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 */
46 static inline void
compute_plane(const GLfloat v0[],const GLfloat v1[],const GLfloat v2[],GLfloat z0,GLfloat z1,GLfloat z2,GLfloat plane[4])47 compute_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 */
79 static inline void
constant_plane(GLfloat value,GLfloat plane[4])80 constant_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) \
89 do { \
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 */
101 static inline GLfloat
solve_plane(GLfloat x,GLfloat y,const GLfloat plane[4])102 solve_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 */
116 static inline GLchan
solve_plane_chan(GLfloat x,GLfloat y,const GLfloat plane[4])117 solve_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
132 static inline GLfloat
plane_dx(const GLfloat plane[4])133 plane_dx(const GLfloat plane[4])
134 {
135 return -plane[0] / plane[2];
136 }
137
138 static inline GLfloat
plane_dy(const GLfloat plane[4])139 plane_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 */
151 static GLfloat
compute_coveragef(const GLfloat v0[3],const GLfloat v1[3],const GLfloat v2[3],GLint winx,GLint winy)152 compute_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
251 static void
rgba_aa_tri(struct gl_context * ctx,const SWvertex * v0,const SWvertex * v1,const SWvertex * v2)252 rgba_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
262 static void
general_aa_tri(struct gl_context * ctx,const SWvertex * v0,const SWvertex * v1,const SWvertex * v2)263 general_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 */
279 void
_swrast_set_aa_triangle_function(struct gl_context * ctx)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