1/*
2 * Mesa 3-D graphics library
3 *
4 * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a
7 * copy of this software and associated documentation files (the "Software"),
8 * to deal in the Software without restriction, including without limitation
9 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
10 * and/or sell copies of the Software, and to permit persons to whom the
11 * Software is furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included
14 * in all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
17 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
20 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
21 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
22 * OTHER DEALINGS IN THE SOFTWARE.
23 */
24
25
26/*
27 * Antialiased Triangle rasterizers
28 */
29
30
31#include "main/glheader.h"
32#include "main/context.h"
33#include "main/macros.h"
34#include "main/state.h"
35#include "s_aatriangle.h"
36#include "s_context.h"
37#include "s_span.h"
38
39
40/*
41 * Compute coefficients of a plane using the X,Y coords of the v0, v1, v2
42 * vertices and the given Z values.
43 * A point (x,y,z) lies on plane iff a*x+b*y+c*z+d = 0.
44 */
45static inline void
46compute_plane(const GLfloat v0[], const GLfloat v1[], const GLfloat v2[],
47              GLfloat z0, GLfloat z1, GLfloat z2, GLfloat plane[4])
48{
49   const GLfloat px = v1[0] - v0[0];
50   const GLfloat py = v1[1] - v0[1];
51   const GLfloat pz = z1 - z0;
52
53   const GLfloat qx = v2[0] - v0[0];
54   const GLfloat qy = v2[1] - v0[1];
55   const GLfloat qz = z2 - z0;
56
57   /* Crossproduct "(a,b,c):= dv1 x dv2" is orthogonal to plane. */
58   const GLfloat a = py * qz - pz * qy;
59   const GLfloat b = pz * qx - px * qz;
60   const GLfloat c = px * qy - py * qx;
61   /* Point on the plane = "r*(a,b,c) + w", with fixed "r" depending
62      on the distance of plane from origin and arbitrary "w" parallel
63      to the plane. */
64   /* The scalar product "(r*(a,b,c)+w)*(a,b,c)" is "r*(a^2+b^2+c^2)",
65      which is equal to "-d" below. */
66   const GLfloat d = -(a * v0[0] + b * v0[1] + c * z0);
67
68   plane[0] = a;
69   plane[1] = b;
70   plane[2] = c;
71   plane[3] = d;
72}
73
74
75/*
76 * Compute coefficients of a plane with a constant Z value.
77 */
78static inline void
79constant_plane(GLfloat value, GLfloat plane[4])
80{
81   plane[0] = 0.0;
82   plane[1] = 0.0;
83   plane[2] = -1.0;
84   plane[3] = value;
85}
86
87#define CONSTANT_PLANE(VALUE, PLANE)	\
88do {					\
89   PLANE[0] = 0.0F;			\
90   PLANE[1] = 0.0F;			\
91   PLANE[2] = -1.0F;			\
92   PLANE[3] = VALUE;			\
93} while (0)
94
95
96
97/*
98 * Solve plane equation for Z at (X,Y).
99 */
100static inline GLfloat
101solve_plane(GLfloat x, GLfloat y, const GLfloat plane[4])
102{
103   assert(plane[2] != 0.0F);
104   return (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
105}
106
107
108#define SOLVE_PLANE(X, Y, PLANE) \
109   ((PLANE[3] + PLANE[0] * (X) + PLANE[1] * (Y)) / -PLANE[2])
110
111
112/*
113 * Solve plane and return clamped GLchan value.
114 */
115static inline GLchan
116solve_plane_chan(GLfloat x, GLfloat y, const GLfloat plane[4])
117{
118   const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
119#if CHAN_TYPE == GL_FLOAT
120   return CLAMP(z, 0.0F, CHAN_MAXF);
121#else
122   if (z < 0)
123      return 0;
124   else if (z > CHAN_MAX)
125      return CHAN_MAX;
126   return (GLchan) lroundf(z);
127#endif
128}
129
130
131static inline GLfloat
132plane_dx(const GLfloat plane[4])
133{
134   return -plane[0] / plane[2];
135}
136
137static inline GLfloat
138plane_dy(const GLfloat plane[4])
139{
140   return -plane[1] / plane[2];
141}
142
143
144
145/*
146 * Compute how much (area) of the given pixel is inside the triangle.
147 * Vertices MUST be specified in counter-clockwise order.
148 * Return:  coverage in [0, 1].
149 */
150static GLfloat
151compute_coveragef(const GLfloat v0[3], const GLfloat v1[3],
152                  const GLfloat v2[3], GLint winx, GLint winy)
153{
154   /* Given a position [0,3]x[0,3] return the sub-pixel sample position.
155    * Contributed by Ray Tice.
156    *
157    * Jitter sample positions -
158    * - average should be .5 in x & y for each column
159    * - each of the 16 rows and columns should be used once
160    * - the rectangle formed by the first four points
161    *   should contain the other points
162    * - the distrubition should be fairly even in any given direction
163    *
164    * The pattern drawn below isn't optimal, but it's better than a regular
165    * grid.  In the drawing, the center of each subpixel is surrounded by
166    * four dots.  The "x" marks the jittered position relative to the
167    * subpixel center.
