1/*
2 * Mesa 3-D graphics library
3 * Version:  6.5.3
4 *
5 * Copyright (C) 1999-2007  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
25
26/*
27 * Antialiased Triangle rasterizers
28 */
29
30
31#include "main/glheader.h"
32#include "main/context.h"
33#include "main/colormac.h"
34#include "main/macros.h"
35#include "main/imports.h"
36#include "main/state.h"
37#include "s_aatriangle.h"
38#include "s_context.h"
39#include "s_span.h"
40
41
42/*
43 * Compute coefficients of a plane using the X,Y coords of the v0, v1, v2
44 * vertices and the given Z values.
45 * A point (x,y,z) lies on plane iff a*x+b*y+c*z+d = 0.
46 */
47static inline void
48compute_plane(const GLfloat v0[], const GLfloat v1[], const GLfloat v2[],
49              GLfloat z0, GLfloat z1, GLfloat z2, GLfloat plane[4])
50{
51   const GLfloat px = v1[0] - v0[0];
52   const GLfloat py = v1[1] - v0[1];
53   const GLfloat pz = z1 - z0;
54
55   const GLfloat qx = v2[0] - v0[0];
56   const GLfloat qy = v2[1] - v0[1];
57   const GLfloat qz = z2 - z0;
58
59   /* Crossproduct "(a,b,c):= dv1 x dv2" is orthogonal to plane. */
60   const GLfloat a = py * qz - pz * qy;
61   const GLfloat b = pz * qx - px * qz;
62   const GLfloat c = px * qy - py * qx;
63   /* Point on the plane = "r*(a,b,c) + w", with fixed "r" depending
64      on the distance of plane from origin and arbitrary "w" parallel
65      to the plane. */
66   /* The scalar product "(r*(a,b,c)+w)*(a,b,c)" is "r*(a^2+b^2+c^2)",
67      which is equal to "-d" below. */
68   const GLfloat d = -(a * v0[0] + b * v0[1] + c * z0);
69
70   plane[0] = a;
71   plane[1] = b;
72   plane[2] = c;
73   plane[3] = d;
74}
75
76
77/*
78 * Compute coefficients of a plane with a constant Z value.
79 */
80static inline void
81constant_plane(GLfloat value, GLfloat plane[4])
82{
83   plane[0] = 0.0;
84   plane[1] = 0.0;
85   plane[2] = -1.0;
86   plane[3] = value;
87}
88
89#define CONSTANT_PLANE(VALUE, PLANE)	\
90do {					\
91   PLANE[0] = 0.0F;			\
92   PLANE[1] = 0.0F;			\
93   PLANE[2] = -1.0F;			\
94   PLANE[3] = VALUE;			\
95} while (0)
96
97
98
99/*
100 * Solve plane equation for Z at (X,Y).
101 */
102static inline GLfloat
103solve_plane(GLfloat x, GLfloat y, const GLfloat plane[4])
104{
105   ASSERT(plane[2] != 0.0F);
106   return (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
107}
108
109
110#define SOLVE_PLANE(X, Y, PLANE) \
111   ((PLANE[3] + PLANE[0] * (X) + PLANE[1] * (Y)) / -PLANE[2])
112
113
114/*
115 * Return 1 / solve_plane().
116 */
117static inline GLfloat
118solve_plane_recip(GLfloat x, GLfloat y, const GLfloat plane[4])
119{
120   const GLfloat denom = plane[3] + plane[0] * x + plane[1] * y;
121   if (denom == 0.0F)
122      return 0.0F;
123   else
124      return -plane[2] / denom;
125}
126
127
128/*
129 * Solve plane and return clamped GLchan value.
130 */
131static inline GLchan
132solve_plane_chan(GLfloat x, GLfloat y, const GLfloat plane[4])
133{
134   const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
135#if CHAN_TYPE == GL_FLOAT
136   return CLAMP(z, 0.0F, CHAN_MAXF);
137#else
138   if (z < 0)
139      return 0;
140   else if (z > CHAN_MAX)
141      return CHAN_MAX;
142   return (GLchan) IROUND_POS(z);
143#endif
144}
145
146
147static inline GLfloat
148plane_dx(const GLfloat plane[4])
149{
150   return -plane[0] / plane[2];
151}
152
153static inline GLfloat
154plane_dy(const GLfloat plane[4])
155{
156   return -plane[1] / plane[2];
157}
158
159
160
161/*
162 * Compute how much (area) of the given pixel is inside the triangle.
163 * Vertices MUST be specified in counter-clockwise order.
164 * Return:  coverage in [0, 1].
165 */
166static GLfloat
167compute_coveragef(const GLfloat v0[3], const GLfloat v1[3],
168                  const GLfloat v2[3], GLint winx, GLint winy)
169{
170   /* Given a position [0,3]x[0,3] return the sub-pixel sample position.
171    * Contributed by Ray Tice.
