dll/opengl/mesa/alpha.c

   1 /* $Id: alpha.c,v 1.5 1997/07/24 01:24:28 brianp Exp $ */
   2
   3 /*
   4  * Mesa 3-D graphics library
   5  * Version:  2.4
   6  * Copyright (C) 1995-1997  Brian Paul
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Library General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Library General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Library General Public
  19  * License along with this library; if not, write to the Free
  20  * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  21  */
  22
  23
  24 /*
  25  * $Log: alpha.c,v $
  26  * Revision 1.5  1997/07/24 01:24:28  brianp
  27  * changed precompiled header symbol from PCH to PC_HEADER
  28  *
  29  * Revision 1.4  1997/05/28 03:23:09  brianp
  30  * added precompiled header (PCH) support
  31  *
  32  * Revision 1.3  1997/03/13 03:07:53  brianp
  33  * optimized gl_alpha_test() by removing conditional from inside loops
  34  *
  35  * Revision 1.2  1996/09/15 14:15:54  brianp
  36  * now use GLframebuffer and GLvisual
  37  *
  38  * Revision 1.1  1996/09/13 01:38:16  brianp
  39  * Initial revision
  40  *
  41  */
  42
  43
  44 #ifdef PC_HEADER
  45 #include "all.h"
  46 #else
  47 #include "alpha.h"
  48 #include "context.h"
  49 #include "types.h"
  50 #include "dlist.h"
  51 #include "macros.h"
  52 #endif
  53
  54
  55
  56 void gl_AlphaFunc( GLcontext* ctx, GLenum func, GLclampf ref )
  57 {
  58    if (INSIDE_BEGIN_END(ctx)) {
  59       gl_error( ctx, GL_INVALID_OPERATION, "glAlphaFunc" );
  60       return;
  61    }
  62    switch (func) {
  63       case GL_NEVER:
  64       case GL_LESS:
  65       case GL_EQUAL:
  66       case GL_LEQUAL:
  67       case GL_GREATER:
  68       case GL_NOTEQUAL:
  69       case GL_GEQUAL:
  70       case GL_ALWAYS:
  71          ctx->Color.AlphaFunc = func;
  72          ctx->Color.AlphaRef = CLAMP( ref, 0.0F, 1.0F );
  73          ctx->Color.AlphaRefUbyte = (GLubyte) (ctx->Color.AlphaRef
  74                                               * ctx->Visual->AlphaScale);
  75          break;
  76       default:
  77          gl_error( ctx, GL_INVALID_ENUM, "glAlphaFunc(func)" );
  78          break;
  79    }
  80 }
  81
  82
  83
  84
  85 /*
  86  * Apply the alpha test to a span of pixels.
  87  * In/Out:  mask - current pixel mask.  Pixels which fail the alpha test
  88  *                 will set the corresponding mask flag to 0.
  89  * Return:  0 = all pixels in the span failed the alpha test.
  90  *          1 = one or more pixels passed the alpha test.
  91  */
  92 GLint gl_alpha_test( GLcontext* ctx,
  93                      GLuint n, const GLubyte alpha[], GLubyte mask[] )
  94 {
  95    GLuint i;
  96    GLubyte ref = ctx->Color.AlphaRefUbyte;
  97
  98    /* switch cases ordered from most frequent to less frequent */
  99    switch (ctx->Color.AlphaFunc) {
 100       case GL_LESS:
 101          for (i=0;i<n;i++) {
 102             mask[i] &= (alpha[i] < ref);
 103          }
 104          return 1;
 105       case GL_LEQUAL:
 106          for (i=0;i<n;i++) {
 107             mask[i] &= (alpha[i] <= ref);
 108          }
 109          return 1;
 110       case GL_GEQUAL:
 111          for (i=0;i<n;i++) {
 112             mask[i] &= (alpha[i] >= ref);
 113          }
 114          return 1;
 115       case GL_GREATER:
 116          for (i=0;i<n;i++) {
 117             mask[i] &= (alpha[i] > ref);
 118          }
 119          return 1;
 120       case GL_NOTEQUAL:
 121          for (i=0;i<n;i++) {
 122             mask[i] &= (alpha[i] != ref);
 123          }
 124          return 1;
 125       case GL_EQUAL:
 126          for (i=0;i<n;i++) {
 127             mask[i] &= (alpha[i] == ref);
 128          }
 129          return 1;
 130       case GL_ALWAYS:
 131          /* do nothing */
 132          return 1;
 133       case GL_NEVER:
 134          /* caller should check for zero! */
 135          return 0;
 136       default:
 137          gl_problem( ctx, "Invalid alpha test in gl_alpha_test" );
 138          return 0;
 139    }
 140    /* Never get here */
 141    return 1;
 142 }