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/imports.h"
35#include "main/state.h"
36#include "s_aatriangle.h"
37#include "s_context.h"
38#include "s_span.h"
39
40
41/*
42 * Compute coefficients of a plane using the X,Y coords of the v0, v1, v2
43 * vertices and the given Z values.
44 * A point (x,y,z) lies on plane iff a*x+b*y+c*z+d = 0.
45 */
46static inline void
47compute_plane(const GLfloat v0[], const GLfloat v1[], const GLfloat v2[],
48              GLfloat z0, GLfloat z1, GLfloat z2, GLfloat plane[4])
49{
50   const GLfloat px = v1[0] - v0[0];
51   const GLfloat py = v1[1] - v0[1];
52   const GLfloat pz = z1 - z0;
53
54   const GLfloat qx = v2[0] - v0[0];
55   const GLfloat qy = v2[1] - v0[1];
56   const GLfloat qz = z2 - z0;
57
58   /* Crossproduct "(a,b,c):= dv1 x dv2" is orthogonal to plane. */
59   const GLfloat a = py * qz - pz * qy;
60   const GLfloat b = pz * qx - px * qz;
61   const GLfloat c = px * qy - py * qx;
62   /* Point on the plane = "r*(a,b,c) + w", with fixed "r" depending
63      on the distance of plane from origin and arbitrary "w" parallel
64      to the plane. */
65   /* The scalar product "(r*(a,b,c)+w)*(a,b,c)" is "r*(a^2+b^2+c^2)",
66      which is equal to "-d" below. */
67   const GLfloat d = -(a * v0[0] + b * v0[1] + c * z0);
68
69   plane[0] = a;
70   plane[1] = b;
71   plane[2] = c;
72   plane[3] = d;
73}
74
75
76/*
77 * Compute coefficients of a plane with a constant Z value.
78 */
79static inline void
80constant_plane(GLfloat value, GLfloat plane[4])
81{
82   plane[0] = 0.0;
83   plane[1] = 0.0;
84   plane[2] = -1.0;
85   plane[3] = value;
86}
87
88#define CONSTANT_PLANE(VALUE, PLANE)	\
89do {					\
90   PLANE[0] = 0.0F;			\
91   PLANE[1] = 0.0F;			\
92   PLANE[2] = -1.0F;			\
93   PLANE[3] = VALUE;			\
94} while (0)
95
96
97
98/*
99 * Solve plane equation for Z at (X,Y).
100 */
101static inline GLfloat
102solve_plane(GLfloat x, GLfloat y, const GLfloat plane[4])
103{
104   assert(plane[2] != 0.0F);
105   return (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
106}
107
108
109#define SOLVE_PLANE(X, Y, PLANE) \
110   ((PLANE[3] + PLANE[0] * (X) + PLANE[1] * (Y)) / -PLANE[2])
111
112
113/*
114 * Solve plane and return clamped GLchan value.
115 */
116static inline GLchan
117solve_plane_chan(GLfloat x, GLfloat y, const GLfloat plane[4])
118{
119   const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
120#if CHAN_TYPE == GL_FLOAT
121   return CLAMP(z, 0.0F, CHAN_MAXF);
122#else
123   if (z < 0)
124      return 0;
125   else if (z > CHAN_MAX)
126      return CHAN_MAX;
127   return (GLchan) IROUND_POS(z);
128#endif
129}
130
131
132static inline GLfloat
133plane_dx(const GLfloat plane[4])
134{
135   return -plane[0] / plane[2];
136}
137
138static inline GLfloat
139plane_dy(const GLfloat plane[4])
140{
141   return -plane[1] / plane[2];
142}
143
144
145
146/*
147 * Compute how much (area) of the given pixel is inside the triangle.
148 * Vertices MUST be specified in counter-clockwise order.
149 * Return:  coverage in [0, 1].
150 */
151static GLfloat
152compute_coveragef(const GLfloat v0[3], const GLfloat v1[3],
153                  const GLfloat v2[3], GLint winx, GLint winy)
154{
155   /* Given a position [0,3]x[0,3] return the sub-pixel sample position.
156    * Contributed by Ray Tice.
157    *
158    * Jitter sample positions -
159    * - average should be .5 in x & y for each column
160    * - each of the 16 rows and columns should be used once
161    * - the rectangle formed by the first four points
162    *   should contain the other points
163    * - the distrubition should be fairly even in any given direction
164    *
165    * The pattern drawn below isn't optimal, but it's better than a regular
166    * grid.  In the drawing, the center of each subpixel is surrounded by
167    * four dots.  The "x" marks the jittered position relative to the
168    * subpixel center.
