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 */
45 static inline void
compute_plane(const GLfloat v0[],const GLfloat v1[],const GLfloat v2[],GLfloat z0,GLfloat z1,GLfloat z2,GLfloat plane[4])46 compute_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 */
78 static inline void
constant_plane(GLfloat value,GLfloat plane[4])79 constant_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) \
88 do { \
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 */
100 static inline GLfloat
solve_plane(GLfloat x,GLfloat y,const GLfloat plane[4])101 solve_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 */
115 static inline GLchan
solve_plane_chan(GLfloat x,GLfloat y,const GLfloat plane[4])116 solve_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
131 static inline GLfloat
plane_dx(const GLfloat plane[4])132 plane_dx(const GLfloat plane[4])
133 {
134 return -plane[0] / plane[2];
135 }
136
137 static inline GLfloat
plane_dy(const GLfloat plane[4])138 plane_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 */
150 static GLfloat
compute_coveragef(const GLfloat v0[3],const GLfloat v1[3],const GLfloat v2[3],GLint winx,GLint winy)151 compute_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
250 static void
rgba_aa_tri(struct gl_context * ctx,const SWvertex * v0,const SWvertex * v1,const SWvertex * v2)251 rgba_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
261 static void
general_aa_tri(struct gl_context * ctx,const SWvertex * v0,const SWvertex * v1,const SWvertex * v2)262 general_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 */
278 void
_swrast_set_aa_triangle_function(struct gl_context * ctx)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