t_vb_fog.c revision 3e21a014c308a87e1dd7bdabba255aad02d3ad1b 
1/*
2 * Mesa 3-D graphics library
3 * Version:  6.5
4 *
5 * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a
8 * copy of this software and associated documentation files (the "Software"),
9 * to deal in the Software without restriction, including without limitation
10 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
11 * and/or sell copies of the Software, and to permit persons to whom the
12 * Software is furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice shall be included
15 * in all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
18 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
20 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
21 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
22 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
23 *
24 * Authors:
25 *    Keith Whitwell <keith@tungstengraphics.com>
26 */
27
28
29#include "glheader.h"
30#include "colormac.h"
31#include "context.h"
32#include "macros.h"
33#include "imports.h"
34#include "mtypes.h"
35
36#include "math/m_xform.h"
37
38#include "t_context.h"
39#include "t_pipeline.h"
40
41
42struct fog_stage_data {
43   GLvector4f fogcoord;		/* has actual storage allocated */
44   GLvector4f input;		/* points into VB->EyePtr Z values */
45};
46
47#define FOG_STAGE_DATA(stage) ((struct fog_stage_data *)stage->privatePtr)
48
49#define FOG_EXP_TABLE_SIZE 256
50#define FOG_MAX (10.0)
51#define EXP_FOG_MAX .0006595
52#define FOG_INCR (FOG_MAX/FOG_EXP_TABLE_SIZE)
53static GLfloat exp_table[FOG_EXP_TABLE_SIZE];
54static GLfloat inited = 0;
55
56#if 1
57#define NEG_EXP( result, narg )						\
58do {									\
59   GLfloat f = (GLfloat) (narg * (1.0/FOG_INCR));			\
60   GLint k = (GLint) f;							\
61   if (k > FOG_EXP_TABLE_SIZE-2) 					\
62      result = (GLfloat) EXP_FOG_MAX;					\
63   else									\
64      result = exp_table[k] + (f-k)*(exp_table[k+1]-exp_table[k]);	\
65} while (0)
66#else
67#define NEG_EXP( result, narg )					\
68do {								\
69   result = exp(-narg);						\
70} while (0)
71#endif
72
73
74/**
75 * Initialize the exp_table[] lookup table for approximating exp().
76 */
77static void
78init_static_data( void )
79{
80   GLfloat f = 0.0F;
81   GLint i = 0;
82   for ( ; i < FOG_EXP_TABLE_SIZE ; i++, f += FOG_INCR) {
83      exp_table[i] = EXPF(-f);
84   }
85   inited = 1;
86}
87
88
89/**
90 * Compute per-vertex fog blend factors from fog coordinates by
91 * evaluating the GL_LINEAR, GL_EXP or GL_EXP2 fog function.
92 * Fog coordinates are distances from the eye (typically between the
93 * near and far clip plane distances).
94 * Note the fog (eye Z) coords may be negative so we use ABS(z) below.
95 * Fog blend factors are in the range [0,1].
96 */
97static void
98compute_fog_blend_factors(GLcontext *ctx, GLvector4f *out, const GLvector4f *in)
99{
100   GLfloat end  = ctx->Fog.End;
101   GLfloat *v = in->start;
102   GLuint stride = in->stride;
103   GLuint n = in->count;
104   GLfloat (*data)[4] = out->data;
105   GLfloat d;
106   GLuint i;
107
108   out->count = in->count;
109
110   switch (ctx->Fog.Mode) {
111   case GL_LINEAR:
112      if (ctx->Fog.Start == ctx->Fog.End)
113         d = 1.0F;
114      else
115         d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
116      for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
117         const GLfloat z = *v;
118         GLfloat f = (end - z) * d;
119	 data[i][0] = CLAMP(f, 0.0F, 1.0F);
120      }
121      break;
122   case GL_EXP:
123      d = ctx->Fog.Density;
124      for ( i = 0 ; i < n ; i++, STRIDE_F(v,stride)) {
125         const GLfloat z = *v;
126         NEG_EXP( data[i][0], d * z );
127      }
128      break;
129   case GL_EXP2:
130      d = ctx->Fog.Density*ctx->Fog.Density;
131      for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
132         const GLfloat z = *v;
133         NEG_EXP( data[i][0], d * z * z );
134      }
135      break;
136   default:
137      _mesa_problem(ctx, "Bad fog mode in make_fog_coord");
138      return;
139   }
140}
141
142
143static GLboolean
144run_fog_stage(GLcontext *ctx, struct tnl_pipeline_stage *stage)
145{
146   TNLcontext *tnl = TNL_CONTEXT(ctx);
147   struct vertex_buffer *VB = &tnl->vb;
148   struct fog_stage_data *store = FOG_STAGE_DATA(stage);
149   GLvector4f *input;
150
151   if (!ctx->Fog.Enabled || ctx->VertexProgram._Current)
152      return GL_TRUE;
153
154
155   if (ctx->Fog.FogCoordinateSource == GL_FRAGMENT_DEPTH_EXT) {
156      GLuint i;
157      GLfloat *coord;
158      /* Fog is computed from vertex or fragment Z values */
159      /* source = VB->ObjPtr or VB->EyePtr coords */
160      /* dest = VB->AttribPtr[_TNL_ATTRIB_FOG] = fog stage private storage */
161      VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;
162
163      if (!ctx->_NeedEyeCoords) {
164         /* compute fog coords from object coords */
165	 const GLfloat *m = ctx->ModelviewMatrixStack.Top->m;
166	 GLfloat plane[4];
167
168	 /* Use this to store calculated eye z values:
169	  */
170	 input = &store->fogcoord;
171
172         /* NOTE: negate plane here so we get positive fog coords! */
173	 /* NOTE2: this doesn't always work (tests/fog - all frag depth fog
174	    coords will be negative). */
175	 plane[0] = -m[2];
176	 plane[1] = -m[6];
177	 plane[2] = -m[10];
178	 plane[3] = -m[14];
179	 /* Full eye coords weren't required, just calculate the
180	  * eye Z values.