169    */
170#define POS(a, b) (0.5+a*4+b)/16
171   static const GLfloat samples[16][2] = {
172      /* start with the four corners */
173      { POS(0, 2), POS(0, 0) },
174      { POS(3, 3), POS(0, 2) },
175      { POS(0, 0), POS(3, 1) },
176      { POS(3, 1), POS(3, 3) },
177      /* continue with interior samples */
178      { POS(1, 1), POS(0, 1) },
179      { POS(2, 0), POS(0, 3) },
180      { POS(0, 3), POS(1, 3) },
181      { POS(1, 2), POS(1, 0) },
182      { POS(2, 3), POS(1, 2) },
183      { POS(3, 2), POS(1, 1) },
184      { POS(0, 1), POS(2, 2) },
185      { POS(1, 0), POS(2, 1) },
186      { POS(2, 1), POS(2, 3) },
187      { POS(3, 0), POS(2, 0) },
188      { POS(1, 3), POS(3, 0) },
189      { POS(2, 2), POS(3, 2) }
190   };
191
192   const GLfloat x = (GLfloat) winx;
193   const GLfloat y = (GLfloat) winy;
194   const GLfloat dx0 = v1[0] - v0[0];
195   const GLfloat dy0 = v1[1] - v0[1];
196   const GLfloat dx1 = v2[0] - v1[0];
197   const GLfloat dy1 = v2[1] - v1[1];
198   const GLfloat dx2 = v0[0] - v2[0];
199   const GLfloat dy2 = v0[1] - v2[1];
200   GLint stop = 4, i;
201   GLfloat insideCount = 16.0F;
202
203   assert(dx0 * dy1 - dx1 * dy0 >= 0.0); /* area >= 0.0 */
204
205   for (i = 0; i < stop; i++) {
206      const GLfloat sx = x + samples[i][0];
207      const GLfloat sy = y + samples[i][1];
208      /* cross product determines if sample is inside or outside each edge */
209      GLfloat cross = (dx0 * (sy - v0[1]) - dy0 * (sx - v0[0]));
210      /* Check if the sample is exactly on an edge.  If so, let cross be a
211       * positive or negative value depending on the direction of the edge.
212       */
213      if (cross == 0.0F)
214         cross = dx0 + dy0;
215      if (cross < 0.0F) {
216         /* sample point is outside first edge */
217         insideCount -= 1.0F;
218         stop = 16;
219      }
220      else {
221         /* sample point is inside first edge */
222         cross = (dx1 * (sy - v1[1]) - dy1 * (sx - v1[0]));
223         if (cross == 0.0F)
224            cross = dx1 + dy1;
225         if (cross < 0.0F) {
226            /* sample point is outside second edge */
227            insideCount -= 1.0F;
228            stop = 16;
229         }
230         else {
231            /* sample point is inside first and second edges */
232            cross = (dx2 * (sy - v2[1]) -  dy2 * (sx - v2[0]));
233            if (cross == 0.0F)
234               cross = dx2 + dy2;
235            if (cross < 0.0F) {
236               /* sample point is outside third edge */
237               insideCount -= 1.0F;
238               stop = 16;
239            }
240         }
241      }
242   }
243   if (stop == 4)
244      return 1.0F;
245   else
246      return insideCount * (1.0F / 16.0F);
247}
248
249
250
251static void
252rgba_aa_tri(struct gl_context *ctx,
253	    const SWvertex *v0,
254	    const SWvertex *v1,
255	    const SWvertex *v2)
256{
257#define DO_Z
258#include "s_aatritemp.h"
259}
260
261
262static void
263general_aa_tri(struct gl_context *ctx,
264               const SWvertex *v0,
265               const SWvertex *v1,
266               const SWvertex *v2)
267{
268#define DO_Z
269#define DO_ATTRIBS
270#include "s_aatritemp.h"
271}
272
273
274
275/*
276 * Examine GL state and set swrast->Triangle to an
277 * appropriate antialiased triangle rasterizer function.
278 */
279void
280_swrast_set_aa_triangle_function(struct gl_context *ctx)
281{
282   SWcontext *swrast = SWRAST_CONTEXT(ctx);
283
284   assert(ctx->Polygon.SmoothFlag);
285
286   if (ctx->Texture._EnabledCoordUnits != 0
287       || _swrast_use_fragment_program(ctx)
288       || swrast->_FogEnabled
289       || _mesa_need_secondary_color(ctx)) {
290      SWRAST_CONTEXT(ctx)->Triangle = general_aa_tri;
291   }
292   else {
293      SWRAST_CONTEXT(ctx)->Triangle = rgba_aa_tri;
294   }
295
296   assert(SWRAST_CONTEXT(ctx)->Triangle);
297}
298