s_alpha.c revision e3a051e0538a605551f4d58294c94f5eb00ed07f 
1/* $Id: s_alpha.c,v 1.1 2000/10/31 18:00:04 keithw 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	 }
66	 return 1;
67      case GL_GEQUAL:
68         for (i=0;i<n;i++) {
69	    mask[i] &= (rgba[i][ACOMP] >= ref);
70	 }
71	 return 1;
72      case GL_GREATER:
73         for (i=0;i<n;i++) {
74	    mask[i] &= (rgba[i][ACOMP] > ref);
75	 }
76	 return 1;
77      case GL_NOTEQUAL:
78         for (i=0;i<n;i++) {
79	    mask[i] &= (rgba[i][ACOMP] != ref);
80	 }
81	 return 1;
82      case GL_EQUAL:
83         for (i=0;i<n;i++) {
84	    mask[i] &= (rgba[i][ACOMP] == ref);
85	 }
86	 return 1;
87      case GL_ALWAYS:
88	 /* do nothing */
89	 return 1;
90      case GL_NEVER:
91         /* caller should check for zero! */
92	 return 0;
93      default:
94	 gl_problem( ctx, "Invalid alpha test in gl_alpha_test" );
95         return 0;
96   }
97   /* Never get here */
98   /*return 1;*/
99}
100