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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 "main/glheader.h"
30 #include "main/colormac.h"
31 #include "main/macros.h"
32 #include "main/imports.h"
33 #include "main/mtypes.h"
34 
35 #include "math/m_xform.h"
36 
37 #include "t_context.h"
38 #include "t_pipeline.h"
39 
40 
41 struct fog_stage_data {
42    GLvector4f fogcoord;		/* has actual storage allocated */
43 };
44 
45 #define FOG_STAGE_DATA(stage) ((struct fog_stage_data *)stage->privatePtr)
46 
47 #define FOG_EXP_TABLE_SIZE 256
48 #define FOG_MAX (10.0)
49 #define EXP_FOG_MAX .0006595
50 #define FOG_INCR (FOG_MAX/FOG_EXP_TABLE_SIZE)
51 static GLfloat exp_table[FOG_EXP_TABLE_SIZE];
52 static GLfloat inited = 0;
53 
54 #if 1
55 #define NEG_EXP( result, narg )						\
56 do {									\
57    GLfloat f = (GLfloat) (narg * (1.0/FOG_INCR));			\
58    GLint k = (GLint) f;							\
59    if (k > FOG_EXP_TABLE_SIZE-2) 					\
60       result = (GLfloat) EXP_FOG_MAX;					\
61    else									\
62       result = exp_table[k] + (f-k)*(exp_table[k+1]-exp_table[k]);	\
63 } while (0)
64 #else
65 #define NEG_EXP( result, narg )					\
66 do {								\
67    result = exp(-narg);						\
68 } while (0)
69 #endif
70 
71 
72 /**
73  * Initialize the exp_table[] lookup table for approximating exp().
74  */
75 static void
init_static_data(void)76 init_static_data( void )
77 {
78    GLfloat f = 0.0F;
79    GLint i = 0;
80    for ( ; i < FOG_EXP_TABLE_SIZE ; i++, f += FOG_INCR) {
81       exp_table[i] = EXPF(-f);
82    }
83    inited = 1;
84 }
85 
86 
87 /**
88  * Compute per-vertex fog blend factors from fog coordinates by
89  * evaluating the GL_LINEAR, GL_EXP or GL_EXP2 fog function.
90  * Fog coordinates are distances from the eye (typically between the
91  * near and far clip plane distances).
92  * Note that fogcoords may be negative, if eye z is source absolute
93  * value must be taken earlier.
94  * Fog blend factors are in the range [0,1].
95  */
96 static void
compute_fog_blend_factors(struct gl_context * ctx,GLvector4f * out,const GLvector4f * in)97 compute_fog_blend_factors(struct gl_context *ctx, GLvector4f *out, const GLvector4f *in)
98 {
99    GLfloat end  = ctx->Fog.End;
100    GLfloat *v = in->start;
101    GLuint stride = in->stride;
102    GLuint n = in->count;
103    GLfloat (*data)[4] = out->data;
104    GLfloat d;
105    GLuint i;
106 
107    out->count = in->count;
108 
109    switch (ctx->Fog.Mode) {
110    case GL_LINEAR:
111       if (ctx->Fog.Start == ctx->Fog.End)
112          d = 1.0F;
113       else
114          d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
115       for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
116          const GLfloat z = *v;
117          GLfloat f = (end - z) * d;
118 	 data[i][0] = CLAMP(f, 0.0F, 1.0F);
119       }
120       break;
121    case GL_EXP:
122       d = ctx->Fog.Density;
123       for ( i = 0 ; i < n ; i++, STRIDE_F(v,stride)) {
124          const GLfloat z = *v;
125          NEG_EXP( data[i][0], d * z );
126       }
127       break;
128    case GL_EXP2:
129       d = ctx->Fog.Density*ctx->Fog.Density;
130       for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
131          const GLfloat z = *v;
132          NEG_EXP( data[i][0], d * z * z );
133       }
134       break;
135    default:
136       _mesa_problem(ctx, "Bad fog mode in make_fog_coord");
137       return;
138    }
139 }
140 
141 
142 static GLboolean
run_fog_stage(struct gl_context * ctx,struct tnl_pipeline_stage * stage)143 run_fog_stage(struct gl_context *ctx, struct tnl_pipeline_stage *stage)
144 {
145    TNLcontext *tnl = TNL_CONTEXT(ctx);
146    struct vertex_buffer *VB = &tnl->vb;
147    struct fog_stage_data *store = FOG_STAGE_DATA(stage);
148    GLvector4f *input;
149 
150 
151    if (!ctx->Fog.Enabled)
152       return GL_TRUE;
153 
154    if (ctx->Fog.FogCoordinateSource == GL_FRAGMENT_DEPTH_EXT && !ctx->VertexProgram._Current) {
155       GLuint i;
156       GLfloat *coord;
157       /* Fog is computed from vertex or fragment Z values */
158       /* source = VB->AttribPtr[_TNL_ATTRIB_POS] or VB->EyePtr coords */
159       /* dest = VB->AttribPtr[_TNL_ATTRIB_FOG] = fog stage private storage */
160       VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;
161 
162       if (!ctx->_NeedEyeCoords) {
163          /* compute fog coords from object coords */
164 	 const GLfloat *m = ctx->ModelviewMatrixStack.Top->m;
165 	 GLfloat plane[4];
166 
167 	 /* Use this to store calculated eye z values:
168 	  */
169 	 input = &store->fogcoord;
170 
171 	 plane[0] = m[2];
172 	 plane[1] = m[6];
173 	 plane[2] = m[10];
174 	 plane[3] = m[14];
175 	 /* Full eye coords weren't required, just calculate the
176 	  * eye Z values.