168    */
169#define POS(a, b) (0.5+a*4+b)/16
170   static const GLfloat samples[16][2] = {
171      /* start with the four corners */
172      { POS(0, 2), POS(0, 0) },
173      { POS(3, 3), POS(0, 2) },
174      { POS(0, 0), POS(3, 1) },
175      { POS(3, 1), POS(3, 3) },
176      /* continue with interior samples */
177      { POS(1, 1), POS(0, 1) },
178      { POS(2, 0), POS(0, 3) },
179      { POS(0, 3), POS(1, 3) },
180      { POS(1, 2), POS(1, 0) },
181      { POS(2, 3), POS(1, 2) },
182      { POS(3, 2), POS(1, 1) },
183      { POS(0, 1), POS(2, 2) },
184      { POS(1, 0), POS(2, 1) },
185      { POS(2, 1), POS(2, 3) },
186      { POS(3, 0), POS(2, 0) },
187      { POS(1, 3), POS(3, 0) },
188      { POS(2, 2), POS(3, 2) }
189   };
190
191   const GLfloat x = (GLfloat) winx;
192   const GLfloat y = (GLfloat) winy;
193   const GLfloat dx0 = v1[0] - v0[0];
194   const GLfloat dy0 = v1[1] - v0[1];
195   const GLfloat dx1 = v2[0] - v1[0];
196   const GLfloat dy1 = v2[1] - v1[1];
197   const GLfloat dx2 = v0[0] - v2[0];
198   const GLfloat dy2 = v0[1] - v2[1];
199   GLint stop = 4, i;
200   GLfloat insideCount = 16.0F;
201
202   assert(dx0 * dy1 - dx1 * dy0 >= 0.0); /* area >= 0.0 */
203
204   for (i = 0; i < stop; i++) {
205      const GLfloat sx = x + samples[i][0];
206      const GLfloat sy = y + samples[i][1];
207      /* cross product determines if sample is inside or outside each edge */
208      GLfloat cross = (dx0 * (sy - v0[1]) - dy0 * (sx - v0[0]));
209      /* Check if the sample is exactly on an edge.  If so, let cross be a
210       * positive or negative value depending on the direction of the edge.
211       */
212      if (cross == 0.0F)
213         cross = dx0 + dy0;
214      if (cross < 0.0F) {
215         /* sample point is outside first edge */
216         insideCount -= 1.0F;
217         stop = 16;
218      }
219      else {
220         /* sample point is inside first edge */
221         cross = (dx1 * (sy - v1[1]) - dy1 * (sx - v1[0]));
222         if (cross == 0.0F)
223            cross = dx1 + dy1;
224         if (cross < 0.0F) {
225            /* sample point is outside second edge */
226            insideCount -= 1.0F;
227            stop = 16;
228         }
229         else {
230            /* sample point is inside first and second edges */
231            cross = (dx2 * (sy - v2[1]) -  dy2 * (sx - v2[0]));
232            if (cross == 0.0F)
233               cross = dx2 + dy2;
234            if (cross < 0.0F) {
235               /* sample point is outside third edge */
236               insideCount -= 1.0F;
237               stop = 16;
238            }
239         }
240      }
241   }
242   if (stop == 4)
243      return 1.0F;
244   else
245      return insideCount * (1.0F / 16.0F);
246}
247
248
249
250static void
251rgba_aa_tri(struct gl_context *ctx,
252	    const SWvertex *v0,
253	    const SWvertex *v1,
254	    const SWvertex *v2)
255{
256#define DO_Z
257#include "s_aatritemp.h"
258}
259
260
261static void
262general_aa_tri(struct gl_context *ctx,
263               const SWvertex *v0,
264               const SWvertex *v1,
265               const SWvertex *v2)
266{
267#define DO_Z
268#define DO_ATTRIBS
269#include "s_aatritemp.h"
270}
271
272
273
274/*
275 * Examine GL state and set swrast->Triangle to an
276 * appropriate antialiased triangle rasterizer function.
277 */
278void
279_swrast_set_aa_triangle_function(struct gl_context *ctx)
280{
281   SWcontext *swrast = SWRAST_CONTEXT(ctx);
282
283   assert(ctx->Polygon.SmoothFlag);
284
285   if (ctx->Texture._EnabledCoordUnits != 0
286       || _swrast_use_fragment_program(ctx)
287       || swrast->_FogEnabled
288       || _mesa_need_secondary_color(ctx)) {
289      SWRAST_CONTEXT(ctx)->Triangle = general_aa_tri;
290   }
291   else {
292      SWRAST_CONTEXT(ctx)->Triangle = rgba_aa_tri;
293   }
294
295   assert(SWRAST_CONTEXT(ctx)->Triangle);
296}
297