s_alpha.c revision 08836341788a9f9d638d9dc8328510ccd18ddeb5 
1/* $Id: s_alpha.c,v 1.3 2001/03/03 20:33:30 brianp Exp $ */
2
3/*
4 * Mesa 3-D graphics library
5 * Version:  3.3
6 *
7 * Copyright (C) 1999-2000  Brian Paul   All Rights Reserved.
8 *
9 * Permission is hereby granted, free of charge, to any person obtaining a
10 * copy of this software and associated documentation files (the "Software"),
11 * to deal in the Software without restriction, including without limitation
12 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
13 * and/or sell copies of the Software, and to permit persons to whom the
14 * Software is furnished to do so, subject to the following conditions:
15 *
16 * The above copyright notice and this permission notice shall be included
17 * in all copies or substantial portions of the Software.
18 *
19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
20 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
21 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
22 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
23 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
24 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
25 */
26
27
28#include "glheader.h"
29#include "context.h"
30#include "colormac.h"
31#include "macros.h"
32#include "mmath.h"
33
34#include "s_alpha.h"
35
36
37
38
39
40/*
41 * Apply the alpha test to a span of pixels.
42 * In:  rgba - array of pixels
43 * In/Out:  mask - current pixel mask.  Pixels which fail the alpha test
44 *                 will set the corresponding mask flag to 0.
45 * Return:  0 = all pixels in the span failed the alpha test.
46 *          1 = one or more pixels passed the alpha test.
47 */
48GLint
49_mesa_alpha_test( const GLcontext *ctx,
50                  GLuint n, CONST GLchan rgba[][4], GLubyte mask[] )
51{
52   GLuint i;
53   GLchan ref = ctx->Color.AlphaRef;
54
55   /* switch cases ordered from most frequent to less frequent */
56   switch (ctx->Color.AlphaFunc) {
57      case GL_LESS:
58         for (i=0;i<n;i++) {
59	    mask[i] &= (rgba[i][ACOMP] < ref);
60	 }
61	 return 1;
62      case GL_LEQUAL:
63         for (i=0;i<n;i++)
64	    mask[i] &= (rgba[i][ACOMP] <= ref);
65	 return 1;
66      case GL_GEQUAL:
67         for (i=0;i<n;i++) {
68	    mask[i] &= (rgba[i][ACOMP] >= ref);
69	 }
70	 return 1;
71      case GL_GREATER:
72         for (i=0;i<n;i++) {
73	    mask[i] &= (rgba[i][ACOMP] > ref);
74	 }
75	 return 1;
76      case GL_NOTEQUAL:
77         for (i=0;i<n;i++) {
78	    mask[i] &= (rgba[i][ACOMP] != ref);
79	 }
80	 return 1;
81      case GL_EQUAL:
82         for (i=0;i<n;i++) {
83	    mask[i] &= (rgba[i][ACOMP] == ref);
84	 }
85	 return 1;
86      case GL_ALWAYS:
87	 /* do nothing */
88	 return 1;
89      case GL_NEVER:
90         /* caller should check for zero! */
91	 return 0;
92      default:
93	 _mesa_problem( ctx, "Invalid alpha test in gl_alpha_test" );
94         return 0;
95   }
96   /* Never get here */
97   /*return 1;*/
98}
99