s_alpha.c

Mesa is an open-source implementation of the OpenGL specification - a system for rendering interacti

/*
 * Mesa 3-D graphics library
 * Version:  6.5.2
 *
 * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/**
 * \file swrast/s_alpha.c
 * \brief Functions to apply alpha test.
 */

#include "glheader.h"
#include "context.h"
#include "colormac.h"
#include "macros.h"

#include "s_alpha.h"
#include "s_context.h"


#define ALPHA_TEST(ALPHA, LOOP_CODE)		\
do {						\
   switch (ctx->Color.AlphaFunc) {		\
      case GL_LESS:				\
         for (i = 0; i < n; i++) {		\
            mask[i] &= (ALPHA < ref);		\
            LOOP_CODE;				\
         }					\
         break;					\
      case GL_LEQUAL:				\
         for (i = 0; i < n; i++) {		\
            mask[i] &= (ALPHA <= ref);		\
            LOOP_CODE;				\
         }					\
         break;					\
      case GL_GEQUAL:				\
         for (i = 0; i < n; i++) {		\
            mask[i] &= (ALPHA >= ref);		\
            LOOP_CODE;				\
         }					\
         break;					\
      case GL_GREATER:				\
         for (i = 0; i < n; i++) {		\
            mask[i] &= (ALPHA > ref);		\
            LOOP_CODE;				\
         }					\
         break;					\
      case GL_NOTEQUAL:				\
         for (i = 0; i < n; i++) {		\
            mask[i] &= (ALPHA != ref);		\
            LOOP_CODE;				\
         }					\
         break;					\
      case GL_EQUAL:				\
         for (i = 0; i < n; i++) {		\
            mask[i] &= (ALPHA == ref);		\
            LOOP_CODE;				\
         }					\
         break;					\
      default:					\
         _mesa_problem(ctx, "Invalid alpha test in _swrast_alpha_test" ); \
         return 0;				\
   }						\
} while (0)



/**
 * Perform the alpha test for an array of pixels.
 * For pixels that fail the test, mask[i] will be set to 0.
 * \return  0 if all pixels in the span failed the alpha test,
 *          1 if one or more pixels passed the alpha test.
 */
GLint
_swrast_alpha_test(const GLcontext *ctx, SWspan *span)
{
   const GLuint n = span->end;
   GLubyte *mask = span->array->mask;
   GLuint i;

   if (ctx->Color.AlphaFunc == GL_ALWAYS) {
      /* do nothing */
      return 1;
   }
   else if (ctx->Color.AlphaFunc == GL_NEVER) {
      /* All pixels failed - caller should check for this return value and
       * act accordingly.
       */
      span->writeAll = GL_FALSE;
      return 0;
   }

   if (span->arrayMask & SPAN_RGBA) {
      /* Use array's alpha values */
      if (span->array->ChanType == GL_UNSIGNED_BYTE) {
         GLubyte (*rgba)[4] = span->array->rgba8;
         GLubyte ref;
         CLAMPED_FLOAT_TO_UBYTE(ref, ctx->Color.AlphaRef);
         ALPHA_TEST(rgba[i][ACOMP], ;);
      }
      else if (span->array->ChanType == GL_UNSIGNED_SHORT) {
         GLushort (*rgba)[4] = span->array->rgba16;
         GLushort ref;
         CLAMPED_FLOAT_TO_USHORT(ref, ctx->Color.AlphaRef);
         ALPHA_TEST(rgba[i][ACOMP], ;);
      }
      else {
         GLfloat (*rgba)[4] = span->array->attribs[FRAG_ATTRIB_COL0];
         const GLfloat ref = ctx->Color.AlphaRef;
         ALPHA_TEST(rgba[i][ACOMP], ;);
      }
   }
   else {
      /* Interpolate alpha values */
      ASSERT(span->interpMask & SPAN_RGBA);
      if (span->array->ChanType == GL_UNSIGNED_BYTE) {
         const GLfixed alphaStep = span->alphaStep;
         GLfixed alpha = span->alpha;
         GLubyte ref;
         CLAMPED_FLOAT_TO_UBYTE(ref, ctx->Color.AlphaRef);
         ALPHA_TEST(FixedToInt(alpha), alpha += alphaStep);
      }
      else if (span->array->ChanType == GL_UNSIGNED_SHORT) {
         const GLfixed alphaStep = span->alphaStep;
         GLfixed alpha = span->alpha;
         GLushort ref;
         CLAMPED_FLOAT_TO_USHORT(ref, ctx->Color.AlphaRef);
         ALPHA_TEST(FixedToInt(alpha), alpha += alphaStep);
      }
      else {
         const GLfloat alphaStep = span->alphaStep;
         GLfloat alpha = span->alpha;
         const GLfloat ref = ctx->Color.AlphaRef;
         ALPHA_TEST(alpha, alpha += alphaStep);
      }
   }

   span->writeAll = GL_FALSE;

   /* XXX examine mask[] values? */
   return 1;
}