177 	  */
178 	 _mesa_dotprod_tab[VB->AttribPtr[_TNL_ATTRIB_POS]->size]
179 	    ( (GLfloat *) input->data,
180 	      4 * sizeof(GLfloat),
181 	      VB->AttribPtr[_TNL_ATTRIB_POS], plane );
182 
183 	 input->count = VB->AttribPtr[_TNL_ATTRIB_POS]->count;
184 
185 	 /* make sure coords are really positive
186 	    NOTE should avoid going through array twice */
187 	 coord = input->start;
188 	 for (i = 0; i < input->count; i++) {
189 	    *coord = FABSF(*coord);
190 	    STRIDE_F(coord, input->stride);
191 	 }
192       }
193       else {
194          /* fog coordinates = eye Z coordinates - need to copy for ABS */
195 	 input = &store->fogcoord;
196 
197 	 if (VB->EyePtr->size < 2)
198 	    _mesa_vector4f_clean_elem( VB->EyePtr, VB->Count, 2 );
199 
200 	 input->stride = 4 * sizeof(GLfloat);
201 	 input->count = VB->EyePtr->count;
202 	 coord = VB->EyePtr->start;
203 	 for (i = 0 ; i < VB->EyePtr->count; i++) {
204 	    input->data[i][0] = FABSF(coord[2]);
205 	    STRIDE_F(coord, VB->EyePtr->stride);
206 	 }
207       }
208    }
209    else {
210       /* use glFogCoord() coordinates */
211       input = VB->AttribPtr[_TNL_ATTRIB_FOG];  /* source data */
212 
213       /* input->count may be one if glFogCoord was only called once
214        * before glBegin.  But we need to compute fog for all vertices.
215        */
216       input->count = VB->AttribPtr[_TNL_ATTRIB_POS]->count;
217 
218       VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;  /* dest data */
219    }
220 
221    if (tnl->_DoVertexFog) {
222       /* compute blend factors from fog coordinates */
223       compute_fog_blend_factors( ctx, VB->AttribPtr[_TNL_ATTRIB_FOG], input );
224    }
225    else {
226       /* results = incoming fog coords (compute fog per-fragment later) */
227       VB->AttribPtr[_TNL_ATTRIB_FOG] = input;
228    }
229 
230    return GL_TRUE;
231 }
232 
233 
234 
235 /* Called the first time stage->run() is invoked.
236  */
237 static GLboolean
alloc_fog_data(struct gl_context * ctx,struct tnl_pipeline_stage * stage)238 alloc_fog_data(struct gl_context *ctx, struct tnl_pipeline_stage *stage)
239 {
240    TNLcontext *tnl = TNL_CONTEXT(ctx);
241    struct fog_stage_data *store;
242    stage->privatePtr = MALLOC(sizeof(*store));
243    store = FOG_STAGE_DATA(stage);
244    if (!store)
245       return GL_FALSE;
246 
247    _mesa_vector4f_alloc( &store->fogcoord, 0, tnl->vb.Size, 32 );
248 
249    if (!inited)
250       init_static_data();
251 
252    return GL_TRUE;
253 }
254 
255 
256 static void
free_fog_data(struct tnl_pipeline_stage * stage)257 free_fog_data(struct tnl_pipeline_stage *stage)
258 {
259    struct fog_stage_data *store = FOG_STAGE_DATA(stage);
260    if (store) {
261       _mesa_vector4f_free( &store->fogcoord );
262       FREE( store );
263       stage->privatePtr = NULL;
264    }
265 }
266 
267 
268 const struct tnl_pipeline_stage _tnl_fog_coordinate_stage =
269 {
270    "build fog coordinates",	/* name */
271    NULL,			/* private_data */
272    alloc_fog_data,		/* dtr */
273    free_fog_data,		/* dtr */
274    NULL,		/* check */
275    run_fog_stage		/* run -- initially set to init. */
276 };
277