172    *
173    * Jitter sample positions -
174    * - average should be .5 in x & y for each column
175    * - each of the 16 rows and columns should be used once
176    * - the rectangle formed by the first four points
177    *   should contain the other points
178    * - the distrubition should be fairly even in any given direction
179    *
180    * The pattern drawn below isn't optimal, but it's better than a regular
181    * grid.  In the drawing, the center of each subpixel is surrounded by
182    * four dots.  The "x" marks the jittered position relative to the
183    * subpixel center.
184    */
185#define POS(a, b) (0.5+a*4+b)/16
186   static const GLfloat samples[16][2] = {
187      /* start with the four corners */
188      { POS(0, 2), POS(0, 0) },
189      { POS(3, 3), POS(0, 2) },
190      { POS(0, 0), POS(3, 1) },
191      { POS(3, 1), POS(3, 3) },
192      /* continue with interior samples */
193      { POS(1, 1), POS(0, 1) },
194      { POS(2, 0), POS(0, 3) },
195      { POS(0, 3), POS(1, 3) },
196      { POS(1, 2), POS(1, 0) },
197      { POS(2, 3), POS(1, 2) },
198      { POS(3, 2), POS(1, 1) },
199      { POS(0, 1), POS(2, 2) },
200      { POS(1, 0), POS(2, 1) },
201      { POS(2, 1), POS(2, 3) },
202      { POS(3, 0), POS(2, 0) },
203      { POS(1, 3), POS(3, 0) },
204      { POS(2, 2), POS(3, 2) }
205   };
206
207   const GLfloat x = (GLfloat) winx;
208   const GLfloat y = (GLfloat) winy;
209   const GLfloat dx0 = v1[0] - v0[0];
210   const GLfloat dy0 = v1[1] - v0[1];
211   const GLfloat dx1 = v2[0] - v1[0];
212   const GLfloat dy1 = v2[1] - v1[1];
213   const GLfloat dx2 = v0[0] - v2[0];
214   const GLfloat dy2 = v0[1] - v2[1];
215   GLint stop = 4, i;
216   GLfloat insideCount = 16.0F;
217
218   ASSERT(dx0 * dy1 - dx1 * dy0 >= 0.0); /* area >= 0.0 */
219
220   for (i = 0; i < stop; i++) {
221      const GLfloat sx = x + samples[i][0];
222      const GLfloat sy = y + samples[i][1];
223      /* cross product determines if sample is inside or outside each edge */
224      GLfloat cross = (dx0 * (sy - v0[1]) - dy0 * (sx - v0[0]));
225      /* Check if the sample is exactly on an edge.  If so, let cross be a
226       * positive or negative value depending on the direction of the edge.
227       */
228      if (cross == 0.0F)
229         cross = dx0 + dy0;
230      if (cross < 0.0F) {
231         /* sample point is outside first edge */
232         insideCount -= 1.0F;
233         stop = 16;
234      }
235      else {
236         /* sample point is inside first edge */
237         cross = (dx1 * (sy - v1[1]) - dy1 * (sx - v1[0]));
238         if (cross == 0.0F)
239            cross = dx1 + dy1;
240         if (cross < 0.0F) {
241            /* sample point is outside second edge */
242            insideCount -= 1.0F;
243            stop = 16;
244         }
245         else {
246            /* sample point is inside first and second edges */
247            cross = (dx2 * (sy - v2[1]) -  dy2 * (sx - v2[0]));
248            if (cross == 0.0F)
249               cross = dx2 + dy2;
250            if (cross < 0.0F) {
251               /* sample point is outside third edge */
252               insideCount -= 1.0F;
253               stop = 16;
254            }
255         }
256      }
257   }
258   if (stop == 4)
259      return 1.0F;
260   else
261      return insideCount * (1.0F / 16.0F);
262}
263
264
265
266static void
267rgba_aa_tri(struct gl_context *ctx,
268	    const SWvertex *v0,
269	    const SWvertex *v1,
270	    const SWvertex *v2)
271{
272#define DO_Z
273#include "s_aatritemp.h"
274}
275
276
277static void
278general_aa_tri(struct gl_context *ctx,
279               const SWvertex *v0,
280               const SWvertex *v1,
281               const SWvertex *v2)
282{
283#define DO_Z
284#define DO_ATTRIBS
285#include "s_aatritemp.h"
286}
287
288
289
290/*
291 * Examine GL state and set swrast->Triangle to an
292 * appropriate antialiased triangle rasterizer function.
293 */
294void
295_swrast_set_aa_triangle_function(struct gl_context *ctx)
296{
297   SWcontext *swrast = SWRAST_CONTEXT(ctx);
298
299   ASSERT(ctx->Polygon.SmoothFlag);
300
301   if (ctx->Texture._EnabledCoordUnits != 0
302       || _swrast_use_fragment_program(ctx)
303       || swrast->_FogEnabled
304       || _mesa_need_secondary_color(ctx)) {
305      SWRAST_CONTEXT(ctx)->Triangle = general_aa_tri;
306   }
307   else {
308      SWRAST_CONTEXT(ctx)->Triangle = rgba_aa_tri;
309   }
310
311   ASSERT(SWRAST_CONTEXT(ctx)->Triangle);
312}
313