src/mesa/swrast/s_aatriangle.c

   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
  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
  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
 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
 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
 133 plane_dx(const GLfloat plane[4])
 134 {
 135    return -plane[0] / plane[2];
 136 }
 137
 138 static inline GLfloat
 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
 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
 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
 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
 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 }