surface blitting in the following ways:</P
186 ><DIV
187 CLASS="INFORMALTABLE"
188 ><A
189 NAME="AEN1642"
190 ></A
191 ><P
192 ></P
193 ><TABLE
194 BORDER="0"
195 CLASS="CALSTABLE"
196 ><TBODY
197 ><TR
198 ><TD
199 ALIGN="LEFT"
200 VALIGN="TOP"
201 >RGBA-&#62;RGB with <TT
202 CLASS="LITERAL"
203 >SDL_SRCALPHA</TT
204 ></TD
205 ><TD
206 ALIGN="LEFT"
207 VALIGN="TOP"
208 ><P
209 >The source is alpha-blended with the destination, using the alpha channel. <TT
210 CLASS="LITERAL"
211 >SDL_SRCCOLORKEY</TT
212 > and the per-surface alpha are ignored.</P
213 ></TD
214 ></TR
215 ><TR
216 ><TD
217 ALIGN="LEFT"
218 VALIGN="TOP"
219 >RGBA-&#62;RGB without <TT
220 CLASS="LITERAL"
221 >SDL_SRCALPHA</TT
222 ></TD
223 ><TD
224 ALIGN="LEFT"
225 VALIGN="TOP"
226 ><P
227 >The RGB data is copied from the source. The source alpha channel and the per-surface alpha value are ignored.</P
228 ></TD
229 ></TR
230 ><TR
231 ><TD
232 ALIGN="LEFT"
233 VALIGN="TOP"
234 >RGB-&#62;RGBA with <TT
235 CLASS="LITERAL"
236 >SDL_SRCALPHA</TT
237 ></TD
238 ><TD
239 ALIGN="LEFT"
240 VALIGN="TOP"
241 ><P
242 >The source is alpha-blended with the destination using the per-surface alpha value. If <TT
243 CLASS="LITERAL"
244 >SDL_SRCCOLORKEY</TT
245 >literal&#62; is set, only the pixels not matching the colorkey value are copied.</P
246 ></TD
247 ></TR
248 ><TR
249 ><TD
250 ALIGN="LEFT"
251 VALIGN="TOP"
252 >RGB-&#62;RGBA without <TT
253 CLASS="LITERAL"
254 >SDL_SRCALPHA</TT
255 ></TD
256 ><TD
257 ALIGN="LEFT"
258 VALIGN="TOP"
259 ><P
260 >The RGB data is copied from the source and the destination alpha is zero to opaque. If <TT
261 CLASS="LITERAL"
262 >SDL_SRCCOLORKEY</TT
263 > is set, only the pixels not matching the colorkey value are copied.</P
264 ></TD
265 ></TR
266 ><TR
267 ><TD
268 ALIGN="LEFT"
269 VALIGN="TOP"
270 >RGBA-&#62;RGBA with <TT
271 CLASS="LITERAL"
272 >SDL_SRCALPHA</TT
273 ></TD
274 ><TD
275 ALIGN="LEFT"
276 VALIGN="TOP"
277 ><P
278 >The source is alpha-blended with the destination using the source alpha channel. The alpha channel in the destination surface is left untouched. <TT
279 CLASS="LITERAL"
280 >SDL_SRCCOLORKEY</TT
281 > is ignored.</P
282 ></TD
283 ></TR
284 ><TR
285 ><TD
286 ALIGN="LEFT"
287 VALIGN="TOP"
288 >RGBA-&#62;RGBA without <TT
289 CLASS="LITERAL"
290 >SDL_SRCALPHA</TT
291 ></TD
292 ><TD
293 ALIGN="LEFT"
294 VALIGN="TOP"
295 ><P
296 >The RGBA data is copied to the destination surface. If <TT
297 CLASS="LITERAL"
298 >SDL_SRCCOLORKEY</TT
299 > is set, only the pixels not matching the colorkey value are copied.</P
300 ></TD
301 ></TR
302 ><TR
303 ><TD
304 ALIGN="LEFT"
305 VALIGN="TOP"
306 >RGB-&#62;RGB with <TT
307 CLASS="LITERAL"
308 >SDL_SRCALPHA</TT
309 ></TD
310 ><TD
311 ALIGN="LEFT"
312 VALIGN="TOP"
313 ><P
314 >The source is alpha-blended with the destination using the per-surface alpha value. If <TT
315 CLASS="LITERAL"
316 >SDL_SRCCOLORKEY</TT
317 > is set, only the pixels not matching the colorkey value are copied.</P
318 ></TD
319 ></TR
320 ><TR
321 ><TD
322 ALIGN="LEFT"
323 VALIGN="TOP"
324 >RGB-&#62;RGB without <TT
325 CLASS="LITERAL"
326 >SDL_SRCALPHA</TT
327 ></TD
328 ><TD
329 ALIGN="LEFT"
330 VALIGN="TOP"
331 ><P
332 >The RGB data is copied from the source. If <TT
333 CLASS="LITERAL"
334 >SDL_SRCCOLORKEY</TT
335 > is set, only the pixels not matching the colorkey value are copied.</P
336 ></TD
337 ></TR
338 ></TBODY
339 ></TABLE
340 ><P
341 ></P
342 ></DIV
343 ></DIV
344 ><DIV
345 CLASS="REFSECT1"
346 ><A
347 NAME="AEN1692"
348 ></A
349 ><H2
350 >See Also</H2
351 ><P
352 ><A
353 HREF="sdlmaprgba.html"
354 ><TT
355 CLASS="FUNCTION"
356 >SDL_MapRGBA</TT
357 ></A
358 >,
359 <A
360 HREF="sdlgetrgba.html"
361 ><TT
362 CLASS="FUNCTION"
363 >SDL_GetRGBA</TT
364 ></A
365 >,
366 <A
367 HREF="sdldisplayformatalpha.html"
368 ><TT
369 CLASS="FUNCTION"
370 >SDL_DisplayFormatAlpha</TT
371 ></A
372 >,
373 <A
374 HREF="sdlblitsurface.html"
375 ><TT
376 CLASS="FUNCTION"
377 >SDL_BlitSurface</TT
378 ></A
379 ></P
380 ></DIV
381 ><DIV
382 CLASS="NAVFOOTER"
383 ><HR
384 ALIGN="LEFT"
385 WIDTH="100%"><TABLE
386 WIDTH="100%"
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388 CELLPADDING="0"
389 CELLSPACING="0"
390 ><TR
391 ><TD
392 WIDTH="33%"
393 ALIGN="left"
394 VALIGN="top"
395 ><A
396 HREF="sdlsetcolorkey.html"
397 >Prev</A
398 ></TD
399 ><TD
400 WIDTH="34%"
401 ALIGN="center"
402 VALIGN="top"
403 ><A
404 HREF="index.html"
405 >Home</A
406 ></TD
407 ><TD
408 WIDTH="33%"
409 ALIGN="right"
410 VALIGN="top"
411 ><A
412 HREF="sdlsetcliprect.html"
413 >Next</A
414 ></TD
415 ></TR
416 ><TR
417 ><TD
418 WIDTH="33%"
419 ALIGN="left"
420 VALIGN="top"
421 >SDL_SetColorKey</TD
422 ><TD
423 WIDTH="34%"
424 ALIGN="center"
425 VALIGN="top"
426 ><A
427 HREF="video.html"
428 >Up</A
429 ></TD
430 ><TD
431 WIDTH="33%"
432 ALIGN="right"
433 VALIGN="top"
434 >SDL_SetClipRect</TD
435 ></TR
436 ></TABLE
437 ></DIV
438 ></BODY
439 ></HTML
440 >