181	  */
182	 _mesa_dotprod_tab[VB->ObjPtr->size]( (GLfloat *) input->data,
183					      4 * sizeof(GLfloat),
184					      VB->ObjPtr, plane );
185
186	 input->count = VB->ObjPtr->count;
187
188	 /* make sure coords are really positive
189	    NOTE should avoid going through array twice */
190	 coord = input->start;
191	 for (i = 0; i < input->count; i++) {
192	    input->data[i][0] = FABSF(*coord);
193	    STRIDE_F(coord, input->stride);
194	 }
195      }
196      else {
197         /* fog coordinates = eye Z coordinates (use ABS later) */
198	 input = &store->fogcoord;
199
200	 if (VB->EyePtr->size < 2)
201	    _mesa_vector4f_clean_elem( VB->EyePtr, VB->Count, 2 );
202
203	 input->stride = 4 * sizeof(GLfloat);
204	 input->count = VB->EyePtr->count;
205	 coord = VB->EyePtr->start;
206	 for (i = 0 ; i < VB->EyePtr->count; i++) {
207	    input->data[i][0] = FABSF(coord[2]);
208	    STRIDE_F(coord, VB->EyePtr->stride);
209	 }
210      }
211   }
212   else {
213      /* use glFogCoord() coordinates */
214      input = VB->AttribPtr[_TNL_ATTRIB_FOG];  /* source data */
215
216      /* input->count may be one if glFogCoord was only called once
217       * before glBegin.  But we need to compute fog for all vertices.
218       */
219      input->count = VB->ObjPtr->count;
220
221      VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;  /* dest data */
222   }
223
224   if (tnl->_DoVertexFog) {
225      /* compute blend factors from fog coordinates */
226      compute_fog_blend_factors( ctx, VB->AttribPtr[_TNL_ATTRIB_FOG], input );
227   }
228   else {
229      /* results = incoming fog coords (compute fog per-fragment later) */
230      VB->AttribPtr[_TNL_ATTRIB_FOG] = input;
231   }
232
233   VB->FogCoordPtr = VB->AttribPtr[_TNL_ATTRIB_FOG];
234   return GL_TRUE;
235}
236
237
238
239/* Called the first time stage->run() is invoked.
240 */
241static GLboolean
242alloc_fog_data(GLcontext *ctx, struct tnl_pipeline_stage *stage)
243{
244   TNLcontext *tnl = TNL_CONTEXT(ctx);
245   struct fog_stage_data *store;
246   stage->privatePtr = MALLOC(sizeof(*store));
247   store = FOG_STAGE_DATA(stage);
248   if (!store)
249      return GL_FALSE;
250
251   _mesa_vector4f_alloc( &store->fogcoord, 0, tnl->vb.Size, 32 );
252   _mesa_vector4f_init( &store->input, 0, NULL );
253
254   if (!inited)
255      init_static_data();
256
257   return GL_TRUE;
258}
259
260
261static void
262free_fog_data(struct tnl_pipeline_stage *stage)
263{
264   struct fog_stage_data *store = FOG_STAGE_DATA(stage);
265   if (store) {
266      _mesa_vector4f_free( &store->fogcoord );
267      FREE( store );
268      stage->privatePtr = NULL;
269   }
270}
271
272
273const struct tnl_pipeline_stage _tnl_fog_coordinate_stage =
274{
275   "build fog coordinates",	/* name */
276   NULL,			/* private_data */
277   alloc_fog_data,		/* dtr */
278   free_fog_data,		/* dtr */
279   NULL,		/* check */
280   run_fog_stage		/* run -- initially set to init. */
281};
282